300-410 ENARSI: Implementing Cisco Enterprise Advanced Routing and ServicesDemo

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QuestionQ44

Infrastructure Services

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Refer to the exhibit. Customer B has decided not to receive any routes from R1 that originated outside the AS 100. Which AS path access list must the engineer choose to meet this requirement?

  • A ip as-path access-list 1 permit ^10[0-9]*$
  • B ip as-path access-list 1 permit ^100$
  • C ip as-path access-list 1 permit _100$
  • D ip as-path access-list 1 permit 100
Explanation

AS path access lists use regex syntax: '^' means start of path and '$' means end of path. '^100$' permits only routes where AS 100 is the entire AS path with no other ASes before or after it. This ensures Customer B receives only routes that originated directly from AS 100 (R1's neighbor) with no paths through other autonomous systems, meeting the requirement to block routes from outside AS 100.

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