I have a local FreePBX server at my house behind a NAT. There is a Yealink remote extension in a house about a mile away. This phone is behind a NAT too. Keepers of the remote ext have been complaining that a missed call notification will come in after the phone doesn’t ring. Today I went over there and disabled SIP ALG. I forwarded ports 5060 and 10,000 to 20,000 to that phone’s internal IP. Everything was working great. I sat there for 30 minutes and it worked fine. About three hours later I got a complaint that the Yealink phone will not stop ringing, even if they try to answer. I checked the logs, nothing is happening. I told them to unplug the phone and plug it in again. After it initializes, it just starts ringing over and over. Where do I even start to diagnose this?
That’s a phone fault. You don’t need working SIP signalling to trip the ring as that is all done locally in the phone.
If you forwarded 5060 and allowed the entire internet to get through the phone the ringing is automated attacks against the port making the phone think that it’s an incoming call which then makes it ring.
You shouldn’t have to forward ports 5060 to the phone as the phone is the one that establishes the registration to the server and that’s what’s used to ring the phone when a call comes in.
You do however need to worry about NAT timeouts and possibly keep alive timers so that either of the firewalls (the one the phone sits behind or the PBX firewall) aren’t killing the registration to the PBX from the phone when it’s actually not being used.
If timers aren’t configured correctly this would cause the phone not to ring when a call comes in after it’s been sitting idle for a while.
I fixed it last night. You are absolutely correct. They were “ghost calls”. As soon as I closed off port 5060 it stopped. How exactly do I configure the timers?
In FreePBX you manage the various timeout settings under Settings → Asterisk SIP Settings and then the General tab for RTP or the specific SIP protocol tab for the keep alive timeouts for the different protocols.
You generally want those to be lower then whatever the NAT timeout defaults on your firewalls are.
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