Below shows a typical topology which we are going to see how we configure HSRP. Hosts on the adjoining LAN segment use the normal Address Resolution Protocol (ARP) process in order to resolve the associated MAC addresses.Įven though HSRP group can be consist of multiple layer 3 devices, in typical enterprise environment distribution block (two aggregation switches) is configured with HSRP to provide gateway redundancy to all access layer VLANs. For example, HSRP group 1 uses the HSRP virtual MAC address of 01. Virtual MAC address that is composed of ** where ** is the HSRP group number in hexadecimal, based on the respective interface. This use of source addressing is necessary so that HSRP routers can correctly identify each other. The standby router sources hellos from its configured IP address and the burned-in MAC address (BIA). The active router sources hello packets from its configured IP address and the HSRP virtual MAC address. IP multicast address 224.0.0.2 is a reserved multicast address that is used to communicate to all routers. These packets are sent to the destination IP multicast address 224.0.0.2 on User Datagram Protocol (UDP) port 1985. Routers that run HSRP communicate HSRP information between each other through HSRP hello packets. Although an arbitrary number of routers may run HSRP, only the active router forwards the packets that are sent to the virtual router IP address. If the active router fails, the standby assumes the packet forwarding duties. Another router is elected as the standby router. This router is known as the active router.

Hot Standby Routing Protocol (HSRP) is Cisco standard of providing redundancy for IP host configured in a LAN network with default gateway address.It enables a set of router interfaces to work together to present the appearance of a single virtual router or default gateway to the hosts on a LAN.Ī single router that is elected from the group is responsible for the forwarding of the packets that hosts send to the virtual router.

Bia mac address