H12-821_V1.0 · Question #874
The BGP_AS_PATH attribute is an optional transition attribute.
The correct answer is B. FALSE. B is correct because AS_PATH is a well-known mandatory BGP attribute - not optional transitive. Every BGP implementation must recognize it, every UPDATE message must include it (when applicable), and it is used to prevent routing loops by tracking the sequence of Autonomous…
Question
Options
- ATRUE
- BFALSE
How the community answered
(49 responses)- A20% (10)
- B80% (39)
Explanation
B is correct because AS_PATH is a well-known mandatory BGP attribute - not optional transitive. Every BGP implementation must recognize it, every UPDATE message must include it (when applicable), and it is used to prevent routing loops by tracking the sequence of Autonomous Systems a route has traversed.
Why A is wrong: Confusing "transitive" (an attribute passed along to non-originating peers) with the attribute's actual classification is a common trap. AS_PATH is indeed passed between peers, but that behavior stems from it being well-known mandatory, not optional transitive. Optional transitive attributes (like COMMUNITY) are optional - BGP speakers may not recognize them but must forward them anyway.
Memory tip: Think of the BGP "Big Three" mandatory attributes - Origin, AS_PATH, Next-Hop - every UPDATE must carry them. If you can't remove it or ignore it, it can't be "optional." The word mandatory directly cancels optional.
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