350-501 Question #583: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. OSPF is running in the given network. R1 was previously running EIGRP on a standalone network, and a network engineer just migrated it to OSPF. The R1 peering with R2 has come up. Which additional action must the engineer take so that R2 receives routes from Area 1 and Area 0 but it is prevented from receiving routes from Area 2?

Options

• AImplement a route map that matches the rules in an ACL from Area 2, and then attach the route
• BImplement a route map that matches R1's next-hop address. and then attach the route map to an
• CImplement a route map that matches R2's interface to R3 and R4, and then attach the route map
• DImplement a route map that matches the routes from Area 2 in a prefix list, and then attach the

Explanation

To prevent R2 from receiving routes specifically from OSPF Area 2 while accepting routes from Area 0 and Area 1, the engineer must implement a route map on R2 that matches routes from Area 2 using an ACL, and then apply this filter.

Common mistakes.

• B. Filtering OSPF routes based on a next-hop address (R1's) is not a practical or comprehensive method for preventing an entire area's routes from being received or installed in the routing table.
• C. Matching R2's interfaces to R3 and R4 in a route map is irrelevant to filtering routing updates based on their originating OSPF area.
• D. While a prefix list is commonly used with route maps for route matching, the correct answer specifically states using an ACL, which is also a valid and frequently used method for defining route filtering criteria in OSPF.

Concept tested. OSPF inter-area route filtering

Reference. https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13697-29.html

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