nathelper Module

Maxim Sobolev

   Sippy Software, Inc.

Juha Heinanen

   TuTPro, Inc.

Edited by

Maxim Sobolev

Bogdan-Andrei Iancu

Juha Heinanen

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. natping_disable_bflag (integer)
              4.11. nortpproxy_str (string)
              4.12. keepalive_timeout (int)
              4.13. udpping_from_path (int)
              4.14. ignore_path (int)
              4.15. append_sdp_oldmediaip (int)
              4.16. filter_server_id (int)
              4.17. nat_addr_mode (int)
              4.18. alias_name (string)

        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([mode])
              5.9. set_contact_alias([trim])
              5.10. set_alias_to_pv(target_avp)

        6. Exported Pseudo Variables

              6.1. $rr_count
              6.2. $rr_top_count

        7. RPC Commands

              7.1. nathelper.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 natping_disable_bflag parameter
   1.11. Set nortpproxy_str parameter
   1.12. Set keepalive_timeout parameter
   1.13. Set udpping_from_path parameter
   1.14. Set ignore_path parameter
   1.15. Set append_sdp_oldmediaip parameter
   1.16. Set filter_server_id parameter
   1.17. Set nat_addr_mode parameter
   1.18. Set alias_name parameter
   1.19. fix_nated_contact usage
   1.20. fix_nated_sdp usage
   1.21. add_rcv_param usage
   1.22. fix_nated_register usage
   1.23. nat_uac_test usage
   1.24. is_rfc1918 usage
   1.25. add_contact_alias usage
   1.26. handle_ruri_alias usage
   1.27. set_contact_alias usage
   1.28. set_alias_to_pv usage
   1.29. $rr_count usage
   1.30. $rr_top_count usage
   1.31. nathelper.enable_ping usage
   1.32. @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. natping_disable_bflag (integer)
        4.11. nortpproxy_str (string)
        4.12. keepalive_timeout (int)
        4.13. udpping_from_path (int)
        4.14. ignore_path (int)
        4.15. append_sdp_oldmediaip (int)
        4.16. filter_server_id (int)
        4.17. nat_addr_mode (int)
        4.18. alias_name (string)

   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([mode])
        5.9. set_contact_alias([trim])
        5.10. set_alias_to_pv(target_avp)

   6. Exported Pseudo Variables

        6.1. $rr_count
        6.2. $rr_top_count

   7. RPC Commands

        7.1. nathelper.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.

   The function fix_nated_contact() rewrites the “Contact” header field
   with request's source address:port pair. The function fix_nated_sdp()
   adds the active direction indication to SDP (flag 0x01) and updates the
   source IP address too (flag 0x02). The function fix_nated_register()
   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 this is not always an issue, it may cause problems
   with strict SIP clients. An alternative is to use add_contact_alias()
   (or set_contact_alias()) that together with the handle_ruri_alias() is
   standards conforming and also supports reuse of TCP/TLS connections.

2. NAT pinging types

   Currently, the nathelper module supports two types of NAT pings:
     * UDP packet - 4 bytes (zero filled) UDP packets are sent to the
       contact address.
          + Advantages: low bandwidth 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 get
            closed.
     * SIP request - a stateless SIP request is sent to the UDP 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 bandwidth 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. natping_disable_bflag (integer)
   4.11. nortpproxy_str (string)
   4.12. keepalive_timeout (int)
   4.13. udpping_from_path (int)
   4.14. ignore_path (int)
   4.15. append_sdp_oldmediaip (int)
   4.16. filter_server_id (int)
   4.17. nat_addr_mode (int)
   4.18. alias_name (string)

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", "127.0.0.1:5060")
...

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 parameter is set to 1 then only contacts that have the behind
   NAT “nat_bflag” flag set in user location records get the NAT ping (the
   “nat_bflag” is specified via modparam of usrloc module). By default the
   ping is done with 4-bytes UDP packet. If sipping_bflag is also set,
   then the ping is done with a stateless SIP request (by default: OPTIONS
   request).

   If it is 0, then all contacts get a NAT ping, by default being the
   4-bytes UDP packet. If it is 0 and sipping_bflag parameter is set, then
   SIP-request-based pinging is sent to all contacts.

   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 in the “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)

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

   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. natping_disable_bflag (integer)

   What branch flag should be used by the module to disable NAT pings on a
   per-registration basis. If the given flag is set for a particular
   registration, then no NAT pings will be sent at all, regardless of any
   other conditions.

