nathelper Module

Maxim Sobolev

   Sippy Software, Inc.

Juha Heinanen

   TuTPro, Inc.

Edited by

Maxim Sobolev

Edited by

Bogdan-Andrei Iancu

Edited by

Juha Heinanen

Edited by

Ovidiu Sas

   Copyright © 2003-2008 Sippy Software, Inc.

   Copyright © 2005 Voice Sistem SRL

   Copyright © 2009 TuTPro Inc.

   Copyright © 2010 VoIPEmbedded Inc.
     __________________________________________________________________

   Table of Contents

   1. Admin Guide

        1. Overview
        2. NAT pinging types
        3. Dependencies

              3.1. Kamailio Modules
              3.2. External Libraries or Applications

        4. Parameters

              4.1. force_socket (string)
              4.2. natping_interval (integer)
              4.3. ping_nated_only (integer)
              4.4. natping_processes (integer)
              4.5. natping_socket (string)
              4.6. received_avp (str)
              4.7. sipping_bflag (integer)
              4.8. sipping_from (string)
              4.9. sipping_method (string)
              4.10. nortpproxy_str (string)
              4.11. keepalive_timeout (int)

        5. Functions

              5.1. fix_nated_contact()
              5.2. fix_nated_sdp(flags [, ip_address])
              5.3. add_rcv_param([flag]),
              5.4. fix_nated_register()
              5.5. nat_uac_test(flags)
              5.6. is_rfc1918(ip_address)
              5.7. add_contact_alias([ip_addr, port, proto])
              5.8. handle_ruri_alias()

        6. Exported Pseudo Variables

              6.1. $rr_count
              6.2. $rr_top_count

        7. MI Commands

              7.1. nh_enable_ping

        8. Selects

              8.1. @nathelper.rewrite_contact[n]

   2. Frequently Asked Questions

   List of Examples

   1.1. Set force_socket parameter
   1.2. Set natping_interval parameter
   1.3. Set ping_nated_only parameter
   1.4. Set natping_processes parameter
   1.5. Set natping_socket parameter
   1.6. Set received_avp parameter
   1.7. Set sipping_bflag parameter
   1.8. Set sipping_from parameter
   1.9. Set sipping_method parameter
   1.10. Set nortpproxy_str parameter
   1.11. Set keepalive_timeout parameter
   1.12. fix_nated_contact usage
   1.13. fix_nated_sdp usage
   1.14. add_rcv_paramer usage
   1.15. fix_nated_register usage
   1.16. add_contact_alias usage
   1.17. handle_ruri_alias usage
   1.18. $rr_count usage
   1.19. $rr_top_count usage
   1.20. nh_enable_ping usage
   1.21. @nathelper.rewrite_contact usage

Chapter 1. Admin Guide

   Table of Contents

   1. Overview
   2. NAT pinging types
   3. Dependencies

        3.1. Kamailio Modules
        3.2. External Libraries or Applications

   4. Parameters

        4.1. force_socket (string)
        4.2. natping_interval (integer)
        4.3. ping_nated_only (integer)
        4.4. natping_processes (integer)
        4.5. natping_socket (string)
        4.6. received_avp (str)
        4.7. sipping_bflag (integer)
        4.8. sipping_from (string)
        4.9. sipping_method (string)
        4.10. nortpproxy_str (string)
        4.11. keepalive_timeout (int)

   5. Functions

        5.1. fix_nated_contact()
        5.2. fix_nated_sdp(flags [, ip_address])
        5.3. add_rcv_param([flag]),
        5.4. fix_nated_register()
        5.5. nat_uac_test(flags)
        5.6. is_rfc1918(ip_address)
        5.7. add_contact_alias([ip_addr, port, proto])
        5.8. handle_ruri_alias()

   6. Exported Pseudo Variables

        6.1. $rr_count
        6.2. $rr_top_count

   7. MI Commands

        7.1. nh_enable_ping

   8. Selects

        8.1. @nathelper.rewrite_contact[n]

1. Overview

   This is a module to help with NAT traversal and reuse of tcp
   connections. In particular, it helps symmetric UAs that don't advertise
   they are symmetric and are not able to determine their public address.

   Function fix_nated_contact() rewrites Contact header field with
   request's source address:port pair. Function fix_nated_sdp() adds the
   active direction ndication to SDP (flag 0x01) and updates source IP
   address too (flag 0x02). Function fix_nated_register() exports exports
   the request's source address:port into an AVP to be used during save()
   and should be used for REGISTER requests.

