Jul 10, 2015

VoIP calls dropping after two minutes over a Fortigate 100D firewall

A Cisco 7960G IP telephone
A Cisco 7960G IP telephone (Photo credit: Wikipedia)
This past week has seriously made me want to drown my sorrows in alcohol. One of the issues we had was all of a sudden users phone calls would drop after 2:30. We just couldn't figure it out. We called our hosted VoIP provider and they double checked that we had SIP ALG and SIP Session Helper disabled on our Fortigate 100D firewall. That didn't help.

Well, after being on the phone with Fortinet support for about three hours the other day my Systems Administrator and Fortinet tech support found out that it was the timeout setting in our traffic shaper for VoIP!

By default the session-ttl timeout is set for 150 seconds (2:30), which is why out calls were dropping out. We increased that number to 14400 (4 hours) and calls stopped dropping!

To configure that from the command line interface (cli) in FortiOS 5.2 run:
  • config system session-ttl
  • set default 14400
  • end
I hope this helps you out because troubleshooting VoIP issues is enough to make you want to kick a cat, drink nine beers out of a funnel then punch someone in the mouth!

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