Common address redundancy protocol

Common Address Redundancy Protocol or CARP is a protocol making it possible a group of hosts on the same segment network to divide a Adresse IP. Name CARP is in fact initials meaning “ Common Address Redundancy Protocol ” (Common protocol Of Redundancy Of Address) not to confuse with “ Cache Array Routing Protocol ” used to make load balancing of Web proxy masks (see RFC 3040).

CARP is a protected and free alternative to the protocols Virtual Router Redundancy Protocol (VRRP), Hot Standby Router Protocol (HSRP) and Foundry Standby Router Protocol (FSRP). It was creates to circumvent patents. This protocol can be used to make Redondance and distribution of load.

CARP supports IPv4 and IPv6, and has the number of protocol 112. It is supported by OpenBSD (3.5) and FreeBSD (on branch 5 from the 5.4 and also in 6.0), but can be used under Linux and NetBSD by using UCARP (in space user).

Principle of the redundancy

One calls a group of hosts using CARP a " group redondance". The group of redundancy sees itself allotting an address IP divided between the members of the group. Within this group, a host is designated like " maître". The other members are called " esclaves". The main host is that which " prend" address IP divided. He answers any traffic or request ARP for submission to this address. Each host can belong to several groups of redundancy. It should be noted that each host must have one second single address IP.

A common use of CARP is the creation of a group of redundant Pare-feu. Virtual address IP allotted to the group of redundancy is indicated as the address of the router by defect on the machines customer. If the main fire wall meets a breakdown or is disconnected from the network, virtual address IP will be taken by one of the fire walls slaves and the service will continue to be returned without interruption.

History

What follows is a translation of anglophone Wikipédia:

Towards the end of 90s IETF started to work with a solution with the problem. In 1997, Cisco informed them that this had already been covered by its patents. In 1998, Cisco their indicated that it had been covered by their patent of HSRP (Hot Standby Router Protocol). Nevertheless, the IETF continued work on VRRP (Virtual Router Redundancy Protocol, Protocole of Redundancy on Virtual Routers). After a discussion, it was decided that patented technologies could be integrated in a standard, as long as that remains in conformity with the conditions of RAND (Reasonable and Non-Discrimatory, Raisonnable and Not-Discriminatory). Since VRRP corrected the problems of the HSRP, Cisco started to use VRRP in the place, while it declaring as being it his.

Cisco informed the developers of OpenBSD which they would impose their patent of HSRP. This was certainly dependant with their lawsuit against Alcatel. Thus, a free use of VRRP would have been impossible. The developers of OpenBSD began the study of CARP like an alternative to the patented VRRP, because RAND did not seem to them to have been reasonable and nondiscriminatory. To circumvent the patent of HSRP, they ensured that CARP was basically different. Because of the orientation of OpenBSD on safety, CARP was conceived with safety like principal policy, and is conceived to use cryptography. It became available, completely free, in October 2003.

See too

Pfsync

External bonds

UCARP : Protocol CARP in space user, functions under Linux (2.4 and 2.6), OpenBSD and NetBSD.
Firewall Failover with pfsync and CARP, article of Ryan McBride
Wire of discussion, on kerneltrap.org, CARP during its development in OpenBSD
High-availability of avoid-fires with CARP and pfsync

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