Support for automatic load balancing and support for multiple gateways are two features that are provided by Gateway Load Balancing Protocol (GLBP) but not by Hot Standby Routing Protocol (HSRP) or Virtual Router Redundancy Protocol (VRRP).
GLBP, HSRP, and VRRP provide a redundant and fault-tolerant solution in case of first-hop router failure in a network. The basic operation of these three protocols is the same. In all three protocols, a group of routers on the same LAN is formed. One of the routers is selected as the active router and another as the standby router.
The router with the highest priority is automatically selected as the active router. If the active router fails, the standby router assumes the responsibilities of the active router. The role of the active router is to forward the packets from the hosts to the virtual router (default gateway).
GLBP provides automatic load balancing between multiple routers by configuring multiple MAC addresses but a single virtual IP address. Every active virtual forwarder (AVF) in the group is configured with the virtual IP address but with different MAC addresses. All such AVFs can then participate in the packet-forwarding process. Multiple gateways then can share the load. On the contrary, HSRP and VRRP do not support automatic load balancing. Both these protocols require additional configuration on all the routers that need to load balance. The additional configuration involves using multiple groups on the routers or assignment of different default gateways for the hosts.
Note that GLBP and VRRP are supported by both Cisco and non-Cisco routers, whereas, HSRP is supported only by Cisco routers.
Single active router and interface tracking both are supported by GLBP, HSRP, and VRRP.
Objective:
Infrastructure Services
Sub-Objective:
Configure and verify first-hop redundancy protocols
References:
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