Which of the following regarding the withdrawal of routes from one BGP speaker to another is TRUE?

Question

Options

• AAn update message is used. Only a single prefix can be withdrawn at a time.
• BAn update message is used. Multiple prefixes can be withdrawn at a time.
• CA withdraw message is used. Only a single prefix can be withdrawn at a time.
• DA withdraw message is used. Multiple prefixes can be withdrawn at a time.

• A
  5% (1)
• B
  91% (20)
• D
  5% (1)

Explanation

BGP uses the UPDATE message for all route advertisements and withdrawals - there is no separate "withdraw message" in the BGP specification (RFC 4271), which immediately eliminates options C and D. Within a single UPDATE message, the Withdrawn Routes field accepts a list of prefixes, meaning multiple routes can be withdrawn in one message, making option A wrong for claiming only one prefix at a time is possible. Option B is correct because it accurately reflects both facts: UPDATE is the message type used, and its structure allows batch withdrawals of multiple prefixes in a single transmission. This design is efficient - a BGP speaker can signal the loss of many routes without sending a separate message per prefix.

Memory tip: BGP has only 4 message types - OPEN, UPDATE, NOTIFICATION, and KEEPALIVE. If an answer mentions a "withdraw message," it's automatically wrong. And since UPDATE carries a list of withdrawn routes, think "one UPDATE, many withdrawals."

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