bird route selection problem

[Daniel Rimal]

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!