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260 Chapter 9: Frame Relay Connection Controlling Traffic Flow
Figure 9-4
Frame Relay Topologies
A topology has some affect on the manner in which routers are configured. By default, Frame
Relay encapsulated interfaces are multipoint in nature. In environments in which the connection
is a single end-to-end PVC with no other connections, there should be no problems. However,
in hub and spoke or partial mesh environments, routing update problems can arise.
Issues When Connecting Multiple Sites Through a Single Router
Interface
When a single physical interface is utilized on a central router to connect multiple remote sites,
routing problems arise. These problems are caused by split horizon. Split horizon is a rule in
routing protocol operation that is designed to eliminate routing loops by not allowing routing
updates to be sent out of the interfaces through which they were received.
Consider the situation in which one serial interface serves multiple remote sites. In this
scenario, split horizon effectively shuts down the passing of routing updates regarding networks
on the far side of the remote sites. Although the central site can receive the updates through
Serial 0, process them, and then make appropriate changes to the routing table, when the time
Partial mesh
Full mesh
Star (hub and spoke)