





Network Working Group                                      P. Radoslavov
Request for Comments: 2909                                     D. Estrin
Category: Experimental                                       R. Govindan
                                                                 USC/ISI
                                                              M. Handley
                                                                   ACIRI
                                                                S. Kumar
                                                                 USC/ISI
                                                               D. Thaler
                                                               Microsoft
                                                          September 2000


            The Multicast Address-Set Claim (MASC) Protocol

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   This document describes the Multicast Address-Set Claim (MASC)
   protocol which can be used for inter-domain multicast address set
   allocation.  MASC is used by a node (typically a router) to claim and
   allocate one or more address prefixes to that node's domain.  While a
   domain does not necessarily need to allocate an address set for hosts
   in that domain to be able to allocate group addresses, allocating an
   address set to the domain does ensure that inter-domain group-
   specific distribution trees will be locally-rooted, and that traffic
   will be sent outside the domain only when and where external
   receivers exist.













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Table of Contents

   1 Introduction ..................................................  4
   1.1 Terminology .................................................  4
   1.2 Definitions .................................................  4
   2 Requirements for Inter-Domain Address Allocation ..............  5
   3 Overall Architecture ..........................................  5
   3.1 Claim-Collide vs. Query-Response Rationale ..................  6
   4 MASC Topology .................................................  6
   4.1 Managed vs Locally-Allocated Space ..........................  8
   4.2 Prefix Lifetime .............................................  8
   4.3 Active vs. Deprecated Prefixes ..............................  9
   4.4 Multi-Parent Sibling-to-Sibling and Internal Peering ........  9
   4.5 Administratively-Scoped Address Allocation ..................  9
   5 Protocol Details .............................................. 10
   5.1 Claiming Space .............................................. 10
   5.1.1 Claim Comparison Function ................................. 12
   5.2 Renewing an Existing Claim .................................. 12
   5.3 Expanding an Existing Prefix ................................ 12
   5.4 Releasing Allocated Space ................................... 13
   6 Constants ..................................................... 13
   7 Message Formats ............................................... 14
   7.1 Message Header Format ....................................... 14
   7.2 OPEN Message Format ......................................... 15
   7.3 UPDATE Message Format ....................................... 17
   7.4 KEEPALIVE Message Format .................................... 21
   7.5 NOTIFICATION Message Format ................................. 21
   8 MASC Error Handling ........................................... 24
   8.1 Message Header Error Handling ............................... 24
   8.2 OPEN Message Error Handling ................................. 25
   8.3 UPDATE Message Error Handling ............................... 26
   8.4 Hold Timer Expired Error Handling ........................... 28
   8.5 Finite State Machine Error Handling ......................... 28
   8.6 NOTIFICATION Message Error Handling ......................... 28
   8.7 Cease ....................................................... 29
   8.8 Connection Collision Detection .............................. 29
   9 MASC Version Negotiation ...................................... 30
   10 MASC Finite State Machine .................................... 30
   10.1 Open/Close MASC Connection FSM ............................. 31
   11 UPDATE Message Processing .................................... 35
   11.1 Accept/Reject an UPDATE .................................... 36
   11.2 PREFIX_IN_USE Message Processing ........................... 38
   11.2.1 PREFIX_IN_USE by PARENT .................................. 38
   11.2.2 PREFIX_IN_USE by SIBLING ................................. 38
   11.2.3 PREFIX_IN_USE by CHILD ................................... 38
   11.2.4 PREFIX_IN_USE by INTERNAL_PEER ........................... 38
   11.3 CLAIM_DENIED Message Processing ............................ 39
   11.3.1 CLAIM_DENIED by CHILD or SIBLING ......................... 39



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   11.3.2 CLAIM_DENIED by INTERNAL_PEER ............................ 39
   11.3.3 CLAIM_DENIED by PARENT ................................... 39
   11.4 CLAIM_TO_EXPAND Message Processing ......................... 39
   11.4.1 CLAIM_TO_EXPAND by PARENT ................................ 39
   11.4.2 CLAIM_TO_EXPAND by SIBLING ............................... 40
   11.4.3 CLAIM_TO_EXPAND by CHILD ................................. 40
   11.4.4 CLAIM_TO_EXPAND by INTERNAL_PEER ......................... 40
   11.5 NEW_CLAIM Message Processing ............................... 41
   11.6 PREFIX_MANAGED Message Processing.  ........................ 41
   11.6.1 PREFIX_MANAGED by PARENT ................................. 41
   11.6.2 PREFIX_MANAGED by CHILD or SIBLING ....................... 41
   11.6.3 PREFIX_MANAGED by INTERNAL_PEER .......................... 41
   11.7 WITHDRAW Message Processing ................................ 42
   11.7.1 WITHDRAW by CHILD ........................................ 42
   11.7.2 WITHDRAW by SIBLING ...................................... 42
   11.7.3 WITHDRAW by INTERNAL ..................................... 42
   11.7.4 WITHDRAW by PARENT ....................................... 43
   11.8 UPDATE Message Ordering .................................... 43
   11.8.1 Parent to Child .......................................... 43
   11.8.2 Child to Parent .......................................... 44
   11.8.3 Sibling to Sibling ....................................... 44
   11.8.4 Internal to Internal ..................................... 44
   12 Operational Considerations ................................... 45
   12.1 Bootup Operations .......................................... 45
   12.2 Leaf and Non-leaf MASC Domain Operation .................... 45
   12.3 Clock Skew Workaround ...................................... 45
   12.4 Clash Resolving Mechanism .................................. 46
   12.5 Changing Network Providers ................................. 47
   12.6 Debugging .................................................. 47
   12.6.1 Prefix-to-Domain Lookup .................................. 47
   12.6.2 Domain-to-Prefix Lookup .................................. 47
   13 MASC Storage ................................................. 47
   14 Security Considerations ...................................... 48
   15 IANA Considerations .......................................... 48
   16 Acknowledgments .............................................. 48
   17 APPENDIX A: Sample Algorithms ................................ 49
   17.1 Claim Size and Prefix Selection Algorithm .................. 49
   17.1.1 Prefix Expansion ......................................... 49
   17.1.2 Reducing Allocation Latency .............................. 50
   17.1.3 Address Space Utilization ................................ 50
   17.1.4 Prefix Selection After Increase of Demand ................ 50
   17.1.5 Prefix Selection After Decrease of Demand ................ 51
   17.1.6 Lifetime Extension Algorithm ............................. 51
   18 APPENDIX B: Strawman Deployment .............................. 51
   19 Authors' Addresses ........................................... 52
   20 References ................................................... 54
   21 Full Copyright Statement ..................................... 56




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1.  Introduction

   This document describes MASC, a protocol for inter-domain multicast
   address set allocation.  The MASC protocol (a Layer-3 protocol in the
   multicast address allocation architecture [MALLOC]) is used by a node
   (typically a router) to claim and allocate one or more address
   prefixes to that node's domain.  Each prefix has an associated
   lifetime, and is chosen out of a larger prefix with a lifetime at
   least as long, in a manner such that prefixes are aggregatable.  At
   any time, each MASC node (a Prefix Coordinator in [MALLOC]) will
   typically advertise several prefixes with different lifetimes and
   scopes, allowing Multicast Address Allocation Servers (MAAS's) in
   that domain or child MASC domains to choose appropriate addresses for
   their clients.

   The set of prefixes ("address set") associated with a domain is
   injected into an inter-domain routing protocol (e.g., BGP4+ [MBGP]),
   where it can be used by an inter-domain multicast tree construction
   protocol (e.g., BGMP [BGMP]) to construct inter-domain group-shared
   trees.

   Note that a domain does not need to allocate an address set for the
   hosts in that domain to be able to allocate group addresses, nor does
   allocating necessarily guarantee that hosts in other domains will not
   use an address in the set (since, for example, hosts are not forced
   to contact a MAAS before using a group address).  Allocating an
   address set to a domain does, however, ensure that inter-domain
   group-specific multicast distribution trees for any group in the
   address set will be locally-rooted, and that traffic will be sent
   outside the given domain only when and where external receivers
   exist.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   Constants used by this protocol are shown as [NAME_OF_CONSTANT], and
   summarized in Section 6.

1.2.  Definitions

   This specification uses a number of terms that may not be familiar to
   the reader. This section defines some of these and refers to other
   documents for definitions of others.





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   MAAS (Multicast Address Allocation Server)
      A host providing multicast address allocation services to end
      users (e.g. via MADCAP [MADCAP]).

   MASC server
      A node running MASC.

   Peer
      Other MASC speakers a node directly communicates with.

   Multicast
      IP Multicast, as defined for IPv4 in [RFC1112] and for IPv6 in
      [RFC2460].

   Multicast Address
      An IP multicast address or group address, as defined in [RFC1112]
      and [RFC2373].  An identifier for a group of nodes.

2.  Requirements for Inter-Domain Address Allocation

   The key design requirements for the inter-domain address allocation
   mechanism are:

   o  Efficient address space utilization when space is scare, which
      naturally implies that address allocations be based on the actual
      address usage patterns, and therefore that it be dynamic.

   o  Address aggregation, that implies that the address allocation
      mechanism be hierarchical.

   o  Minimize flux in the allocated address sets (e.g. the address sets
      should be reused when possible).

   o  Robustness, by using decentralized mechanisms.

   The timeliness in obtaining an address set is not a major design
   constraint as this is taken care of at a lower level [MALLOC].

3.  Overall Architecture

   The Multicast Address Set Claim (MASC) protocol is used by MASC
   domains to claim and allocate address sets for use by Multicast
   Address Allocation Servers (MAASs) within each domain.  Typically one
   or more border routers of each domain that requires multicast address
   space of its own would run MASC.  Throughout this document, the term
   "MASC domain" refers to a domain that has at least one node running
   MASC; typically these domains will be Autonomous Systems (AS's).  A
   MASC node (on behalf of its domain) chooses an address set to claim,



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   sends a claim to other MASC domains in the network, and waits while
   listening for any colliding claims. If there is a collision, the
   losing claimer gives up the colliding claim and claims a different
   address set.

   After a sufficiently long collision-free waiting period, the address
   set chosen by a MASC node is considered allocated to that node's
   domain.  Three things may then happen:

   a) The allocated prefix can then be injected as a "multicast route"
      into the inter-domain routing protocol  (e.g., BGP4+ [MBGP]) as
      "G-RIB" Network Layer Reachability Information (NLRI), where it
      may be used by an inter-domain multicast routing protocol (e.g.,
      BGMP [BGMP]) to construct group-shared trees.  To reduce the size
      and slow the growth of the G-RIB, MASC nodes may perform CIDR-like
      aggregation [CIDR] of the multicast NLRI information.  This
      motivates the need for an algorithm to select prefixes for domains
      in such a way as to ensure good aggregation in addition to
      achieving good address space utilization.

   b) The node's domain may assign to itself a sub-prefix which can be
      used by MAASs within the domain.

   c) Sub-prefixes may be allocated to child domains, if any.

3.1.  Claim-Collide vs. Query-Response Rationale

   We choose a claim-collide mechanism instead of a query-response
   mechanism for the following reasons.  In a query-response mechanism,
   replicas of the MASC node would be needed in parent MASC domains in
   order to make their responses be robust to failures.  This brings
   about the associated problem of synchronization of the replicas and
   possibly additional fragmentation of the address space.  In addition,
   even in this mechanism, address collisions would still need to be
   handled.  We believe the proposed claim-collide mechanism is simpler
   and more robust than a query-response mechanism.

4.  MASC Topology

   The domain hierarchy used by MASC is congruent to the somewhat
   hierarchical structure of the inter-domain topology, e.g., backbones
   connected to regionals, regionals connected to metropolitan
   providers, etc.  As in BGP, MASC connections are locally configured.
   A MASC domain that is a customer of other MASC domains will have one
   or more of those provider domains as its parent.  For example, a MASC
   domain that is a regional provider will choose one (or more) of its
   backbone provider domains as its parent(s).  Children are configured
   with their parent MASC domain, and parents are configured with their



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   children domains.  At the top, a  number of Top-Level Domains are
   connected in a (sparse) mesh and share the global multicast address
   space.  To improve the robustness, a pair of children of the same
   parent domain MAY be configured as siblings with regard to that
   parent.

