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CCNP Routing and Switching ROUTE 300-101: Official Cert Guide by Kevin Wallace

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BGP ASNs and the AS_SEQ Path Attribute

BGP uses BGP path attributes for several purposes. PAs define information about a path, or route, through a network. Some BGP PAs describe information that can be useful in choosing the best BGP route, using the best-path algorithm. BGP also uses some PAs for purposes other than choosing the best path.

By default, if no BGP PAs have been explicitly set, BGP routers use the BGP AS_PATH (autonomous system path) PA when choosing the best route among many competing routes. The AS_PATH PA itself has many subcomponents, only some of which matter to the depth of the CCNP coverage of the topic. However, the most obvious component of AS_PATH, the AS_SEQ (AS_SEQUENCE), can be easily explained with an example when ...

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