   Default value is -1 (disabled).

   Example 1.10. Set natping_disable_bflag parameter
...
modparam("nathelper", "natping_disable_bflag", 8)
...

4.11. nortpproxy_str (string)

   The parameter sets the SDP attribute used by nathelper to mark the
   packet SDP that information 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 1.11. Set nortpproxy_str parameter
...
modparam("nathelper", "nortpproxy_str", "a=sdpmangled:yes\r\n")
...

4.12. keepalive_timeout (int)

   The parameter sets the interval in seconds 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 1.12. Set keepalive_timeout parameter
...
modparam("nathelper", "keepalive_timeout", 120)
...

4.13. udpping_from_path (int)

   Enable sending UDP pings (keepalives) using raw socket from Path
   address.

   Default value is “0” (feature disabled).

   Example 1.13. Set udpping_from_path parameter
...
modparam("nathelper", "udpping_from_path", 1)
...

4.14. ignore_path (int)

   Enable ignore of Path header address when sending UDP pings
   (keepalives).

   Default value is “0” (feature disabled). UDP pings are sent to Path
   header if header is present.

   Example 1.14. Set ignore_path parameter
...
modparam("nathelper", "ignore_path", 1)
...

4.15. append_sdp_oldmediaip (int)

   The parameter controls if oldmediaip field should be appended to the
   SDP.

   Default value is “1” (feature enabled).

   Example 1.15. Set append_sdp_oldmediaip parameter
...
modparam("nathelper", "append_sdp_oldmediaip", 1)
...

4.16. filter_server_id (int)

   Filter contacts by “server_id” core parameter. Use this parameter to
   limit pinging. When set to “1”, only proxy instances which send packets
   are those where core server_id matches server_id saved in usrloc.
   Default value is “0” (disabled).

   Example 1.16. Set filter_server_id parameter
...
modparam("nathelper", "filter_server_id", 1)
...

4.17. nat_addr_mode (int)

   If set to 0, only default private net addresses are checked by
   nat_uac_test(). If set to 1, other reserved net addresses are checked
   by nat_uac_test() as well.

   Default private net addresses are:
     * 10.0.0.0/8
     * 172.16.0.0/12
     * 192.168.0.0/16
     * 100.64.0.0/10 - RFC6598 - Carrier Grade NAT
     * 192.0.0.0/29 - RFC7335 - IPv4 Service Continuity Prefix

   Reserved net addresses are:
     * 192.0.0.0/24 - RFC7335 - IETF Protocol Assignments

   Default value is “1”.

   Example 1.17. Set nat_addr_mode parameter
...
modparam("nathelper", "nat_addr_mode", 0)
...

4.18. alias_name (string)

   The parameter sets the name of the Contact URI parameter set by
   set_contact_alias() or add_contact_alias() and processed by
   handle_ruri_alias() in R-URI.

   Default value is “alias”.

   Example 1.18. Set alias_name parameter
...
modparam("nathelper", "alias_name", "saddr")
...

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([mode])
   5.9. set_contact_alias([trim])
   5.10. set_alias_to_pv(target_avp)

5.1.  fix_nated_contact()

   Rewrites the “Contact” header to contain the request's source
   address:port.

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

   Example 1.19. 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 order to facilitate NAT traversal. What
   changes to be performed may be controlled 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. (a=rtcp) param will be
            rewritten if exists. (the provided 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. (a=rtcp)
            param will be rewritten if exists. (the provided IP address
            take precedence over the source address).
     * ip_address - IP to be used for rewriting 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. Must be
       IPv4 address family.

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

   Example 1.20. fix_nated_sdp usage
...
if (search("User-Agent: Cisco ATA.*") {fix_nated_sdp("3");};
...

5.3.  add_rcv_param([flag]),

   Add a received parameter to the “Contact” header fields (available for
   all transports) or to the Contact URI (available only for UDP traffic).

