CARP and pfsync

Common Address Redundancy Protocol (CARP)

• Introduced with OpenBSD 3.5

• Patent free alternative to VRRP (RFC 2281, 3768, patent owners: Cisco, IBM, Nokia)

• Firewall/server redundancy

• Virtual network interface for automatic failover

pfsync

• Virtual network interface (assigned to physical interface)

• Handles syncronization between PF firewalls (in advance of failover)

Best reference: http://www.countersiege.com/doc/pfsync-carp/