I have two offices set in two distant locations, connected through a IPSec VPN (using pfSense). On one office, I have an Asterisk PBX where all the extensions connect, and the Asterisk PBX is configured with a Flowroute trunk.
Here's some ascii diagram:
-------------- --------------- -------------
| office 1 | IPSec | office 2 | lan | Asterisk |
| pfsense | -------- | pfsense |-------------| |
-------------- --------------- -------------
| |
| |
internet link 1 internet link 2
When I make calls from office 2 through Flowroute, they work perfectly fine. However, when I make calls from office 1, there's some echo. I'm using IP phones, so the echo is not caused by analog terminals.
My guess is that the SIP traffic from office 1 is going through the VPN and then routed to Flowroute (through internet link 2).
How can I make it so the traffic is routed through internet link 1 instead? I only want to use SIP traffice over IPSec for internal calls (extensions on office 1 calling extensions on office 2, where some echo is acceptable).
Put another Asterisk server in Office 1.
Have the two servers talk to each other (e.g. IAX) for inter-office calls, and have each of them route PSTN calls directly to your upstream provider. The provider should be able to give you sub-accounts for each of your servers, so that incoming calls can be routed to the correct one.