Which of the following regarding "well-known discretionary" BGP attributes is TRUE?

Question

Options

• AThey must be recognized by all peers and included in all BGP updates.
• BThey are discarded if not recognized by the recipient.
• CThey must be recognized by all peers and optionally included in BGP updates.
• DThe receiving router sends a notification if a well-known discretionary attribute is not present in an update.

• A
  3% (1)
• B
  6% (2)
• C
  91% (29)

Explanation

Well-known discretionary attributes split cleanly along two axes: recognition (all peers must know them) and inclusion (not required in every update). "Well-known" mandates universal recognition; "discretionary" gives senders the choice of whether to include the attribute - making C the accurate description.

Why the distractors fail:

• A describes well-known mandatory attributes (e.g., ORIGIN, AS_PATH, NEXT_HOP), which must appear in every UPDATE message - "mandatory" is the key word that distinguishes them.
• B describes optional non-transitive attributes; those get silently discarded when unrecognized. Well-known attributes are, by definition, recognized by everyone, so "not recognized" can't apply.
• D has it backwards: a NOTIFICATION error fires when a well-known mandatory attribute is missing, not a discretionary one - because discretionary absence is perfectly legal.

Memory tip: Break the phrase apart - well-known = "everyone must speak this language," discretionary = "but you don't have to say it every time." LOCAL_PREF is a classic example: every iBGP router understands it, yet a speaker may choose to omit it.

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