
nathelper Module

Maxim Sobolev

   PortaOne

Edited by

Maxim Sobolev

   Copyright © 2003 Porta Software Ltd.
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   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)

        1.4. Exported Functions

              1.4.1. fix_nated_contact()

        1.5. Exported Functions

              1.5.1. fix_nated_sdp(mode)
              1.5.2. force_rtp_proxy()
              1.5.3. force_rtp_proxy(ip_address)
              1.5.4. 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. fix_nated_contact usage
   1-4. fix_nated_sdp usage
   1-5. force_rtp_proxy usage
   1-6. force_rtp_proxy usage
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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">
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1.2. Dependencies

1.2.1. SER Modules

   The following modules must be loaded before this module:

     * No dependencies on other SER modules.
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1.2.2. External Libraries or Applications

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

     * None.
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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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1.4. Exported Functions

1.4.1. fix_nated_contact()

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

   Example 1-3. fix_nated_contact usage
...
if (search("User-Agent: Cisco ATA.*") {fix_nated_contact();};
...
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1.5. Exported Functions

1.5.1. 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).

   Example 1-4. fix_nated_sdp usage
...
if (search("User-Agent: Cisco ATA.*") {fix_nated_sdp("3");};
...
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1.5.2. force_rtp_proxy()

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

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

   Rewrites SDP body with given IP address to ensure that media
   is passed through an RTP proxy.

   Meaning of the parameters is as follows:

     * ip_address - new SDP IP address.

   Example 1-6. force_rtp_proxy usage
...
if (search("User-Agent: Cisco ATA.*") {force_rtp_proxy("1.2.3.4");};
...
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1.5.4. 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 occurence of RFC1918
   addresses. Both flags can be bitwise combined, the test
   returns true if any of the tests identified a NAT.
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Chapter 2. Developer's Guide

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