   Figure 1 illustrates a sample topology.  Double-line links denote
   intra-domain TCP peering sessions, and single-line links denote
   inter-domain TCP connections. T1 and T2 are Top-Level Domains (e.g.,
   backbone providers), containing MASC speakers T1a and T2a,
   respectively.  P3 and P4 are regional domains, containing (P3a, P3b),
   and (P4a, P4b) respectively.  P3 has a single customer (or "child"),
   C5, containing (C5a, C5b, C5c).  P4 has three children, C5, C6, C7,
   containing (C5a, C5b, C5c), (C6a, C6b), and (C7a) respectively.

                         T1a-----------T2a
                          |             |
                          |             |
                          |             |
                  P3a====P3b           P4a====P4b
                   |      |           / |    / | \
                   |      |   _______/  |   /  |  \
                   |      |  /          |  /   |   \______
                   |      | /           | /    |          \
                  C5a====C5b           C6a====C6b----------C7a
                    \\  //
                     \\//
                     C5c

                  Figure 1: Example MASC Topology

   All MASC communications use TCP. Each MASC node is connected to and
   communicates directly with other MASC nodes.  The local node acts in
   exactly one of the following four roles with respect to each remote
   note:

   INTERNAL_PEER
      The local and remote nodes are both in the same MASC domain.  For
      example, P4b is an INTERNAL_PEER of P4a.

   CHILD
      A customer relationship exists whereby the local node may obtain
      address space from the remote node.  For example, C6a is a CHILD
      in its session with P4a.







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   PARENT
      A provider relationship exists whereby the remote node may obtain
      address space from the local node.  For example, T2a is a PARENT
      in its session with P4a.  Whether space is actually requested is
      up to the implementation and local policy configuration.

   SIBLING
      No customer-provider relationship exists.  For example, T2a is a
      SIBLING in its session with T1a (Top-Level Domain SIBLING
      peering).  Also, C6b is a SIBLING in its session with C7a with
      regard to their common parent P4.

   A node's message will be propagated to its parent, all siblings with
   the same parent, and its children.  Since a domain need not have a
   direct peering session with every sibling, a MASC domain must
   propagate messages from a child domain to other children, can
   propagate messages from a parent domain to other siblings, and, if a
   Top-Level Domain, it must propagate messages from a sibling to other
   siblings, otherwise may propagate messages from a sibling domain to
   its parent and other siblings.

4.1.  Managed vs Locally-Allocated Space

   Each domain has a "Managed" Address Set, and a "Locally-Allocated"
   Address Set.  The "managed" space includes all address space which a
   domain has successfully claimed via MASC.  The "locally-allocated"
   space, on the other hand, includes all address space which MAASs
   inside the domain may use.  Thus, the locally-allocated space is a
   subset of the managed space, and refers to the portion which a domain
   allocates for its own use.

   For leaf domains (ones with no children), these two sets are
   identical, since all claimed space is allocated for local use.  A
   parent domain, on the other hand, "manages" all address space which
   it has claimed via MASC, while sub-prefixes can be allocated to
   itself and to its children.

4.2.  Prefix Lifetime

   Each prefix has an associated lifetime.  If a domain wants to use a
   prefix longer than its lifetime, that domain must "renew" the prefix
   BEFORE its lifetime expires (see Section 5.2).  If the lifetime
   cannot be extended, then the domain should either retry later to
   extend, or should choose and claim another prefix.







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   After a prefix's lifetime expires, MASC nodes in the domain that own
   that prefix must stop using that prefix.  The corresponding entry
   from the G-RIB database must be removed, and all information
   associated with the expired prefix may be deleted from the MASC
   node's local memory.

4.3.  Active vs. Deprecated Prefixes

   Each prefix advertised by a parent to its children can be either
   "active" or "deprecated".  A "deprecated" prefix is a prefix that the
   parent wishes to discontinue to use after its lifetime expires.  The
   "active" prefixes only are candidates for size expansion or lifetime
   extension.  Usually, this information will be used by a child as a
   hint to know which of the parent's prefixes might have their lifetime
   extended.

4.4.  Multi-Parent Sibling-to-Sibling and Internal Peering

   Two sibling nodes that have more than one common parent will create
   and use between them a number of transport-level connections, one per
   each common parent.  The information associated with a parent will be
   sent over the connection that corresponds to the same parent.
   Internal peers do not need to open multiple connections between them;
   a single connection is used for all information.

4.5.  Administratively-Scoped Address Allocation

   MASC can also be used for sub-allocating prefixes of addresses within
   an administrative scope zone [SCOPE], but only if the scope is
   "divisible" (as described in [MALLOC] and [MZAP]).  A MASC node can
   learn what scopes it resides within by listening to MZAP [MZAP]
   messages.

   A "Zone TLD" is a domain which has no parent domain within the scope
   zone.  Zone TLDs act as TLDs for the prefix associated with the
   scope.  Figure 2 gives an example, where a scope boundary around
   domains P3 and C5 has been added to Figure 1.  Domain P3 is a Zone
   TLD, since its only parent (T1) is outside the boundary.  Hence, P3
   can claim space directly out of the prefix associated with the scope
   itself.  Domain C5, on the other hand, has a parent within the scope
   (namely, P3), and hence is not a Zone TLD.










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                                 T1a-----------T2a
                                  |             |
                      ............|.......      |
                      .           |      .      |
                      .   P3a====P3b     .     P4a
                      .    |      |      .    /
                      .    |      |   _______/
                      .    |      |  /   .
                      .    |      | /    .
                      .   C5a====C5b     .
                      .     \\  //       .
                      .      \\//        .
                      .      C5c         .
                      .                  .
                      . Admin Scope Zone .
                      ....................

                 Figure 2: Scope Zone Example

   It is assumed that the role of a node (as discussed in Section 4)
   with respect to a given peering session is the same for every scope
   in which both ends are contained.  A peering session that crosses a
   scope boundary (such as the session between C5b and P4a in Figure 2)
   is ignored when propagating messages that pertain to the given scope.
   That is, such messages are not sent across such sessions.

5.  Protocol Details

5.1.  Claiming Space

   When a MASC node, on behalf of a MASC domain, needs more address
   space, it decides locally the size and the value of the address
   prefix(es) it will claim from one of its parents.  For example, the
   decision might be based on the knowledge this node has about its
   parent's address set, its siblings' claims and allocations, its own
   address set, the claim messages from its siblings, and/or the demand
   pattern of its children and the local domain.  A sample algorithm is
   given in Appendix A.

   A MASC node which is not in a top-level domain can initiate a claim
   toward a parent MASC domain if and only if it currently has an
   established connection with at least one node in that parent domain.

   After the prefix address and size are decided, the claim proceeds as
   follows:






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   a) The claim is scheduled to be sent after a random delay in the
      interval (0, [INITIATE_CLAIM_DELAY]).  If a claim originated by a
      node from the same MASC domain is received, and that claim
      eliminates the need for the local claim, the local claim is
      canceled and no further action is taken.

   b) The claim is sent to one of the parents (if the domain is not a
      top-level domain), all known siblings with the same parent, and
      all internal peers.  A Claim-Timer is then started at
      [WAITING_PERIOD], and the MASC node starts listening for colliding
      claims.

   c) If a colliding claim is received while the Claim-Timer is running,
      that claim is compared with the locally initiated claim using the
      function described in Section 5.1.1.  If the local claim is the
      loser, a new prefix must be chosen to claim, and the loser claim's
      Claim-Timer must be canceled.  The loser claim can be either
      explicitly withdrawn, or can be left to expire without taking
      further actions.  If the winning claim was originated by a node
      from the same MASC domain, no new claim will be initiated.  If the
      local claim is the winner, no actions need to be taken.

   d) If the Claim-Timer expires, the claimed prefix becomes associated
      with the claimer's domain, i.e. it is considered allocated to that
      domain and the following actions can be performed:

      o  Advertise the prefix to its parent, and to all siblings with
         the same parent, by sending a PREFIX_IN_USE claim to them.

      o  Inject the prefix into the G-RIB of the inter-domain routing
         protocol.

      o  Send a PREFIX_MANAGED message to all children and internal
         peers, informing them that they may issue claims within the
         managed space.  A sub-prefix may then be claimed for local
         usage (see Section 12.2).

   Each MASC node receives all claims from its siblings and children.  A
   received claim must be evaluated against all claims saved in the
   local cache using the function described in Section 5.1.1.  The
   output of the function will define the further processing of that
   claim (see Section 11).









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5.1.1.  Claim Comparison Function

   Each claim message includes:

   o  a "type", being one of: PREFIX_IN_USE, CLAIM_DENIED,
      CLAIM_TO_EXPAND, or NEW_CLAIM  (PREFIX_MANAGED and WITHDRAW are
      not considered as claims that have to be compared)

   o  timestamp when the claim was initiated

   o  the claimed prefix and lifetime

   o  MASC Identifier of the node that originated the claim

   When two claims are compared, first the type is compared based on the
   following precedence:

   PREFIX_IN_USE > CLAIM_DENIED > CLAIM_TO_EXPAND > NEW_CLAIM

   If the type is the same, then the timestamps are used to compare the
   claims.  In practice, two claims will have the same type if the type
   is either NEW_CLAIM (ordinary collision) or PREFIX_IN_USE (signal for
   a clash).  When the timestamps are compared, the claim with the
   smallest, i.e. earliest timestamp wins.  If the timestamps are the
   same, then the claim with the smallest Origin Node Identifier wins.

5.2.  Renewing an Existing Claim

   The procedure for extending the lifetime of prefixes already in use
   is the same as claiming new space (see Section 5.1), except that the
   claim type must be CLAIM_TO_EXPAND, while the Address and the Mask of
   the claim (see Section 7.3) must be the same as the already allocated
   prefix.  If the Claim-Timer expires and there is no collision, the
   desired lifetime is assumed.

5.3.  Expanding an Existing Prefix

   The procedure for extending the lifetime of prefixes already in use
   is the same as claiming new space (see Section 5.1), except that the
   claim type must be CLAIM_TO_EXPAND, while the Address and the Mask of
   the claim (see Section 7.3) must be set to the desired values.  If
   the Claim-Timer expires and there is no collision, the desired larger
   prefix is associated with the local domain.








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5.4.  Releasing Allocated Space

   If the lifetime of a prefix allocated to the local domain expires and
   the domain does not need to reuse it, all resources associated with
   this prefix are deleted and no further actions are taken.  If the
   lifetime of the prefix has not expired, and if no subranges of that
   prefix have being allocated for local usage or by some of the
   children domains, the space may be released by sending a withdraw
   message to the parent domain, all known siblings with the same
   parent, and all internal peers.

6.  Constants

   MASC uses the following constants:

   [PORT_NUMBER]
      2587.  The TCP port number used to listen for incoming MASC
      connections, as assigned by IANA.

   [WAITING_PERIOD]
      The amount of time (in seconds) that must pass between a NEW_CLAIM
      (or CLAIM_TO_EXPAND), and a PREFIX_IN_USE for the same prefix.
      This must be long enough to reasonably span any single inter-
      domain network partition.  Default: 172800 seconds (i.e. 48
      hours).

   [INITIATE_CLAIM_DELAY]
      The amount of time (in seconds) a MASC node must wait before
      initiating a new claim or a claim for space expansion. This must
      be a random value in the interval (0, [INITIATE_CLAIM_DELAY]).
      Default value for [INITIATE_CLAIM_DELAY]: 600 seconds (i.e. 10
      minutes).

   [TLD_ID]
      The Parent Domain Identifier used by a Top-Level Domain (which has
      no parent). Must be 0.

   [HOLDTIME]
      The amount of time (in seconds) that must pass without any
      messages received from a remote node before considering the
      connection is down.  Default: 240 seconds (i.e. 4 minutes).










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7.  Message Formats

   This section describes message formats used by MASC.

   Messages are sent over a reliable transport protocol connection.  A
   message is processed only after it is entirely received.  The maximum
   message size is 4096 octets.  All implementations are required to
   support this maximum message size.

7.1.  Message Header Format

   Each message has a fixed-size (4-octets) header.  There may or may
   not be a data portion following the header, depending on the message
   type.  The layout of these fields is shown below:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Length               |      Type     |   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Length:
      This 2-octet unsigned integer indicates the total length of the
      message, including the header, in octets.  Thus, e.g., it allows
      one to locate in the transport-level stream the start of the next
      message.  The value of the Length field must always be at least 4
      and no greater than 4096, and may be further constrained,
      depending on the message type.  No "padding" of extra data after
      the message is allowed, so the Length field must have the smallest
      value required given the rest of the message.

