Which of the following descriptions of routing interactions between BGP peers are correct? (Multiple choice)

Question

Options

• AWhen routing is updated, the BGP device only sends updated BGP routes.
• BThe BGP device will publish the BGP routes obtained from iBGP peers to all its peers.
• CThe route sent by peers are not imported by the BGP device.
• DWhen there are multiple valid routes to the same destination address, the BGP device only advertises the optimal route to the peer.

• A
  79% (33)
• B
  14% (6)
• C
  7% (3)

Explanation

A is correct because BGP uses incremental updates - once a full routing table is exchanged during session establishment, only changed routes (additions, withdrawals, modifications) are sent in subsequent UPDATE messages, not the entire table.

D is correct because BGP's best-path selection algorithm picks a single optimal route per destination, and only that best route is advertised to peers - even if multiple valid paths exist in the local BGP table.

B is wrong due to the iBGP split-horizon rule: routes learned from an iBGP peer cannot be re-advertised to other iBGP peers (only to eBGP peers). Saying "all peers" violates this fundamental loop-prevention rule.

C is wrong because BGP devices absolutely do import routes received from peers into their BGP RIB (Routing Information Base) for processing and best-path selection - that's the entire purpose of receiving UPDATE messages.

Memory tip: Think of BGP as "efficient and selective" - it sends only what changed (incremental updates, A) and only the best (optimal route advertisement, D). For B, remember the iBGP rule as "don't gossip inside the family to outsiders… or to other family members."

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