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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.
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Lab Activity
Lab Exercise: Preventing Routing Updates Through an Interface
This lab is to prevent routing updates
through an interface to regulate advertised routes.
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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.
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