Refer to me exhibit. Refer to the exhibit. A network engineer sets up a multihoming eBGP topology where multiple Autonomous Systems connect to ASN 64501. The engineer wants to block all the routes…

Question

Exhibit

Options

• AThe AS-PATH filter must be defined inside the route-map mode
• BAt the end ip as-path access-list 10 permit .* must be included
• CThe statement must be modified with ip as-path access-list 1 deny 64502
• DThe statement must CM modified with ip as path access list 1 deny A64502$

• A
  7% (2)
• B
  83% (25)
• C
  7% (2)
• D
  3% (1)

Explanation

Option B is correct because Cisco IOS AS-path access lists, like standard ACLs, carry an implicit deny all at the end. The existing deny _64502$ statement correctly blocks routes originating from AS 64502, but without an explicit permit .* statement afterward, every other route is also silently dropped - the opposite of the intended behavior. Adding ip as-path access-list 10 permit .* allows all remaining AS paths through, since .* is a regex wildcard meaning "match any sequence of characters."

Why the distractors are wrong:

• A is wrong because AS-path access lists are defined globally in config mode and then referenced in a route-map - they don't need to be defined inside one.
• C is wrong on two counts: changing $ to a trailing _ would alter the regex match (no longer anchoring to the path end), and renumbering the list from 10 to 1 would break the existing reference without fixing the real problem.
• D is wrong because A64502$ is not valid regex syntax - A has no special meaning as a boundary character in IOS AS-path regex, making the filter malformed.

Memory tip: Think of AS-path ACLs exactly like IP ACLs - always end with an explicit permit or your traffic disappears. The phrase "deny specific, permit dot-star" is your reminder that .* is the BGP equivalent of permit any.

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