At 3:19 AM +0000 3/12/03, Priscilla Oppenheimer wrote: >I'll take a stab at it since nobody else did. > >Oliver Hensel wrote: >> >> Hi! >> >> Can someone point me to a document which explains >> what happens with a prefix that is dampened if >> it's distributed via two providers. > >I don't think you'll find a document that answers the question explicitly >because the implicit answer is sort of obvious, as I think you realize. > >It's a route that's dampened, not a prefix. With two providers, in most >cases, there would be two distinct routes to your prefix. A BGP route has >path attributes including an AS_Path, which is a list of Autonomous System >numbers. With two providers, the two routes will be distinct and have a >different set of AS numbers in most situations. Otherwise what would be the >point?
Depending on how deeply you want to go, there is a very nuanced range of ideas in BGP information and how it is propagated. In our http://www.ietf.org/internet-drafts/draft-ietf-bmwg-conterm-04.txt , there was tremendous effort to clarify, and part of this clarification means that you probably have to understand the differences among a dozen or so seemingly alike concepts. These are also being refined in the new BGP standard, which is at draft 19 when last I looked -- and probably still has a round or two to go. Let's put it this way...we ducked going deeply into route flaps, much less dampening (an important difference -- they are NOT equivalent) in this version of the document. There are concepts that need to be most thoroughly internalized -- grokked if you will -- before dealing with flap control and propagation. Quite a bit of theoretical analysis is available, but the associated global scalability issues are by no means solved. > >> >> Will only the penalized route dampened, that is >> will we still have connectivity if one link is >> flapping. I think so, but I'd like to have some >> confirmation for that. > >If just one of your links is flapping, then just one of your routes will get >dampened. The other one will still be usable. > >If your two links share a circuit to the telco or physically share a path >that has been dug up by the proverbial back-hoe operator, it's possible both >links could be flapping, and then they will both get dampened, but hopefully >you have a network design that avoids that problem. Don't let BGP rain on >your parade and dampen too much at once! Have good physical diversity. ;-) > >Priscilla > >> >> Thanks and best regards, >> >> Oliver >> >> >> -- >> Oliver Hensel >> telematis Netzwerke GmbH >> mailto: [EMAIL PROTECTED] >> Siemensstrasse 23, D-76275 Ettlingen >> Tel: +49 (0) 7243-3448-0, Fax: -498 >> visit us: http://telematis.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=65126&t=65086 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
