{"id":358,"date":"2010-12-02T14:07:41","date_gmt":"2010-12-02T13:07:41","guid":{"rendered":""},"modified":"2019-11-19T10:08:45","modified_gmt":"2019-11-19T09:08:45","slug":"configuring-nat-traversal-using-kamailio-31-and-rtpproxy-server","status":"publish","type":"post","link":"https:\/\/nil.uniza.sk\/en\/configuring-nat-traversal-using-kamailio-31-and-rtpproxy-server\/","title":{"rendered":"Configuring NAT traversal using Kamailio 3.1 and the Rtpproxy server"},"content":{"rendered":"

This article continues on series of articles about the Kamailio 3.1.x SIP proxy server deployed on the debian lenny and its features. In previous articles we have focused on:<\/p>\n

1) installing clear Kamailio 3.1.x server <\/a><\/p>\n

2) adding of the Mysql support <\/a>for persistance location storage<\/p>\n

3) installing of the SIREMIS web management interface for our Kamailio server<\/a>.<\/p>\n

4) configuring the IM and presence service on Kamailio 3.1 – Howto<\/a><\/p>\n

5) configuring the XCAP support for SIMPLE<\/a>.<\/p>\n

6) configuring TLS support<\/a><\/p>\n

Now we will take a closer look on the NAT traversal solution with the usage of the Rtpproxy server.<\/p>\n

Prerequisities<\/h2>\n

1) Installed and working Kamailio (OpenSER) 3.1.0<\/a> server.<\/p>\n

2) Installed and running<\/a> rtpproxy server. For this guide (as you see at the end, rtpproxy 1.2.1 does not work, 1.1.2 does)<\/p>\n

3) usrloc (user location) module<\/a> of the kamailio loaded<\/p>\n

 Configuration<\/h2>\n

Kamailio 3.1 has for the NAT traversal preconfigured zone block prepared for the the rtpproxy server usage. So open \/etc\/kamailio\/kamailio.cfg and find lines starting with:<\/p>\n

