The output of a certain router ip as-path-filter is shown in the figure. [Huawei]display ip as-path-filter As path filter number: 1 permit ^12345_(0-9)*$ [Huawei] So which of the following…

Question

Options

• AThis configuration matches traffic originating from any AS and reaching the router. The router belongs to AS 12345.
• BThis configuration matches traffic originating from AS 12345, passing through any AS and any other AS, and finally reaching the router.
• CThis configuration matches traffic originating from AS 12345 and passing through any AS to reach the router.
• DThis configuration matches traffic originating from any AS and passing through AS 12345 to reach the router.

• A
  7% (2)
• B
  11% (3)
• C
  78% (21)
• D
  4% (1)

Explanation

Option C is correct because the regex ^12345_(0-9)*$ anchors AS 12345 at the very start of the AS path (^), identifying it as the originating AS, while _(0-9)* matches any number of intermediate transit ASes (including zero), and $ marks the end of the path at the local router. Option A is wrong on two counts: ^12345 specifies the originating AS in the path, not the router's own AS number, and the route does not originate from "any AS." Option B is wrong because the phrasing implies at least one required transit hop, but the * quantifier (zero or more) means the route can arrive directly from AS 12345 with no intermediate ASes at all. Option D has the role of AS 12345 backwards: ^12345 places it at the origin of the path, not in the middle as a transit AS; matching a transit AS would require a pattern like _12345_ somewhere in the middle, not anchored at ^.

Memory tip: Think of ^ as "born here" - ^12345 means the route was born (originated) in AS 12345. The * on the transit portion means "zero or more hops in between," so the route may or may not pass through other ASes before arriving.

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