BGP Routing Policies - Route Filtering and Route Summarization - Filtering BGP Updates by Matching the AS_PATH PA

3 important questions on BGP Routing Policies - Route Filtering and Route Summarization - Filtering BGP Updates by Matching the AS_PATH PA

What are the command to filter AS_PATH PA?

-ip as-path access-list number {permit | deny} regex
-neighbor neighbor-id filter-list as-path-filter-number {in|out}

What does the regex character .* mean and when is it used?

All AS_PATH
Useful as a final match to change the default from deny to permit

What does the regex character ^$ mean?

Null (empty)
Use for NLRIs originated in same AS

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