>From what I understand the IOS Stateful Firewall Feature is available in 12.4(6)T. This allows for the tcp and udp session information to be replicated between two routers. This should be able to be combined with the stateful NAT feature. The complaint I have is that it does not support ZFW. That might be good for the lab though.
http://www.cisco.com/en/US/docs/ios/12_4t/12_4t11/ht_sfo.html
