I've a scenario here where I'm receiving inbound traffic from a Mitel PBX on a LAN environment with a bunch of router hops between kamailio and the Mitel. Sometimes, not always, I get traffic from the MItel PBX where the source port is changed in transit (some kind of NAT, still don't know where exactly) from 5060 to a dynamic port different from 5060. Every INVITE comes with rport in via header as:

..

Via: SIP/2.0/UDP 10.21.252.35:5060;branch=z9hG4bK-524287-1---d6bac01809527627;rport

..

when this happens kamailio sends all the replies to the $si:$sp symmetrically (force_rport behavior) and I would like to force the opposite instead, making it asymmetric and sending the traffic to $si:5060 everytime.

I'm having a hard time forcing the unforce_rport() behavior. Does anyone have a good suggestion for this?

Looking forward to hear from you.

Cheers,