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<!-- Module User's Guide -->
<chapter>
<title>&adminguide;</title>
<section>
<title>Overview</title>
<para>
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).
</para>
<para>
Works with multipart messages that contain an SDP part,
but not with multi-layered multipart messages.
</para>
</section>
<section>
<title>NAT pinging types</title>
<para>
Currently, the nathelper module supports two types of NAT pings:
</para>
<itemizedlist>
<listitem>
<para>
<emphasis>UDP package</emphasis> - 4 bytes (zero filled) UDP
packages are sent to the contact address.
</para>
<itemizedlist>
<listitem>
<para><emphasis>Advantages:</emphasis> low bandwitdh traffic,
easy to generate by &osips;;
</para>
</listitem>
<listitem>
<para><emphasis>Disadvantages:</emphasis> 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.
</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<para>
<emphasis>SIP request</emphasis> - a stateless SIP request is
sent to the contact address.
</para>
<itemizedlist>
<listitem>
<para><emphasis>Advantages:</emphasis> 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.
</para>
</listitem>
<listitem>
<para><emphasis>Disadvantages:</emphasis> higher bandwitdh
traffic, more expensive (as time) to generate by &osips;;
</para>
</listitem>
</itemizedlist>
</listitem>
</itemizedlist>
</section>
<section>
<title>Dependencies</title>
<section>
<title>&osips; Modules</title>
<para>
The following modules must be loaded before this module:
<itemizedlist>
<listitem>
<para>
<emphasis>usrloc</emphasis> module - only if the NATed
contacts are to be pinged.
</para>
</listitem>
</itemizedlist>
</para>
</section>
<section>
<title>External Libraries or Applications</title>
<para>
The following libraries or applications must be installed before
running &osips; with this module loaded:
<itemizedlist>
<listitem>
<para>
<emphasis>None</emphasis>.
</para>
</listitem>
</itemizedlist>
</para>
</section>
</section>
<section>
<title>Exported Parameters</title>
<section>
<title><varname>natping_interval</varname> (integer)</title>
<para>
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.
</para>
<note><para>
Enabling the NAT pinging functionality will force the module to
bind itself to USRLOC module.
</para></note>
<para>
<emphasis>
Default value is 0.
</emphasis>
</para>
<example>
<title>Set <varname>natping_interval</varname> parameter</title>
<programlisting format="linespecific">
...
modparam("nathelper", "natping_interval", 10)
...
</programlisting>
</example>
</section>
<section>
<title><varname>ping_nated_only</varname> (integer)</title>
<para>
If this variable is set then only contacts that have
<quote>behind_NAT</quote> flag in user location database set will
get ping.
</para>
<para>
<emphasis>
Default value is 0.
</emphasis>
</para>
<example>
<title>Set <varname>ping_nated_only</varname> parameter</title>
<programlisting format="linespecific">
...
modparam("nathelper", "ping_nated_only", 1)
...
</programlisting>
</example>
</section>
<section>
<title><varname>natping_processes</varname> (integer)</title>
<para>
How many timer processes should be created by the module for the
exclusive task of sending the NAT pings.
</para>
<para>
<emphasis>
Default value is 1.
</emphasis>
</para>
<example>
<title>Set <varname>natping_processes</varname> parameter</title>
<programlisting format="linespecific">
...
modparam("nathelper", "natping_processes", 3)
...
</programlisting>
</example>
</section>
<section>
<title><varname>natping_socket</varname> (string)</title>
<para>
Spoof the natping's source-ip to this address. Works only for IPv4.
</para>
<para>
<emphasis>
Default value is NULL.
</emphasis>
</para>
<example>
<title>Set <varname>natping_socket</varname> parameter</title>
<programlisting format="linespecific">
...
modparam("nathelper", "natping_socket", "192.168.1.1:5006")
...
</programlisting>
</example>
</section>
<section>
<title><varname>received_avp</varname> (str)</title>
<para>
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.
</para>
<note>
<para>
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.
</para>
</note>
<para>
<emphasis>
Default value is "NULL" (disabled).
