NATHELPER module
Admin Guide
Section titled “Admin Guide”Overview
Section titled “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).
Works with multipart messages that contain an SDP part, but not with multi-layered multipart messages.
NAT pinging types
Section titled “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.
- Disadvantages: higher bandwitdh traffic, more expensive (as time) to generate by OpenSIPS;
Dependencies
Section titled “Dependencies”OpenSIPS Modules
Section titled “OpenSIPS Modules”The following modules must be loaded before this module:
- usrloc module - only if the NATed contacts are to be pinged.
External Libraries or Applications
Section titled “External Libraries or Applications”The following libraries or applications must be installed before running OpenSIPS with this module loaded:
- None.
Exported Parameters
Section titled “Exported Parameters”natping_interval (integer)
Section titled “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.
Default value is 0.
...modparam("nathelper", "natping_interval", 10)...ping_nated_only (integer)
Section titled “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.
...modparam("nathelper", "ping_nated_only", 1)...natping_processes (integer)
Section titled “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.
...modparam("nathelper", "natping_processes", 3)...natping_socket (string)
Section titled “natping_socket (string)”Spoof the natping’s source-ip to this address. Works only for IPv4.
Default value is NULL.
...modparam("nathelper", "natping_socket", "192.168.1.1:5006")...received_avp (str)
Section titled “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.
Default value is “NULL” (disabled).
...modparam("nathelper", "received_avp", "$avp(received_avp)")...force_socket (string)
Section titled “force_socket (string)”Socket to be forced when sending pings. It makes sense only for UDP communication. If no one specified, the OS will choose.
Default value is “NULL”.
...modparam("nathelper", "force_socket", "localhost:33333")...sipping_bflag (integer)
Section titled “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).
...modparam("nathelper", "sipping_bflag", 7)...sipping_from (string)
Section titled “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”.
...modparam("nathelper", "sipping_from", "sip:pinger@siphub.net")...sipping_method (string)
Section titled “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”.
...modparam("nathelper", "sipping_method", "INFO")...nortpproxy_str (string)
Section titled “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.
Default value is “a=nortpproxy:yes\r\n”.
...modparam("nathelper", "nortpproxy_str", "a=sdpmangled:yes\r\n")...Exported Functions
Section titled “Exported Functions”fix_nated_contact([uri_params])
Section titled “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;
This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE, BRANCH_ROUTE.
...if (search("User-Agent: Cisco ATA.*") { fix_nated_contact(";ata=cisco");} else { fix_nated_contact();}...fix_nated_sdp(flags [, ip_address])
Section titled “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” paramter.
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.
...if (search("User-Agent: Cisco ATA.*") {fix_nated_sdp("3");};...add_rcv_param([flag]),
Section titled “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.
...add_rcv_param(); # add the parameter to the Contact header....add_rcv_param("1"); # add the paramter to the Contact URI...fix_nated_register()
Section titled “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.
...fix_nated_register();...nat_uac_test(flags)
Section titled “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 - address in Contact is compared against source IP address of signaling
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.
Exported MI Functions
Section titled “Exported MI Functions”nh_enable_ping
Section titled “nh_enable_ping”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.
...$ opensipsctl fifo nh_enable_pingStatus:: 1$$ opensipsctl fifo nh_enable_ping 0$$ opensipsctl fifo nh_enable_pingStatus:: 0$...Frequently Asked Questions
Section titled “Frequently Asked Questions”Q: Where can I find more about OpenSIPS?
Take a look at http://www.opensips.org/.
Q: 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 users@lists.opensips.org and e-mails regarding development versions should be sent to devel@lists.opensips.org.
If you want to keep the mail private, send it to users@lists.opensips.org.
Q: How can I report a bug?
Please follow the guidelines provided at: https://github.com/OpenSIPS/opensips/issues.
Contributors
Section titled “Contributors”By Commit Statistics
Section titled “By Commit Statistics”Top contributors by DevScore(1), authored commits(2) and lines added/removed(3)
| # | Name | DevScore | Commits | Lines++ | Lines— |
|---|---|---|---|---|---|
| 1. | Maksym Sobolyev (@sobomax) | 177 | 39 | 3675 | 6412 |
| 2. | Bogdan-Andrei Iancu (@bogdan-iancu) | 113 | 86 | 1723 | 722 |
| 3. | Daniel-Constantin Mierla (@miconda) | 22 | 17 | 144 | 126 |
| 4. | Anca Vamanu | 22 | 4 | 1646 | 229 |
| 5. | Andrei Pelinescu-Onciul | 21 | 17 | 125 | 114 |
| 6. | Jan Janak (@janakj) | 21 | 11 | 795 | 144 |
| 7. | Ancuta Onofrei | 19 | 3 | 1049 | 381 |
| 8. | Razvan Crainea (@razvancrainea) | 18 | 14 | 124 | 93 |
| 9. | Jiri Kuthan (@jiriatipteldotorg) | 18 | 10 | 764 | 47 |
| 10. | Stefan Darius (@dariusstefan) | 11 | 4 | 588 | 101 |
All remaining contributors: Andrei Dragus, Ovidiu Sas (@ovidiusas), Vlad Paiu (@vladpaiu), Henning Westerholt (@henningw), Marcus Hunger, Klaus Darilion, Sergio Gutierrez, Nils Ohlmeier, Emmanuel Buu, Carsten Bock, Jeremie Le Hen, Christophe Sollet (@csollet), Bayan Towfiq, Laurent Schweizer, Walter Doekes (@wdoekes), John Riordan, Konstantin Bokarius, 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
(3) ignoring whitespace edits, renamed files and auto-generated files
By Commit Activity
Section titled “By Commit Activity”| # | Name | Commit Activity |
|---|---|---|
| 1. | Stefan Darius (@dariusstefan) | Jun 2026 - Jul 2026 |
| 2. | Razvan Crainea (@razvancrainea) | Dec 2010 - Jun 2026 |
| 3. | Bogdan-Andrei Iancu (@bogdan-iancu) | Nov 2003 - Dec 2013 |
| 4. | Walter Doekes (@wdoekes) | Aug 2013 - Aug 2013 |
| 5. | Vlad Paiu (@vladpaiu) | Aug 2010 - Feb 2012 |
| 6. | Maksym Sobolyev (@sobomax) | May 2003 - Mar 2011 |
| 7. | Anca Vamanu | Feb 2009 - Feb 2011 |
| 8. | Ovidiu Sas (@ovidiusas) | Sep 2010 - Sep 2010 |
| 9. | John Riordan | Aug 2010 - Aug 2010 |
| 10. | Emmanuel Buu | Mar 2010 - Mar 2010 |
All remaining contributors: Andrei Dragus, Christophe Sollet (@csollet), 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
Documentation
Section titled “Documentation”Contributors
Section titled “Contributors”Last edited by: Razvan Crainea (@razvancrainea), Maksym Sobolyev (@sobomax), Anca Vamanu, Bogdan-Andrei Iancu (@bogdan-iancu), Ovidiu Sas (@ovidiusas), Vlad Paiu (@vladpaiu), Christophe Sollet (@csollet), 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).
License
Section titled “License”All documentation files (i.e. .md extension) are licensed under the Creative Common License 4.0