UCARP allows a pair of hosts to share common virtual IP addresses in order to provide automatic fail-over. It is a portable user-land implementation of the secure and patent-free Common Address Redundancy Protocol (CARP, OpenBSD's alternative to the VRRP).

Strong points of the CARP protocol are: very low overhead, cryptographically signed messages, interoperability between different operating systems and no need for any dedicated extra network link between redundant hosts.