path Module

Andreas Granig

   Inode GmbH

Edited by

Andreas Granig

Richard Fuchs

   Copyright © 2006 Inode GmbH
     __________________________________________________________________

   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

   Table of Contents

   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)

1. Overview

   1.1. Path Insertion For Registrations
   1.2. Outbound routing to NAT'ed UACs

   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
   2.2. External Libraries or Applications

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)
   3.2. received_format (int)
   3.3. enable_r2 (int)

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()
   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)

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.

   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;received=sip:2.3.4.5:1234;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 1.8. 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");
        ...
};
...
