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

Question

Options

• AOrigin
• BAS_PATH
• CLocal-Preference
• DMED

• A
  3% (1)
• B
  6% (2)
• C
  84% (27)
• D
  6% (2)

Explanation

Local-Preference (C) is a well-known discretionary BGP attribute that is only valid within an Autonomous System (AS). RFC 4271 explicitly states it must only be exchanged between iBGP peers - sending it to an eBGP neighbor is a protocol violation and the attribute must be stripped before any external update.

Origin (A) and AS_PATH (B) are both well-known mandatory attributes, meaning they are required in every BGP Update message regardless of whether the session is iBGP or eBGP - leaving them out would make the Update invalid.

MED (D), while optional and non-transitive, is specifically designed to be sent to eBGP peers to influence how neighboring ASes enter your network, so it is permitted in external Update messages.

Memory tip: Think "Local means local" - Local-Preference stays local to the AS and never crosses an AS boundary. If you see an attribute with "local" in the name, it's a strong hint it shouldn't leave the AS.

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