From: Howard C. Berkowitz (hcb@xxxxxxxxxxxx)
Date: Mon Jun 17 2002 - 18:05:34 GMT-3
(sending to the list for general information)
My understanding was that R1 and R2 are in different AS. If they are
in the same AS, NO-ADVERTISE would be the appropriate well-known
community.
I'm really starting to wonder where the original question came from,
as it certainly doesn't reflect the way one should use BGP in the
real world...whatever that may have to do with the CCIE lab.
At 3:22 PM -0400 6/17/02, Lance wrote:
>No-export does not prevent R2 from installing the route. It only prevents
>R2 from exporting the route to another AS.
>At least that is how I understand it, Ive been wrong before.
>
>----- Original Message -----
>From: "Howard C. Berkowitz" <hcb@gettcomm.com>
>To: "\mit Askan (TK-Network Gvz|mleri )" <umit.askan@probil.com.tr>;
><ccielab@groupstudy.com>
>Sent: Monday, June 17, 2002 2:34 PM
>Subject: RE: BGP no-filter
>
>
>> I'm copying this to the list so others can benefit.
>>
>>
>> >this is a question for preparing the lab. I couldn't find how can I
>> >solve.
>> >But Bhisham's answer agrees with all the rules.
>> >if you prepend R2's AS to the 10.10.20.0 route
>> >R2 won't take it because of the BGP process rules.
>>
>> The point is that you are describing something that the NO-EXPORT
>> community is specifically intended to solve.
>>
>> AS path prepending is not part of the current BGP standard, and
>> indeed there is a Cisco knob to disable it in the decision process.
>> It will be part of the new draft standard, but there are definitely
>> implementations that won't understand it -- especially Cisco or
>> others that are configured to follow the strict IETF algorithm.
>>
>> If your topology changes and the second AS is no longer adjacent, AS
>> path prepending may not work any longer, so you've created a
>> potential long-term maintenance vulnerability.
>>
>> Again, this is a case of using best current practice in the real
>> world, rather than using any protocol feature that seems to meet the
>> need. I really would find it hard to believe Cisco would prefer AS
>> path prepending to NO-EXPORT, because NO-EXPORT is a supported Cisco
>> feature.
>>
>> >Best Regards
>> >umit
>> >
>> >-----Original Message-----
>> >From: Howard C. Berkowitz [mailto:hcb@gettcomm.com]
>> >Sent: Monday, June 17, 2002 20:31
>> >To: Ccie (E-mail)
>> >Subject: Re: BGP no-filter
>> >
>> >
>> >At 3:59 PM +0300 6/17/02, \mit As8kan (TK-Network Gvz|mleri) wrote:
>> >>Hi,
>> >>
>> >>I have got a problem like that :
>> >>
>> >>network 10.10.10.0 R1-------EBGP--------R2
>> >>network 10.10.20.0
>> >>
>> >>I want to see only 10.10.10.0 at R2 bgp table. But if you look to the
>> >>R1's advertised routes to R2, you will see 10.10.10.0 and 10.10.20.0.
>> >>You can't do anything on R2 for that routes.
>> >>
>> >
>> >I'm assuming R1 learns 10.10.20.0 through an IGP, static route, or
>> >direct connection. Is there some reason that you can't tag it with
>> >the well-known BGP community, NO-EXPORT, when it enters BGP? The
>> >purpose of that community is to keep the route inside your AS.
>> >--
>> >"What Problem are you trying to solve?"
>> >***send Cisco questions to the list, so all can benefit -- not
>> >directly to me***
>> >************************************************************************
>> >********
>> >Howard C. Berkowitz hcb@gettcomm.com
>> >Chief Technology Officer, GettLab/Gett Communications
>> >http://www.gettlabs.com
>> >Technical Director, CertificationZone.com
>> >http://www.certificationzone.com
>> >"retired" Certified Cisco Systems Instructor (CID) #93005
This archive was generated by hypermail 2.1.4 : Tue Jul 02 2002 - 08:12:36 GMT-3