Gateway Load Balancing Protocol (GLBP) provides redundancy for IP networks, ensuring that user traffic immediately and transparently recovers from first hop router failures, while allowing packet load sharing between a group of redundant routers.

GLBP provides load balancing over multiple routers (gateways) using a single virtual IP address and multiple virtual MAC addresses. Each host is configured with the same virtual IP address, and all routers in the virtual router group participate in forwarding packets. GLBP members communicate between each other through hello messages sent every 3 seconds to the multicast address 224.0.0.102

The following sample configuration sets up two routers R1 and R2 as GLBP, gateways serving the 192.168.1.0/25 network with 192.168.1.1 as the virtual gateway address.This is the default gateway that would be configured on all the hosts in the 192.168.1.0/24 network.

The configuration can be:

R1(config)#interface vlan10
R1(config-if)#ip address 192.168.1.10 255.255.255.0
R1(config-if)#glbp 1 ip 192.168.1.1
R1(config-if)#glbp 1 preempt
R1(config-if)#glbp 1 priority 150

Now the configuration on the Router 2:

R2(config)#interface vlan10
R2(config-if)#ip address 192.168.1.11 255.255.255.0
R2(config-if)#glbp 1 ip 192.168.1.1