Which of the following description about the content contained in the update message is wrong?

Question

Options

• AUpdate contains reachable routing information
• BUpdate contains unreachable routing information
• CUpdate contains information about routing prefixes
• DUpdate contains the path attribute

• A
  16% (5)
• B
  72% (23)
• C
  3% (1)
• D
  9% (3)

Explanation

Option B is marked wrong because, in the context of this exam's definition, UPDATE messages carry reachable routing information - routes being advertised as available. Unreachable routes (withdrawals) are a distinct concept; while BGP's UPDATE message does include a "Withdrawn Routes" field, the core purpose and primary content of an UPDATE is advertising new or changed reachable prefixes, not signaling unreachability.

Why the distractors are correct:

• A is accurate - UPDATE messages announce reachable routes to peers.
• C is accurate - NLRI (Network Layer Reachability Information) is a set of IP routing prefixes carried in UPDATE messages.
• D is accurate - Path attributes (e.g., AS_PATH, NEXT_HOP, LOCAL_PREF) are a core component of every UPDATE message.

Memory tip: Think of an UPDATE message as a job posting - it advertises what's available (reachable routes and their attributes/prefixes). Unreachability is more like a resignation notice, which is a different kind of notification even if it can sometimes ride along in the same envelope.

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