# &adminguide;

## 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.

### 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.

### 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.

## Dependencies

### &osips; Modules

The following modules must be loaded before this module:

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

### External Libraries or Applications

The following libraries or applications must be installed before running &osips; with this module loaded:

- None.

## Exported Parameters

### `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.

#### Set `use_received` parameter

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

### `enable_double_path` (integer)

There are some situations when the server needs to insert two Path header fields instead of one. For example when using two disconnected networks or doing cross-protocol forwarding from UDP->TCP. This parameter enables inserting of 2 Paths.

Default value is 1 (yes).

#### Set `enable_double_path` parameter

    ...
    modparam("path", "enable_double_path", 0)
    ...

## Exported Functions

### `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.

This function can be used from REQUEST_ROUTE.

#### `add_path` usage

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

### `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.

This function can be used from REQUEST_ROUTE.

#### `add_path(user)` usage

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

### `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 it's 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.

#### `add_path_received()` usage

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

### `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, it's 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.

#### `add_path_received(user)` usage

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