FHRP

First Hop Redundancy protocols will allow default gateway redundancy, meaning, having more than one default gateway enabled, in the event of a router failure there’s a backup device that will kick in and almost transparently to users, continue to forward traffic to remote networks, thus avoiding the situation of isolation

A first hop redundancy protocol (FHRP) is a computer networking protocol which is designed to protect the default gateway used on a subnetwork by allowing two or more routers to provide backup for that address; in the event of failure of an active router, the backup router will take over the address, usually within a few seconds.
 In fact, such protocols can also be used to protect other services like layer 3 switches as well ,operating on a single IP address

We will talk about 3 types of protocols:

• Hot Standby Router Protocol (HSRP) - Cisco's initial, proprietary standard
• Virtual Router Redundancy Protocol (VRRP) - an open standard protocol
•  Gateway Load Balancing Protocol (GLBP) - a more recent proprietary standard from Cisco that permits load balancing as well as redundancy 

Hot Standby Router Protocol (HSRP) is a Cisco-proprietary redundancy protocol for establishing a fault-tolerant default gateway. It is described in RFC 2281. HSRP provides a transparent failover mechanism to the end stations on the network. This provides users at the access layer with uninterrupted service to the network if the primary gateway becomes inaccessible.


The Virtual Router Redundancy Protocol (VRRP) is a standards-based alternative to HSRP and is defined in RFC 3768. The two technologies are similar but not compatible.

 The main disadvantage of HSRP and VRRP is that only one gateway is elected to be the active gateway and used to forward traffic while the rest are unused until the active one fails. 
Gateway Load Balancing Protocol (GLBP) is a Cisco proprietary protocol and performs the similar function to HSRP and VRRP but it supports load balancing among members in a GLBP group.

 We will explain each one in the next articles.