400-007: Cisco Certified Design ExpertDemo

By Cisco · Question Mode

QuestionQ79

Security Design

Question Image

Refer to the exhibit. An engineer has been asked to redesign traffic flow toward AS 111 originating from AS 500. Traffic destined for the AS 111 network 91.7.0.0/16 must enter through AS 100, while traffic destined for every other network in AS 111 must continue using the existing path. Which BGP attributes are best suited to control this inbound traffic from BGP AS 500 into the 91.7.0.0/16 network?

  • A Use local preference on R1 for the networks that AS 500 advertises to AS 111
  • B Prepend AS path for the 91.7.0.0/16 network and set it for neighbor in AS 200
  • C Use extended community for the 91.7.0.0/16 network, not advertising it to the bi-lateral peer
  • D Set higher MED for neighbor in AS 100 to influence incoming traffic for the 91.7.0.0/16 network
Explanation

AS-path prepending applied to the 91.7.0.0/16 advertisement sent toward AS 200 makes that path appear longer to AS 500. AS 500 therefore prefers the shorter path through AS 100 for that prefix, while advertisements for all other prefixes remain unchanged and continue to use their existing path. Local preference is an attribute used within the receiving AS, and a higher MED is less preferred and is not the appropriate general mechanism for influencing this external AS's path choice.

Learn more

Community Discussion

No comments yet. Be the first to start the discussion!