I've migrated one of my firewalls from M0n0wall to OPNSense. I'm having trouble with one of my IPSEC tunnels. prior to the migration I had the two m0n0walls configured with two IPSEC tunnels (each with their own P1 and P2 entries). Reason is because I had multiple networks behind each of the appliances that needed IPSEC tunnels (see diagram). It worked well.
(http://venus.morante.net/downloads/unibia/screenshots/tunnels.png)
I'm having trouble getting the same setup migrated over to OPNSense. I tried setting up one Phase 1 and two Phase 2, but the m0n0wall end has trouble making the connection.
Looks like you can just setup the multiple phase 2's on the OPNSense end and it does indeed work okay. I had to make sure the two Phase 1's are the same on the m0n0wall end.