</emphasis>
</para>
<example>
<title>Set <varname>received_avp</varname> parameter</title>
<programlisting format="linespecific">
...
modparam("nathelper", "received_avp", "$avp(received_avp)")
...
</programlisting>
</example>
</section>
<section>
<title><varname>force_socket</varname> (string)</title>
<para>
Socket to be forced when sending pings. It makes sense only
for UDP communication. If no one specified, the OS will choose.
</para>
<para>
<emphasis>
Default value is <quote>NULL</quote>.
</emphasis>
</para>
<example>
<title>Set <varname>force_socket</varname> parameter</title>
<programlisting format="linespecific">
...
modparam("nathelper", "force_socket", "localhost:33333")
...
</programlisting>
</example>
</section>
<section>
<title><varname>sipping_bflag</varname> (integer)</title>
<para>
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.
</para>
<para>
<emphasis>
Default value is -1 (disabled).
</emphasis>
</para>
<example>
<title>Set <varname>sipping_bflag</varname> parameter</title>
<programlisting format="linespecific">
...
modparam("nathelper", "sipping_bflag", 7)
...
</programlisting>
</example>
</section>
<section>
<title><varname>sipping_from</varname> (string)</title>
<para>
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.
</para>
<para>
<emphasis>
Default value is <quote>NULL</quote>.
</emphasis>
</para>
<example>
<title>Set <varname>sipping_from</varname> parameter</title>
<programlisting format="linespecific">
...
modparam("nathelper", "sipping_from", "sip:pinger@siphub.net")
...
</programlisting>
</example>
</section>
<section>
<title><varname>sipping_method</varname> (string)</title>
<para>
The parameter sets the SIP method to be used in generating the SIP
requests for NAT ping purposes.
</para>
<para>
<emphasis>
Default value is <quote>OPTIONS</quote>.
</emphasis>
</para>
<example>
<title>Set <varname>sipping_method</varname> parameter</title>
<programlisting format="linespecific">
...
modparam("nathelper", "sipping_method", "INFO")
...
</programlisting>
</example>
</section>
<section>
<title><varname>nortpproxy_str</varname> (string)</title>
<para>
The parameter sets the SDP attribute used by nathelper to mark
the packet SDP informations have already been mangled.
</para>
<para>
If empty string, no marker will be added or checked.
</para>
<note><para>
The string must be a complete SDP line, including the EOH (\r\n).
</para></note>
<para>
<emphasis>
Default value is <quote>a=nortpproxy:yes\r\n</quote>.
</emphasis>
</para>
<example>
<title>Set <varname>nortpproxy_str</varname> parameter</title>
<programlisting format="linespecific">
...
modparam("nathelper", "nortpproxy_str", "a=sdpmangled:yes\r\n")
...
</programlisting>
</example>
</section>
</section>
<section>
<title>Exported Functions</title>
<section>
<title>
<function moreinfo="none">fix_nated_contact([uri_params])</function>
</title>
<para>
Rewrites the URI Contact <acronym>HF</acronym> to contain request's
source address:port. If a list of URI parameter is provided, it will
be added to the modified contact;
</para>
<para>
This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE, BRANCH_ROUTE.
</para>
<example>
<title><function>fix_nated_contact</function> usage</title>
<programlisting format="linespecific">
...
if (search("User-Agent: Cisco ATA.*") {
fix_nated_contact(";ata=cisco");
} else {
fix_nated_contact();
}
...
</programlisting>
</example>
</section>
<section>
<title>
<function moreinfo="none">fix_nated_sdp(flags [, ip_address])</function>
</title>
<para>
Alters the SDP information in orer to facilitate NAT traversal. What
changes to be performed may be controled via the
<quote>flags</quote> paramter.
