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HSRP Configuration using Four Cisco 3750 Switches

Hot Standby Router Protocol (HSRP) is a technology by Cisco to implement router redundancy using layer 3 switches or routers.

Basic idea of HSRP is it lets an virtual IP be hosted and shared by two different hardware units. I deployed a solution using 4 Cisco 3750 stackwise switches for client. They had two 3750 switches at the core of their network. They were connected into a single virtual unit using the stackwise technology. Which increase the resilience of the core network to some extend. My solution added another set of 3750 switches in to the cluster creating a complete HSRP cluster while increasing reliability and extending the number of ports per vlan.

Below is the solution design diagram I put together for the client.

HSRP Solution

How to implement HSRP using Cisco 3750.

To enable HSRP on an interface use the following command;

(config-if)# standby ip

Mainly using HSRP in a organize manner it is advisable to implement the HSRP group. Specially if you are using HSRP clustering.

Clients network consisted of 7 vlans and each vlan’s default gateway address were set to the 7 HSRP virtual router addresses. Furthermore the HSRP can implement load sharing using the priority to select which physical units take ownership (active router) of the virtual router in normal operation (MHSRP). HSRP priority is between 1 and 255, highest numbered router interface per HSRP group becomes the active router which holds the virtual router process.

Don’t forget to set the preempt so when a active router recovers from a failure it can become the active router for that HSRP group automatically, keeping that load sharing in place in normal operation.

Below is a complete interface configuration in order to implement HSRP.

Switch# configure terminal



(config)# interface vlan 1



(config-if)# ip address 192.168.0.1 255.255.255.0



(config-if)# standby 1 ip 192.168.0.254



(config-if)# standby 1 priority 110



(config-if)# standby 1 preempt



(config-if)# standby 1 authentication word



(config-if)# standby 1 timers 5 15



(config-if)# standby 1 name VR_VLAN1

Timers set advertising time (heart-beat) between interfaces participating in the HSRP group and authentication keeps unauthorized routing interfaces participating in the HSRP group.

After configuring all of the interfaces in a cluster with the HSRP settings, enable the cluster HSRP using the command below.

(config)# cluster standby-group VR_VLAN1 routing-redundancy

I would like to add another note in HSRP which I learn through this project. If you have ACL applied to vlan or any interface which you are implementing HSRP, make sure you add the following line in to your ACL. This allows the HSRP multicasting packets between participating interfaces.

permit udp any eq 1985 host 224.0.0.2 eq 1985



All in all it was a good project. Learn a lot and it is always good to brush up on switch solutions and implementations.