   Type:
      This 1-octet unsigned integer indicates the type code of the
      message.  The following type codes are defined:

            1 - OPEN
            2 - UPDATE
            3 - NOTIFICATION
            4 - KEEPALIVE

   Reserved:
      This 1-octet field is reserved.  MUST be set to zero by the sender,
      and MUST be ignored by the receiver.








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7.2.  OPEN Message Format

   After a transport protocol connection is established, the first
   message sent by each side is an OPEN message.  If the OPEN message is
   acceptable, a KEEPALIVE message confirming the OPEN is sent back.
   Once the OPEN is confirmed, UPDATE, KEEPALIVE, and NOTIFICATION
   messages may be exchanged.

   The minimum length of the OPEN message is 20 octets (including
   message header).  In addition to the fixed-size MASC header, the OPEN
   message contains the following fields:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Version    |R| AddrFam |Rol|           Hold Time           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Sender Domain Identifier    (variable length)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Sender MASC Node Identifier (variable length)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Parent's Domain Identifier  (variable length)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                     (Optional Parameters)                     |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Version:
      This 1-octet unsigned integer indicates the protocol version
      number of the message.  The current MASC version number is 1.

   R bit:
      This 1-bit field is reserved.  MUST be set to zero by the sender,
      and MUST be ignored by the receiver.

   AddrFam:
      This 5-bit field is the IANA-assigned address family number of the
      encoded prefix [IANA].  These include (among others):

      Number    Description
      ------    -----------
         1      IP (IP version 4)
         2      IPv6 (IP version 6)







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   My Role (Rol):
      This 2-bit field indicates the proposed relationship of the
      sending system to the receiving system:
         00 = INTERNAL_PEER (sent from one internal peer to another)
         01 = CHILD (sent from a child to its parent)
         10 = SIBLING (sent from one sibling to another)
         11 = PARENT (sent from a parent to its child)

   Hold Time:
      This 2-octet unsigned integer indicates the number of seconds that
      the sender proposes for the value of the Hold Timer.  Upon receipt
      of an OPEN message, a MASC speaker MUST calculate the value of the
      Hold Timer by using the smaller of its configured Hold Time for
      that peer and the Hold Time received in the OPEN message.  The
      Hold Time MUST be either zero or at least three seconds.  An
      implementation may reject connections on the basis of the Hold
      Time.  The calculated value indicates the maximum number of
      seconds that may elapse between the receipt of successive
      KEEPALIVE and/or UPDATE messages by the sender.  RECOMMENDED value
      is [HOLDTIME] seconds.

   Sender Domain Identifier:
      A globally unique identifier.  Its length is determined based on
      the Address Family, and should be treated as an unsigned integer
      (e.g. a 4-octet integer for IPv4, or a 16-octet integer for IPv6),
      but must be at least 4 octets long.  It should be set to the
      Autonomous System number of the sender, but the network unicast
      prefix address is also acceptable.

   Sender MASC Node Identifier:
      This field's length and format are same as the Sender Domain
      Identifier field, and indicates the MASC Node Identifier of the
      sender.  A given MASC speaker sets the value of its MASC Node
      Identifier to a globally-unique value assigned to that MASC
      speaker (e.g., an IPv4 or IPv6 address).  The value of the MASC
      Node Identifier is determined on startup and is the same for every
      MASC session opened.

   Parent's Domain Identifier:
      This field's length and format are same as the Sender Domain
      Identifier field, and is set to the Domain Identifier of the
      sender's parent (e.g. the parent's Autonomous System number, or
      network prefix address), or is set to [TLD_ID] if the sender is a
      TLD.  Used only when Rol is INTERNAL_PEER or SIBLING, otherwise is
      ignored.  This field is used to determine the common parents
      between siblings, to associate each sibling-to-sibling connection
      with a particular parent, and to discover TLD-related




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      configuration problems among internal peers.  If a non-TLD node
      does not know yet the Domain ID of any of its parents, it can use
      its own Domain ID in the OPEN messages to its internal peers.

   Optional Parameters:
      This field may contain a list of optional parameters, where each
      parameter is encoded as a <Parameter Length, Parameter Type,
      Parameter Value> triplet.  The combined length of all optional
      parameters can be derived from the Length field in the message
      header.

       0                   1
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
      |  Parm. Length |  Parm. Type   |  Parameter Value (variable)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...

      Parameter Length is a one octet field that contains the length of
      the Parameter Value field in octets.  Parameter Type is a one
      octet field that unambiguously identifies individual parameters.
      Parameter Value is a variable length field that is interpreted
      according to the value of the Parameter Type field.  Unrecognized
      optional parameters MUST be silently ignored.

      This document does not define any optional parameters.

7.3.  UPDATE Message Format

   UPDATE messages are used to transfer Claim/Collision/PrefixManaged
   information between MASC speakers.  The UPDATE message always
   includes the fixed-size MASC header, and one or more attributes as
   described below.  The minimum length of the UPDATE message is 40
   octets (including the message header).

   Each attribute is of the form:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Length           |     Type      |   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Data ...                                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   All attributes are 4-octets aligned.






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   Length:
      The Length is the length of the entire attribute, including the
      length, type, and data fields.  If other attributes are nested
      within the data field, the length includes the size of all such
      nested attributes.

   Type:
      This 1-octet unsigned integer indicates the type code of the
      attribute.  The following type codes are defined:

         0 = PREFIX_IN_USE (prefix is being used by the origin)
         1 = CLAIM_DENIED (the claim is refused (probably by the
             origin's parent domain))
         2 = CLAIM_TO_EXPAND (origin is trying to expand the size of
             an existing prefix)
         3 = NEW_CLAIM (origin is trying to claim a new prefix)
         4 = PREFIX_MANAGED (parent is informing child of space
             available)
         5 = WITHDRAW (origin is withdrawing a previous claim)

      Types 128-255 are reserved for "optional" attributes.  If a
      required attribute is unrecognized, a NOTIFICATION with UPDATE
      Error Code and Unrecognized Required Attribute subcode will be
      sent.  Unrecognized optional attributes are simply ignored.

   Reserved:
      This 1-octet field is reserved.  MUST be set to zero by the
      sender, and MUST be ignored by the receiver.

   Types 0-3 are collectively called "CLAIMs".  The message format below
   describes the encoding of a CLAIM, PREFIX_MANAGED and WITHDRAW.




















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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Reserved1   |D| AddrFam |Rol|           Reserved2           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Claim Timestamp                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Claim Lifetime                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Claim Holdtime                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Origin Domain Identifier (variable length) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Origin Node Identifier   (variable length) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Address (variable length)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Mask    (variable length)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                     (Optional Parameters)                     |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Reserved1:
      This 1-octet field is reserved.  MUST be set to zero by the
      sender, and MUST be ignored by the receiver.

   D-bit:
      DEPRECATED_PREFIX bit. If set, indicates that the advertised
      address prefix is Deprecated, otherwise the prefix is Active (see
      Section 4.3).

   AddrFam:
      This 5-bit field is the IANA-assigned address family number of the
      encoded prefix [IANA].

   Rol:
      This 2-bit field indicates the relationship/role of the Origin of
      the message to the node sending that message:
         00 = INTERNAL (originated by the sender's domain)
         01 = CHILD (originated by a child of the sender's domain)
         10 = SIBLING (originated by a sibling of the sender's domain)
         11 = PARENT (originated by a parent of the sender's domain)

   Reserved2:
      This 2-octet field is reserved.  MUST be set to zero by the
      sender, and MUST be ignored by the receiver.



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   Claim Timestamp:
      The timestamp of the claim when it was originated. The timestamp
      is expressed in number of seconds since midnight (0 hour), January
      1, 1970, Greenwich.

   Claim Lifetime:
      The time in seconds between the Claim Timestamp, and the time at
      which the prefix will become free.

   Claim Holdtime:
      The time in seconds between the Claim Timestamp, and the time at
      which the claim should be deleted from the local cache. For
      PREFIX_IN_USE and PREFIX_MANAGED claims it should be equal to
      Claim Lifetime; for CLAIM_TO_EXPAND, NEW_CLAIM, and CLAIM_DENIED
      it should be equal to [WAITING_PERIOD].

   Origin Domain Identifier:
      The domain identifier of the claim originator.  Its length and
      format definition are same as the Sender Domain Identifier (see
      Section 7.2).

   Origin Node Identifier:
      The MASC Node ID of the claim originator.  Its length and format
      definition are same as the Sender MASC Node Identifier (see
      Section 7.2).

   Address:
      The address associated with the given prefix to be encoded.  The
      length is determined based on the Address Family (e.g. 4 octets
      for IPv4, 16 for IPv6)

   Mask:
      The mask associated with the given prefix.  The length is the same
      as the Address field and is determined based on the Address
      Family. The field contains the full bitmask.

   Optional Parameters:
      This field may contain a list of optional parameters, where each
      parameter is encoded using same format as the optional parameters
      of an OPEN message (see Section 7.2).  Unrecognized optional
      parameters MUST be silently ignored.  This document does not
      define any optional parameters.









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7.4.  KEEPALIVE Message Format

   MASC does not use any transport protocol-based keep-alive mechanism
   to determine if peers are reachable.  Instead, KEEPALIVE messages are
   exchanged between peers often enough as not to cause the Hold Timer
   to expire.  A reasonable maximum time between the last KEEPALIVE or
   UPDATE message sent, and the time at which a KEEPALIVE message is
   sent, would be one third of the Hold Time interval.  KEEPALIVE
   messages MUST NOT be sent more frequently than one per second.  An
   implementation MAY adjust the rate at which it sends KEEPALIVE
   messages as a function of the Hold Time interval.

   If the negotiated Hold Time interval is zero, then periodic KEEPALIVE
   messages MUST NOT be sent.

   A KEEPALIVE message consists of only a message header, and has a
   length of 4 octets.

7.5.  NOTIFICATION Message Format

   A NOTIFICATION message is sent when an error condition is detected.
   Depending on the error condition, the MASC connection might or must
   be closed immediately after sending the message.  If the sender of
   the NOTIFICATION decides that the connection is to be closed, it will
   indicate this by zeroing the O-bit in the NOTIFICATION message (see
   below).

   In addition to the fixed-size MASC header, the NOTIFICATION message
   contains the following fields:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |O| Error code  | Error subcode |           Data                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   O-bit:
      Open-bit.  If zero, it indicates that the sender will close the
      connection.  If '1', it indicates that the sender has chosen to
      keep the connection open.

   Error Code:
      This 7-bit unsigned integer indicates the type of NOTIFICATION.
      The following Error Codes have been defined:





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         Error Code       Symbolic Name               Reference

           1         Message Header Error             Section 8.1

           2         OPEN Message Error               Section 8.2

           3         UPDATE Message Error             Section 8.3

           4         Hold Timer Expired               Section 8.4

           5         Finite State Machine Error       Section 8.5

           6         NOTIFICATION Message Error       Section 8.6

           7         Cease                            Section 8.7

   Error subcode:
      This 1-octet unsigned integer provides more specific information
      about the nature of the reported error.  Each Error Code may have
      one or more Error Subcodes associated with it.  If no appropriate
      Error Subcode is defined, then a zero (Unspecific) value is used
      for the Error Subcode field, and the O-bit must be zero (i.e. the
      connection will be closed).  The notation used in the error
      description below is: MC = Must Close connection = O-bit is zero;
      CC = Can Close connection = O-bit might be zero.