   Note: fix_nated_contact changes the Contact header, thus it breaks the
   RFC. Although usually this is not an issue, it may cause problems with
   strict SIP clients. An alternative is to use add_contact_alias() that
   together with handle_ruri_alias() is standards conforming and also
   supports reuse of TCP/TLS connections.

   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/products_feature
   _guide09186a0080110bf9.html">

2. NAT pinging types

   Currently, the nathelper module supports two types of NAT pings:
     * UDP package - 4 bytes (zero filled) UDP packages are sent to the
       contact address.
          + Advantages: low bandwitdh traffic, easy to generate by
            Kamailio;
          + Disadvantages: unidirectional traffic through NAT (inbound -
            from outside to inside); As many NATs do update the bind
            timeout only on outbound traffic, the bind may expire and
            closed.
     * SIP request - a stateless SIP request is sent to the contact
       address.
          + Advantages: bidirectional traffic through NAT, since each PING
            request from Kamailio (inbound traffic) will force the SIP
            client to generate a SIP reply (outbound traffic) - the NAT
            bind will be surely kept open.
          + Disadvantages: higher bandwitdh traffic, more expensive (as
            time) to generate by Kamailio;

3. Dependencies

   3.1. Kamailio Modules
   3.2. External Libraries or Applications

3.1. Kamailio Modules

   The following modules must be loaded before this module:
     * usrloc module - only if the NATed contacts are to be pinged.

3.2. External Libraries or Applications

   The following libraries or applications must be installed before
   running Kamailio with this module loaded:
     * None.

4. Parameters

   4.1. force_socket (string)
   4.2. natping_interval (integer)
   4.3. ping_nated_only (integer)
   4.4. natping_processes (integer)
   4.5. natping_socket (string)
   4.6. received_avp (str)
   4.7. sipping_bflag (integer)
   4.8. sipping_from (string)
   4.9. sipping_method (string)
   4.10. nortpproxy_str (string)
   4.11. keepalive_timeout (int)

4.1. force_socket (string)

   Socket to be used when sending NAT pings for UDP communication. If no
   one specified, the OS will choose a socket.

   Default value is "NULL".

   Example 1.1. Set force_socket parameter
...
modparam("nathelper", "force_socket", "localhost:33333")
...

4.2. natping_interval (integer)

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

Note

   Enabling the NAT pinging functionality will force the module to bind
   itself to USRLOC module.

   Default value is 0.

   Example 1.2. Set natping_interval parameter
...
modparam("nathelper", "natping_interval", 10)
...

4.3. ping_nated_only (integer)

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

   Default value is 0.

   Example 1.3. Set ping_nated_only parameter
...
modparam("nathelper", "ping_nated_only", 1)
...

4.4. natping_processes (integer)

   How many timer processes should be created by the module for the
   exclusive task of sending the NAT pings.

   Default value is 1.

   Example 1.4. Set natping_processes parameter
...
modparam("nathelper", "natping_processes", 3)
...

4.5. natping_socket (string)

   Spoof the natping's source-ip to this address. Works only for IPv4.

   Default value is NULL.

   Example 1.5. Set natping_socket parameter
...
modparam("nathelper", "natping_socket", "192.168.1.1:5006")
...

4.6. received_avp (str)

   The name 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.

Note

   You must set this parameter if you use "fix_nated_register". In such
   case you must set the parameter with same name of "registrar" module to
   same value.

   Default value is "NULL" (disabled).

   Example 1.6. Set received_avp parameter
...
modparam("nathelper", "received_avp", "$avp(i:42)")
...

4.7. sipping_bflag (integer)

   What branch flag should be used by the module to identify NATed
   contacts for which it should perform NAT ping via a SIP request instead
   if dummy UDP package.

   Default value is -1 (disabled).

   Example 1.7. Set sipping_bflag parameter
...
modparam("nathelper", "sipping_bflag", 7)
...

4.8. sipping_from (string)

   The parameter sets the SIP URI to be used in generating the SIP
   requests for NAT ping purposes. To enable the SIP request pinging
   feature, you have to set this parameter. The SIP request pinging will
   be used only for requests marked so.

   Default value is "NULL".

   Example 1.8. Set sipping_from parameter
...
modparam("nathelper", "sipping_from", "sip:pinger@siphub.net")
...

4.9. sipping_method (string)

   The parameter sets the SIP method to be used in generating the SIP
   requests for NAT ping purposes.

   Default value is "OPTIONS".

   Example 1.9. Set sipping_method parameter
...
modparam("nathelper", "sipping_method", "INFO")
...

4.10. nortpproxy_str (string)

   The parameter sets the SDP attribute used by nathelper to mark the
   packet SDP informations have already been mangled.

   If empty string, no marker will be added or checked.

