Good evening, > I don't understand here why a route received directly from eBGP peer (casa190) > has one more ASN (15685) in as_path than route received from iBGP peer r2, > which is (i assume) connected to the similar set of eBGP peers. To what eBGP > peers are r1 and r2 connected?
It is correct, because R1 and R2 is connected do completely different provider, which has shorter aspath. > > It is also strange that i don't see here the route from the the other bird > (r4 if this is from r3), but that might be OK if there are different local > preferences. > > It would be useful to send that output from both R3 and R4 (should be slightly > different), together with their configuration. routes was the same, best via R2 and next routes via 190 and 189 > Generally, it is not a good idea to change LOCAL_PREF attribute on iBGP link. > That could easily lead to some kind of strange behavior. This attribute is > assumed be set only on eBGP links (to describe the preference of that > external link for the AS). Right, it was my fault. I assumed algoritmus will make decision on third step: # Prefer route with the highest Local Preference attribute. # Prefer route with the shortest AS path. # Prefer IGP origin over EGP and EGP over incomplete. However change local pref on ibgp links has no sense, at least in my case. > And what was the setting of local_pref on eBGP links? If you only set > for example 500 on iBGP and keep default (100) on eBGP, that would lead > to an unstable configuration. It was my case, i have larger local_pref on iBGP then eBGP links. Thank you very much for your help and explanation!