Redundancy and Failover: CARP and pfsync

High availability and uninterrupted service have been both marketing buzzwords and coveted goals for IT professionals and network administrators as long as most of us can remember. To meet this perceived need and solve a few related problems, CARP and pfsync were added as two highly anticipated features in OpenBSD 3.5.

Common Address Redundancy Protocol (CARP) was developed as a non – patent-encumbered alternative to VRRP (Virtual Router Redundancy Protocol, RFC 2281, RFC 3768), which was quite far along the track to becoming an IETF-sanctioned standard, even though possible patent issues have not been resolved. [40]

One of the main purposes of CARP is to ensure that the network will keep functioning as usual ...

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