Outgoing calls fail on UDP

Asterisk Asterisk SIP
1

Some of our SIP devices suddenly stopped being able to make calls. After some investigation using sngrep on the Asterisk server I noticed that the INVITE messages are rejected:

95 INVITE 905@mydomain.com 7973@mydomain.com 3 x.x.x.x:51654 y.y.y.y:5060 REJECTED

→ INVITE
← 401 UNAUTHORIZED (containing the WWW-Authenticate header)
→ ACK

I would assume that after receiving the 401 the client would send another INVITE containing the proper authentication header but for some reason it doesn’t.
At first I thought this is a client issue but what’s puzzling me is that REGISTER works perfectly fine:

→ REGISTER
← 401 UNAUTHORIZED
→ REGISTER
← OK

Even more puzzling is that when I connect the client to a different network (behind a different FW, 4G network for example) OR set the client to use TCP instead of UDP everything works fine. Also, the whole setup used to work fine on UDP until a few weeks ago.

I suspect that the firewall (Meraki MX64) is at least part of the problem but I have no clue what to look at.

Any hint on where to look would be highly appreciated!

2

[pahlevoon] the first thing I would try is Wireshark. Do a sip trace their you will find that most likely you’ve got the wrong heading. Which means wrong dialplan for your “Carrier”

3

You could check your firewall for any types of SIP inspection, some firewalls has settings for rejecting/dropping repeated packets, and this could be faulty.

It’s also possible that the firewall performs NAT, and somehow messes up the packets, I’ve seen things like cable modems changing a port from 5060 to 506060, due to a faulty NAT implementation.