RE: BGP Path Selection - eBGP vs iBGP

That's not always true - otherwise why have attributes in BGP? If eBGP was
always selected over iBGP you could never manipulate routing within your own
AS (ok...well not easily). AD only plays a role further down in the BGP best
path selection process and inside the IP RIB not necessarily the BGP RIB.

Can we see the output of "show ip bgp 10.0.0.0" on R5? The command output
from "sho ip bgp" can be a little confusing as it won't show a local pref
assigned to eBGP prefixes, but if you look at the actual prefix in the BGP
RIB you will see it still gets assigned (default of 100 on both prefixes).
If this is the case, then you will in fact choose the eBGP prefix over iBGP
since all criteria will be tied until you get to this decision point.......

HTH....

A. Browning
CCIE #21901 (R&S)

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
Florian Frotzler
Sent: Tuesday, February 16, 2010 3:34 AM
To: Cisco certification
Subject: Re: BGP Path Selection - eBGP vs iBGP

I don't know what you hacked with 28.8k, but certainly not IP ;-) eBGP
and iBGP are considered different protocols and are therefore selected
by administrative distance.

Cheers,
Florian

2010/2/16 Garth Bryden <hacked.the.planet.on.28.8k.dialup_at_gmail.com>:
> Hello Group!
>
> I have what is probably a fairly simple question, but I am slightly
confused
> with my BGP Labs.
>
> I have a simple topology.
>
> R1 and R3 are in AS 1 and iBGP Peers
>
> R4 and R5 are in AS 2 and iBGP Peers
>
> R1 and R4 are eBGP Peers
>
> R3 and R5 are eBGP Peers
>
> I have the network 10.0.0.0/16 being advertised by R3
>
> On R5 I recieve the NLRI with two paths. One is eBGP via R3 the other iBGP
> via R4... R4 sends the iBGP prefix with a Local Preference of 100 and of
> course since it's external R3 doesn't send a Local Preference attribute...
> Now since the second method of best path selection is "Highest Local
> Preference" why do my routers choose eBGP over iBGP?
>
> Here is the BGP RIB.....
>
> Network Next Hop Metric LocPrf Weight Path
> * i10.0.0.0/16 155.1.45.4 0 100 0 2 i
> *> 155.1.0.3 0 2 i
>
>
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Received on Tue Jun 16 2009 - 08:47:32 ART