Cisco designed a proprietary load-balancing protocol, Gateway Load Balancing Protocol
(GLBP), to allow automatic selection and simultaneous use of multiple available gateways,
as well as permit automatic failover between those gateways. GLBP takes an active/active
approach on a per-subnet basis to support first-hop (default router) traffic when implemented
with two routers on the same LAN. Multiple routers share the load of frames that, from a
client perspective, are sent to a single default gateway address, as shown in Figure 17.10.