Building the Network You Need with OpenBSD's PF: BSDCan, Ottawa May 6th, 2009
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# 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/