By Josh E. The Cisco 642-813 SWITCH exam requires you to be able to implement first-hop router redundancy protocols. Three first hop redundancy protocols are supported by Cisco: Gateway Load Balancing Protocol, Hot Standby Router Protocol, and Virtual Router Redundancy Protocol. This article will provide an overview of each protocol.
GLBP is a router redundancy protocol, which also provides load balancing. GLBP allows you to create multiple routers and group them together. The routers receive traffic to a virtual address that has been assigned to the group. Each GLBP group has an active virtual gateway (AVG). It is determined based on which router has the highest priority or multiple routers with the highest IP addresses. Other routers in the GLBP Group can be configured as primary or second active virtual forwarders. In a GLBP group, up to four primary AVFs may be configured. The primary AVFs are allowed to participate in forwarding traffic. Multiple routers can be used simultaneously to provide load balancing in the GLBP group.
HSRP is a protocol for router redundancy that was defined in Request for Comments (RFC 2281). Similar to GLBP HSRP can be used as a backup router coverage in the event that the primary gateway is unavailable. Multiple routers can be assigned to an HSRP group. The routers work as a single gateway. An HSRP group consists of one active router and one standing router. The active router is the router that has the highest priority value. The standby router is defined as the router that has the second-highest priority. Other routers in HSRP are in the listen status. If the active router fails, the standing router takes over the active router role. A new standby router is elected.
Cisco supports VRRP, another protocol for router redundancy. A VRRP group is a group that assigns routers to. This group acts as a single gateway for clients. A VRRP group is composed of one master router. This router has the highest priority value. All other routers within the VRRP group are backups. Clients can identify the VRRP group by using a virtual Media Access Control address (MAC). The virtual MAC address of VRRP groups is 0000.5e00.01xx. xx is a hexadecimal number that identifies the VRRP group number. VRRP Group 1 would, for example, be identified by the virtual MAC number 0000.5e00.0101.
Photo: Rich Bowen
