[Freeswitch-users] bypass media only if on same subnet?

[Tim St. Pierre]

Hello,

In order to eliminate NAT issues, we have built routable tunnels to our 
larger customers so that their phones are on a private subnet that is 
routable to a private subnet at our datacenter.  Each Freeswitch system 
has a profile called nonat that uses an interface and address bound to 
this network.  The remaining customers register to the "internal" 
profile, which is bound to a public IP address.

At the moment, everything works just great - no nat issues, instant 
failover between the primary and secondary (shared registrations in DB), 
but all media flows through our network.

If someone in office A calls another phone in office A, I would like FS 
to instruct the phones to send their media direct.  The addresses and 
ports are all correct in this case.
If someone in office A calls a phone in office B, I want Freeswitch to 
stay in the media path, as these two offices are not routable to each 
other, even though each is routable to Freeswitch.

Is there a way to set up a profile (or dialplan) so that FS will bypass 
media only if the two endpoints are on the same subnet?   An ACL isn't 
really the right thing, since it would require an exponential number of 
ACLs.  Also, many calls go to ring groups, where several phones ring and 
we don't know which one will answer until it actually does (eliminating 
some sort of dialplan code using the rtp variables).

Is this possible?