               Message Header Error subcodes:
                        0 - Unspecific                        (MC)
                        1 - Bad Message Length                (MC)
                        2 - Bad Message Type                  (CC)

               OPEN Message Error subcodes:

                        0 - Unspecific                        (MC)
                        1 - Unsupported Version Number        (MC)
                        2 - Bad Peer Domain ID                (MC)
                        3 - Bad Peer MASC Node ID             (MC)
                        6 - Unacceptable Hold Time            (MC)
                        7 - Invalid Parent Configuration      (MC)
                        8 - Inconsistent Role                 (MC)
                        9 - Bad Parent Domain ID              (MC)
                       10 - No Common Parent                  (MC)
                       13 - Unrecognized Address Family       (MC)








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               UPDATE Message Error subcodes:
                        0 - Unspecific                        (MC)
                        1 - Malformed Attribute List          (MC)
                        2 - Unrecognized Required Attribute   (CC)
                        5 - Attribute Length Error            (MC)
                       10 - Invalid Address field             (CC)
                       11 - Invalid Mask field                (CC)
                       12 - Non-Contiguous Mask               (CC)
                       13 - Unrecognized Address Family       (MC)
                       14 - Claim Type Error                  (CC)
                       15 - Origin Domain ID Error            (CC)
                       16 - Origin Node ID Error              (CC)
                       17 - Claim Lifetime Too Short          (CC)
                       18 - Claim Lifetime Too Long           (CC)
                       19 - Claim Timestamp Too Old           (CC)
                       20 - Claim Timestamp Too New           (CC)
                       21 - Claim Prefix Size Too Small       (CC)
                       22 - Claim Prefix Size Too Large       (CC)
                       23 - Illegal Origin Role Error         (CC)
                       24 - No Appropriate Parent Prefix      (CC)
                       25 - No Appropriate Child Prefix       (CC)
                       26 - No Appropriate Internal Prefix    (CC)
                       27 - No Appropriate Sibling Prefix     (CC)
                       28 - Claim Holdtime Too Short          (CC)
                       29 - Claim Holdtime Too Long           (CC)

         Hold Timer Expired subcodes (the O-bit is always zero):

                        0 - Unspecific                        (MC)

               Finite State Machine Error subcodes:

                        0 - Unspecific                        (MC)
                        1 - Open/Close MASC Connection FSM Error (MC)
                        2 - Unexpected Message Type FSM Error (MC)

               Cease subcodes (the O-bit is always zero):

                        0 - Unspecific                        (MC)

               NOTIFICATION subcodes (the O-bit is always zero):

                        0 - Unspecific                        (MC)

   Data:
      This variable-length field is used to diagnose the reason for the
      NOTIFICATION.  The contents of the Data field depend upon the
      Error Code and Error Subcode.  See Section 8 for more details.



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      Note that the length of the Data field can be determined from the
      message Length field by the formula:

         Message Length = 6 + Data Length

      The minimum length of the NOTIFICATION message is 6 octets
      (including message header).

8.  MASC Error Handling

   This section describes actions to be taken when errors are detected
   while processing MASC messages.  MASC Error Handling is similar to
   that of BGP [BGP].

   When any of the conditions described here are detected, a
   NOTIFICATION message with the indicated Error Code, Error Subcode,
   and Data fields is sent.  In addition, the MASC connection might be
   closed.  If no Error Subcode is specified, then a zero (Unspecific)
   must be used.

   The phrase "the MASC connection is closed" means that the transport
   protocol connection has been closed and that all resources for that
   MASC connection have been deallocated.

   Unless specified explicitly, the Data field of the NOTIFICATION
   message is empty.

8.1.  Message Header Error Handling

   All errors detected while processing the Message Header are indicated
   by sending the NOTIFICATION message with Error Code Message Header
   Error.  The Error Subcode elaborates on the specific nature of the
   error.  The Data field contains the erroneous Message (including the
   message header).

   If the Length field of the message header is less than 4 or greater
   than 4096, or if the length of an OPEN message is less  than the
   minimum length of the OPEN message, or if the length of an UPDATE
   message is less than the minimum length of the UPDATE message, or if
   the length of a KEEPALIVE message is not equal to 4, then the Error
   Subcode is set to Bad Message Length.

   If the Type field of the message header is not recognized, then the
   Error Subcode is set to Bad Message Type.







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8.2.  OPEN Message Error Handling

   All errors detected while processing the OPEN message are indicated
   by sending the NOTIFICATION message with Error Code OPEN Message
   Error.  The Error Subcode elaborates on the specific nature of the
   error.  The Data field contains the erroneous OPEN Message (excluding
   the Message Header), unless stated otherwise.

   If the version number contained in the Version field of the received
   OPEN message is not supported, then the Error Subcode is set to
   Unsupported Version Number.  The Data field is a 1-octet unsigned
   integer, which indicates the largest locally supported version number
   less than the version the remote MASC node bid (as indicated in the
   received OPEN message).

   If the Sender Domain Identifier field of the OPEN message is
   unacceptable, then the Error Subcode is set to Bad Peer Domain ID.
   The determination of acceptable Domain IDs is outside the scope of
   this protocol.

   If the Sender MASC Node Identifier field of the OPEN message is
   unacceptable, then the Error Subcode is set to Bad Peer MASC Node ID.
   The determination of acceptable Node IDs is outside the scope of this
   protocol.

   If the Hold Time field of the OPEN message is unacceptable, then the
   Error Subcode MUST be set to Unacceptable Hold Time.  An
   implementation MUST reject Hold Time values of one or two seconds.
   An implementation MAY reject any proposed Hold Time.  An
   implementation which accepts a Hold Time MUST use the negotiated
   value for the Hold Time.

   If the remote system's proposed Role is INTERNAL_PEER, and either
   (but not both) the local system or the remote system's Parent Domain
   ID is [TLD_ID], then the Error Subcode is set to Invalid Parent
   Configuration.  The Data field must be filled with all the local
   system's Parent Domain IDs.

   If the remote system's proposed Role conflicts with its expected role
   (based on the local system's configured Role), then the Error Subcode
   is set to Inconsistent Role.  The Data field is 1-octet long, and
   contains the local system's configured Role.

   If the remote system's Parent Domain ID is unacceptable, then the
   Error Subcode is set to Bad Parent Domain ID, and the Data field is
   filled with the erroneous Parent Domain ID.  The determination of
   acceptable Parent Domain ID is outside the scope of this protocol.




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   If the remote system is supposed to be a sibling, but it does not
   have a common parent with the local system (based on the Parent
   Domain ID information in the OPEN message), the Error Subcode is set
   to No Common Parent, and the Data field is filled with all Parent
   Domain IDs of the local MASC domain.

   If the Address Family is unrecognized, then the Error Subcode is set
   to Unrecognized Address Family.

8.3.  UPDATE Message Error Handling

   All errors detected while processing the UPDATE message are indicated
   by sending the NOTIFICATION message with Error Code UPDATE Message
   Error.  The error subcode elaborates on the specific nature of the
   error.  The Data field contains the erroneous UPDATE Message
   (including the attribute header, but excluding the Message Header),
   unless stated otherwise.

   If any recognized attribute has an Attribute Length that conflicts
   with the expected length (based on the attribute type code), then the
   Error Subcode is set to Attribute Length Error.

   If any of the mandatory well-known attributes are not recognized,
   then the Error Subcode is set to Unrecognized Required Attribute.

   If the Address field includes an invalid address (except 0), then the
   Error Subcode is set to Invalid Address.

   If the Mask field includes an invalid mask (for example, starting
   with 0), then the Error Subcode is set to Invalid Mask.

   If the Mask field includes a non-contiguous bitmask, and that MASC
   server does not support, or is not configured to use non-contiguous
   masks, then the Error Subcode is set to Non-Contiguous Mask.

   If the Address Family is unrecognized, then the Error Subcode is set
   to Unrecognized Address Family.

   If the Origin Role/Claim Type combination is not one of the
   following, then the Error Subcode is set to Claim Type Error.











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      Origin  Claim
      Role    Type

      ICS     PREFIX_IN_USE   (0)
      I  P    CLAIM_DENIED    (1)
      ICS     CLAIM_TO_EXPAND (2)
      ICS     NEW_CLAIM       (3)
      I  P    PREFIX_MANAGED  (4)
      ICSP    WITHDRAW        (5)

   If there is a reason to believe that the Origin Domain ID is invalid,
   then the Error Subcode is set to Origin Domain ID Error.  The same
   applies for Origin Node ID (the corresponding error is Origin Node ID
   Error).

   If a node (usually a parent receiving a claim from a child) decides
   that the Claim Lifetime is too short (for example, less than 172800,
   i.e. 48 hours), it MAY send an UPDATE Message Error with subcode
   Claim Lifetime Too Short.

   If a node (usually a parent receiving a claim from a child) decides
   that the Claim Lifetime is too long (for example, more than
   15,768,000, i.e. half year), then it MAY send an UPDATE Message Error
   with subcode Claim Lifetime Too Long.  Note that usually a parent
   MASC node should send first CLAIM_DENIED collision messages with
   Claim Lifetime field filled with the longest acceptable lifetime.  If
   the child refuses to claim with shorter lifetime, then Claim Lifetime
   Too Long should be sent.

   If a node (usually a parent receiving a claim from a child) decides
   that the Claim Timestamp is too small, i.e. too old (for example, if
   a node is self-confident that its clock is quite accurate), then it
   MUST send an UPDATE Message Error with subcode Claim Timestamp Too
   Old.  Claim Timestamp Too New is defined similarly.

   If a node (usually a parent receiving a claim from a child) decides
   that the prefix size implied by the Mask field is too small (for
   example, smaller than 16 addresses), then it MAY send an UPDATE
   Message Error with subcode Claim Prefix Size Too Small.

   If a node (usually a parent receiving a claim from a child) decides
   that the prefix size implied by the Mask field is too large, then it
   MAY send an UPDATE Message Error with subcode Claim Prefix Size Too
   Large.  Note that usually a parent MASC node should send first
   CLAIM_DENIED collision messages for some subrange of the child's
   large claimed address range.  If the child refuses to shrink the
   claim size, then Claim Prefix Size Too Large should be sent.




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   If the received UPDATE message's computed Updated Origin Role is
   illegal (see Table 1 in Section 11.1), then the Error Subcode is set
   to Illegal Origin Role Error.

   If the received UPDATE message needs to be associated with a parent's
   prefix, but the association is not successful, then the Error Subcode
   is set to No Appropriate Parent Prefix.  The No Appropriate Child
   Prefix, No Appropriate Internal Prefix, and No Appropriate Sibling
   Prefix Error Subcodes are defined similarly.

   If a node decides that the Claim Holdtime is too short (for example,
   just few seconds), it MAY send an UPDATE Message Error with subcode
   Claim Holdtime Too Short.

   If a node decides that the Claim Holdtime is too long (for example,
   more than 15,768,000, i.e. half year), then it SHOULD send an UPDATE
   Message Error with subcode Claim Holdtime Too Long.

   If any other error is encountered when processing attributes, then
   the Error Subcode is set to Malformed Attribute List, and the erratic
   attribute is included in the data field.

8.4.  Hold Timer Expired Error Handling

   If a system does not receive successive KEEPALIVE and/or UPDATE
   and/or NOTIFICATION messages within the period specified in the Hold
   Time field of the OPEN message, then the NOTIFICATION message with
   Hold Timer Expired Error Code must be sent and the MASC connection
   closed.

8.5.  Finite State Machine Error Handling

   Any error detected by the MASC Finite State Machine (e.g., receipt of
   an unexpected event) is indicated by sending the NOTIFICATION message
   with Error Code Finite State Machine Error.  The Error Subcode
   elaborates on the specific nature of the error.

8.6.  NOTIFICATION Message Error Handling

   If a node sends a NOTIFICATION message, and there is an error in that
   message, and the O-bit of that message is not zero, a NOTIFICATION
   with O-bit zeroed, Error Code of NOTIFICATION Error, and subcode
   Unspecific must be sent.  In addition, the Data field must include
   the erratic NOTIFICATION message.  However, if the erratic
   NOTIFICATION message had the O-bit zeroed, then any error, such as an
   unrecognized Error Code or Error Subcode, should be noticed, logged





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   locally, and brought to the attention of the administrator of the
   remote node.  The means to do this, however, lies outside the scope
   of this document.

8.7.  Cease

   In absence of any fatal errors (that are indicated in this section),
   a MASC node may choose at any given time to close its MASC connection
   by sending the NOTIFICATION message with Error Code Cease.  However,
   the Cease NOTIFICATION message must not be used when a fatal error
   indicated by this section does exist.

8.8.  Connection Collision Detection

   If a pair of MASC speakers try simultaneously to establish a TCP
   connection to each other, then two parallel connections between this
   pair of speakers might well be formed.  We refer to this situation as
   connection collision.  Clearly, one of these connections must be
   closed.  Note that if the nodes were siblings, and each of those
   connections was associated with a different parent, then we do not
   consider this situation as collision (see Section 4.4).

   Based on the value of the MASC Node Identifier a convention is
   established for detecting which MASC connection is to be preserved
   when a connection collision does occur.  The convention is to compare
   the MASC Node Identifiers of the remote nodes involved in the
   collision and to retain only the connection initiated by the MASC
   speaker with the higher-valued MASC Node Identifier.

