An Alcatel-Lucent 7750 SR is configured with a local preference of 250. If it receives a BGP update with a local preference of 500, what local preference is sent to its eBGP peers?

The correct answer is D. None. Local preference is an iBGP-only attribute - it is never advertised to eBGP peers, making D (None) correct regardless of whether the value is 100, 250, or 500. RFC 4271 explicitly states that the LOCAL_PREF attribute must be stripped before updates are sent to external…

BGP Attributes and Path Selection

Question

An Alcatel-Lucent 7750 SR is configured with a local preference of 250. If it receives a BGP update with a local preference of 500, what local preference is sent to its eBGP peers?

Options

A100
B250
C500
DNone

How the community answered

(58 responses)

A
2% (1)
B
2% (1)
C
7% (4)
D
90% (52)

Explanation

Local preference is an iBGP-only attribute - it is never advertised to eBGP peers, making D (None) correct regardless of whether the value is 100, 250, or 500. RFC 4271 explicitly states that the LOCAL_PREF attribute must be stripped before updates are sent to external neighbors.

Why the distractors fail:

A (100) - the default BGP local preference in many implementations, but the default is irrelevant; the attribute simply doesn't cross AS boundaries
B (250) - the locally configured preference on this router, but local means local: it stays within the AS for iBGP path selection only
C (500) - the received value from the incoming update, which influences internal route selection but is never forwarded outbound to eBGP peers

Memory tip: The word "local" is the clue - local preference is local to your AS. Any time a question asks what eBGP peers receive regarding local preference, the answer is always nothing.

Topics

#Local Preference#eBGP vs iBGP#BGP Attributes#Attribute Scope

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