SIP Registration Failed - Odd Issue

[nfletcher2]

So I have ran into a bizarre issue I was hoping the community could help with. I came in this morning to our SIP lines down.... Needless to say it wasn't a great morning!

So it looks like the SIP lines kept giving the error:

Call or Registration to $$$$$$$$ has failed. sip:[email protected]:5060 replied: 503 DNS Timeout; internal

Or should I say, most of the SIP lines. We actually had 1 that would register fine.

This would lead one to investigate DNS, so that is what I did. The odd part was that I could resolve everything just fine. I even switched the server to a public DNS server and could still resolve fine.

So a little background... We have a Mikrotik router as our gateway device. We are in the process of switching everything over to a Watchguard. About two weeks ago I moved the phone server, it's public IP, and all NAT rules over. The public IP never changed in this process. I ran a firewall check then (and today) and everything necessary passed. I say everything necessary because we only allow about 200 of the media ports through, but that wouldn't cause the issues.

So when this occurred this morning I actually moved the phone server back to the Mikrotik and it still failed to register. I even created firewall rules on the WatchGuard that allowed everything in/out. Still no luck.

The last thing I did was go into the settings and change the network settings to use STUN instead of a static IP address. I flipped back to the SIP lines and Boom! all registered.

Am I missing something? Does this make sense? Can someone help enlighten me on what I am missing?

 

[eddv123]

Firstly I am not familiar with your SIP trunking provider - can you identify whether they are a registration based provider or IP authenticated.

FYI: If IP authenticated 3CX (in the trunk connections) will show it as green/registered whether it is registered or not (IP authenticated does not "SIP Register" as such).

A little insight to the fix to your issue (last paragraph). A static IP connection will be exactly that - a direct registration connection to the UAS where STUN uses a STUN server in order for it to identify its public IP address: https://www.3cx.com/pbx/what-is-a-stun-server/

There is another post on the forums here which includes your error - it might give you some ideas possibly: https://www.3cx.com/community/threads/503-dns-timeout-on-pbx.51522/

 

[nfletcher2]

Firstly I am not familiar with your SIP trunking provider - can you identify whether they are a registration based provider or IP authenticated.

FYI: If IP authenticated 3CX (in the trunk connections) will show it as green/registered whether it is registered or not (IP authenticated does not "SIP Register" as such).

A little insight to the fix to your issue (last paragraph). A static IP connection will be exactly that - a direct registration connection to the UAS where STUN uses a STUN server in order for it to identify its public IP address: https://www.3cx.com/pbx/what-is-a-stun-server/

There is another post on the forums here which includes your error - it might give you some ideas possibly: https://www.3cx.com/community/threads/503-dns-timeout-on-pbx.51522/

I will look at the links. We use registration based authentication.

 

[eddv123]

Sure, take a look and see if it makes sense - I would also be keen to see a PCAP trace - which can be done from the logging/Activity log section of the PBX now - a refresh of the registration (since it is registration based SIP trunk) in the trunks section of 3CX would suffice - do you get the same DNS error here.

 

[YiannisH_3CX]

Hello @nfletcher2

Unless your public IP changed during the weekend i do not see how changing your IP from static to dynamic would help with the trunk registration. If your Public IP did change then that change was needed for the PBX to identify the new IP. If the issue reoccurs i would recommend running a packet capture to see the registration message leaving the PBX and the response from the provider.

 

[nfletcher2]

Hello @nfletcher2

Unless your public IP changed during the weekend i do not see how changing your IP from static to dynamic would help with the trunk registration. If your Public IP did change then that change was needed for the PBX to identify the new IP. If the issue reoccurs i would recommend running a packet capture to see the registration message leaving the PBX and the response from the provider.

The IP address itself did not change recently, but the router that it was assigned to did. Would this effectively need the same change? And if so, is it safe to change back to static?

 

[nfletcher2]

Sure, take a look and see if it makes sense - I would also be keen to see a PCAP trace - which can be done from the logging/Activity log section of the PBX now - a refresh of the registration (since it is registration based SIP trunk) in the trunks section of 3CX would suffice - do you get the same DNS error here.

I will look at doing the trace, but since we are no longer receiving the error since changing to STUN it may not help. I will familiarize myself with this though in the event it occurs again.

 

[YiannisH_3CX]

The IP address itself did not change recently, but the router that it was assigned to did. Would this effectively need the same change? And if so, is it safe to change back to static?

I am not sure how the change could have affected the system so i cannot answer that without looking at a capture. Since you have a static IP i believe it's safe switching the setting back to static.