@Rhongomiant:
Well the first question is will the gif tunnel close of fw1 and initiate on fw2 when there is a failover from fw1 to fw2. When I actually have the abaily to get my ISP running on both firewalls I will test this. If only ISPs would start offering IPv6!
There is no open or close with GIF tunnel, they just pass packets with the proper encapsulation, there isn't any tunnel setup as with a VPN.
In theory, the traffic would only go to/from the master, but that also assumes the slave itself wouldn't send any IPv6 traffic uninitiated. It may "just work", but I'm not aware of anyone who has tried it yet.
@Rhongomiant:
Often when there are two firewall, each is connected to a different switch. Are you telling me that if the switch connected to fw1 looses it's uplink, but the switch connected to fw2 is fine, there will be no failover? Then again I can't think of a situation where that would happen with out the firewalls being able to communicate with each other unless you have a bad network design with loops.
If FW1 and FW2 can communicate with each other on the segment, then no failover will happen. If they lose communication, the slave will attempt to take over, but unless FW1 loses interface link, it wouldn't demote itself.
In your case "Often" isn't really correct these days - more often than your scenario, at least with our customers, firewalls are connected to both switches using LACP (LAGG in pfSense) so each firewall has a connection to each switch in a stack.
@Rhongomiant:
The router idea is not terrible, but what I wanted to avoid. Do you know of good NAT router that is fast and does not have all the unneeded junk like a firewall since I have pfsense for that? Maybe I'll get something basic that can run ddwrt and I'll turn off everything but NAT, hmm. If only Verizon FIOS was not such a pain regarding static IPs!
I'm not aware of any specific models, but anything that would do decent throughput and could run DD-WRT should suffice. Some people just use their existing modem/router for that since those tend to be simplistic, but if what you have is purely a modem, then some other NAT device would be needed there.