An Alcatel-Lucent 7750 SR receives two updates for the same route with local preferences 200 and 300, respectively. What local preference is sent to eBGP peers?

The correct answer is D. None. Local preference (LOCAL_PREF) is an iBGP-only attribute - it is never advertised to external BGP (eBGP) peers, regardless of its value. The router uses the higher value (300) to make its own internal path selection, but strips the LOCAL_PREF attribute entirely before sending…

BGP Attributes and Path Selection

Question

An Alcatel-Lucent 7750 SR receives two updates for the same route with local preferences 200 and 300, respectively. What local preference is sent to eBGP peers?

Options

A100
B200
C300
DNone

How the community answered

(32 responses)

B
3% (1)
C
3% (1)
D
94% (30)

Explanation

Local preference (LOCAL_PREF) is an iBGP-only attribute - it is never advertised to external BGP (eBGP) peers, regardless of its value. The router uses the higher value (300) to make its own internal path selection, but strips the LOCAL_PREF attribute entirely before sending any update to an eBGP neighbor.

Why the distractors fail:

A (100): This is the default LOCAL_PREF value, which is a common distractor, but defaults are irrelevant here since the attribute isn't sent to eBGP at all.
B (200): The losing preference - it wouldn't be chosen even for internal use, and still wouldn't be forwarded externally.
C (300): The winning preference used internally, but winning the selection doesn't change the rule: LOCAL_PREF never crosses AS boundaries.

Memory tip: The word "local" is your clue - LOCAL_PREF is local to your AS. Anything that stays local never leaves to eBGP peers. If an attribute says "local," think "iBGP only."

Topics

#Local Preference#eBGP Attributes#iBGP vs eBGP#BGP Path Selection

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