nathelper Module

Table of Contents

1. Admin Guide
1.1. Overview
1.2. NAT pinging types
1.3. Dependencies
1.3.1. OpenSIPS Modules
1.3.2. External Libraries or Applications
1.4. Exported Parameters
1.4.1. natping_interval (integer)
1.4.2. ping_nated_only (integer)
1.4.3. natping_partitions (integer)
1.4.4. natping_socket (string)
1.4.5. received_avp (str)
1.4.6. force_socket (string)
1.4.7. sipping_bflag (string/integer)
1.4.8. remove_on_timeout_bflag (string/integer)
1.4.9. sipping_latency_flag (string/integer)
1.4.10. sipping_ignore_rpl_codes (CSV string)
1.4.11. sipping_from (string)
1.4.12. sipping_method (string)
1.4.13. nortpproxy_str (string)
1.4.14. natping_tcp (integer)
1.4.15. oldip_skip (string)
1.4.16. ping_threshold (int)
1.4.17. max_pings_lost (int)
1.5. Exported Functions
1.5.1. fix_nated_contact([uri_params])
1.5.2. fix_nated_sdp(flags [, ip_address [, sdp_fields]])
1.5.3. add_rcv_param([flag]),
1.5.4. fix_nated_register()
1.5.5. nat_uac_test(flags)
1.6. Exported MI Functions
1.6.1. nh_enable_ping
2. Frequently Asked Questions
3. Contributors
3.1. By Commit Statistics
3.2. By Commit Activity
4. Documentation
4.1. Contributors

List of Tables

3.1. Top contributors by DevScore(1), authored commits(2) and lines added/removed(3)
3.2. Most recently active contributors(1) to this module

List of Examples

1.1. Set natping_interval parameter
1.2. Set ping_nated_only parameter
1.3. Set natping_partitions parameter
1.4. Set natping_socket parameter
1.5. Set received_avp parameter
1.6. Set force_socket parameter
1.7. Set sipping_bflag parameter
1.8. Set remove_on_timeout_bflag parameter
1.9. Set sipping_latency_flag parameter
1.10. Set sipping_ignore_rpl_codes parameter
1.11. Set sipping_from parameter
1.12. Set sipping_method parameter
1.13. Set nortpproxy_str parameter
1.14. Set natping_tcp parameter
1.15. Set oldip_skip parameter
1.16. Set ping_threshold parameter
1.17. Set max_pings_lost parameter
1.18. fix_nated_contact usage
1.19. fix_nated_sdp usage
1.20. add_rcv_paramer usage
1.21. fix_nated_register usage
1.22. nh_enable_ping usage

Chapter1.Admin Guide


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).

Since version 2.2, stateful ping(only SIP Pings) for nathelper is available. This allows you to remove contacts from usrloc location table when max_pings_lost pings are not responded to, each ping having a response timeout of ping_threshold seconds. In order to have this functionality, contacts must have remove_on_timeout_bflag flag set when inserted into the location table.

Works with multipart messages that contain an SDP part, but not with multi-layered multipart messages.

1.2.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 OpenSIPS;

    • 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 OpenSIPS (inbound traffic) will force the SIP client to generate a SIP reply (outbound traffic) - the NAT bind will be surely kept open. Since version 2.2, one can also choose to remove contacts from the location table if a certain threshold is detected.

    • Disadvantages: higher bandwitdh traffic, more expensive (as time) to generate by OpenSIPS;


1.3.1.OpenSIPS Modules

The following modules must be loaded before this module:

  • usrloc module - only if the NATed contacts are to be pinged.

1.3.2.External Libraries or Applications

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

  • None.

1.4.Exported Parameters

1.4.1.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.


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

Default value is 0.

Example1.1.Set natping_interval parameter

modparam("nathelper", "natping_interval", 10)

1.4.2.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.

