Today’s topic is HSRP (Hot Standby Routing Protocol). HSRP is a Cisco proprietary “First Hop Redundancy Protocol”. It is typically used for redundancy at the first hop from a client segment. It is used with two or more routers in a group who share a virtual IP address. One router is active at a given time and will reply to ARP requests. In this example, we have R1 and R2 in standby group 100 with a virtual IP of 192.168.100.1. This IP will be the default gateway for all hosts in VLAN 100. Here is the topology:

This is a basic topology, both R1 and R2 have connections to the internet. They are running HSRP on their FastEthernet 0/0 interfaces. Here’s the basic HSRP config:

R1(config)#interface fa0/0
R1(config-if)#ip address 192.168.100.2 255.255.255.0
R1(config-if)#standby 100 ip 192.168.100.1
 
R2(config)#interface fa0/0
R2(config-if)#ip address 192.168.100.3 255.255.255.0
R2(config-if)#standby 100 ip 192.168.100.1

Very simple so far. We use the “standby [0-255] ip [virtual ip address]” command.

Let’s verify the config: