Refer to the exhibit. After troubleshooting BGP traffic steering issue, which action did the network operator take to achieve the correct effect of this configuration?

The correct answer is A. Routes that have passed through AS 65517 have the local preference set to 150.. The configuration uses a route-map with an 'ip as-path access-list' matching AS 65517 anywhere in the AS_PATH attribute, then sets local-preference to 150. Because the AS_PATH match uses a regex that detects any route whose path includes AS 65517 (not just routes originated by it

Routing Policy and Manipulation

Question

Exhibit

Options

ARoutes that have passed through AS 65517 have the local preference set to 150.
BRoutes that have originated through AS 65517 have the local preference set to 150.
CRoutes directly attached to AS 65517 have the local preference set to 150.
DRoutes that have passed through AS 65517 have the local preference set to 150 and the traffic is

How the community answered

(48 responses)

A
73% (35)
B
15% (7)
C
4% (2)
D
8% (4)

Explanation

The configuration uses a route-map with an 'ip as-path access-list' matching AS 65517 anywhere in the AS_PATH attribute, then sets local-preference to 150. Because the AS_PATH match uses a regex that detects any route whose path includes AS 65517 (not just routes originated by it), this applies to all routes that have transited AS 65517 - not just originated ones. Local preference is used within an AS to influence outbound path selection; a higher value (150 vs. the default 100) makes these routes preferred, steering traffic toward paths that passed through AS 65517.

Topics

#BGP Local Preference#BGP AS_PATH#BGP Traffic Engineering#BGP Policy

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