Foundation Summary

The Foundation Summary provides a convenient review of many key concepts in this chapter. If you are already comfortable with the topics in this chapter, this summary might help you recall a few details. If you just read this chapter, this review should help solidify some key facts. If you are doing your final prep before the exam, the following lists and tables are a convenient way to review the day before the exam.

Various methods enable you to control the routing information sent between routers. These methods include the following:

  • Passive interfaces

  • Default route

  • Static routes

  • The null interface

  • Distribute lists

  • Route maps

Table 11-13 shows the requirements of automatic redistribution between routing protocols.

Table 11-13. Redistribution Between Routing Protocols
Routing ProtocolRedistribution Policy
StaticRequires manual redistribution.
ConnectedUnless in the network command for the routing process, requires manual redistribution.
RIPRequires manual redistribution.
EIGRPWill automatically redistribute between IGRP and EIGRP if the AS number is the same. Otherwise, requires manual redistribution.
OSPFRequires manual redistribution between different OSPF process IDs and routing protocols.

The following list explains the logic used in a distribute list:

  1. The router receives a routing update or is about to send a routing update about one or more networks.

  2. The router looks at the appropriate interface involved with the action to check for filtering.

  3. If a filter is present, the router examines the access list to see if there is a match on any of the networks in the routing update.

  4. If there is no filter on the interface, the routing update is sent directly to the routing process, as normal.

  5. If there is a filter, the route entry is processed according to the distribute list: advertise the route if matched by a permit statement or do not advertise if it is matched by a deny statement.

  6. If no match is found in the distribute list, the implicit deny any at the end of the access list will cause the update to be dropped.