   Upon receipt of an OPEN message, the local system must examine all of
   its connections that are in the OpenConfirm state.  A MASC speaker
   may also examine connections in an OpenSent state if it knows the
   MASC Node Identifier of the remote node by means outside of the
   protocol.  If among these connections there is a connection to a
   remote MASC speaker whose MASC Node Identifier equals the one in the
   OPEN message, and, in case of a sibling-to-sibling connection, the
   Parent Domain ID of that connection equals the one in the OPEN
   message, then the local system performs the following connection
   collision resolution procedure:

   1. The MASC Node Identifier of the local system is compared to the
      MASC Node Identifier of the remote system (as specified in the
      OPEN message).  Comparing MASC Node Identifiers is done by
      treating them as unsigned integers (e.g. 4-octets long for IPv4
      and 16-octets long for IPv6).






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   2. If the value of the local MASC Node Identifier is less than the
      remote one, the local system closes MASC connection that already
      exists (the one that is already in the OpenConfirm state), and
      accepts the MASC connection initiated by the remote system.

   3. Otherwise, the local system closes the newly created MASC
      connection (the one associated with the newly received OPEN
      message), and continues to use the existing one (the one that is
      already in the OpenConfirm state).

   A connection collision with an existing MASC connection that is in
   the Established state causes unconditional closing of the newly
   created connection.  Note that a connection collision cannot be
   detected with connections that are in Idle, or Connect, or Active
   states (see Section 10).

   Closing the MASC connection (that results from the collision
   resolution procedure) is accomplished by sending the NOTIFICATION
   message with the Error Code Cease.

9.  MASC Version Negotiation

   MASC speakers may negotiate the version of the protocol by making
   multiple attempts to open a MASC connection, starting with the
   highest version number each supports.  If an open attempt fails with
   an Error Code OPEN Message Error, and an Error Subcode Unsupported
   Version Number, then the MASC speaker has available the version
   number it tried, the version number the remote node tried, the
   version number passed by the remote node in the NOTIFICATION message,
   and the version numbers that it supports.  If the two MASC speakers
   do support one or more common versions, then this will allow them to
   rapidly determine the highest common version. In order to support
   MASC version negotiation, future versions of MASC must retain the
   format of the OPEN and NOTIFICATION messages.

10.  MASC Finite State Machine

   This section specifies MASC operation in terms of a Finite State
   Machine (FSM).  The FSM and the operations are peer peering session.
   Following is a brief summary and overview of MASC operations by state
   as determined by this FSM.

   Initially the peering session is in the Idle state.








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10.1.  Open/Close MASC Connection FSM

   Idle state:

      In this state MASC refuses all incoming MASC connections from the
      peer.  No resources are allocated to the remote node.  In response
      to the Start event (initiated by either system or operator) the
      local system initializes all MASC resources, starts the
      ConnectRetry timer, initiates a transport connection to the remote
      node, while listening for a connection that may be initiated by
      the remote MASC node, and changes its state to Connect.  The exact
      value of the ConnectRetry timer is a local matter, but should be
      sufficiently large to allow TCP initialization.

      If a MASC speaker detects an error, it shuts down the connection
      and changes its state to Idle. Getting out of the Idle state
      requires generation of the Start event.  If such an event is
      generated automatically, then persistent MASC errors may result in
      persistent flapping of the speaker.  To avoid such a condition it
      is recommended that Start events should not be generated
      immediately for a node that was previously transitioned to Idle
      due to an error. For a node that was previously transitioned to
      Idle due to an error, the time between consecutive generation of
      Start events, if such events are generated automatically, shall
      exponentially increase. The value of the initial timer shall be 60
      seconds. The time shall be doubled for each consecutive retry, but
      shall not be longer than 24 hours.

      Any other event received in the Idle state is ignored.

   Connect state:

      In this state MASC is waiting for the transport protocol
      connection to be completed.

      If the transport protocol connection succeeds, the local system
      clears the ConnectRetry timer, completes initialization, sends an
      OPEN message to the remote node, and changes its state to
      OpenSent. If the transport protocol connect fails (e.g.,
      retransmission timeout), the local system restarts the
      ConnectRetry timer, continues to listen for a connection that may
      be initiated by the remote MASC node, and changes its state to
      Active state.








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      In response to the ConnectRetry timer expired event, the local
      system restarts the ConnectRetry timer, initiates a transport
      connection to the other MASC node, continues to listen for a
      connection that may be initiated by the remote MASC node, and
      stays in the Connect state.

      The Start event is ignored in the Connect state.

      In response to any other event (initiated by either system or
      operator), the local system releases all MASC resources associated
      with this connection and changes its state to Idle.

   Active state:

      In this state MASC is trying to acquire a remote node by listening
      for a transport protocol connection initiated by the remote node.

      If the transport protocol connection succeeds, the local system
      clears the ConnectRetry timer, completes initialization, sends an
      OPEN message to the remote node, sets its Hold Timer to a large
      value, and changes its state to OpenSent.  A Hold Timer value of
      [HOLDTIME] seconds is suggested.

      In response to the ConnectRetry timer expired event, the local
      system restarts the ConnectRetry timer, initiates a transport
      connection to other MASC node, continues to listen for a
      connection that may be initiated by the remote MASC node, and
      changes its state to Connect.

      If the local system detects that a remote node is trying to
      establish a MASC connection to it, and the IP address of the
      remote node is not an expected one, the local system restarts the
      ConnectRetry timer, rejects the attempted connection, continues to
      listen for a connection that may be initiated by the remote MASC
      node, and stays in the Active state.

      The Start event is ignored in the Active state.

      In response to any other event (initiated by either system or
      operator), the local system releases all MASC resources associated
      with this connection and changes its state to Idle.

   OpenSent state:

      In this state MASC waits for an OPEN message from the remote node.
      When an OPEN message is received, all fields are checked for
      correctness.  If the MASC message header checking or OPEN message
      checking detects an error (see Section 8.2), or a connection



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      collision (see Section 8.8) the local system sends a NOTIFICATION
      message and, if the connection is to be closed, it changes its
      state to Idle.

      If the locally configured role is SIBLING and there is no parent
      domain with Domain ID equal to the Parent Domain ID in the OPEN
      message, the local system sends a NOTIFICATION Open Message  Error
      with Error Subcode set to No Common Parent, the connection must be
      closed, and the state of the local system must be changed to Idle.

      If there are no errors in the OPEN message, MASC sends a KEEPALIVE
      message and sets a KeepAlive timer.  The Hold Timer, which was
      originally set to a large value (see above), is replaced with the
      negotiated Hold Time value (see Section 7.2).  If the negotiated
      Hold Time value is zero, then the Hold Time timer and KeepAlive
      timers are not started.  If the value of the MASC Domain ID field
      is the same as the local MASC Domain ID, and if the Role field of
      the OPEN message is set to INTERNAL_PEER, then the connection is
      an "internal" connection; otherwise, it is "external".  Finally,
      the state is changed to OpenConfirm.

      If a disconnect notification is received from the underlying
      transport protocol, the local system closes the MASC connection,
      restarts the ConnectRetry timer, while continue listening for
      connection that may be initiated by the remote MASC node, and goes
      into the Active state.

      If the Hold Timer expires, the local system sends a NOTIFICATION
      message with error code Hold Timer Expired and changes its state
      to Idle.

      In response to the Stop event (initiated by either system or
      operator) the local system sends a NOTIFICATION message with Error
      Code Cease and changes its state to Idle.

      The Start event is ignored in the OpenSent state.

      In response to any other event the local system sends a
      NOTIFICATION message with Error Code Finite State Machine Error
      and Error Subcode Open/Close MASC Connection FSM Error, and
      changes its state to Idle.

      Whenever MASC changes its state from OpenSent to Idle, it closes
      the MASC (and transport-level) connection and releases all
      resources associated with that connection.






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   OpenConfirm state:

      In this state MASC waits for a KEEPALIVE or NOTIFICATION message.

      If the local system receives a KEEPALIVE message, it changes its
      state to Established.

      If the Hold Timer expires before a KEEPALIVE message is received,
      the local system sends a NOTIFICATION message with error code Hold
      Timer Expired and changes its state to Idle.

      If the local system receives a NOTIFICATION message with the O-bit
      zeroed, it changes its state to Idle.

      If the KeepAlive timer expires, the local system sends a KEEPALIVE
      message and restarts its KeepAlive timer.

      If a disconnect notification is received from the underlying
      transport protocol, the local system changes its state to Idle.

      In response to the Stop event (initiated by either system or
      operator) the local system sends a NOTIFICATION message with Error
      Code Cease and changes its state to Idle.

      The Start event is ignored in the OpenConfirm state.

      In response to any other event the local system sends a
      NOTIFICATION message with Error Code Finite State Machine Error
      and Error Subcode Unspecific, and changes its state to Idle.

      Whenever MASC changes its state from OpenConfirm to Idle, it
      closes the MASC (and transport-level) connection and releases all
      resources associated with that connection.

   Established state:

      In the Established state MASC can exchange UPDATE, NOTIFICATION,
      and KEEPALIVE messages with the remote node.

      If the local system receives an UPDATE, or KEEPALIVE message, or
      NOTIFICATION message with O-bit set, it restarts its Hold Timer,
      if the negotiated Hold Time value is non-zero.

      If the local system receives a NOTIFICATION message, with the O-
      bit zeroed, it changes its state to Idle.






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      If the local system receives an UPDATE message and the UPDATE
      message error handling procedure (see Section 8.3) detects an
      error, the local system sends a NOTIFICATION message and, if the
      O-bit was zeroed, changes its state to Idle.

      If a disconnect notification is received from the underlying
      transport protocol, the local system changes its state to Idle.

      If the Hold Timer expires, the local system sends a NOTIFICATION
      message with Error Code Hold Timer Expired and changes its state
      to Idle.

      If the KeepAlive timer expires, the local system sends a KEEPALIVE
      message and restarts its KeepAlive timer.

      Each time the local system sends a KEEPALIVE or UPDATE message, it
      restarts its KeepAlive timer, unless the negotiated Hold Time
      value is zero.

      In response to the Stop event (initiated by either system or
      operator), the local system sends a NOTIFICATION message with
      Error Code Cease and changes its state to Idle.

      The Start event is ignored in the Established state.

      After entering the Established state, if the local system has
      UPDATE messages that are to be sent to the remote node, they must
      be sent immediately (see Section 11.8).

      In response to any other event, the local system sends a
      NOTIFICATION message with Error Code Finite State Machine Error
      with the O-bit zeroed and Error Subcode Unspecific, and changes
      its state to Idle.

      Whenever MASC changes its state from Established to Idle, it
      closes the MASC (and transport-level) connection, releases all
      resources associated with that connection, and deletes all state
      derived from that connection.

11.  UPDATE Message Processing

   The UPDATE message are accepted only when the system is in the
   Established state.

   In the text below, a MASC domain is considered a child of itself with
   regard to the claims that are related to the address space with local
   usage purpose (i.e. to be used by the MAASs within that domain).  For




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   example, a NEW_CLAIM initiated by a MASC node to obtain more space
   for local usage from a prefix managed by that domain will have field
   Role = CHILD.

   If an UPDATE is to be propagated further, it should not be sent back
   to the node that UPDATE was received from, unless there is an
   indication that the connection to that node was down and then
   restored.

   If the local system receives an UPDATE message, and there is no
   indication for error, it checks whether to accept or reject the
   message, and if it is not rejected, the UPDATE is processed based on
   its type.

   If an UPDATE message must be associated with a parent domain, then
   there must be a PREFIX_MANAGED by some parent domain for a prefix
   that covers the prefix of the particular UPDATE.

11.1.  Accept/Reject an UPDATE

   The Origin Role field is first compared against the local system's
   configured Role, according to Table 1, to determine the relationship
   of the origin to the local system, where Locally-Configured Role is
   the local configuration with regard to the peer-forwarder of the
   message.  A result of "---" means that receiving such an UPDATE is
   illegal and should generate a NOTIFICATION.  Any other result is the
   value to use as the "Updated" Origin Role when propagating the UPDATE
   to others.  This is analogous to updating a metric upon receiving a
   route, based on the metric of the link.

