The Common Address Redundancy Protocol or CARP is a computer networking protocol which allows multiple hosts on the same local area network to share a set of IP addresses.
If, however, there are two computers running a packet filter, running CARP, then if one fails, the other will take over, and computers on either side of the packet filter will not be aware of the failure, so operation will continue as normal.
In order to make sure the new active/primary operates the same as the old one, the packet filter used must support synchronization of state between the two computers.
In the late 1990s the Internet Engineering Task Force (IETF) began work on a protocol for router redundancy.
After some debate, the IETF VRRP working group decided to approve the standard, despite its reliance on patented techniques, as long as Cisco made the patent available to third parties under reasonable and non-discriminatory licensing terms.
Requirements include participating in a collaborative, lengthy discussion process within the IETF and producing a detailed textual specification of the protocol.
OpenBSD's website states the following:[5] As a final note of course, when we petitioned IANA, the IETF body regulating[sic] "official" internet protocol numbers, to give us numbers for CARP and pfsync, our request was denied.
We informed IANA of these decisions, but they declined to reply.IANA had assigned protocol number 112 to VRRP (in 1998, via RFC 2338).
CARP also uses a range of Ethernet MAC addresses which IEEE had assigned to IANA/IETF for the VRRP protocol.