Which of the following description about the reliable routing update of BGP is correct?

Question

Options

• ABGP works on top of UDP, and the transport layer protocol is 179
• BBGP does not need a periodically advertised routing information
• CBGP sends complete routing table information for each routing update
• DBGP uses multicast update

• A
  16% (6)
• B
  73% (27)
• C
  5% (2)
• D
  5% (2)

Explanation

B is correct because BGP (Border Gateway Protocol) only sends incremental updates - after the initial full table exchange, it only advertises changes (new routes, withdrawn routes). There is no periodic re-advertisement of the entire routing table, which makes it highly efficient for large-scale internet routing.

Why the distractors are wrong:

• A - BGP runs over TCP (not UDP), port 179. TCP provides the reliable, connection-oriented transport BGP needs; the port number is right but the protocol is wrong.
• C - BGP only sends the full routing table on initial session establishment. After that, only incremental (delta) updates are sent - the opposite of what C claims.
• D - BGP uses unicast between specifically configured neighbor peers (established via TCP sessions), not multicast. BGP neighbors must be explicitly defined.

Memory tip: Think of BGP as a "change-only" protocol once it's warmed up - like a news feed that only pushes new stories, not the entire newspaper every hour. The acronym TCP-179 is worth memorizing as a single unit: "BGP = TCP + port 179."

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