Gateway Load Balancing Protocol (GLBP) is a Cisco proprietary load balancing protocol to load balance traffic between different routers. Therefore, it uses all the routers in place of letting only one router to process all traffic. GLBP routers must be placed in a router group to be able to perform.
When operating with GLBP, the host needs to point its gateway to a virtual IP address virtual router. Although the IP address is the same, the MAC address of each physical router is different. When ARP request is sent from the host, one of the routers will give their MAC address to the host and will serve that host. However, another host that comes directly after will be given another MAC address of a different router.
One of the router (with the highest priority) acts as Active Virtual Gateway (AVG). The second highest priority is set as standby, and all other routers is set into listening state. The AVG will assign a virtual MAC address to all the other routers and enables Active Virtual Forwarders (AVF). Each AVF will process packets that are sent to its virtual MAC address based on load balancing methods. If AVF on a router fails, another router will handle the request since routers can communicate with each other using the multicast IP address 224.0.0.102 and UDP port 3222.
Load balancing method in GLBP consists of 3 methods of MAC address assignments:
1. Round robin, where each router will get a packet fairly each turn. If there are 4 hosts (1,2,3,4 coming in order) and 2 routers (A,B) then host 1 will go to A, host 2 will go to B, host 3 will go to A and host 4 will go to B.
2. Host dependent, which is used if a host needs to get the same MAC address serving router.
3. Weighted, where traffic can be assigned to routers with certain weights. For example if there are 3 routers , where one router (A) has 2x capacity than other two (B,C) then the traffic can be weighted with the value 2:1:1. In that way, 2 clients will be served by router A, 1 client by router B and 1 client by router C.
To apply GLBP use the command in the interface mode:
(config-if)#glbp ip
To change GBLP priority use:
(config-if)#glbp priority
To enable preempt:
(config-if)#glbp preempt
When operating with GLBP, the host needs to point its gateway to a virtual IP address virtual router. Although the IP address is the same, the MAC address of each physical router is different. When ARP request is sent from the host, one of the routers will give their MAC address to the host and will serve that host. However, another host that comes directly after will be given another MAC address of a different router.
One of the router (with the highest priority) acts as Active Virtual Gateway (AVG). The second highest priority is set as standby, and all other routers is set into listening state. The AVG will assign a virtual MAC address to all the other routers and enables Active Virtual Forwarders (AVF). Each AVF will process packets that are sent to its virtual MAC address based on load balancing methods. If AVF on a router fails, another router will handle the request since routers can communicate with each other using the multicast IP address 224.0.0.102 and UDP port 3222.
Load balancing method in GLBP consists of 3 methods of MAC address assignments:
1. Round robin, where each router will get a packet fairly each turn. If there are 4 hosts (1,2,3,4 coming in order) and 2 routers (A,B) then host 1 will go to A, host 2 will go to B, host 3 will go to A and host 4 will go to B.
2. Host dependent, which is used if a host needs to get the same MAC address serving router.
3. Weighted, where traffic can be assigned to routers with certain weights. For example if there are 3 routers , where one router (A) has 2x capacity than other two (B,C) then the traffic can be weighted with the value 2:1:1. In that way, 2 clients will be served by router A, 1 client by router B and 1 client by router C.
To apply GLBP use the command in the interface mode:
(config-if)#glbp
To change GBLP priority use:
(config-if)#glbp
To enable preempt:
(config-if)#glbp
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