How does hsrp work

There are a limited number of Token Ring functional addresses available and many of them are reserved for other functions. You can use the following three addresses with HSRP:.

When this standby router becomes active, stations on the same ring as the old active router need a new RIF in order to send packets to the new active router. However, since the standby new active router is using the same functional address as the previous active router the stations are not aware that they must send explorers for a new RIF.

For this reason, the use-bia command was introduced. Click on a feature to see a detailed description. An interim release number indicates in which release a feature first appeared, or a release where the functionality of that feature changed. The HSRP preemption feature enables the router with highest priority to immediately become the Active router.

Priority is determined first by the priority value that you configure, and then by the IP address. In each case a higher value is of greater priority. When a higher priority router preempts a lower priority router, it sends a coup message.

When a lower priority active router receives a coup message or hello message from a higher priority active router, it changes to the speak state and sends a resign message.

The preempt delay feature allows preemption to be delayed for a configurable time period, allowing the router to populate its routing table before becoming the active router. In Cisco IOS release To configure HSRP priority and preemption, use the standby [ group ] [priority number ] [preempt [delay [minimum] seconds ] [sync seconds ]] command.

Interface tracking allows you to specify another interface on the router for the HSRP process to monitor in order to alter the HSRP priority for a given group. If the specified interface's line protocol goes down, the HSRP priority of this router is reduced, allowing another HSRP router with higher priority can become active if it has preemption enabled.

To configure HSRP interface tracking, use the standby [group] track interface [priority] command. When multiple tracked interfaces are down, the priority is reduced by a cumulative amount. If you explicitly set the decrement value, then the value is decreased by that amount if that interface is down, and decrements are cumulative. If you do not set an explicit decrement value, then the value is decreased by 10 for each interface that goes down, and decrements are cumulative.

Before Cisco IOS release The use-bia command is also useful in networking situations where a device's BIA has been configured in other devices on the LAN.

The newly active router sends a gratuitous ARP response, but not all host implementations handle the gratuitous ARP correctly. Proxy ARP breaks when use-bia is configured. A atandby router cannot cover for the lost proxy ARP database of a failed router.

Prior to Cisco IOS release When you configure the use-bia command on a subinterface, it actually shows up on the main interface and is applied to all subinterfaces. This feature further enables redundancy and load-sharing within networks, and allows redundant routers to be more fully utilized.

While a router is actively forwarding traffic for one HSRP group, it can be in standby or in the listen state for another group. As of Cisco IOS release The end stations are configured with a default gateway.

However, HSRP can provide first hop redundancy for other protocols. In this case, it is often necessary to be able to specify the virtual MAC address using the standby mac-address command. The virtual IP address is unimportant for these protocols. The actual syntax of the command is standby [group] mac-address mac-address.

This feature allows for more efficient logging and tracking of the current active and standby routers on syslog servers. To enable HSRP debugging, you would simply use the debug standby command, which enabled output of HSRP state and packet information for all standby groups on all interfaces. Follow us on :. Times Drive Desk. Updated Mar 11, IST. Ministry of Road Transport and Highways MoRTH mandates all vehicles in the country sold before 1 April, to have a high security registration plate and colour coded stickers.

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This field is used to elect the active and standby routers. When comparing priorities of two different routers, the router with the numerically higher priority wins. In the case of routers with equal priority the router with the higher IP address wins. This field identifies the standby group.

For Token Ring, values between 0 and 2 inclusive are valid. For other media values between 0 and inclusive are valid. Authentication Data. This field contains a clear text 8 character reused password. Virtual IP Address. The virtual IP address used by this group.

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