What is HSRP?
HSRP (Hot Standby Router Protocol) has been developed by Cisco to provide redundancy for your network on both sides. For example in a datacentre situation providing a redundant uplink to a single rack cabinet, you would have HSRP configured on the datacentre’s switches, and then HSRP on the switches within the rack itself. HSRP allows you to have a “floating” or standby IP address configured on two seperate switches / routers, which is then used as your gateway. In the event that the link state of one uplink goes down, the secondary switch automatically takes over using the same gateway IP address, allowing traffic to flow again with minimal interruption.
Configuring HSRP on a Cisco Switch/Router
This example is of a standard active/passive configuration, although HSRP can also be used for load balancing.
Here is the basics for configuring HSRP on a compatible Cisco switch / router:
For your primary switch / router:
(config-if)#ip address 10.10.10.100 255.255.255.0
(config-if)#standby 1 preempt
(config-if)#standby 1 ip 10.10.10.254
(config-if)#standby 1 priority 100
For your secondary switch / router:
(config-if)#ip address 10.10.10.200 255.255.255.0
(config-if)#standby 1 preempt
(config-if)#standby 1 ip 10.10.10.254
(config-if)#standby 1 priority 95
With this configured you would now get a response from 10.10.10.254 and can use this as your default gateway on all clients.
You can either configure the above directly on a physical interface or under a VLAN depending on what you’d prefer.
If the link state of the uplink interface for your primary switch goes down, the secondary switch would become live on the 10.10.10.254 IP address and start accepting traffic.
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