Example1.2.Set ping_nated_only parameter

modparam("nathelper", "ping_nated_only", 1)

1.4.3.natping_partitions (integer)

How many partitions/chunks to be used for sending the pingings. One partition means sending all pingings together. Two partitions means to send half pings and second half at a time.

Default value is 1.

Example1.3.Set natping_partitions parameter

modparam("nathelper", "natping_partitions", 4)

1.4.4.natping_socket (string)

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

Default value is NULL.

Example1.4.Set natping_socket parameter

modparam("nathelper", "natping_socket", "")

1.4.5.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.


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).

Example1.5.Set received_avp parameter

modparam("nathelper", "received_avp", "$avp(received)")

1.4.6.force_socket (string)

Sending socket to be used for pinging contacts without local socket information (the local socket information may be lost during a restart or contact replication). If no one specified, OpenSIPS will choose the first listening interface matching the destination protocol and AF family.

Default value is NULL.

Example1.6.Set force_socket parameter

modparam("nathelper", "force_socket", "localhost:33333")

1.4.7.sipping_bflag (string/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.

WARNING: Setting INT flags is deprecated! Use quoted strings instead!

Default value is "NULL" (disabled).

Example1.7.Set sipping_bflag parameter

modparam("nathelper", "sipping_bflag", "SIPPING_ENABLE")

1.4.8.remove_on_timeout_bflag (string/integer)

What branch flag to be used in order to activate usrloc contact removal when the ping_threshold is exceeded.

WARNING: Setting INT flags is deprecated! Use quoted strings instead!

Default value is "NULL" (disabled).

Example1.8.Set remove_on_timeout_bflag parameter

modparam("nathelper", "remove_on_timeout_bflag", "SIPPING_RTO")

1.4.9.sipping_latency_flag (string/integer)

The branch flag which will be used in order to enable contact pinging latency computation and reporting via the usrloc E_UL_LATENCY_UPDATE event.

Default value is "NULL" (disabled).

Example1.9.Set sipping_latency_flag parameter

modparam("nathelper", "sipping_latency_flag", "SIPPING_CALC_LATENCY")

1.4.10.sipping_ignore_rpl_codes (CSV string)

A comma-separated list of SIP reply status codes to contact pings which are to be discarded. This may be useful for "full-sharing" user location topologies, where the location nodes are not directly facing the UAs, hence the intermediary SIP component may generate replies to offline contact ping attempts (e.g. 408 - Request Timeout) -- such ping replies should be ignored.

Default value is "NULL" (all reply status codes are accepted).

Example1.10.Set sipping_ignore_rpl_codes parameter

modparam("nathelper", "sipping_ignore_rpl_codes", "408, 480, 404")

1.4.11.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.

Example1.11.Set sipping_from parameter

modparam("nathelper", "sipping_from", "")

1.4.12.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.

Example1.12.Set sipping_method parameter

modparam("nathelper", "sipping_method", "INFO")

1.4.13.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.


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

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

Example1.13.Set nortpproxy_str parameter

modparam("nathelper", "nortpproxy_str", "a=sdpmangled:yes\r\n")

1.4.14.natping_tcp (integer)

If the flag is set, TCP/TLS clients will also be pinged with SIP OPTIONS messages.

Default value is 0 (not set).

Example1.14.Set natping_tcp parameter

modparam("nathelper", "natping_tcp", 1)

1.4.15.oldip_skip (string)

Parameter which specifies whether old media ip and old origin ip shall be put in the sdp body. The parameter has two values : 'o' ("a=oldoip" field shall be skipped) and 'c' ("a=oldcip" field shall be skipped).

Default value is 0 (not set).

Example1.15.Set oldip_skip parameter

modparam("nathelper", "oldip_skip", "oc")

1.4.16.ping_threshold (int)

If a contact does not respond in ping_threshold seconds since the ping has been sent, the contact shall be removed after max_pings_lost unresponded pings.

Default value is 3 (seconds).