# *** To enable nat traversal execute:\n#     - define WITH_NAT\n#     - install RTPProxy: http:\/\/www.rtpproxy.org\n#     - start RTPProxy:\n#        rtpproxy -l _your_public_ip_ -s udp:localhost:7722\n<\/pre>\n
They recommends to define „WITH_NAT“ directive and to install rtpproxy with recommended parameters. We have rtpproxy already installed, thus we need to define the zone block directive only<\/p>\n
#!define WITH_NAT\n<\/pre>\n
Going next, in module loading part of the config file, we may find zone block:<\/p>\n
#!ifdef WITH_NAT\nloadmodule \"nathelper.so\"\nloadmodule \"rtpproxy.so\"\n#!endif\n<\/pre>\n
which will load modules (nathelper <\/a>and rtpproxy<\/a>) required for the NAT traversal,  conditional of the WITH_NAT directive defined. We did it in previous step, so following modules will be loaded during the next restart of the Kamailio server.<\/p>\n
Going next, in module param section of the kamailio.cfg we will find zone block:<\/p>\n
#!ifdef WITH_NAT\n# ----- rtpproxy params -----\nmodparam(\"rtpproxy\", \"rtpproxy_sock\", \"udp:127.0.0.1:7722<\/span>\")\n\n# ----- nathelper params -----\nmodparam(\"nathelper\", \"natping_interval\", 30)\nmodparam(\"nathelper\", \"ping_nated_only\", 1)\nmodparam(\"nathelper\", \"sipping_bflag\", FLB_NATSIPPING)\nmodparam(\"nathelper\", \"sipping_from\", \"sip:pinger@kamailio.org\")\n\n# params needed for NAT traversal in other modules\nmodparam(\"nathelper|registrar\", \"received_avp\", \"$avp(RECEIVED)\")\nmodparam(\"usrloc\", \"nat_bflag\", FLB_NATB)\n#!endif\n<\/pre>\n
This part of the Kamailio config file we have to modify slightly. Our topology is using the Kamamilio and the Rtpproxy running in the same machine, and they will communicate between each other using the localhost IP address. So, if we are using the Rtpproxy server with default configuration, we have to open \/etc\/default\/rtpproxy file and uncomment following line regarding of udp socket, that will be sued for interconnection:<\/p>\n
CONTROL_SOCK=udp:127.0.0.1:22222\n<\/pre>\n
and than we have to modify first modparam line from above kamailio.cfg block to reflect the actual rtpproxy configuration:<\/p>\n
modparam(\"rtpproxy\", \"rtpproxy_sock\", \"udp:127.0.0.1:22222<\/span>\")<\/pre>\n
Next line of the configuration, modparam(„nathelper“, „natping_interval“, 30)<\/em> define <\/em>in seconds how often NAT ping will be send to keep NAT binding opened, here 30second. We do not need to modify it.<\/p>\n
Line modparam(„nathelper“, „ping_nated_only“, 1)<\/em> define, that only SIP UAs which are behind NAT will be pinged. We do not need to modify it.<\/p>\n
Line modparam(„nathelper“, „sipping_bflag“, FLB_NATSIPPING)<\/em> <\/em>define which branch flag of nat-ed client will be used for nat pinging. We do not need to modify it. By default the 7th flag is set and is named FLB_NATSIPPING, we may find it in  ####### Defined Values ######### part of the kamailo.cfg<\/p>\n
# - flags\n#   FLT_ - per transaction (message) flags\n#       FLB_ - per branch flags\n#!define FLT_ACC 1\n#!define FLT_ACCMISSED 2\n#!define FLT_ACCFAILED 3\n#!define FLT_NATS 5\n#!define FLB_NATB 6\n#!define FLB_NATSIPPING 7<\/span><\/pre>\n
Tutorial about Kamailio flags is available at the link<\/a>. Currently there are 31 tags defined, which can be named (like here).<\/p>\n
 <\/p>\n
Next line modparam(„nathelper“, „sipping_from“, „sip:pinger@kamailio.org“)<\/em>  I will change to reflect my server DNS name:<\/p>\n
modparam(\"nathelper\", \"sipping_from\", \"sip:pinger@ps.sip.uniza.sk\")<\/pre>\n
Line modparam(„nathelper|registrar“, „received_avp“, „$avp(RECEIVED)“)<\/em> define, I cited module documentation:<\/p>\n
name of the Attribute-Value-Pair (AVP) used to store the URI  \t\tcontaining the received IP, port, and protocol. The URI is created  \t\tby fix_nated_register function of nathelper module and the attribute  \t\tis then used by the registrar to store the received parameters. Do  \t\tnot forget to change the value of corresponding parameter in \t\tregistrar module if you change the value of this parameter. \t\t<\/em><\/p><\/blockquote>\n
Line modparam(„usrloc“, „nat_bflag“, FLB_NATB)<\/em>  tell to the usrloc <\/em>module to save branch parameter, that will be used as the NAT marker (decide if the contact  \t\tis or not natted). This is a branch flag and it will be imported and  \t\tused by nathelper module.<\/p>\n
Route logic<\/h3>\n
route[NAT]<\/h4>\n
The first routing logic which is working with NAT traversal is the route [NAT]<\/em> called from the main route logic. route [NAT] <\/em>detects if a caller is behind a NAT. It is used for all methods which are generated from an UAC.<\/p>\n
# Caller NAT detection route\nroute[NAT] {\n#!ifdef WITH_NAT\n        force_rport();\n        if (nat_uac_test(\"19\")) {\n                if (method==\"REGISTER\") {\n                        fix_nated_register();\n                } else {\n                        fix_nated_contact();\n                }\n                setflag(FLT_NATS);\n        }\n#!endif\n        return;\n}\n<\/pre>\n
Function force_rport()<\/a> adds the rport parameter to the first Via header of the received message. Rport parameters <\/a>cause that proxy will send subsequence responses back to this source port (this is the „public“ port after NAT-ing).<\/p>\n
Then inside of the logic test if UAC is behind NAT is done (nat_uac_test(„19“)<\/a>), from the docu 19 = 1 + 2 + 16 (i.e.<\/p>\n
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