                       Locally-Configured Role
   Origin
   Role     || INTERNAL_PEER | CHILD   | SIBLING | PARENT
   =========++===============+=========+=========+=========
   INTERNAL || INTERNAL_PEER | PARENT  | SIBLING | CHILD
   CHILD    || CHILD         | SIBLING | ---     | ---
   SIBLING  || SIBLING       | ---     | SIBLING | CHILD
   PARENT   || PARENT        | ---     | PARENT  | ---

                Table 1: Updated Origin Role Computation

   After the Origin Role is updated, the following additional processing
   needs to be applied:

   o  If the output from the Updated Origin Role Computation is SIBLING,
      but the Origin Domain ID is the same as the local MASC domain, the
      Updated Origin Role is changed to INTERNAL.  This is necessary in
      case a MASC node receives from a parent or sibling its own UPDATEs



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      after reboot, or if because of internal partitioning, the
      INTERNAL_PEERs are exchanging UPDATEs via other MASC domains
      (either parent or sibling(s)).

   o  If both Locally-Configured Role, and Origin Role are equal to
      PARENT, and the Origin Domain ID is the same as the local MASC
      domain, the Updated Origin Role is changed to INTERNAL.  This is
      necessary to allow a parent to receive its own UPDATEs through its
      own children, although the parent might drop those UPDATEs if it
      has a reason not to believe its children.

   o  If both Locally-Configured Role, and Origin Role are equal to
      PARENT, and the Origin Domain ID is the same as the remote MASC
      domain, and the UPDATE type is CLAIM_DENIED, the Updated Origin
      Role is changed to INTERNAL.  This is necessary to allow a parent
      to receive the CLAIM_DENIED it has originated through the child
      whose claim was denied.  If the Origin Domain ID is not same as
      the remote MASC domain, but is same as some of the other MASC
      children domains, the Updated Origin Role still should be changed
      to INTERNAL, although the parent might drop this UPDATE if it has
      a reason not to believe a third party child.

   If the Updated Origin Role is INTERNAL, but the Origin Domain ID
   differs from the local Domain ID, a NOTIFICATION of <UPDATE Message
   Error, Illegal Origin Role> must be sent back, and the claim is
   rejected.

   If Claim Timestamp and Claim Holdtime indicate that the claim has
   expired (e.g. Timestamp + Claim Holdtime <= CurrentTime), the UPDATE
   is silently dropped and no further actions are taken.

   Each new arrival UPDATE is compared with all claims in the local
   cache.  The following fields are compared, and if all of them are the
   same, the message is silently rejected and no further actions are
   taken:

   o  Role, D-bit, Type

   o  AddrFam

   o  Claim Timestamp

   o  Claim Lifetime

   o  Claim Holdtime

   o  Origin Domain Identifier




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   o  Origin Node Identifier

   o  Address

   o  Mask

   Further processing of an UPDATE is based on its type and the Updated
   Origin Role.

11.2.  PREFIX_IN_USE Message Processing

11.2.1.  PREFIX_IN_USE by PARENT

   The claim is rejected, and a NOTIFICATION of <UPDATE Message Error,
   Illegal Origin Role> should be sent back.

11.2.2.  PREFIX_IN_USE by SIBLING

   If the claim cannot be associated with any parent's PREFIX_MANAGED,
   the claim is dropped, a NOTIFICATION of <UPDATE Message Error, No
   Appropriate Parent Prefix> must be sent back and no further actions
   should be taken.

   If the claim collides with some of the local domain's pending claims,
   the local claims must not be considered further, and the Claim-Timer
   of each of them must be canceled. If the received PREFIX_IN_USE claim
   clashes with and wins over some of the local domain's allocated
   prefixes, resolve the clash according to Section 12.4. Finally, the
   claim must be propagated further to all INTERNAL_PEERs, all MASC
   nodes from the corresponding parent MASC domain and all known
   siblings with the same parent domain.

11.2.3.  PREFIX_IN_USE by CHILD

   If the claim's prefix is not a subrange of any of the local domain's
   PREFIX_MANAGED, the claim is dropped, a NOTIFICATION of <UPDATE
   Message Error, No Appropriate Parent Prefix> must be sent back and no
   further actions should be taken.  Otherwise, the claim must be
   propagated further to all INTERNAL_PEERs and all MASC children
   domains.

11.2.4.  PREFIX_IN_USE by INTERNAL_PEER

   If the MASC node decides that the local domain does not need that
   prefix any more, it may be withdrawn, otherwise, the claim is
   processed as PREFIX_MANAGED.





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11.3.  CLAIM_DENIED Message Processing

11.3.1.  CLAIM_DENIED by CHILD or SIBLING

   The message is rejected, and a NOTIFICATION of <UPDATE Message Error,
   Illegal Origin Role> should be sent back.

11.3.2.  CLAIM_DENIED by INTERNAL_PEER

   Propagate to all INTERNAL_PEERs and all MASC children nodes.

11.3.3.  CLAIM_DENIED by PARENT

   If the Origin Domain ID is not same as the local domain ID, and the
   UPDATE cannot be associated with any parent domain, the message is
   dropped, a NOTIFICATION of <UPDATE Message Error, No Appropriate
   Parent Prefix> must be sent back and no further actions should be
   taken.

   If the Origin Domain ID is not same as the local domain ID, and the
   UPDATE can be associated with a parent domain, the message is
   propagated to all nodes from that parent domain, all INTERNAL_PEERs,
   and all known SIBLINGs with regard to that parent.

   If the Origin Domain ID is same as the local domain ID, and there is
   no corresponding pending claim originated by the local MASC domain
   (i.e. a NEW_CLAIM or CLAIM_TO_EXPAND with same AddrFam, Origin Domain
   ID, Claim Timestamp, Address and Mask), a NOTIFICATION of <UPDATE
   Message Error, No Appropriate Internal Prefix> must be sent back and
   no further actions should be taken. Otherwise, the matching NEW_CLAIM
   or CLAIM_TO_EXPAND's Claim-Timer must be canceled and the claim must
   not be considered further. Finally, the received CLAIM_DENIED must be
   propagated to all INTERNAL_PEERs, all MASC nodes from the
   corresponding parent MASC domain, and all known SIBLINGs with regard
   to that parent.

11.4.  CLAIM_TO_EXPAND Message Processing

11.4.1.  CLAIM_TO_EXPAND by PARENT

   The claim is rejected, and a NOTIFICATION of <UPDATE Message Error,
   Illegal Origin Role> should be sent back.









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11.4.2.  CLAIM_TO_EXPAND by SIBLING

   If the claim cannot be associated with any parent's PREFIX_MANAGED,
   the claim is dropped, a NOTIFICATION of <UPDATE Message Error, No
   Appropriate Parent Prefix> must be sent back and no further actions
   should be taken.

   If there is no overlapping PREFIX_IN_USE by the same MASC domain, the
   claim is dropped, a NOTIFICATION of <UPDATE Message Error, No
   Appropriate Sibling Prefix> must be sent back and no further actions
   should be taken.

   If the claim collides with and wins over some of the local domain's
   pending claims, the loser claims must not be considered further, and
   the Claim-Timer of the each of them must be canceled.  Also, the
   received claim must be propagated further to all INTERNAL_PEERs, all
   MASC nodes from the corresponding parent MASC domain and all known
   siblings with the same parent domain.

11.4.3.  CLAIM_TO_EXPAND by CHILD

   If the claim cannot be associated with any of the local domain's
   PREFIX_MANAGED, the claim is dropped, a NOTIFICATION of <UPDATE
   Message Error, No Appropriate Parent Prefix> must be sent back and no
   further actions should be taken.

   If there is no overlapping PREFIX_IN_USE by the same MASC domain, the
   claim is dropped, a NOTIFICATION of <UPDATE Message Error, No
   Appropriate Child Prefix> must be sent back and no further actions
   should be taken.

   Otherwise, the claim has to be propagated to all INTERNAL_PEERs.  If
   the lifetime of the claim is longer than the lifetime of the
   corresponding prefix managed by the local domain, or if there is an
   administratively configured reason to prevent the child from
   succeeding allocating the claimed prefix, a CLAIM_DENIED must be sent
   to all MASC children nodes that have same Domain ID as Origin Domain
   ID in the received message.  The CLAIM_DENIED must be the same as the
   received claim, except Rol=INTERNAL, and Claim Lifetime should be set
   to the maximum allowed lifetime.  Otherwise, propagate the claim to
   all children as well.

11.4.4.  CLAIM_TO_EXPAND by INTERNAL_PEER

   If the claim cannot be associated with any parent's PREFIX_MANAGED,
   the claim is dropped, a NOTIFICATION of <UPDATE Message Error, No
   Appropriate Parent Prefix> must be sent back and no further action
   should be taken.



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   If there is no overlapping PREFIX_IN_USE by the local MASC domain,
   the claim is dropped, a NOTIFICATION of <UPDATE Message Error, No
   Appropriate Internal Prefix> must be sent back and no further actions
   should be taken.

   If the MASC node decides that the local domain does not need that
   pending claim any more, it MAY be withdrawn. Otherwise, the claim
   must be propagated to all INTERNAL_PEERs and all MASC nodes from the
   corresponding parent MASC domain.

11.5.  NEW_CLAIM Message Processing

   If the claim's Address field is 0 (i.e. a hint by a child to a parent
   to obtain more space), the claim should be propagated only among the
   nodes that belong to the child Origin Domain and the parent domain.

   Otherwise, process like CLAIM_TO_EXPAND, except that no check for
   overlapping PREFIX_IN_USE needs to be performed.

11.6.  PREFIX_MANAGED Message Processing.

11.6.1.  PREFIX_MANAGED by PARENT

   If the Origin Domain ID matches one of the parents' domain ID's, the
   prefix is recorded, and can be used by the address allocation
   algorithm for allocating subranges.  Also, the message is propagated
   to all MASC nodes of the corresponding parent domain, all
   INTERNAL_PEERs, and SIBLINGs with same parent.

11.6.2.  PREFIX_MANAGED by CHILD or SIBLING

   The message is rejected, and a NOTIFICATION of <UPDATE Message Error,
   Illegal Origin Role> should be sent back.

11.6.3.  PREFIX_MANAGED by INTERNAL_PEER

   The prefix is recorded as allocated to the local domain, propagated
   to all INTERNAL_PEERs, and can be used for (all items apply):

   a) address ranges/prefixes advertisements to all MASC children and
      local domain's MAASs;

   b) injection into G-RIB;

   c) further expansion by the address allocation algorithm (see
      Appendix A);





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11.7.  WITHDRAW Message Processing

11.7.1.  WITHDRAW by CHILD

   If the WITHDRAW cannot be associated with any of the child domain's
   PREFIX_IN_USE (i.e. no child's PREFIX_IN_USE covers WITHDRAW's
   range), or if the WITHDRAW does not match any of the child domain's
   NEW_CLAIM or CLAIM_TO_EXPAND (i.e. there is no child's claim with
   same Address, Mask and Timestamp), the message is dropped, a
   NOTIFICATION of <UPDATE Message Error, No Appropriate Child Prefix>
   must be sent back and no further actions should be taken. Otherwise,
   propagate to all INTERNAL_PEERs and children.

11.7.2.  WITHDRAW by SIBLING

   If the WITHDRAW cannot be associated with any of the siblings'
   PREFIX_IN_USE (i.e. no sibling's PREFIX_IN_USE covers WITHDRAW's
   range), or if the WITHDRAW does not match any of the sibling domain's
   NEW_CLAIM or CLAIM_TO_EXPAND (i.e. there is no sibling's claim with
   same Address, Mask and Timestamp), the message is dropped, a
   NOTIFICATION of <UPDATE Message Error, No Appropriate Sibling Prefix>
   must be sent back and no further actions should be taken. Otherwise,
   propagate to all INTERNAL_PEERs, all MASC nodes from the same parent
   MASC domain and all known siblings with the same parent domain.

11.7.3.  WITHDRAW by INTERNAL

   If the WITHDRAW cannot be associated with any of the local domain's
   PREFIX_IN_USE or PREFIX_MANAGED (i.e. no local domain's prefix covers
   WITHDRAW's range), or if the WITHDRAW does not match any of the local
   domain's NEW_CLAIM or CLAIM_TO_EXPAND (i.e. there is no local
   domain's claim with same Address, Mask and Timestamp) the message is
   dropped, a NOTIFICATION of <UPDATE Message Error, No Appropriate
   Internal Prefix> must be sent back and no further actions should be
   taken.

