What Does Common Address Redundancy Protocol (CARP) Mean?
Common Address Redundancy Protocol (CARP) is an automatic failover and redundancy protocol introduced by OpenBSD in October 2003. CARP is designed to share a common IP address among multiple hosts in same network segment in order to provide failover redundancy to multiple servers or hosts. It is an alternative to Internet Engineering Task Force’s (IETF) Virtual Router Redundancy Protocol (VRRP) and Cisco’s Hot Standby Redundancy Protocol (HSRP). CARP is designed as a free and open source alternate to VRRP that Cisco claimed had some technical resemblance to their proprietary HSRP. CARP works by allowing a group of hosts on the same network segment to share an IP address. This group of hosts is referred to as a redundancy group. The redundancy group is assigned an IP address and a common virtual host ID (VHID). The VHID allows group members to identify which redundancy group they belong to. Within the group, one host is designated as the master host and the rest as backup hosts. The master host is the owner of the shared IP address. The master host responds to any traffic or ARP requests directed towards it.
Techopedia Explains Common Address Redundancy Protocol (CARP)
Each host may belong to more than one redundancy group at a time through multiple physical interfaces. The master host sends CARP advertisements to the backup hosts. These CARP advertisements or CARP packets are composed of two values:
