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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It listens for Hello messages from those routers. This set is known as an HSRP group or a standby group. 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. Another router is elected as the standby router.
The protocol is designed for use over multi-access, multicast or broadcast capable LANs e. This field contains a clear text 8 character reused password. If the active router fails, the standby router takes over as the active router. The time is given in seconds. The protocol establishes an association between gateways in order to achieve default gateway failover if the primary gateway becomes inaccessible.
If the link of the primary router goes down, the backup router will take over the primary functionality and thus retain connectivity to the gateway. A large class of legacy host implementations that do not support dynamic discovery are capable of configuring a default router.
A router cannot enter Speak state unless it has the virtual IP address.
HSRP, Hot Standby Router Protocol
Herp this state the router is still waiting to hear from the active router. If multiple groups are used on a single LAN, load splitting can be achieved by distributing hosts among different standby groups. From Wikipedia, the free encyclopedia.
It contains the approximate period between the Hello messages that the router sends. The router is currently forwarding packets that are sent to the group’s virtual MAC address. HSRP is not shrp routing protocol as it does not advertise IP routes or affect the routing table in any way.
This field identifies the standby group. In the case of routers with equal priority the router with the higher IP address wins. In the event that the active router fails, the standby assumes the packet forwarding duties of the active router. This field is used to elect the active and standby routers. This state is entered via a configuration change or when an interface first comes up. Although an arbitrary number usrp routers may run HSRP, only the active router forwards the packets sent to the virtual router.
The virtual IP address used by this group. For other media values between 0 and inclusive are valid. 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. It is not compatible with version 1 HSRP.
If the Hellotime is not configured on a router, then it MAY be learned from the Hello message from the active router. A single router elected from the group is responsible for forwarding the packets that hosts send to the virtual router. For each standby group, a single well-known MAC address is allocated to the group, as well as an IP address.
HSRP provides failover services to those hosts. This router is known as hsep active router. This can be useful for dual branch routers each with a single link back to the gateway. The router is a candidate to become the next active router and sends periodic Hello messages. When comparing priorities of two different routers, the router with the numerically higher priority wins. Version 2 of the protocol introduces stability, scalability and diagnostic improvements. HSRP has the ability to trigger a failover if one or more interfaces on the router go down.
This field describes the current state of the router sending the message. If a router sends a Hello message, then receivers should consider that Hello message to be valid for one Holdtime. Views Read Edit View history.
Information on RFC » RFC Editor
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. Tfc from ” https: It contains the amount of time that the current Hello message should be considered valid. For Token Ring, values between 0 and 2 inclusive are valid.
The router knows the virtual IP address, but is neither the active router nor the standby router. Each standby group emulates a rvc virtual router. If the virtual IP address is not configured on a router, then it MAY be learned from the Hello message from the active router.
Hot Standby Router Protocol
This page was last edited on 28 Decemberat If the Holdtime is not configured on a router, then it MAY be learned from the Hello message from the active router. The router sends periodic Hello messages. On a particular LAN, multiple hot standby groups may coexist and overlap.