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

Release

Modification

12.2(14)S

This feature was introduced.