Increasing the Length of the AS_Path Using AS_Path Prepend

ImageLesson 4: The AS Path Attribute

Step 4 of the BGP best-path algorithm examines the length of the AS_Path PA. The length of the AS_Path might appear to be obvious: Just add the number of ASNs listed in the AS_Path. However, some BGP features outside the scope of this book actually impact the AS_Path length calculation as well. However, for the purposes of this book, AS_Path length is simply the number of ASNs listed in the AS_Path.

The AS_Path prepend tool gives engineers a means to increase the length of an AS_Path by adding ASNs to the AS_Path, while not impacting the loop-prevention role ...

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