How to Pass SIP VOIP traffic
through a 3rd-party Firewall
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The assumption is that you are trying to pass external VOIP
traffic through an inexpensive broadband router to the local
network where your VOIP phones are located. This example is
based on the D-Link DI-604 and DI-724 broadband routers and
the DGL-4300 wireless broadband router. The basics are the
same for wireless routers and other brands such as SMC
Barricade routers. The concepts covered here are easily
transferred to most other routers or firewalls. Passing SIP through your Firewall The goal of configuring your firewall is to allow a VOIP phones outside of the local subnet to register with the CyverONE hosted PBX server. The local subnet would be firewalled from the outside world. There's few issues with getting SIP to work through a firewall. SIP uses port 5060 for setup and RTP (real time protocol) ports 10,000 to 20,000 for transporting the voice. NAT (network address translation) can cause issues if the firewall also performs PAT (port address translation). A common effect of a firewall that is performing PAT is one way audio. (You can hear the other person - but they cannot hear you). You can check the firewall logs to see if a VOIP phone outside of the firewall is being blocked. If you see the IP address in the log, then its most likely being blocked as the logs generally record problems. The steps to solve these issues at the firewall is: For SIP, allow port 5060 UDP traffic to pass to the server. This example uses a Virtual Server to pass data through a Dlink Broadband router
Testing your Installation: More settings and resources about configuring your
network for VOIP traffic:
Allied Telisis - Configure the
Firewall VoIP Support Service (PDF) |
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