
nathelper Module

Maxim Sobolev

   PortaOne

Edited by

Maxim Sobolev

   Copyright © 2003 Porta Software Ltd.
     _________________________________________________________

   Table of Contents
   1. User's Guide

        1.1. Overview
        1.2. Dependencies

              1.2.1. SER Modules
              1.2.2. External Libraries or Applications

        1.3. Exported Parameters

              1.3.1. natping_interval (integer)
              1.3.2. ping_nated_only (integer)
              1.3.3. rtpproxy_sock (string)
              1.3.4. rtpproxy_disable (integer)
              1.3.5. rtpproxy_disable_tout (integer)
              1.3.6. rtpproxy_retr (integer)
              1.3.7. rtpproxy_tout (integer)
              1.3.8. received_avp (integer)
              1.3.9. force_socket (string)

        1.4. Exported Functions

              1.4.1. fix_nated_contact()
              1.4.2. fix_nated_sdp(mode)
              1.4.3. force_rtp_proxy()
              1.4.4. add_rcv_param()
              1.4.5. fix_nated_register()
              1.4.6. force_rtp_proxy([options [, new_ip]])
              1.4.7. nat_uac_test(mode)

   2. Developer's Guide
   3. Frequently Asked Questions

   List of Examples
   1-1. Set natping_interval parameter
   1-2. Set ping_nated_only parameter
   1-3. Set received_avp parameter
   1-4. fix_nated_contact usage
   1-5. fix_nated_sdp usage
   1-6. force_rtp_proxy usage
   1-7. add_rcv_paramer usage
   1-8. fix_nated_register usage
   1-9. force_rtp_proxy usage
     _________________________________________________________

Chapter 1. User's Guide

1.1. Overview

   This is a module to help with NAT traversal. In particular, it
   helps symmetric UAs that don't advertise they are symmetric
   and are not able to determine their public address.
   fix_nated_contact rewrites Contact header field with request's
   source address:port pair. fix_nated_sdp adds the active
   direction indication to SDP (flag 0x01) and updates source IP
   address too (flag 0x02).

   Known devices that get along over NATs with nathelper are ATAs
   (as clients) and Cisco Gateways (since 12.2(T)) as servers.
   See
   http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/product
   s_feature_guide09186a0080110bf9.html">
     _________________________________________________________

1.2. Dependencies

1.2.1. SER Modules

   The following modules must be loaded before this module:

     * No dependencies on other SER modules.
     _________________________________________________________

1.2.2. External Libraries or Applications

   The following libraries or applications must be installed
   before running SER with this module loaded:

     * None.
     _________________________________________________________

1.3. Exported Parameters

1.3.1. natping_interval (integer)

   Period of time in seconds between sending short UDP packets to
   all currently registered UAs to keep their NAT bindings alive.
   Value of 0 disables this functionality.

   Default value is 0. 

   Example 1-1. Set natping_interval parameter
...
modparam("nathelper", "natping_interval", 10)
...
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1.3.2. ping_nated_only (integer)

   If this variable is set then only contacts that have
   "behind_NAT" flag in user location database set set will get
   ping.

   Default value is 0. 

   Example 1-2. Set ping_nated_only parameter
...
modparam("nathelper", "ping_nated_only", 1)
...
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1.3.3. rtpproxy_sock (string)

   The name of the socket for the communication between SER and
   RTPProxy.

   Default value is "unix:/var/run/rtpproxy.sock". 
     _________________________________________________________

1.3.4. rtpproxy_disable (integer)

   This parameter can be used to disable communication with
   RTPproxy completely.

   Default value is 0 (communication with RTPproxy enabled). 
     _________________________________________________________

1.3.5. rtpproxy_disable_tout (integer)

   This parameter controls the minimum interval between periodic
   attempts to establish communication with RTPProxy. SER
   periodically tries to establish communication with RTPProxy if
   it failed previously, for example due to wrong protocol
   version or RTPProxy not running. The value of -1 will disable
   peridic attempts to reach RTPproxy.

   Default value is 60 s. 
     _________________________________________________________

1.3.6. rtpproxy_retr (integer)

   This parameter controls the number of attempts of SER to
   establish communication with RTPProxy.

   Default value is 5 attempts. 
     _________________________________________________________

1.3.7. rtpproxy_tout (integer)

   The value of this parameter controls how long SER waits for a
   reply from RTPProxy.

   Default value is 1 s. 
     _________________________________________________________

1.3.8. received_avp (integer)

   The number of the Attribute-Value-Pair (AVP) used to store the
   URI containing the received IP, port, and protocol. The URI is
   created by fix_nated_register function of nathelper module and
   the attribute is then used by the registrar to store the
   received parameters. Do not forget to change the value of
   corresponding parameter in registrar module if you change the
   value of this parameter.

   Default value is 42. 

   Example 1-3. Set received_avp parameter
...
modparam("nathelper", "received_avp", 43)
...
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1.3.9. force_socket (string)

   This parameter controls the socket that will be used to send
   NAT pings. This can be something like "udp:10.0.0.1:5060".

   Default value is disabled. 
     _________________________________________________________

1.4. Exported Functions

1.4.1. fix_nated_contact()

   Rewrites Contact HF to contain request's source address:port.

