path Module

Andreas Granig

Inode GmbH

Edited by

Andreas Granig

Edited by

Richard Fuchs


Table of Contents

1. Admin Guide
1. Overview
1.1. Path Insertion For Registrations
1.2. Outbound routing to NAT'ed UACs
2. Dependencies
2.1. Kamailio Modules
2.2. External Libraries or Applications
3. Parameters
3.1. use_received (int)
3.2. received_format (int)
3.3. enable_r2 (int)
4. Functions
4.1. add_path()
4.2. add_path(user)
4.3. add_path(user, parameters)
4.4. add_path_received()
4.5. add_path_received(user)
4.6. add_path_received(user, parameters)

List of Examples

1.1. Add Supported header
1.2. Set use_received parameter
1.3. Set received_format parameter
1.4. Set enable_r2 parameter
1.5. add_path usage
1.6. add_path(user) usage
1.7. add_path(user, parameters) usage
1.8. add_path_received() usage
1.9. add_path_received(user) usage
1.10. add_path_received(user, parameters) usage

Chapter 1. Admin Guide

1. Overview

This module is designed to be used at intermediate sip proxies like loadbalancers in front of registrars and proxies. It provides functions for inserting a Path header including a parameter for passing forward the received-URI of a registration to the next hop. It also provides a mechanism for evaluating this parameter in subsequent requests and to set the destination URI according to it.

1.1. Path Insertion For Registrations

For registrations in a scenario like [UAC] -> [P1] -> [REG], the "path" module can be used at the intermediate proxy P1 to insert a Path header into the message before forwarding it to the registrar REG. Two functions can be used to achieve this:

  • add_path(...) adds a Path header in the form of Path: <sip:1.2.3.4;lr> to the message using the address of the outgoing interface. A port is only added if it's not the default port 5060.

    If a username is passed to the function, it is also included in the Path URI, like Path: <sip:username@1.2.3.4;lr>.

  • add_path_received(...) also add a Path header in the same form as above, but also adds a parameter indicating the received-URI of the message, like Path: <sip:1.2.3.4;received=sip:2.3.4.5:1234;lr>. This is especially useful if the proxy does NAT detection and wants to pass the NAT'ed address to the registrar.

    If the function is called with a username, it's included in the Path URI too.

Note that some SIP registrars may check if header Supported includes 'path'. It can be added in Kamailio.cfg using append_hf() from textops module.

Example 1.1. Add Supported header

...
append_hf("Supported: path\r\n");
...

1.2. Outbound routing to NAT'ed UACs

If the NAT'ed address of an UAC is passed to the registrar, the registrar routes back subsequent requests using the Path header of the registration as Route header of the current request. If the intermediate proxy had inserted a Path header including the received parameter during the registration, this parameter will show up in the Route header of the new request as well, allowing the intermediate proxy to route to this address instead of the one propagated in the Route URI for tunneling through NAT. This behaviour can be activated by setting the module parameter use_received.

2. Dependencies

2.1. Kamailio Modules

The following modules must be loaded before this module:

  • The "rr" module is needed for outbound routing according to the received parameter.

  • The "outbound" module is needed for outbound routing as per RFC 5626.

2.2. External Libraries or Applications

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

  • None.

3. Parameters

3.1. use_received (int)

If set to 1, the received parameter of the first Route URI is evaluated and used as destination-URI if present.

Default value is 0.

Example 1.2. Set use_received parameter

...
modparam("path", "use_received", 1)
...

3.2. received_format (int)

If set to 0, the received parameter value will be in the escaped SIP URI format.

If set to 1, the received parameter value will be in the same format as the alias parameter added by set_contact_alias() from nathelper module (i.e., ip~port~protid). This is a solution with some SIP applications that incorrectly match the transport from received parameter instead of the one from the SIP URI.

Default value is 0.

Example 1.3. Set received_format parameter

...
modparam("path", "received_format", 1)
...

3.3. enable_r2 (int)

If set to 1, the module will add two Path headers, similar to the double Record-Route done by rr module. One Path headers corresponds to incoming network socket and the other to outgoing network socket. The URIs in the Path headers will have the 'r2=on' parameter as well.

Note: if enabled, the module adds the two Path headers even when the incoming socket is the same as outgoing socket. Improvements to skip the second Path header in this case may be introduced in the future, meanwhile, if you need to enable this parameter but also deal with same socket routing, use 'insert_hf("Path: <$Ru>\r\n")'.

Default value is 0.

Example 1.4. Set enable_r2 parameter

...
modparam("path", "enable_r2", 1)
...

4. Functions

4.1.  add_path()

This function is used to insert a Path header in the form Path: <sip:1.2.3.4;lr>, where 1.2.3.4 is the address of the outgoing interface.

If the outbound module was loaded before this module, and outbound is required for this request, the header will be in the form Path: <sip:flowtoken@1.2.3.4;lr;ob>, where flowtoken is the RFC 5626 flow-token that can be used to identify the source and local address and transport the request was received on, and where 1.2.3.4 is the address of the outgoing interface.

This function can be used from REQUEST_ROUTE.

Example 1.5. add_path usage

...
if (!add_path()) {
	sl_send_reply("503", "Internal Path Error");
	...
};
...

4.2.  add_path(user)

This function adds a Path header in the form Path: <sip:user@1.2.3.4;lr>.

Meaning of the parameters is as follows:

  • user - The username to be inserted as user part. SPVE is supported.

This function can be used from REQUEST_ROUTE.

Example 1.6. add_path(user) usage

...
if (!add_path("loadbalancer")) {
	sl_send_reply("503", "Internal Path Error");
	...
};
...

4.3.  add_path(user, parameters)

This function adds a Path header in the form Path: <sip:user@1.2.3.4;lr> and appends the given parameters as additional URI parameters.

Meaning of the parameters is as follows:

  • user - The username to be inserted as user part. SPVE is supported.

  • parameters - Additional URI parameters to be appended to the URI. The semicolon separator is added automatically. The script writer is responsible for proper URI escaping. SPVE is supported.

This function can be used from REQUEST_ROUTE.

Example 1.7. add_path(user, parameters) usage

...
if (!add_path("loadbalancer", "ob")) {
	sl_send_reply("503", "Internal Path Error");
	...
};
...

4.4.  add_path_received()

This function adds a Path header in the form Path: <sip:1.2.3.4;received=sip:2.3.4.5:1234;lr>, setting its own outgoing address as domain-part, and the address the request has been received from as received-parameter.

This function can be used from REQUEST_ROUTE.

Example 1.8. add_path_received() usage

...
if (!add_path_received()) {
	sl_send_reply("503", "Internal Path Error");
	...
};
...

4.5.  add_path_received(user)

This function adds a Path header in the form Path: <sip:user@1.2.3.4;received=sip:2.3.4.5:1234;lr>, setting 'user' as username part of address, its own outgoing address as domain-part, and the address the request has been received from as received-parameter.

This function can be used from REQUEST_ROUTE.

Example 1.9. add_path_received(user) usage

...
if (!add_path_received("inbound")) {
	sl_send_reply("503", "Internal Path Error");
	...
};
...

4.6.  add_path_received(user, parameters)

This function adds a Path header in the form Path: <sip:user@1.2.3.4;received=sip:2.3.4.5:1234;lr>, setting 'user' as username part of address, its own outgoing address as domain-part, and the address the request has been received from as received-parameter.

This function can be used from REQUEST_ROUTE.

Example 1.10. add_path_received(user, parameters) usage

...
if (!add_path_received("inbound", "ob")) {
	sl_send_reply("503", "Internal Path Error");
	...
};
...