# &adminguide;

## Overview

This is a module to help with &nat; traversal. In particular, it helps symmetric &ua;s 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.

## 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 &osips;;

  - 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 &osips; (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 &osips;;

## Dependencies

### &osips; 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

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

- None.

## Exported Parameters

### `natping_interval` (integer)

Period of time in seconds between sending the NAT pings to all currently registered &ua;s 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.

#### Set `natping_interval` parameter

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

### `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.

#### Set `ping_nated_only` parameter

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

### `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.

#### Set `natping_partitions` parameter

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

### `natping_socket` (string)

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

Default value is NULL.

#### Set `natping_socket` parameter

    ...
    modparam("nathelper", "natping_socket", "192.168.1.1:5006")
    ...

### `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).

#### Set `received_avp` parameter

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

### `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.

#### Set `force_socket` parameter

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

### `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).

#### Set `sipping_bflag` parameter

    ...
    modparam("nathelper", "sipping_bflag", "SIP_PING_FLAG")
    ...

### `remove_on_timeout_bflag` (string/integer)

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

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

Default value is "NULL" (disabled).

#### Set `remove_on_timeout_bflag` parameter

    ...
    modparam("nathelper", "remove_on_timeout_bflag", "RM_ONTO_FLAG")
    ...

### `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.

#### Set `sipping_from` parameter

    ...
    modparam("nathelper", "sipping_from", "sip:pinger@siphub.net")
    ...

### `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.

#### Set `sipping_method` parameter

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

### `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.

#### Set `nortpproxy_str` parameter

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

### `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).

#### Set `natping_interval` parameter

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

### `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).

#### Set `natping_interval` parameter

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

### `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).

#### Set `ping_threshold` parameter

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

### `max_pings_lost` (int)

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

Default value is 3 (pings).

#### Set `ping_threshold` parameter

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

## Exported Functions

### `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.

#### `fix_nated_contact` usage

    ...
    if (search("User-Agent: Cisco ATA.*") {
        fix_nated_contact(";ata=cisco");
    } else {
        fix_nated_contact();
    }
    ...

### `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 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 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 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.

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

#### `fix_nated_sdp` usage

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

#### `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
    ...

### `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` usage

    ...
    fix_nated_register();
    ...

### `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.

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

### MI Commands

#### `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.

##### `nh_enable_ping` usage

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