   Otherwise, propagate to all INTERNAL_PEERs, all MASC nodes of the
   corresponding parent domain of that prefix, all known siblings with
   that parent domain, and all children.  If the WITHDRAW can be
   associated with some of local domain's PREFIX_IN_USE or
   PREFIX_MANAGED, stop advertising the WITHDRAW range to the MAASs and
   withdraw that range from the G-RIB database.  In the special case
   when there is an indication that the WITHDRAW has been originated by
   the local domain because of a clash, and the range specified in
   WITHDRAW is a subrange of the local PREFIX_MANAGED, and the Claim
   Holdtime of WITHDRAW is shorter than the Claim Holdtime of





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   PREFIX_MANAGED, the WITHDRAW's range should not be withdrawn from the
   G-RIB.  If the WITHDRAW matches a local domain's NEW_CLAIM or
   CLAIM_TO_EXPAND, cancel the matching claim's Claim-Timer.

11.7.4.  WITHDRAW by PARENT

   If the WITHDRAW cannot be associated with any parent domain, a
   NOTIFICATION of <UPDATE Message Error, No Appropriate Parent Prefix>
   must be sent back and no further actions should be taken.

   Otherwise, propagate to all INTERNAL_PEERs and all known siblings
   with the same parent domain. Also, originate a WITHDRAW message for
   each intersection of a locally owned PREFIX_MANAGED/PREFIX_IN_USE and
   the received WITHDRAW.  The locally originated WITHDRAW message's
   Claim Holdtime should be at least equal to the Claim Holdtime in the
   WITHDRAW message received from the parent; the Origin Node ID should
   be the same as the particular PREFIX_MANAGED/PREFIX_IN_USE.

11.8.  UPDATE Message Ordering

   To simplify consistency and sanity check implementations, if there is
   more than one UPDATE message that needs to be send to a peer (for
   example, after a connection (re)establishment), some of the UPDATEs
   must be sent before others.

   The rules that always apply are:

   o  PREFIX_IN_USE must always be sent BEFORE CLAIM_TO_EXPAND,
      NEW_CLAIM, and WITHDRAW by the same MASC domain

   o  WITHDRAW must always be sent AFTER PREFIX_IN_USE, CLAIM_TO_EXPAND,
      NEW_CLAIM, and PREFIX_MANAGED by the same MASC domain

   Any further ordering is defined below by the roles of the sender and
   the receiver.

11.8.1.  Parent to Child

   Messages are sent in the following order:

   1) Parent's PREFIX_MANAGED and WITHDRAWs.

   2) All children's PREFIX_IN_USE, CLAIM_TO_EXPAND, and NEW_CLAIMs.
      CLAIMs from third party children that are hints for more space
      (i.e. address = 0) should not be propagated; if propagated, the
      child should drop them.





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   3) Parent initiated CLAIM_DENIED and children initiated WITHDRAWs.
      CLAIM_DENIED regarding third party children's claims/hints with
      address = 0 should not be propagated; if propagated, the child
      should drop them.

11.8.2.  Child to Parent

   Messages are sent in the following order:

   1) Parent's PREFIX_MANAGED and WITHDRAWs.

   2) All PREFIX_IN_USE, CLAIM_TO_EXPAND, and NEW_CLAIMSs from that
      parent's space, initiated by that child and all its siblings.

   3) Parent's initiated CLAIM_DENIED, and all WITHDRAWSs that can be
      associated with that parent's space and are initiated by the local
      domain or all known siblings with that parent.

11.8.3.  Sibling to Sibling

   Messages are sent in the following order:

   1) All common parent's PREFIX_MANAGED and WITHDRAWs.

   2) PREFIX_IN_USE, CLAIM_TO_EXPAND, and NEW_CLAIMs, initiated by
      siblings.

   3) CLAIM_DENIEDs initiated by common parent, and WITHDRAWs initiated
      by local domain and all known siblings with that parent.

11.8.4.  Internal to Internal

   Messages are sent in the following order:

   1) All parents' PREFIX_MANAGED and WITHDRAWs.

   2) Local domain's and all siblings' PREFIX_IN_USE, CLAIM_TO_EXPAND,
      and NEW_CLAIMs.  CLAIMs from siblings that are hints for more
      space (i.e. address = 0) should not be propagated; if propagated,
      the recipient should drop them.

   3) CLAIM_DENIEDs initiated by all parents, and WITHDRAWs initiated by
      local domain and all known siblings.

   4) All children's PREFIX_IN_USE, CLAIM_TO_EXPAND, and NEW_CLAIMs.

   5) All local domain initiated CLAIM_DENIED regarding children claims
      and all children initiated WITHDRAWs.



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12.  Operational Considerations

12.1.  Bootup Operations

   To learn about its parent domains' IDs and prefixes, a MASC node
   SHOULD try to establish connections to its PARENT nodes before
   initiating a connection to a SIBLING node.  To avoid learning about
   its own PREFIX_MANAGED from its children or siblings, a MASC node
   SHOULD try to establish connections to its PARENT nodes and
   INTERNAL_PEER nodes before initiating a connection to a CHILD or
   SIBLING node.

12.2.  Leaf and Non-leaf MASC Domain Operation

   A non-leaf MASC domain (i.e. a domain that has children domains)
   should advertise its PREFIX_MANAGED addresses to its children, and
   should claim from that space the sub-ranges that would be advertised
   to the internal MAASs (the claim wait time SHOULD be equal to
   [WAITING_PERIOD]).  A MASC node that belongs to a non-leaf MASC
   domain should perform dual functions by being a child of itself with
   regard to the claiming and management of the sub-ranges for local
   usage.  A leaf MASC domain should advertise all PREFIX_MANAGED
   addresses to its MAASs without explicitly claiming them for internal
   usage.  A MASC node can assume that it belongs to a leaf domain if it
   simply does not have any UPDATEs by children domains.  If an UPDATE
   by a child is received, the domain MUST switch from "leaf" to "non-
   leaf" mode, and if it needs more addresses for internal usage, it
   MUST claim them from that domain's PREFIX_MANAGED.  After the last
   UPDATE originated by a child expires, the domain can switch back to
   "leaf" mode.

12.3.  Clock Skew Workaround

   Each UPDATE has "Claim Timestamp" field that is set to the absolute
   time of the MASC node that originated that UPDATE. The timestamp is
   used for two purposes: to resolve collisions, and to define how long
   an UPDATE should be kept in the local cache of other MASC nodes. A
   skew in the clock could result in unfair collision decision such that
   the claims originated by nodes that have their clock behind the real
   time will always win; however, because collisions are presumably
   rare, this will not be an issue.  Skew in the clock however might
   result in expiring an UPDATE earlier than it really should be
   expired, and a node might assume too early that the expired
   UPDATE/prefix is free for allocation. To compensate for the clock
   skew, an UPDATE message should be kept longer than the amount of time
   specified in the Claim Holdtime. For example, keeping UPDATEs for an
   additional 24 hours will compensate for clock skew for up to 24
   hours.



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12.4.  Clash Resolving Mechanism

   If a MASC node receives a PREFIX_IN_USE claim originated by a sibling
   and the claim overlaps with some of the local prefixes, the clash
   must be resolved.  Two MASC domains should not manage overlapping
   address ranges, unless the domains have an ancestor-descendant (e.g.
   parent-child) relationship in the MASC hierarchy.  Also, two MASC
   domains should not have locally-allocated overlapping address ranges.
   The clashed address ranges should not be advertised to the MAASs and
   allocated to multicast applications/sessions.  If a clashed address
   has being allocated to an application, the application should be
   informed to stop using that address and switch to a new one.

   The G-RIB database must be consistent, such that it does not have
   ambiguous entries.  "Ambiguous G-RIB entries" are those entries that
   might cause the multicast routing protocol to loop or lose
   connectivity.  In MASC the WITHDRAW message is used to solve this
   problem.  When a clashing PREFIX_IN_USE is received, it is compared
   (using the function describe in Section 5.1.1) against all prefixes
   allocated to the local domain.  If the local PREFIX_IN_USE is the
   winner, no further actions are taken.  If the local PREFIX_IN_USE is
   the loser, the clashing address range must be withdrawn by initiating
   a WITHDRAW message. The message must have Role = INTERNAL, Origin
   Node ID and Origin Domain ID must be the same as the corresponding
   local PREFIX_IN_USE message, while Claim Timestamp, Claim Lifetime,
   Claim Holdtime, Address and Mask must be the same as the received
   winning PREFIX_IN_USE.  The initiated WITHDRAW message must be
   processed as described in Section 11.7.

   If a cached WITHDRAW times out and the local MASC domain owns an
   overlapping PREFIX_MANAGED or PREFIX_IN_USE, the overlapping prefix
   ranges can be injected back into the G-RIB database.  Similarly, the
   address ranges that were not advertised to the local domain's MAASs
   due to the WITHDRAW, can now be advertised again.

   In addition to the automatic resolving of clashes, a MASC
   implementation should support manual resolving of clashes.  For
   example, after a clash is detected, the network administrator should
   be informed that a clash has occurred.  The specific manual
   mechanisms are outside the scope of this protocol.

   A MASC node must be configured to operate using either manual or
   automatic clash resolution mechanisms.








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12.5.  Changing Network Providers

   If a MASC domain changes a network provider, such that the old
   provider cannot be used to provide connectivity, any traffic for
   sessions that are in progress and use that MASC domain as the root of
   multicast distribution trees will not be able to reach that domain.

   If the new network provider is willing to carry the traffic for the
   old sessions rooted at the customer domain, then it must propagate
   the customer's old prefixes through the G-RIB.  However, at least one
   MASC node in the customer domain must maintain a TCP connection to
   one of the old network provider's MASC nodes.  Thus, it can continue
   to "defend" the customer's prefixes, and should continue until the
   old prefixes' lifetimes expire.

   If the new network provider is not willing to propagate the old
   prefixes, then the customer should remove its prefixes from the G-
   RIB.  If BGMP is in use, the old network provider's domain will
   automatically become the Root Domain for the customer's old groups
   due to the lack of a more specific group route.  MASC nodes in the
   customer domain MAY still connect with the old provider's MASC nodes
   to defend their allocation.

12.6.  Debugging

12.6.1.  Prefix-to-Domain Lookup

   Use mtrace [MTRACE] to find the BGMP/MASC root domain for a group
   address chosen from that prefix.

12.6.2.  Domain-to-Prefix Lookup

   We can find the address space allocated to a particular MASC domain
   by directly querying one of the MASC servers within that domain, by
   observing the state in parents, siblings, or children MASC domains,
   or by observing the G-RIB information originated by that domain.
   From those three methods, the first method can provide the most
   detailed information. Finding the address of one of the MASC nodes
   within a particular domain is outside the scope of MASC.

13.  MASC Storage

   In general, MASC will be run by a border routers, which, in general
   do not have stable storage.  In this case, MASC must use the Layer 2
   protocol/mechanism (e.g., ([AAP]) as described in [MALLOC] to store
   the important information (the prefixes allocated by the local
   domain) in the domain's MAASs who should have stable storage.  If the




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   MASC speaker has local storage, it should use it instead of the Layer
   2 protocol/mechanism.  Claims that are in progress do not have to be
   saved by using the Layer 2 protocol/mechanism.

14.  Security Considerations

   IPsec [IPSEC] can be used to address security concerns between two
   MASC peering nodes.  However, because of the store-and-forward nature
   of the UPDATE messages, it is possible that if a non-trustworthy MASC
   node can connect to some point of the MASC topology, then this node
   can undetectably inject malicious UPDATEs that may disturb the normal
   operation of other MASC nodes.  To address this problem, each MASC
   node should allow peering only with trustworthy nodes.

   After a reboot, a MASC node/domain can restore its state from its
   neighbors (internal peers, parents, siblings, children). Typically,
   the state received from a parent or internal peer will be
   trustworthy, but a node may choose to drop its own UPDATEs that were
   received through a sibling or a child.

   A misbehaving node may attempt a Denial of Service attack by sending
   a large number of colliding messages that would prevent any of its
   siblings from allocating more addresses.  A single mis-behaving node
   can easily be identified by all of its siblings, and all of its
   UPDATEs can be ignored.  A Denial of Service attack that uses
   multiple origin addresses can be prevented if a third-party UPDATE
   (e.g. by a non-directly connected sibling) is accepted only if it is
   sent via the common parent domain, and the MASC nodes in the parent
   domain accept children UPDATEs only if they come via an internal
   peer, or come directly from a child node that is same as the Origin
   Node ID.

