Router R2 receives a route to 192.168.4.0/29 from router R4 and sets the local preference to 110. Router R1 receives the route to 192.168.4.0/29 from router R3 and sets the local preference to 80…

Question

Options

• AR5-R2-R4-R8
• BR5-R1-R3-R4-R8
• CR5-R1-R2-R4-R8
• DR5-R1-R3-R7-R8

• A
  5% (3)
• B
  17% (11)
• C
  71% (47)
• D
  8% (5)

Explanation

Option C is correct because BGP local preference determines the preferred exit point within an AS, and higher values win - R2's local preference of 110 beats R1's 80, so all routers in AS 65540 (including R5) prefer to exit via R2. However, R5 has no direct physical link to R2, so it must first traverse its only physical neighbor, R1, before reaching R2 and then the external path through R4 to R8.

Why the distractors fail:

• A (R5-R2-R4-R8): Ignores the physical topology - R5 has no direct link to R2, making this path impossible.
• B (R5-R1-R3-R4-R8): Uses the lower local preference path (80 via R3); BGP eliminates this before even considering AS path length.
• D (R5-R1-R3-R7-R8): Also uses the losing local preference path and follows a different external route entirely.

Memory tip: Think "Higher = Happier exit" for BGP local preference - the AS always prefers the highest value as its exit door, but the router still has to walk through whatever physical hallways exist to reach that door.

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