Hi,
I am sorry if i misunderstood your query , but you can configure ZBF on a single Router as well.
You can configure ZBF on any number of routers.
Refer:-
http://packetlife.net/blog/2012/jan/30/ios-zone-based-firewall/
http://www.cisco.com/c/en/us/support/docs/security/ios-firewall/109479-zbf-vpn-traffic.html
https://supportforums.cisco.com/document/115191/ios-zone-based-firewall-step-step-basic-configuration
Also , if you were asking about redundancy with ZBF:-
http://www.cisco.com/en/US/docs/ios-xml/ios/sec_data_zbf/configuration/15-2mt/sec-data-zbf-ha.html
Thanks and Regards,
Vibhor Amrodia