Note

   The string must be a complete SDP line, including the EOH (\r\n).

   Default value is "a=nortpproxy:yes\r\n".

   Example 1.10. Set nortpproxy_str parameter
...
modparam("nathelper", "nortpproxy_str", "a=sdpmangled:yes\r\n")
...

4.11. keepalive_timeout (int)

   The parameter sets the interval in secods after which a natted contact
   is removed from location table if it does not reply to SIP keepalives
   (usually OPTIONS ping requests).

   The features is available only for UDP contacts that are stored in
   memory (not working for db only mode for usrloc module).

   Keepalives are sent stateless, not using TM module. The value of this
   parameter has to be few times higher than natping_interval.

   Default value is "0" (feature disabled).

   Example 1.11. Set keepalive_timeout parameter
...
modparam("nathelper", "keepalive_timeout", 120)
...

5. Functions

   5.1. fix_nated_contact()
   5.2. fix_nated_sdp(flags [, ip_address])
   5.3. add_rcv_param([flag]),
   5.4. fix_nated_register()
   5.5. nat_uac_test(flags)
   5.6. is_rfc1918(ip_address)
   5.7. add_contact_alias([ip_addr, port, proto])
   5.8. handle_ruri_alias()

5.1. fix_nated_contact()

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

   This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE,
   BRANCH_ROUTE.

   Example 1.12. fix_nated_contact usage
...
if (search("User-Agent: Cisco ATA.*") {fix_nated_contact();};
...

5.2. fix_nated_sdp(flags [, ip_address])

   Alters the SDP information in orer to facilitate NAT traversal. What
   changes to be performed may be controled via the "flags" parameter.
   Return value is -1 if error occurred, 1 if ip's were replaced, 2 if no
   ip's were replaced.

   Meaning of the parameters is as follows:
     * flags - the value may be a bitwise OR of the following flags:
          + 0x01 - adds "a=direction:active" SDP line;
          + 0x02 - rewrite media IP address (c=) with source address of
            the message or the provided IP address (the provide IP address
            take precedence over the source address).
          + 0x04 - adds "a=nortpproxy:yes" SDP line;
          + 0x08 - rewrite IP from origin description (o=) with source
            address of the message or the provided IP address (the provide
            IP address take precedence over the source address).
     * ip_address - IP to be used for rewritting SDP. If not specified,
       the received signalling IP will be used. The parameter allows
       pseudo-variables usage. NOTE: For the IP to be used, you need to
       use 0x02 or 0x08 flags, otherwise it will have no effect.

   This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE,
   FAILURE_ROUTE, BRANCH_ROUTE.

   Example 1.13. fix_nated_sdp usage
...
if (search("User-Agent: Cisco ATA.*") {fix_nated_sdp("3");};
...

5.3. add_rcv_param([flag]),

   Add received parameter to Contact header fields or Contact URI. 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.

   Meaning of the parameters is as follows:
     * flag - flags to indicate if the parameter should be added to
       Contact URI or Contact header. If the flag is non-zero, the
       parameter will be added to the Contact URI. If not used or equal to
       zero, the parameter will go to the Contact header.

   This function can be used from REQUEST_ROUTE.

   Example 1.14. add_rcv_paramer usage
...
add_rcv_param(); # add the parameter to the Contact header
....
add_rcv_param("1"); # add the parameter to the Contact URI
...

5.4. 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 received cloumn in the location table.

   Note: You have to set the received_avp parameter of the nathelper
   module and the registrar module (both module parameters must have the
   same value) to use this function.

   This function can be used from REQUEST_ROUTE.

   Example 1.15. fix_nated_register usage
...
fix_nated_register();
...

5.5. nat_uac_test(flags)

   Tries to guess if client's request originated behind a nat. The
   parameter determines what heuristics is used.

   Meaning of the flags is as follows:
     * 1 - Contact header field is searched for occurrence of RFC1918
       addresses.
     * 2 - the "received" test is used: address in Via is compared against
       source IP address of signaling
     * 4 - Top Most VIA is searched for occurrence of RFC1918 addresses
     * 8 - SDP is searched for occurrence of RFC1918 addresses
     * 16 - test if the source port is different from the port in Via
     * 32 - test if the source IP address of signaling is a RFC1918
       address
     * 64 - test if the source connection of signaling is a WebSocket
     * 128 - test if the Contact URI port differs from the source port of
       the request (Warning: this is might be legal or even intended
       combination in non natted scenarios)

   All flags can be bitwise combined, the test returns true if any of the
   tests identified a NAT.

   This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE,
   FAILURE_ROUTE, BRANCH_ROUTE.

