Which expression, when used with the as-path-set command, matches the AS path attribute of the route?

Question

Options

• Aneighbor-is
• Bdfa-regtex
• Cios-regex
• DLength

• B
  4% (1)
• C
  88% (22)
• D
  8% (2)

Explanation

On Cisco IOS XR, the as-path-set command is used within RPL (Routing Policy Language) to define sets of AS path patterns for matching BGP routes. The ios-regex keyword specifies that the pattern uses IOS-style regular expressions (the same regex syntax familiar from Cisco IOS ip as-path access-list commands). For example: as-path-set MY_SET / ios-regex '^65001' / end-set. Option A ('neighbor-is') is not a valid keyword in this context. Option B ('dfa-regex') is a different regex engine available in IOS XR RPL (deterministic finite automaton regex, which is faster for complex patterns) - but 'dfa-regtex' as spelled here is not a valid keyword. Option D ('Length') is an AS path attribute length match condition, not a pattern matching expression. The ios-regex keyword is the standard way to apply familiar IOS regex syntax within an as-path-set definition.

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