Layer 3 Redundancy
The remainder of this chapter focuses on Layer 3 redundancy issues. When you think of Layer 3 redundancy, you're normally dealing with having multiple paths to a destination. This section, however, deals with another type of Layer 3 redundancy: default gateways and server load balancing. I'll begin by talking about some of the issues of default gateway redundancy and some of the solutions that are available, but don't work very well. The main part of this section deals with Cisco's Hot Standby Routing Protocol (HSRP), as well as other solutions that are better at dealing with default gateway redundancy, such as the Single Router Mode (SRM) redundancy and Gateway Load Balancing Protocol (GLBP) solutions.