Example1.16.Set ping_threshold parameter

modparam("nathelper", "ping_threshold", 10)

1.4.17.max_pings_lost (int)

Number of unresponded pings after which the contact shall be removed from the location table.

Default value is 3 (pings).

Example1.17.Set max_pings_lost parameter

modparam("nathelper", "max_pings_lost", 5)

1.5.Exported Functions

1.5.1. fix_nated_contact([uri_params])

Rewrites the URI Contact HF to contain request's source address:port. If a list of URI parameter is provided, it will be added to the modified contact;

IMPORTANT NOTE: Changes made by this function shall not be seen in the async resume route. So make sure you call it in all the resume routes where you need the contact fixed.

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

Example1.18.fix_nated_contact usage

if (search("User-Agent: Cisco ATA.*") {
} else {

1.5.2. fix_nated_sdp(flags [, ip_address [, sdp_fields]])

Alters the SDP information in orer to facilitate NAT traversal. What changes to be performed may be controled via the flags parameter. Since version 1.12 the name of the old ip fields are "a=oldoip" for old origin ip and "a=oldcip" for old meda ip.

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 provided IP address takes 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 provided IP address takes precedence over the source address).

    • 0x10 - force rewrite of null media IP and/or origin IP address. Without this flag, null IPs are left untouched.

  • 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.

  • sdp_fields - SDP field(s) to be appended to SDP. Note: Each SDP field must be preceded by "\r\n".


Example1.19.fix_nated_sdp usage

# Add "a=direction:active" SDP line
# Rewrite media IP (c= line)
# Add extra "a=x-attr1" SDP line
# Add extra "a=x-attr2" SDP line
if (search("User-Agent: Cisco ATA.*")

1.5.3. 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.

Example1.20.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

1.5.4. 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 user location database.

This function can be used from REQUEST_ROUTE.

Example1.21.fix_nated_register usage


1.5.5. 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 / RFC6598 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 / RFC6598 addresses

  • 8 - SDP is searched for occurrence of RFC1918 / RFC6598 addresses

  • 16 - test if the source port is different from the port in Via

  • 32 - address in Contact is compared against source IP address of signaling

  • 64 - Port in Contact is compared against source port of signaling

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


1.6.Exported MI Functions


Enables natping if parameter value greater than 0. Disables natping if parameter value is 0. With no parameter, it returns the current natping status.

The function may takean optional parameter (for set operations) - a number in decimal format.

Example1.22.nh_enable_ping usage

$ opensipsctl fifo nh_enable_ping
Status:: 1
$ opensipsctl fifo nh_enable_ping 0
$ opensipsctl fifo nh_enable_ping
Status:: 0

Chapter2.Frequently Asked Questions


Where can I find more about OpenSIPS?

Take a look at


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:

E-mails regarding any stable OpenSIPS release should be sent to and e-mails regarding development versions should be sent to .

If you want to keep the mail private, send it to .


How can I report a bug?

Please follow the guidelines provided at:


3.1.By Commit Statistics

Table3.1.Top contributors by DevScore(1), authored commits(2) and lines added/removed(3)

NameDevScoreCommitsLines ++Lines --
1. Maksym Sobolyev (@sobomax)1533935334766
2. Bogdan-Andrei Iancu (@bogdan-iancu)1431131823788
3. Liviu Chircu (@liviuchircu)4031392254
4. Ionut Ionita (@ionutrazvanionita)40151598627
5. Razvan Crainea (@razvancrainea)3225146237
6. Daniel-Constantin Mierla (@miconda)2217142124
7. Jan Janak (@janakj)2111780129
8. Anca Vamanu2141602185
9. Andrei Pelinescu-Onciul2017121110
10. Ovidiu Sas (@ovidiusas)1813110173

All remaining contributors: Jiri Kuthan (@jiriatipteldotorg), Ancuta Onofrei, Andrei Dragus, Vlad Paiu (@vladpaiu), Henning Westerholt (@henningw), Dan Pascu (@danpascu), Christophe Sollet (@csollet), Marcus Hunger, Vlad Patrascu (@rvlad-patrascu), Klaus Darilion, Sergio Gutierrez, Nils Ohlmeier, Emmanuel Buu, Carsten Bock, Shlomi Gutman, Jeremie Le Hen, Bayan Towfiq, Laurent Schweizer, Jasper Hafkenscheid (@hafkensite), Konstantin Bokarius, John Riordan, Walter Doekes (@wdoekes), Elena-Ramona Modroiu, Edson Gellert Schubert.

