The Common Address Redundancy Protocol or CARP is a protocol which allows multiple hosts on the same local network to share a set of IP addresses. Its primary purpose is to provide failover redundancy, but in some configurations CARP can also provide load balancing functionality.

=History=

It has been started by OpenBSD developers as an alternative to the patented Virtual router redundancy protocol. It [http://marc.theaimsgroup.com/l=openbsd-misc&m=106642790513590 became available] in October 2003.

== From OpenBSD.org ==

As a final note of course, when we petitioned IANA, the IETF body regulating official internet protocol numbers, to give us numbers for CARP and pfsync our request was denied. Apparently we had failed to go through an official standards organization. Consequently we were forced to choose a protocol number which would not conflict with anything else of value, and decided to place CARP at IP protocol 112. We also placed pfsync at an open and unused number. We informed IANA of these decisions, but they declined to reply.

The reason for this is that no specification for CARP has every been written. The closest thing to specifications is the implementation in OpenBSD.

Note that VRRP also uses IP protocol 112, having been assigned it by IANA.

=See also=

=External links=