By Josh E.
Being able to implement first hop router redundancy protocols is one of the objectives listed for Cisco’s 642-813 SWITCH exam. Cisco supports three first hop redundancy protocols: Gateway Load Balancing Protocol (GLBP), Hot Standby Router Protocol (HSRP), and Virtual Router Redundancy Protocol (VRRP). This article provides an overview of each of these protocols.
GLBP is a router redundancy protocol that also provides load balancing. GLBP enables you to configure multiple routers as a GLBP group; the routers in the group receive traffic sent to a virtual IP address that is configured for the group. Each GLBP group contains an active virtual gateway (AVG) that is elected based on which router is configured with the highest priority value, or with the highest IP address if multiple routers are configured with the highest priority value. The other routers in the GLBP group are configured as primary or secondary active virtual forwarders (AVFs). Up to four primary AVFs can be configured in a GLBP group, and the primary AVFs can participate in forwarding traffic. Consequently, multiple routers can be used simultaneously to provide load balancing for the GLBP group.