Zentyal 3.4.7 Failover issue

[ronb]

Hi,

I have a challenge configuring failover rules.

This is my configuration:
I have 2 WAN ports and configured failover which works fine. If WAN1 (default GW) is unavailable Zentyal uses WAN2. If WAN1 is available again Zentyal is using WAN1. So far no problem.
My VoIP traffic is in a VLAN which is using WAN2 as default GW. This is configured by a multi-gateway rule and works fine too.

So all normal traffic is using WAN1 and is routed to WAN2 in case of unavaillability of WAN1.
All VoIP traffic is using WAN2 by default.

My challenge is to send my VoIP traffic (which is using WAN2 by default) to WAN1 in case of unavaillability of WAN2.

Can someone give me a hint?

Thank you in advance.

Ron