</para>
<para>Meaning of the parameters is as follows:</para>
<itemizedlist>
<listitem><para>
<emphasis>flags</emphasis> - the value may be a bitwise OR of
the following flags:
</para>
<itemizedlist>
<listitem>
<para><emphasis>0x01</emphasis> - adds
<quote>a=direction:active</quote> SDP line;
</para>
</listitem>
<listitem>
<para><emphasis>0x02</emphasis> - 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).</para>
</listitem>
<listitem>
<para><emphasis>0x04</emphasis> - adds
<quote>a=nortpproxy:yes</quote> SDP line;</para>
</listitem>
<listitem>
<para><emphasis>0x08</emphasis> - 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).</para>
</listitem>
</itemizedlist>
</listitem>
<listitem><para>
<emphasis>ip_address</emphasis> - 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.
</para>
</listitem>
</itemizedlist>
<para>
This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE,
FAILURE_ROUTE, BRANCH_ROUTE.
</para>
<example>
<title><function>fix_nated_sdp</function> usage</title>
<programlisting format="linespecific">
...
if (search("User-Agent: Cisco ATA.*") {fix_nated_sdp("3");};
...
</programlisting>
</example>
</section>
<section>
<title>
<function moreinfo="none">add_rcv_param([flag])</function>,
</title>
<para>
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.
</para>
<para>Meaning of the parameters is as follows:</para>
<itemizedlist>
<listitem><para>
<emphasis>flag</emphasis> - 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.
</para></listitem>
</itemizedlist>
<para>
This function can be used from REQUEST_ROUTE.
</para>
<example>
<title><function>add_rcv_paramer</function> usage</title>
<programlisting format="linespecific">
...
add_rcv_param(); # add the parameter to the Contact header
....
add_rcv_param("1"); # add the paramter to the Contact URI
...
</programlisting>
</example>
</section>
<section>
<title>
<function moreinfo="none">fix_nated_register()</function>
</title>
<para>
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.
</para>
<para>
This function can be used from REQUEST_ROUTE.
</para>
<example>
<title><function>fix_nated_register</function> usage</title>
<programlisting format="linespecific">
...
fix_nated_register();
...
</programlisting>
</example>
</section>
<section>
<title>
<function>nat_uac_test(flags)</function>
</title>
<para>
Tries to guess if client's request originated behind a nat.
The parameter determines what heuristics is used.
</para>
<para>Meaning of the flags is as follows:</para>
<itemizedlist>
<listitem><para>
<emphasis>1</emphasis> - Contact header field is searched
for occurrence of RFC1918 addresses.
</para></listitem>
<listitem><para>
<emphasis>2</emphasis> - the "received" test is used: address
in Via is compared against source IP address of signaling
</para></listitem>
<listitem><para>
<emphasis>4</emphasis> - Top Most VIA is searched
for occurrence of RFC1918 addresses
</para></listitem>
<listitem><para>
<emphasis>8</emphasis> - SDP is searched for occurrence of
RFC1918 addresses
</para></listitem>
<listitem><para>
<emphasis>16</emphasis> - test if the source port is different
from the port in Via
</para></listitem>
<listitem><para>
<emphasis>32</emphasis> - address in Contact is compared against
source IP address of signaling
</para></listitem>
</itemizedlist>
<para>
All flags can be bitwise combined, the test returns true if any of
the tests identified a NAT.
</para>
<para>
This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE, FAILURE_ROUTE, BRANCH_ROUTE.
</para>
</section>
<section>
<title><acronym>MI</acronym> Commands</title>
<section>
<title><function moreinfo="none">nh_enable_ping</function></title>
<para>
Enables natping if parameter value greater than 0.
Disables natping if parameter value is 0.
With no parameter, it returns the current natping status.
</para>
<para>
The function may takean optional parameter (for set operations) -
a number in decimal format.
</para>
<example>
<title><function moreinfo="none">nh_enable_ping</function> usage</title>
<programlisting format="linespecific">
...
$ opensipsctl fifo nh_enable_ping
Status:: 1
$
$ opensipsctl fifo nh_enable_ping 0
$
$ opensipsctl fifo nh_enable_ping
Status:: 0
$
...
</programlisting>
</example>
</section>
</section>
</section>
</chapter>