15.  IANA Considerations

   This document defines several number spaces (MASC message types, MASC
   OPEN message optional parameters types, MASC UPDATE message attribute
   types, MASC UPDATE message optional parameters types, and MASC
   NOTIFICATION message error codes and subcodes).  For all of these
   number spaces, certain values are defined in this specification.  New
   values may only be defined by IETF Consensus, as described in [IANA-
   CONSIDERATIONS].  Basically, this means that they are defined by RFCs
   approved by the IESG.

16.  Acknowledgments

   The authors would like to thank the participants of the IETF for
   their assistance with this protocol.




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17.  APPENDIX A: Sample Algorithms

   DISCLAIMER: This section describes some preliminary suggestions by
   various people for algorithms which could be used with MASC.

17.1.  Claim Size and Prefix Selection Algorithm

   This section covers the algorithms used by a MASC node (on behalf of
   a MASC domain) to satisfy the demand for multicast addresses.  The
   allocated addresses should be aggregatable, the address utilization
   should be reasonably high, and the allocation latency to the MAASs
   should be shorter than [WAITING_PERIOD] whenever possible.

17.1.1.  Prefix Expansion

   For ease of implementation and troubleshooting, MASC should use
   contiguous masks to specify the address ranges, i.e. prefixes.
   (Research indicates that sufficiently good results can be achieved
   using contiguous masks only.)  The chosen prefixes should be as
   expandable as possible.  The method used to choose the children sub-
   prefixes from the parent's prefix is the so called Reverse Bit
   Ordering (idea by Dave Thaler; inspired by Kampai [KAMPAI]).  For
   example, if the parent's prefix width is four bits, the addresses of
   the sub-prefixes are chosen in the following order:

   Parent:       xxxx

   Child A:      0000
   Child B:      1000
   Child C:      0100
   Child D:      1100

   If some of the children need to expand their sub-prefix, they try to
   double the corresponding sub-prefix starting from the right:

   Child A:      000x
   Child A:      00xx
   Child D:      110x
   Child D:      11xx

   and so on.

   However, because the address ordering is very strict, to reduce the
   probability for collision, when a new sub-prefix has to be chosen,
   the choice should be random among all candidates with the same
   potential for expandability.  For example, if the free sub-prefixes
   are 01xx, 10xx, 110x, then the new prefix to claim should be chosen
   with probability of 50% for 01xx and 50% for 10xx for example.



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17.1.2.  Reducing Allocation Latency

   To reduce the allocation latency, a MASC node uses pre-allocation.
   It constantly monitors the demand for addresses from its children (or
   MAASs), and predicts what would be the address usage after
   [WAITING_PERIOD].  Only if the available addresses will be used up
   within [WAITING_PERIOD], a MASC node claims more addresses in
   advance.

17.1.3.  Address Space Utilization

   Because every prefix size is a power of two, if a node tries to
   allocate just a single prefix, the utilization at that node (i.e. at
   that node's domain) can be as low as 50%.  To improve the
   utilization, a MASC node can have more than one prefix allocated at a
   time (typically, each of them with different size).  By using a pre-
   allocation and allocating several prefixes of different size (see
   below), a MASC node should try to keep its address utilization in the
   range 70-90%.

17.1.4.  Prefix Selection After Increase of Demand

   To additionally reduce the allocation latency by reducing the
   probability for collision, and to improve the aggregability of the
   allocated addresses, a MASC node carefully chooses the prefixes to
   claim. The first prefix is chosen at random among all reasonably
   expandable candidates.  If a node chooses to allocate another,
   smaller prefix, then, instead of doubling the size of the first one
   which might reduce significantly the address utilization, a second
   "neighbor" prefix is chosen.  For example, if prefix 224.0/16 was
   already allocated, and the MASC domain needs 256 more addresses, the
   second prefix to claim will be 224.1.0/24. If the domain needs more
   addresses, the second prefix will eventually grow to 224.1/16, and
   then both prefixes can be automatically aggregated into 224.0/15.
   Only if 224.0.1/24 could not be allocated, a MASC node will choose
   another prefix (eventually random among the unused prefixes).

   If the number of allocated prefixes increases above some threshold,
   and none of them can be extended when more addresses are needed,
   then, to reduce the amount of state, a MASC node should claim a new
   larger prefix and should stop re-claiming the older non-expandable
   prefixes.  Research results show that up to three prefixes per MASC
   domain is a reasonable threshold, such that the address utilization
   can be in the range 70-90%, and at the same time the prefix flux will
   be reasonably low.






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17.1.5.  Prefix Selection After Decrease of Demand

   If the demand for addresses decreases, such that its address space is
   under-utilized, a MASC node implicitly returns the unused prefixes
   after their lifetimes expire, or re-claims some smaller sub-prefixes.
   For example, if prefix 224.0/15 is 50% used by the MAASs and/or
   children MASC domains, and the overall utilization is such that
   approximately 2^16 (64K) addresses should be returned, a MASC node
   should stop reclaiming 224.0/15 and should start reclaiming either
   224.0/16 or 224.1/16 (whichever sub-prefix utilization is higher).

17.1.6.  Lifetime Extension Algorithm

   If the demand for addresses did not decrease, then a MASC node re-
   claims the prefixes it has allocated before their lifetime expires.
   Each prefix (or sub-prefix if the demand has decreased) should be
   re-claimed every 48 hours.

18.  APPENDIX B: Strawman Deployment

   At the moment of writing, 225.0.0.0-225.255.255.255 is temporarily
   allocated to MALLOC.  Presumably this block of addresses will be used
   for experimental deployment and testing.

   If MASC were widely deployed on the Internet, we might expect numbers
   similar to the following:

   o  Initially will have approximately 128 Top-Level Domains

   o  Assume initially approximately 8192 level-2 MASC domains; on
      average, a TLD will have approximately 64 children domains.

   o  MASC managed global addresses:

      The following (large) ranges are not allocated yet (2^N represents
      the size of the contiguous mask prefixes):

       225.0.0.0 - 231.255.255.255 = 2^26 + 2^25 + 2^24
       234.0.0.0 - 238.255.255.255 = 2^25 + 2^25 + 2^24
       ---------------------------
       Total:   12*2^24 addresses

      Initially, the range 228.0.0.0 - 231.255.255.255 (4*2^24 = 2^26 =
      64M) could be used by MASC as the global addresses pool. The rest
      (8*2^24) should be reserved.  Part of it could be added later to
      MASC, or can be used to enlarge the pool of administratively
      scoped addresses (currently 239.X.X.X), or the pool for static
      allocation (233.X.X.X).



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   o  If the multicast addresses are evenly distributed, each TLD would
      have a maximum of 2^19 (512K) addresses, while each level-2 MASC
      domain would have 8192 addresses.

   o  Initial claim size: 256 addresses/MASC domain

   o  Could use soft and hard thresholds to specify the maximum amount
      of claimed+allocated addresses per domain.  For example, trigger a
      warning message if claimed+allocated addresses by a domain is >=
      1.0*average_assumed_per_domain (a strawman default soft
      threshold):

         * if a TLD claim+allocation >= 512K
         * if a second level MASC domain claim+allocation >= 8K

      The hard threshold (for example, 2.0*average_assumed_per_domain)
      can be enforced by sending an explicit DENIED message.

      The TLDs thresholds (with regard to the claims by the second level
      MASC domains) is a private matter and is a part of the particular
      TLD policy: the thresholds could be per customer, and the warnings
      to the administrators could be a signal that it is time to change
      the policy.

   o  Initial claim lifetime is of the order of 30 days.  Prefix
      lifetime is periodically (every 48 hours) reclaimed/extended,
      unless the prefix is under-utilized (see APPENDIX A).  Because the
      allocation is demand-driven, the allocated prefix lifetime will be
      automatically extended if the MAASs need longer prefix lifetime
      (e.g. 3-6 months).

   o  A level-2 MASC domain could have children (i.e. level-3) MASC
      domains.

   o  If a level-2 or level-3 MASC domain uses less than 128 addresses,
      a Layer 2 protocol/mechanism (e.g. AAP) should be run among that
      domain and its parent MASC domain.

19.  Authors' Addresses

   Pavlin Radoslavov
   Computer Science Department
   University of Southern California/ISI
   Los Angeles, CA 90089
   USA

   EMail: pavlin@catarina.usc.edu




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   Deborah Estrin
   Computer Science Department
   University of Southern California/ISI
   Los Angeles, CA 90089
   USA

   EMail: estrin@isi.edu


   Ramesh Govindan
   University of Southern California/ISI
   4676 Admiralty Way
   Marina Del Rey, CA 90292
   USA

   EMail: govindan@isi.edu


   Mark Handley
   AT&T Center for Internet Research at ISCI (ACIRI)
   1947 Center St., Suite 600
   Berkeley, CA 94704
   USA

   EMail: mjh@aciri.org


   Satish Kumar
   Computer Science Department
   University of Southern California/ISI
   Los Angeles, CA 90089
   USA

   EMail: kkumar@usc.edu


   David Thaler
   Microsoft
   One Microsoft Way
   Redmond, WA 98052
   USA

   EMail: dthaler@microsoft.com








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20.  References

   [AAP]                 Handley, M. and S. Hanna, "Multicast Address
                         Allocation Protocol (AAP)", Work in Progress.

   [API]                 Finlayson, R., "An Abstract API for Multicast
                         Address Allocation", RFC 2771, February 2000.

   [BGMP]                Thaler, D., Estrin, D. and D. Meyer, "Border
                         Gateway Multicast Protocol (BGMP): Protocol
                         Specification", Work in Progress.

   [BGP]                 Rekhter, Y. and T. Li, "A Border Gateway
                         Protocol 4 (BGP-4)", RFC 1771, March 1995.

   [CIDR]                Rekhter, Y. and C. Topolcic, "Exchanging
                         Routing Information Across Provider Boundaries
                         in the CIDR Environment", RFC 1520, September
                         1993.

   [IANA]                Reynolds, J. and J. Postel, "Assigned Numbers",
                         STD 2, RFC 1700, October 1994.

   [IANA-CONSIDERATIONS] Alvestrand, H. and T. Narten, "Guidelines for
                         Writing an IANA Considerations Section in
                         RFCs", BCP 26, RFC 2434, October 1998.

   [IPSEC]               Kent, S. and R. Atkinson, "Security
                         Architecture for the Internet Protocol", RFC
                         2401, November 1998.

   [KAMPAI]              Tsuchiya, P., "Efficient and Flexible
                         Hierarchical Address Assignment", INET92, June
                         1992, pp. 441--450.

   [MADCAP]              Hanna, S., Patel, B. and M. Shah, "Multicast
                         Address Dynamic Client Allocation Protocol
                         (MADCAP)", RFC 2730, December 1999.

   [MALLOC]              Thaler, D., Handley, M. and D. Estrin, "The
                         Internet Multicast Address Allocation
                         Architecture", RFC 2908, September 2000.

   [MBGP]                Bates, T., Chandra, R., Katz, D. and Y.
                         Rekhter, "Multiprotocol Extensions for BGP-4",
                         RFC 2283, September 1997.





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   [MTRACE]              Fenner, W., and S. Casner, "A `traceroute'
                         facility for IP Multicast", Work in Progress.

   [MZAP]                Handley, M, Thaler, D. and R. Kermode
                         "Multicast-Scope Zone Announcement Protocol
                         (MZAP)", RFC 2776, February 2000.

   [RFC1112]             Deering, S., "Host Extensions for IP
                         Multicasting", STD 5, RFC 1112, August 1989.

   [RFC2119]             Bradner, S., "Key words for use in RFCs to
                         Indicate Requirement Levels", BCP 14, RFC 2119,
                         March 1997.

   [RFC2373]             Hinden, R. and S. Deering, "IP Version 6
                         Addressing Architecture", RFC 2373, July 1998.

   [RFC2460]             Deering, S. and R. Hinden, "Internet Protocol,
                         Version 6 (IPv6) Specification", RFC 2460,
                         December 1998.

   [SCOPE]               Meyer, D., "Administratively Scoped IP
                         Multicast", RFC 2365, July 1998.




























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21.  Full Copyright Statement

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
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Radoslavov, et al.            Experimental                     [Page 56]

