Which of the following characteristics meet the following conditions. A BGP router may not support these attributes, but it will still receive such attributes and pass them on to other peers…

Question

Options

• ACommunity
• BAggregator
• CMulti_Exit_Disc
• DLocal_Pref

• A
  81% (26)
• B
  3% (1)
• C
  6% (2)
• D
  9% (3)

Explanation

Community is an optional transitive BGP attribute, meaning a router that doesn't recognize it is still required to accept it and forward it to other peers unchanged (setting the "partial" flag). This matches the condition exactly: unknown but passed along.

B (Aggregator) is actually also optional transitive by RFC definition - this question likely contains an error, as Aggregator meets the same condition as Community. It's worth knowing both for the exam.

C (Multi_Exit_Disc / MED) is optional non-transitive: if a router doesn't recognize it, it must drop it rather than forward it, so it fails the "pass it on" condition.

D (Local_Pref) is a well-known discretionary attribute - "well-known" means every BGP router must recognize and support it, so the premise "may not support" doesn't apply.

Memory tip: Think of transitive = "tourist passing through" - the router doesn't speak the language (unrecognized) but still forwards the message. Non-transitive = "dead end" - message is dropped. Well-known = universal language - everyone speaks it, so "not supporting" is impossible.

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