So Cisco IOS software puts the information from the source with the lowest distance in the forwarding table. Often the folks running servers are a different group than those configuring the enterprise routers. A router running RIP will believe anything it's told via RIP, including information from RIP-based servers. This could result in less than optimal paths being chosen through the network. This way, RIP can still make good decisions for server connectivity but not adversely affect the rest of the network by propagating inappropriate information.
Network managers can tune the distance factors to optimize traffic flows across their networks.
For example, they can assign believability weights to individual source IP addresses or to source IP address ranges. They can even assign a weight to an individual route advertisement. Regardless of the reasons driving the use of multiple protocols, a solid knowledge of each protocol's capabilities, limitations, features, and operations is essential for optimum network routing. Filtering Routing Updates Cisco IOS software can filter incoming and outgoing routing updates using access lists via the distribute-list command. Conversely, routers can be configured to not accept advertisements for selected routes, most often for default routes.