ER Load-Balancing: Lock VoIP/PBX to one Route

Hi there,

I'm setting up an ER-X with load balancing two PPPoE-Connections. Everything is fine, except the VoIP-Connection for one of the ISPs (WAN1) (all others SIP-Numbers work like a charm and completely independent which route is used) which connects the call but not the audio. So we have a NAT-Problem here.

When I disconnect WAN2 everything is fine. The easiest solution is to limit everything to or from the PBX to only the WAN1-Route.

I found http://community.ubnt.com/t5/EdgeMAX/Dual-WAN-with-some-hosts-using-only-one-WAN/m-p/703493#M22093 as a possible solution. But it's from 2014 and there have been a few firmware updates since then with a myriad of new features…

So… Is this solution still state of the art or is there something better available?

Thanks in advance,

   Pascal