We have two offices:
- Master: 192.168.1.0/24
- Satellite: 192.168.128.0/24
Master contains the Shoretel phone system. Both offices use Draytek Vigor 2860ac routers They are connected using an IPSec LAN-2-LAN VPN connection. This stays up perfectly and does not drop.
Problem: phones across offices do not send audio. Phoning externally to a mobile/cell phone from the satellite does provide audio one way (to the external device). Phones in the master office still work perfectly.
Two phones in the satellite office can communicate perfectly (two way audio) so this seems to indicate a routing problem.
What could cause this issue?
Other notes:
- We ran wireshark on the phone in the satellite office using port mirroring on the switch and could see RTP packets being sent both ways. The only difference between a working audio capture and no audio capture was a couple of failed ping requests at the start. These eventually resolve anyway (I think this is because it has 3 hops [localgateway-remotegateway-remotedevice] rather than 1 [localdevice])
- Offices can ping devices in the alternate subnet (their traceroute hits the local gateway, the remote gateway and the correct device)
- sip_alg is disabled on both devices
- I've played with MTU but this seems to make no difference - currently set to 1472 on both routers but it was 1492