(1) DevScore = author_commits + author_lines_added / (project_lines_added / project_commits) + author_lines_deleted / (project_lines_deleted / project_commits)

(2) including any documentation-related commits, excluding merge commits. Regarding imported patches/code, we do our best to count the work on behalf of the proper owner, as per the "fix_authors" and "mod_renames" arrays in opensips/doc/ If you identify any patches/commits which do not get properly attributed to you, please submit a pull request which extends "fix_authors" and/or "mod_renames".

(3) ignoring whitespace edits, renamed files and auto-generated files

3.2.By Commit Activity

Table3.2.Most recently active contributors(1) to this module

NameCommit Activity
1. Liviu Chircu (@liviuchircu)Jan 2013 - Sep 2020
2. Bogdan-Andrei Iancu (@bogdan-iancu)Nov 2003 - Jul 2020
3. Jasper Hafkenscheid (@hafkensite)Mar 2020 - Mar 2020
4. Razvan Crainea (@razvancrainea)Dec 2010 - Sep 2019
5. Dan Pascu (@danpascu)May 2019 - May 2019
6. Shlomi GutmanMar 2018 - Mar 2018
7. Ovidiu Sas (@ovidiusas)Sep 2010 - Feb 2018
8. Vlad Patrascu (@rvlad-patrascu)May 2017 - Aug 2017
9. Ionut Ionita (@ionutrazvanionita)Nov 2014 - Nov 2016
10. Walter Doekes (@wdoekes)May 2014 - May 2014

All remaining contributors: Christophe Sollet (@csollet), Vlad Paiu (@vladpaiu), Maksym Sobolyev (@sobomax), Anca Vamanu, John Riordan, Emmanuel Buu, Andrei Dragus, Sergio Gutierrez, Klaus Darilion, Daniel-Constantin Mierla (@miconda), Konstantin Bokarius, Edson Gellert Schubert, Henning Westerholt (@henningw), Ancuta Onofrei, Marcus Hunger, Carsten Bock, Jeremie Le Hen, Laurent Schweizer, Bayan Towfiq, Andrei Pelinescu-Onciul, Elena-Ramona Modroiu, Jiri Kuthan (@jiriatipteldotorg), Jan Janak (@janakj), Nils Ohlmeier.

(1) including any documentation-related commits, excluding merge commits



Last edited by: Jasper Hafkenscheid (@hafkensite), Liviu Chircu (@liviuchircu), Bogdan-Andrei Iancu (@bogdan-iancu), Ovidiu Sas (@ovidiusas), Ionut Ionita (@ionutrazvanionita), Razvan Crainea (@razvancrainea), Walter Doekes (@wdoekes), Christophe Sollet (@csollet), Vlad Paiu (@vladpaiu), Maksym Sobolyev (@sobomax), Anca Vamanu, Andrei Dragus, Sergio Gutierrez, Klaus Darilion, Daniel-Constantin Mierla (@miconda), Konstantin Bokarius, Edson Gellert Schubert, Carsten Bock, Ancuta Onofrei, Marcus Hunger, Jeremie Le Hen, Bayan Towfiq, Elena-Ramona Modroiu, Jan Janak (@janakj), Jiri Kuthan (@jiriatipteldotorg).

doc copyrights:

Copyright 2018 VoIP Embedded, Inc.

Copyright 2003-2008 Sippy Software, Inc.

Copyright 2005 Voice Sistem SRL