FHRP

First Hop Redundancy Protocol is a redundancy protocol for the default gateway.

 Say you have a simple network as follows:


In this network, you have a default gateway of 10.1.1.1 on your server(10.1.1.10). What if 10.1.1.1 goes down? The network experience of your server's user is impacted and there needs to be a manual change to 10.1.1.2.

FHRP technologies help us alleviate this issue by letting the 2 routers work in High Availability mode.

 

There are 2 Cisco proprietary FHRP technologies:

1) HSRP - Hot Standby Routing Protocol

 2) GLBP - Gateway Load Balancing Protocol

Open source:

 3) VRRP - Virtual Router Redundancy Protocol


With all of the three technologies, you setup a virtual IP, e.g. 10.1.1.3 on both the routers and let the two routers know that they are in a group with the third IP, this way if one of the routers go down, the other takes up the default gateway job and the network in not impacted.

 

---

 

Cisco commands to setup HSRP on a Cisco switch:

---> First find the interface that is used as the default gateway for the server -> Say it is gig0/0.

> enable

# show standby

# conf t

# interf gig0/0

# standby 1


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