CARP, 1:1 NAT, multiple WAN subnets



  • I've done a lot of searching and reading, but I'm not sure if what I want to do is possible.

    For IPv4 conservation reasons the campus network my WAN port is plugged into has two subnets; one publicly routable, and one for machines that only need to be accessed from elsewhere on campus.  I have machines with both types of addresses, routed through my pfSense firewall via proxy ARP and 1:1 NAT.  So far this all works fine.

    My question is, is it possible to make CARP failover work in a situation like this?  Can I switch the PARP IPs to CARP, or will this cause problems since they're not all on the same subnet?



  • So, I set up a test network and answered my own question: No, it doesn't work.  I can have multiple CARP IPs on an interface but they all have to be on the same subnet.



  • Also, found a gotcha with Virtual IP sync that's worth noting.  The sync doesn't work properly – the virtual IP appears on the slave, but in the CARP Status page it lacks a carp interface.  It won't function until you edit the virtual IP assignment (on the slave) and click Save without making any changes -- after that it functions.


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