   The parameter will contain the URI created from the source IP, port,
   and protocol (if different than UDP) 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 1.21. add_rcv_param 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 column 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 1.22. 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 - The “Contact” header field is searched for occurrence of
       RFC1918 or RFC6598 addresses.
     * 2 - the "received" test is used: address in the “Via” header is
       compared against source IP address of signaling. If the “Via”
       header contains no port, it uses the default SIP port 5060
     * 4 - The Top Most “Via” is searched for occurrence of RFC1918 or
       RFC6598 addresses
     * 8 - The SDP is searched for occurrence of RFC1918 or RFC6598
       addresses
     * 16 - Test if the source port is different from the port in the
       “Via” header. If the “Via” header contains no port, it uses the
       default SIP port 5060
     * 32 - Test if the source IP address of signaling is a RFC1918 or
       RFC6598 address
     * 64 - Test if the source connection of signaling is a WebSocket
     * 128 - Test if the “Contact” header URI port differs from the source
       port of the request (Warning: this is might be legal or even
       intended combination in non NATted scenarios)
     * 256 - Test if the SDP connection address is different from source
       IP address. It will work also with multiple connection address
       lines.
     * 512 - Test if the target addresses are different or over websocket.
       For requests, it compares host and port in R-URI ($rU) and D-URI
       ($du). For replies, it compares host and port in 2nd Via with
       received and rport parameters.

   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.

   Example 1.23. nat_uac_test usage
...
if(nat_uac_test("19")) {
    rtpproxy_manage("co");
}
...

5.6.  is_rfc1918(ip_address)

   Determines if the address in the parameter is an rfc1918 or rfc6598
   address. The parameter allows pseudo-variables usage.

   This function can be used from ANY_ROUTE.

   Example 1.24. is_rfc1918 usage
...
if(is_rfc1918("$rd")) {
    # domain in r-uri is private address
}
...

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

   Adds an “;alias=ip~port~transport” parameter to the contact URI
   containing either received ip, port, and transport protocol or those
   given as parameters. If called without parameters, “;alias” parameter
   is only added if received ip, port, or transport protocol differs from
   that in contact URI.

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

   Example 1.25. 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([mode])

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

   The optional parameter mode can be 0 to consume first alias parameter,
   otherwise it consumes the last alias parameter. If the parameter mode
   is not provided, it consumes the first parameter.

   Returns 1 if “;alias” parameter was found and “$du” was set and the
   “$ru” rewritten, 2 if the alias parameter 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 1.26. 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;
         };
    };
...

5.9.  set_contact_alias([trim])

   Adds an “;alias=ip~port~transport” parameter to the contact URI
   containing the received ip, port, and transport protocol. The update of
   contact URI is signaled to a few other modules in the way the
   fix_nated_contact() does it by using the internal flags. The new value
   is not visible to pseudo-variables and it does not change the SIP
   message buffer.

   Meaning of parameters:
     * trim - by default, set_contact_alias() will not detect and trim an
       already existing alias parameter. If this optional parameter is set
       to "1", set_contact_alias() will trim the existing alias before
       adding a new one.

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

   Example 1.27. set_contact_alias usage
...
    if (!is_present_hf("Record-Route")) {
        if (!set_contact_alias()) {
            xlog("L_ERR", "Error in aliasing contact $ct\n");
            send_reply("400", "Bad request");
            exit;
        };
    };
...

5.10.  set_alias_to_pv(target_avp)

   Reads “;alias=ip~port~transport” from Contact header then writes to
   target pseudo-variable as a sip uri.

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

   Example 1.28. set_alias_to_pv usage
...
                set_alias_to_pv("$avp(aliasuri)");
...

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 1.29. $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 1.30. $rr_top_count usage
...
    if ($rr_count == $avp(rr_count) + $rr_top_count) {
        route(ADD_CONTACT_ALIAS);
    };
...

7. RPC Commands

   7.1. nathelper.enable_ping

7.1. nathelper.enable_ping

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

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

   Example 1.31. nathelper.enable_ping usage
...
$ kamctl rpc nathelper.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 parts are left
   unchanged. Full nameaddr is supported.

   Example 1.32. @nathelper.rewrite_contact usage
...
$c = @nathelper.rewrite_contact[1];
...
$c2 = @nathelper.rewrite_contact[1].nameaddr.uri;

Chapter 2. Frequently Asked Questions

   2.1. What happened 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 happened 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 https://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 -
       https://lists.kamailio.org/mailman3/postorius/lists/sr-users.lists.
       kamailio.org/
     * Developer Mailing List -
       https://lists.kamailio.org/mailman3/postorius/lists/sr-dev.lists.ka
       mailio.org/

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

   2.4.

   How can I report a bug?

   Please follow the guidelines provided at:
   https://github.com/kamailio/kamailio/issues.