5.6. is_rfc1918(ip_address)

   Determines if the address in the parameter is an rfc1918 address. The
   parameter allows pseudo-variables usage.

   This function can be used from ANY_ROUTE.

5.7. add_contact_alias([ip_addr, port, proto])

   Adds ;alias=ip~port~transport parameter to contact URI containing
   either received ip, port, and transport protocol or those given as
   parameters.

   This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE,
   BRANCH_ROUTE, and LOCAL_ROUTE.

   Example 1.16. add_contact_alias usage
...
    if (!is_present_hf("Record-Route")) {
        if (!add_contact_alias("$var(src_ip)", "$Rp", "tcp")) {
            xlog("L_ERR", "Error in aliasing contact $ct\n");
            send_reply("400", "Bad request");
            exit;
        };
    };
...

5.8. handle_ruri_alias()

   Checks if Request URI has alias param and if so, removes it and sets
   $du based on its value. Note that this means that routing of request is
   based on ;alias parameter value of Request URI rather than Request URI
   itself. If you call handle_ruri_alias() on a request, make thus sure
   that you screen alias parameter value of Request URI the same way as
   you would screen Request URI itself.

   Returns 1 if ;alias param was found and $du was set and $ru rewritten,
   2 if alias param was not found and nothing was done, or -1 in case of
   error.

   This function can be used from REQUEST_ROUTE, BRANCH_ROUTE, and
   LOCAL_ROUTE.

   Example 1.17. handle_ruri_alias usage
...
    if ($du == "") {
        handle_ruri_alias();
        switch ($rc) {
        case -1:
            xlog("L_ERR", "Failed to handle alias of R-URI $ru\n");
            send_reply("400", "Bad request");
            exit;
        case 1:
            xlog("L_INFO", "Routing in-dialog $rm from $fu to $du\n");
            break;
        case 2:
            xlog("L_INFO", "Routing in-dialog $rm from $fu to $ru\n");
            break;
         };
    };
...

6. Exported Pseudo Variables

   6.1. $rr_count
   6.2. $rr_top_count

6.1. $rr_count

   Number of Record Routes in received SIP request or reply.

   Example 1.18. $rr_count usage
...
    $avp(rr_count) = $rr_count;
...

6.2. $rr_top_count

   If topmost Record Route in received SIP request or reply is a double
   Record Route, value of $rr_top_count is 2. If it a single Record Route,
   value of $rr_top_count is 1. If there is no Record Route(s), value of
   $rr_top_count is 0.

   Example 1.19. $rr_top_count usage
...
    if ($rr_count == $avp(rr_count) + $rr_top_count) {
        route(ADD_CONTACT_ALIAS);
    };
...

7. MI Commands

   7.1. nh_enable_ping

7.1. nh_enable_ping

   Enables natping if parameter value greater than 0. Disables natping if
   parameter value is 0.

   The function takes only one parameter - a number in decimal format.

   Example 1.20. nh_enable_ping usage
...
$ kamctl fifo nh_enable_ping 1
...

8. Selects

   8.1. @nathelper.rewrite_contact[n]

8.1. @nathelper.rewrite_contact[n]

   Get n-th Contact value with IP:Port rewritten to source ip:port. N is
   counted from 1. Only IP:port is rewritten, remaining part are left
   unchanged. Full nameaddr is supported.

   Example 1.21. @nathelper.rewrite_contact usage
...
$c = @nathelper.rewrite_contact[1];
...
$c2 = @nathelper.rewrite_contact[1].nameaddr.uri;

Chapter 2. Frequently Asked Questions

   2.1. What happend with "rtpproxy_disable" parameter?
   2.2. Where can I find more about Kamailio?
   2.3. Where can I post a question about this module?
   2.4. How can I report a bug?

   2.1.

   What happend with "rtpproxy_disable" parameter?

   It was removed as it became obsolete - now "rtpproxy_sock" can take
   empty value to disable the rtpproxy functionality.

   2.2.

   Where can I find more about Kamailio?

   Take a look at http://www.kamailio.org/.

   2.3.

   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:
     * User Mailing List -
       http://lists.sip-router.org/cgi-bin/mailman/listinfo/sr-users
     * Developer Mailing List -
       http://lists.sip-router.org/cgi-bin/mailman/listinfo/sr-dev

   E-mails regarding any stable Kamailio release should be sent to
   <sr-users@lists.sip-router.org> and e-mails regarding development
   versions should be sent to <sr-dev@lists.sip-router.org>.

   If you want to keep the mail private, send it to
   <sr-users@lists.sip-router.org>.

   2.4.

   How can I report a bug?

   Please follow the guidelines provided at:
   http://sip-router.org/tracker.
