Colocation, Single WAN NIC, Multiple subnets, two pfSense devices with HA

  • Excuse me if this has been asked. I searched and "came close" but no definite solution.

    I have several servers behind two pfSense appliances - set up for failover.
    Due to a change of IPv4 allocations I'm going from one subnet to two. On one subnet I only get 3 usable IPs, on the other I get 11.

    I tried simply setting up some CARP VIPs but the system won't allow it (Sorry, we could not locate an interface with a matching subnet for xxx. Please add an IP alias in this subnet on this interface.)

    What is the correct way to set this up, earning in mind that I want to have failover in place? As I understand, an "IP Alias" doesn't facilitate HA.

    The diagram below should look familiar.

    I tried adding a 2nd WAN to the same NIC, but I can't connect to the device any longer :( …. looks like a three-hour round trip to my colo provider