BGP decision chain


I did some playing with BGP and OSPF, and came across something i was expection to behaves differentlly.

I was under the impresion that the Administrative Distance is the first that is looked when you have 2 "identical routes", but not in case of iBGP and eBGP.

I did the following: RA conected to R1, R2 and R3.


R2-RA is iBGP

R3-RA is eBGP

R1,R2,R3 inject the same prefix A


I got what i expected the eBGP os prefered, the OSPF then iBGP.

Then i played with LocalPref and modify the LP on the iBGP from R2 to 130.

For me nothing should have changed, but i did :( The OSPF toute is the best one, then the iBGP and at the end the eBGP.


The conclusion i got is that: the BGP decision making is done first on the sum of iB and eB prefixes, then the AD.


Is my conclusion a good one?






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