Multi wan, routing voip traffic over dedicated WAN interface

[uht]

Hello everyone,

at our site, there are two DSL connections provided by the same ISP. Our pfsense balances the outgoing traffic over both connections.
With each connection respectively contract, we got some VOIP accounts. To work in a correct way, the traffic for the VOIP account registration at the ISP's servers needs to be routed over their dedicated DSL connection respectively WAN interface of the pfsense.
We would like to use the same telephone system (same source IP) for all VOIP accounts. This is why I need to find a solution to route the VOIP traffic over the correct WAN interface.
To set up according firewall rules for routing the traffic over the correct gateway (WAN1 or WAN2) I need a property with which the traffic can be distinguished. But the destination url and port (5060) of the ISP's server needs to be identical.

I tried to use two different ports within the telephone system's profiles (5060 and 5061) and than set up a port forward on the pfsense's VOICE_LAN interface which forwards the port 5061 to 5060 again. The problem is, that the generated firewall rule still cannot distinguish the traffic (see attached image), since there the port 5060 is used again.

Are there any other approaches for distinguishing outgoing traffic by the destination url or port and then route it over different gateways to the same destination server (url and port)?

Thanks and regards