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Hot Standby Router Protocol
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<p>In computer networking, the Hot Standby Router Protocol (HSRP) is a <a href="/facts/Cisco/ocDgQt6T">Cisco</a> <a href="/facts/Proprietary_protocol/o902Cmmh">proprietary</a> redundancy protocol for establishing a <a href="/facts/Fault-tolerant/rasrYlJk">fault-tolerant</a> <a href="/facts/Default_gateway/fWMLvKCu">default gateway</a>. Version 1 of the protocol was described in <a href="/facts/RFC_(identifier)/esftTvE7">RFC</a> <a href="https://datatracker.ietf.org/doc/html/rfc2281">2281</a> in 1998. Version 2 of the protocol includes improvements and supports IPv6 but there is no corresponding RFC published for this version. </p><p>The protocol establishes an association between gateways in order to achieve default gateway failover if the primary gateway becomes inaccessible. HSRP gateways send <a href="/facts/Multicast_address/cIau2Hee">multicast</a> <i>hello</i> messages to other gateways to notify them of their priorities (which gateway is preferred) and current status (<i>active</i> or <i>standby</i>). </p>