Router R1 is advertising prefix 192.168.1.0/27 with community "no-export. Which routers will receive an update for that prefix?

Question

Options

• ARouter R2 only.
• BRouters R2 and R3 only.
• CRouters R2, R3 and R4 only.
• DRouters R2, R3, R4and R5.

• B
  12% (2)
• C
  6% (1)
• D
  82% (14)

Explanation

All routers R2 through R5 receive the update because the BGP no-export community only prevents a prefix from being advertised to eBGP peers in other autonomous systems - it does not restrict advertisement to iBGP peers within the same AS. Since R2, R3, R4, and R5 are all iBGP peers inside the same AS as R1, they all receive the update normally.

Options A, B, and C are wrong because they imply no-export progressively limits how far a prefix propagates within the AS - as if it somehow "fades out" as it travels to more distant routers. That is not how it works; the community has no effect on intra-AS flooding at all.

Memory tip: Think of no-export as a "border wall" - the prefix freely roams inside the AS but is blocked the moment it tries to cross the AS boundary to an eBGP neighbor. If the exam topology shows routers entirely within one AS, no-export changes nothing for those routers.

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