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Part IX: Appendixes > Chapter 10

Chapter 10

1.E. Because OSPF does not use hop count as a metric, the information about the number of hops is not available in OSPF routes in the IP routing table. The other answers list items that can be matched with the route map match subcommand.
2.A. The deny clauses in the route map mean that the route map will filter routes matched by that clause. The permit or deny action of the referenced ACLs just defines whether the route is matched. So, routes permitted by ACL “two” will be matched and then filtered due to the route-map clause deny action. Routes denied by ACL “one” simply do not match the route map clause numbered 10; such routes may or may not be redistributed depending on the next two clauses. Clause number 100 does not have a match command, meaning it matches all routes not otherwise matched, with a permit action, allowing these routes to be redistributed.
3.A and C. The problem states that R1 has learned OSPF intra-area routes for, so show ip route will display that subnet. As an intra-area route based on a Type 2 LSA, the show ip ospf database command lists the summary of the LSAs, including the subnet number for that Type 2 LSA. However, because the redistribution filtering discards subnet, this value will not be included in the EIGRP topology table.
4.B. The external 2 parameters on the redistribute command act as matching logic; only routes from the source routing protocol (in this case OSPF 2) that match this extra logic will be considered for redistribution by this redistribute command. The set metric-type type-1 route-map subcommand sets the route type as it is injected into the destination routing protocol (in this case OSPF 1); this logic is not used for matching the source routes. The routes permitted by ACL 1 will be redistributed, but only those that are also E2 routes from the (source) OSPF 2 domain. The redistribute function will not change the attributes of routes inside a single routing domain, but only in the destination routing domain (OSPF 1), so the configuration has no effect on the OSPF 2 routes that remain in OSPF 2.
5.C. EIGRP, by default, sets a different AD for internal (90) and external (170) routes. The rest of the answers are accurate regarding default settings.
6.A. All the answers list reasonable options in some cases, but the only feature listed that is useful with all three routing protocols is the route tag feature. RIPv2 does not support the concept of differentiating between internal and external routes, so the two answers that suggest setting administrative distance (AD) based on the route type (internal or external) could not be used in all three routing domains, as required by the question. All three routing protocols support setting route tags and setting the AD per route; however, because RIPv2 cannot match based on the route type (internal/external), the option to set the route tags is the only option that applies to all three routing domains.
7.D. AD can be used to prevent the domain loop problem with two routing domains by making each routing protocol’s AD for internal routes be better (lower) than the other routing protocol’s AD for external routes. RIP uses AD 120 for all routes, with no distinction of internal or external. As such, OSPF’s internal default AD settings of 110 meet the requirement that OSPF’s internal AD (110) is better than RIP’s external (120). However, RIP’s default of 120 is not better than OSPF’s default for externals (110), so the distance ospf external 180 command changes that setting to meet both requirements. The three wrong answers, while syntactically valid, do not help meet the requirements.
8.E. Route tags are unitless integers that can be given to a route and even passed between different routing protocols by routers that perform redistribution.


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