Re: BGP Path Selection - eBGP vs iBGP

Thanks heaps!

This worked, so all routes be ebgp or ibgp get assigned a local pref
of 100 by default, only the ibgp routes local pref shows up in the
show ip bgp summ it seems!

The more details show ip bgp 10.0.0.0/16 showed both had a local pref
of 100.

To confirm the test I set the ibgp routes local pref to 200 and all
the routes where then prefered over the iBGP path :-)

Problem solved thanks for the input guys this was a great help!

Regards

Garth

On 16/06/2009, at 8:47 PM, "Aundra Browning" <aundra.browning_at_earthlink.net
> wrote:

> 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 Feb 16 2010 - 22:02:20 ART