Cisco 6921 registering with Asterisk but no calls coming through?

Question

Asterisk

Hello!
There are a number of Cisco 6921 phones that connect to Asterisk in the cloud. All phones are flashed with the same configuration file, only the login data changes. Devices are connected in three offices.
In one of the offices, phones work correctly.
In the remaining two, they are registered, but calls do not go.
In the Asterisk log there are messages like this:
res_pjsip/pjsip_distributor.c: Request 'REFER' from '' failed for 'ip' (callid:[email protected]) - No matching enpoind found
mac - mac address phone, ip - external ip of the office where the device is connected.
If you connect the same device in the first office - everything works.
In both offices where the problem is observed, the same provider, the Mikrotik router.
Thank you!

Answer 1

I suspect that the other two offices are behind nat and you need to either enable nat in the firmware and pervert with it, but it’s better to enable nat for users in the asterisk accounts, and either allocate two udp forwarding to each phone, or make sure that there are no torrents on the network sip ports.
If the offices are connected by vpn, then you need to turn off masquerading (nat) and configure the correct routing.
I myself use asterisk, mikrotik and tsiska through many many vpn, nat and routes work if you don’t mow anywhere.