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Chapter 11: Optimizing Routing Update OperationThis chapter discusses some of the more commonly used capabilities for controlling when and how routers receive and send routing updates. The capabilities covered include passive interfaces, default routes, static routes, route filtering, and redistributing routes between different routing protocols.
Understanding these capabilities and configurations enables you to design and configure the most efficient routing environment.
CONTROLLING ROUTING UPDATE TRAFFICThus far, you have learned a variety of routing protocols and how they propagate routing information throughout an internetwork. There are times, however, when you do not want routing information propagated, as in the following examples:
- When using an on-demand WAN link-You may want to minimize, or stop entirely, the exchange of routing update information across this type of link; otherwise, the link will remain up constantly.
- When you want to prevent routing loops-Many companies have large enough networks where redundant paths are prominent. In some cases, for example, when a path is learned to the same destination by two different routing protocols, you may want to filter the propagation of one of the paths.
When you want to preserve bandwidth-Available bandwidth becomestraffic a precious resource as networks grow. You can ensure maximum bandwidth availability for data traffic by reducing unnecessary routing update traffic
This section discusses the following ways you can control or prevent routing update exchange and propagation:
- Passive interface-Prevents all routing updates from being sent through an interface. For EIGRP and OSPF, this method includes hello protocol packets.
- Default routes-Instructs the router that if it does not have a route for a given destination, to send the packet to the default route.
- Static routes-A route to a destination that you configured in the router. In contrast, dynamic routes are those learned via routing protocol such as RIP or EIGRP.
- Route update filtering-doUse access lists to filter route update traffic about specific networks.
In order to make these capabilities effective, you must know your network traffic patterns and know what the intended goal is when applying the capabilities. If you do not know the problem you want to resolve when using these capabilities, you will not know how to verify that they are being effective.