Which of the following description about MED is correct? (Multiple choice)

Question

Options

• AThe default value of MED is 0
• BThe default value of MED is 100
• CMED can only be transferred within this AS
• DMED is an optional non-transitional attribute

• A
  71% (29)
• B
  5% (2)
• C
  7% (3)
• D
  17% (7)

Explanation

MED (Multi-Exit Discriminator) defaults to 0 in BGP - when a route is advertised without a MED value, receiving routers treat it as 0, which is also the lowest possible value and thus the most preferred under standard MED comparison rules.

Why the distractors are wrong:

• B (100): 100 is the default value of LOCAL_PREFERENCE, not MED - a classic mix-up on BGP exams.
• C: MED does the opposite - it is sent to neighboring (external) ASes to influence which entry point they use. It's LOCAL_PREFERENCE that stays confined within a single AS.
• D: The correct BGP term is "optional non-transitive," not "non-transitional." Non-transitive means the attribute is not forwarded beyond the directly receiving AS, but "non-transitional" is not a valid BGP attribute classification.

Memory tip: Pair the two defaults: MED = 0, LOCAL_PREF = 100. If you remember that LOCAL_PREF defaults to 100, then MED must be the one that starts at 0. Also remember their scopes in reverse: LOCAL_PREF stays local (inside your AS), while MED goes out to your neighbor.

No community discussion yet for this question.