Why does eBGP have an AD of 20

Just wondering. This means that a route learned by an IGP will not choosen over eBGP.

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FrankGuthrie wrote: »

Just wondering. This means that a route learned by an IGP will not choosen over eBGP.

Frank,

Someone may be able to chime in on the paper text 100% exact reason it was designed that way... however just to keep it simple keep in mind that EBGP is for external routes; i.e. the "internet" and are managed by the individuals who own / lease those ip addresses and BGP interacts with there routers exchanging routes - when they change their routes / networks i.e. you want that information to be chosen over what you last had as being right.

Keep in mind once it crosses your enterprise edge to another BGP peer it becomes IBGP which is not preferred over IGP.

One way to think about it is them being serving different functions.... IGP handles your private network and BGP handles public networks.

MickQ

iBGP is also slow to converge. Your IGPs will do a better job in the vast majority of cases.

JavonR

FrankGuthrie wrote: »

Just wondering. This means that a route learned by an IGP will not choosen over eBGP.

External BGP routes are treated like gold because you have a BGP peer telling you directly that the route is outside of your autonomous system. If other IGP neighbors were chosen first for the same route you would then be routing the traffic through your AS, and it would have to end up leaving your network anyway (inefficient and could cause looping). That's how the logic was explained to me.