7/17/2019 How to Configure BGP as Path Prepending

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How to configure BGP AS Path Prepending

The fourth BGP attribute is called AS Path:

• BGP prefers the shortest AS path to get to a destination. Less is more!

• We can manipulate this by using AS path prepending.

Let me sho you an eample:

"n my eample AS # ants to ma$e sure traffic enters the autonomous system through router%acob. We can add our on autonomous system number multiple times so the as path becomes

longer. Since BGP prefers a shorter AS path e can influence our routing. This is called AS path

prepending. Let&s see hat this loo$s li$e on 'isco routers( this is the topology that " ill use:

7/17/2019 How to Configure BGP as Path Prepending

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Abo)e e ha)e * routers. +outer %im and %ohn are both in AS # ad)ertising the same netor$,#.#.#.-/01 to router %ac$. We can use AS Path prepending to ma$e router %ac$ prefer a certain

 path.