(GLBP)   Gateway Load Balancing Protocol

Feature History

Release	Modification
12.2(14)S	This feature was introduced.

This document describes the Gateway Load Balancing Protocol feature in Cisco IOS Release 12.2(14)S and it includes the following sections:

Feature Overview

The Gateway Load Balancing Protocol feature provides automatic router backup for IP hosts configured with a single default gateway on an IEEE 802.3 LAN. Multiple first hop routers on the LAN combine to offer a single virtual first hop IP router while sharing the IP packet forwarding load. Other routers on the LAN may act as redundant Gateway Load Balancing Protocol (GLBP) routers that will become active if any of the existing forwarding routers fail.

GLBP performs a similar, but not identical, function for the user as the Hot Standby Router Protocol (HSRP) and the Virtual Router Redundancy Protocol (VRRP). HSRP and VRRP protocols allow multiple routers to participate in a virtual router group configured with a virtual IP address. One member is elected to be the active router to forward packets sent to the virtual IP address for the group. The other routers in the group are redundant until the active router fails. These standby routers have unused bandwidth that the protocol is not using. Although multiple virtual router groups can be configured for the same set of routers, the hosts must be configured for different default gateways, which results in an extra administrative burden. 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, User Datagram Protocol (UDP) port 3222 (source and destination).