Which of the following attributes may not be included in the Update message of a BGP route? (Multiple choice)

Question

Options

• AAS_Path
• BLocal Preference
• COrigin
• DMCD

• A
  14% (10)
• B
  79% (56)
• C
  7% (5)

Explanation

B (Local Preference) is excluded from eBGP Update messages because it is a well-known discretionary attribute used only within an autonomous system (AS) via iBGP - routers never advertise it to external BGP peers, so it "may not be included" in a BGP Update depending on the peering type. D (MCD) is simply not a real BGP attribute - the actual attribute is MED (Multi-Exit Discriminator); "MCD" doesn't exist in the BGP specification and would never appear in any valid Update message.

Why A is wrong: AS_PATH is a well-known mandatory attribute and must be present in every BGP Update message - no exceptions.

Why C is wrong: Origin is also well-known mandatory, always required in Update messages to indicate how the route was learned (IGP, EGP, or Incomplete).

Memory tip: Use the acronym "ONH = Mandatory 3" - Origin, Next-Hop, and AS_Path must always appear. Local Preference stays local (iBGP only), and when you see an unfamiliar attribute name on an exam, treat it as a trap - BGP has a fixed, well-documented attribute set, so a misspelled or invented name (like MCD) is almost certainly a distractor.

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