Click the exhibit. After router A receives the BGP update for the 10.3.3.0/24 prefix, which routers will the route be propagated to?

Question

Options

• AAll routers with which it has a BGP session.
• BAll routers with which it has a BGP session, except the router it received the update from, which is router C.
• CAll routers with which it has a BGP session, except the router it received the update from, which is router D.
• DAll routers with which it has a BGP session, except the router it received the update from, which is router E.
• EOnly eBGP neighbors.

• A
  3% (1)
• C
  6% (2)
• D
  10% (3)
• E
  81% (25)

Explanation

Option E is correct because of the iBGP split-horizon rule: a route learned from an iBGP peer cannot be re-advertised to other iBGP peers. Since the exhibit shows Router A received the 10.3.3.0/24 update from an iBGP neighbor (within the same AS), it may only propagate that route to its eBGP neighbors - those in different autonomous systems.

Options B, C, and D are wrong because they describe eBGP propagation behavior: when a route is received from an eBGP peer, it is forwarded to all other BGP neighbors (both iBGP and eBGP) except the source. Option A is similarly incorrect because it ignores the split-horizon restriction entirely. The specific routers named in B, C, and D (router C, D, E) are distractors drawn from the exhibit topology.

Memory tip: Think of iBGP as a "dead end" for gossip - if your iBGP buddy tells you something, you can't repeat it to your other iBGP buddies, only to outsiders (eBGP peers). This rule exists to prevent routing loops inside an AS, which is why full-mesh or route reflectors are needed in iBGP designs.

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