| 7.2 |  | RIP |
| 7.2.7 |  | Preventing routing updates through an interface |

| Route filtering works by regulating the routes that are entered into or advertised out of a route table. These have different effects on link-state routing protocols than they do on distance vector protocols. A router running a distance vector protocol advertises routes based on what is in its route table. As a result, a route filter influences which routes the router advertises to its neighbors. On the other hand, routers running link state protocols determine routes based on information in the link-state database, rather than the neighboring router advertised route entries. Route filters have no effect on link-state advertisements or the link-state database. For this reason, the information in this document only applies to distance vector IP Routing Protocols such as Routing Information Protocol (RIP), and Interior Gateway Routing Protocol (IGRP). Using the passive interface command can prevent routers from sending routing updates through a router interface. Keeping routing update messages from being sent through a router interface prevents other systems on that network from learning about routes dynamically. Router E uses the command to keep routing updates from being sent. For RIP and IGRP, the passive interface command stops the router from sending updates to a particular neighbor, but the router continues to listen and use routing updates from that neighbor. Keeping routing update messages from being sent through a router interface prevents other systems on the interface from learning about routes dynamically.
| Lab Activity Lab Exercise: Preventing Routing Updates Through an Interface This lab is to prevent routing updates through an interface to regulate advertised routes.
| Lab Activity e-Lab Activity: Preventing Routing Updates through an Interface In this lab, the students will learn to prevent routing updates through an interface to regulate advertised routes and observe the results.