Comprehensive and Detailed Step-by-Step Explanation:
1. Understanding the AS-Path Filter:
* The as-path-filter command is used in BGP to filter routes based on the AS_PATH attribute.
* In this configuration:
* The filter si is defined with the regular expression _65500$.
* The _65500$ expression specifies that the AS_PATH must end with 65500, meaning that the route's last hop must have passed through AS 65500.
2. Option Analysis:
Option A: It accepts only the routes whose AS_Path contains AS 65500.
* Incorrect.
* The _65500$ filter specifically matches routes where AS 65500 is the last AS in the AS_PATH. A route may contain AS 65500 somewhere in the middle of the AS_PATH but will not match this filter unless it is the last AS.
Option B: It accepts only the routes originated from AS 65500.
* Incorrect.
* Routes that originate from AS 65500 have an AS_PATH that starts with 65500. However, the filter
_65500$ only matches routes where AS 65500 is the last AS, not the first AS.
Option C: It accepts only the routes that last pass through AS 65500.
* Correct.
* The _65500$ filter ensures that the AS_PATH ends with 65500. This means that the route must have last passed through AS 65500 before being received by the local BGP router.
Option D: It accepts only the routes forwarded by AS 65500.
* Incorrect.
* While AS 65500 may forward the route, this is not what the filter _65500$ specifically checks for. It only ensures that AS 65500 is the last AS in the AS_PATH.
3. Summary:
* The as-path-filter with _65500$ accepts only the routes where AS 65500 is the last AS in the AS_PATH.