The router received two BGP routes containing the following attributes. Network: M 192.168.1.0, N 192.168.1.0 NextHop: 10.1.1.1, 10.1.1.2 MED: 30, 20 LocPrf: (empty), (empty) PrefVal: 0, 0 Path/Ogn…

Question

Options

• AThe optimal route is route N because its AS-Path is shorter than route M.
• BThe optimal route is route N because its MED is smaller than route M.
• CThe optimal route is route M because its AS-Path is shorter than route N.
• DThe optimal route is route M because its MED is larger than route N.

• A
  7% (3)
• B
  5% (2)
• C
  76% (31)
• D
  12% (5)

Explanation

Route M's AS-Path (100 i) indicates the route was originated within the local AS (AS 100), giving it an effective AS-Path length of 0. Route N's AS-Path (200 i) shows the route traversed AS 200 before arrival, giving it a length of 1. BGP selection evaluates AS-Path length before MED, so since M has a shorter path, it wins - MED is never reached in this comparison.

Why the distractors are wrong:

• A has the AS-Path comparison backwards - N has the longer path (length 1), not the shorter one.
• B is wrong because although N's MED of 20 is lower (which would normally favor N), MED is only evaluated after AS-Path. Since AS-Path already distinguishes the routes and picks M, MED is irrelevant here.
• D is doubly wrong: M's MED is larger (30 > 20), not a reason to prefer it, and MED still isn't reached in the selection process anyway.

Memory tip: Use the BGP attribute priority order - Weight → Local Pref → Locally originated → AS-Path → Origin → MED. Think "WL LA OM" - AS-Path always beats MED, so if AS-Path lengths differ, stop there and don't be tempted by MED values.

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