Hot Standby Router Protocol (HSRP) is a protocol developed by Cisco which provides high RFC , which are defined in Finding Feature Information; Information About FHRP – HSRP MIB; How to to RFC , which are defined in In computer networking, the Hot Standby Router Protocol (HSRP) is a Cisco proprietary redundancy protocol for establishing a fault-tolerant default gateway. Version 1 of the protocol was described in RFC in

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If the Holdtime is not configured on a router, then it MAY be learned from the Hello message from the active router.

This field is only meaningful in Hello messages. In the event that the active router fails, the standby assumes the packet forwarding duties of the active router.

There is no RFC for version 2 of the protocol. In the case of routers with equal priority the router with the higher IP address wins. Each standby group emulates a single virtual router. The router sends periodic Hello messages. A router cannot enter Speak state unless it has the virtual IP address. If the primary router should fail, the router with the next-highest priority would take over the gateway IP address and answer ARP requests with the same MAC address, thus achieving transparent default gateway failover.

It listens for Hello messages from those routers. This page was last edited on 28 Decemberat The router is currently forwarding packets that are sent to the group’s virtual MAC address. A router which is in active state MUST NOT learn new values for hhsrp Hellotime and the Holdtime from other rrfc, although it may hhsrp to use values which it learned from the previous active router. The time hsfp given in seconds. If the standby router fails or becomes the active router, another router is elected as the standby router.


Hot Standby Router Protocol – Wikipedia

This can be useful for dual branch routers each with a single link back to the gateway. It contains the approximate period between the Hello messages that the router sends. For each standby group, a single well-known MAC address is allocated to the group, as well as an IP address.

If the virtual IP address is not configured on a router, then it MAY be learned from the Hello message from the active router. It is not compatible with version 1 HSRP. On a particular LAN, multiple hot standby groups may coexist and overlap. If the active router fails, the standby router takes over as the active router.

It contains the amount of time that the current Hello message should be considered valid. HSRP is not a routing protocol as it does not advertise IP routes or affect the routing table in any way. This field identifies the standby group.

HSRP, Hot Standby Router Protocol

A single router elected from the group is responsible for forwarding the packets that hosts send to the virtual router. The router knows the virtual IP address, but is neither the active router nor the standby router. If multiple groups are used on a single LAN, load splitting can be achieved by distributing hosts among different standby groups.

HSRP provides failover services to those bsrp.

Hot Standby Router Protocol

If a router sends a Hello message, then receivers should consider that Hello message to be valid for one Holdtime. To minimize network traffic, only the active and the standby routers send periodic HSRP messages once the protocol has completed the election process.


Version 2 of the protocol introduces stability, scalability and diagnostic improvements. If the Hellotime is not configured on a router, then it MAY be learned from the Hello message from the active router. When comparing priorities of two different routers, the router with the numerically higher priority wins.

In particular, the protocol protects against the failure of the first hop router when the source host cannot learn the IP address of the first hop router dynamically.

The router has not determined the virtual IP address, and not yet seen an authenticated Hello message from the active router. This router is known as the active router. Views Read Edit View history. For other media values between 0 and inclusive are valid.

The router is a candidate to become the next active router and sends periodic Hello messages. This is the starting state and indicates that HSRP is not running. Retrieved from ” https: Although an arbitrary number of routers may run HSRP, only the active router forwards the packets sent to the virtual router. HSRP gateways send multicast hello messages to other gateways to notify them of their priorities which gateway is preferred and current status active or standby.

The protocol is designed for use over multi-access, multicast or broadcast capable LANs e. This state is entered via a configuration change or when an interface first comes up.

Another router is elected as the standby router.