   Example 1-4. fix_nated_contact usage
...
if (search("User-Agent: Cisco ATA.*") {fix_nated_contact();};
...
     _________________________________________________________

1.4.2. fix_nated_sdp(mode)

   Rewrites Contact HF to contain request's source address:port.

   Meaning of the parameters is as follows:

     * mode - 0x01 (add direction=active), 0x02 (rewrite media IP
       address with source address of the message). The value of
       mode parameter is bitwise OR of the numbers (0x03 for both
       tests).

   Example 1-5. fix_nated_sdp usage
...
if (search("User-Agent: Cisco ATA.*") {fix_nated_sdp("3");};
...
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1.4.3. force_rtp_proxy()

   Rewrites SDP body to ensure that media is passed through an
   RTP proxy.

   Example 1-6. force_rtp_proxy usage
...
if (search("User-Agent: Cisco ATA.*") {force_rtp_proxy();};
...
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1.4.4. add_rcv_param()

   Add received parameter to Contact header fields. The parameter
   will contain URI created from the source IP, port, and
   protocol of the packet containing the SIP message. The
   parameter can be then processed by another registrar, this is
   useful, for example, when replicating register messages using
   t_replicate function to another registrar.

   Example 1-7. add_rcv_paramer usage
...
add_rcv_param();
...
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1.4.5. fix_nated_register()

   The function creates a URI consisting of the source IP, port,
   and protocol and stores the URI in an Attribute-Value-Pair.
   The URI will be appended as "received" parameter to Contact in
   200 OK and registrar will store it in the user location
   database.

   Example 1-8. fix_nated_register usage
...
fix_nated_register();
...
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1.4.6. force_rtp_proxy([options [, new_ip]])

   Rewrites SDP body with given IP address to ensure that media
   is passed through an RTP proxy. The function accepts 0, 1, or
   2 parameters. Default value of options parameter is an empty
   string and default value of new_ip parameter is the
   destination IP of the SIP request.

   Meaning of the parameters is as follows:

     * options - String containing various options to control
       behavior of force_rtp_proxy function. Each option is
       represented by one character in the string. The function
       supports the following options:
          + A - The originator of the SIP message does not
            support symmetric RTP.
          + I - The originator of the SIP message is in the same
            LAN as RTPProxy. Useful when RTPProxy is running in
            bridging mode.
          + E - The originator of the SIP message is reachable
            through external interface, not LAN. Useful when
            RTPProxy is running in bridging mode.
          + L - Do not create a new session in RTPProxy, instead
            lookup existing sessions and rewrite SDP only if it
            exists. This is only useful for SIP requests, this
            flag is automatically enabled when the function is
            executed during reply processing (from onreply_route
            blocks).
          + F - This flag instructs nathelper to ignore marks
            inserted by another nathelper instance along the path
            of the message to indicate that the session is
            already passing through another RTPProxy. This allows
            chains of RTP proxies.
          + R - The IP in SDP should be trusted. Without this
            flag, nathelper would ignore address in SDP and use
            source address of the SIP message as media address
            which is passed to the RTPProxy.
     * new_ip - Replace the IP address in SDP with the value of
       this parameter if present.

   Example 1-9. force_rtp_proxy usage
...
if (search("User-Agent: Cisco ATA.*") {
    force_rtp_proxy("IF", 1.2.3.4");
};
...
     _________________________________________________________

1.4.7. nat_uac_test(mode)

   Tries to guess if client's request originated behind a nat.
   The parameter determines what heuristics is used. If flag 1 is
   set, the "received" test is used -- address in Via is compared
   against source IP address of signaling. If flag 2 is set,
   Contact header field is searched for occurrence of RFC1918
   addresses. If flag 4 is set the address in Via is compared
   with "private" RFC1918 addresses. If flag 8 is set the ip in
   the SDP message body is compared with RFC1918 addresses. If
   flag 16 is set the rport test is used: the source port of the
   message is compared with the source port advertised in Via
   (good to catch broken STUN implementations, but might cause
   problems for UAs with asymmetric signaling). All the flags can
   be bitwise combined, the test returns true if any of the tests
   identified a NAT (e.g. nat_uac_test(19) will return true if
   any of the received test, contact RFC1918 test or. rport test
   are true).
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Chapter 2. Developer's Guide

   The module does not provide any sort of API to use in other
   SER modules.
     _________________________________________________________

Chapter 3. Frequently Asked Questions

   3.1. Where can I find more about SER?
   3.2. Where can I post a question about this module?
   3.3. How can I report a bug?

   3.1. Where can I find more about SER?

   Take a look at http://iptel.org/ser.

   3.2. Where can I post a question about this module?

   First at all check if your question was already answered on
   one of our mailing lists:

     * http://mail.iptel.org/mailman/listinfo/serusers
     * http://mail.iptel.org/mailman/listinfo/serdev

   E-mails regarding any stable version should be sent to
   <serusers@iptel.org> and e-mail regarding development versions
   or CVS snapshots should be send to <serdev@iptel.org>.

   If you want to keep the mail private, send it to
   <serhelp@iptel.org>.

   3.3. How can I report a bug?

   Please follow the guidelines provided at:
   http://iptel.org/ser/bugs
