----- Original Message ----- From: "Peter van Oene" To: Sent: Wednesday, May 29, 2002 1:11 AM Subject: Re: BGP addressing..i think i understand but i am not sure [7:45235]
> Hey Nigel, > > I'm not sure where to point you. All I can tell you is that it is > commonplace and likely will continue to be so. I'm currently not aware of > any routing issues that this behavior would induce. > > Pete > > > At 08:04 PM 5/27/2002 -0400, Nigel Taylor wrote: > >Peter, > > It would seem that Cable&Wireless and Above along with RIPE are > the > >main culprits. > > > >It would seem to me that this inconsistent route issue would present > >problems, what I'm I missing? It maybe that I'm not totally > >clear on what constitutes an "inconsistent route". RFC 1930 clearly states > >that "one-prefix, one originating AS". I know it's been > >mentioned in this thread and I see it noted that the RSNG Project will > >notify peers of inconsistent policies registered in the IRR. > >So, how effective is this initiative if most of the community feels it's not > >something to be worried about. > > > >Anyone care to point me in a specific direction. > > > >thanks > >Nigel > > > >----- Original Message ----- > >From: "Peter van Oene" > >To: > >Sent: Monday, May 27, 2002 6:31 PM > >Subject: Re: BGP addressing..i think i understand but i am not sure > >[7:45169] > > > > > > > quick comment in line. > > > > > > At 04:53 PM 5/27/2002 -0400, Chuck wrote: > > > >I have a question, Howard - in line: > > > > > > > > > > > >""Howard C. Berkowitz"" wrote in message > > > >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > > This is one of those posts where the attributions have gotten very > > > > > confused. Comments inline. > > > > > > > > >snip for brevity > > > > > > > > > > It can be done, if both ISPs agree to it and coordinate their routing > > > > > policies. A public AS, however, is justified in this circumstance. > > > > > > > > > > While doesn't quite describe this situation, look at RFC 2270 for the > > > > > general strategy. Both ISPs have to remove private AS. This will > > > > > also cause more than one ISP to appear to originate the route, which > > > > > is a technical violation of BGP (i.e., it's an "inconsistent route"), > > > > > but that isn't that uncommon and doesn't seem to break anything. > > > > > > > > > > > > >Question: in an ideal world, what would happen when an "inconsistant > >route" > > > >shows up? idealy, would that route be black holed? > > > >Since it is "common" and since it "doesn't seem to break anything" in > ral > > > >terms, what happens? BGP advertises reachability to other BGP routers, > be > > > >they internal or external. But in terms of a packet traveling from my > >house > > > >to a destination that is "inconsistant" what happens? What matters? My > > > >packet continues to be passed from here to there until some directly > > > >connected router receives it. I'm assuming that "inconsistant" does not > > > >imply "loop" > > > > > > > >thanks. > > > > > > You are correct in that inconsistent advertisements do not represent > >looped > > > routes. In the case of a prefix seemingly existing in two AS's, a remote > > > router simply passes that prefix through the basic BGP path selection > > > algorithm and selects the more preferable of the two for export to the > >main > > > routing table. Once a route hits the routing table, transiting packets > > > are forwarded as usual. > > > > > > Any potential concern lies in the handling of routes that show up as > > > inconsistent. I have seen discussions from various communities (RIPE > >comes > > > first to mind) about specifying a globally accepted behavior for such > > > routes, but haven't seen a consensus on this issue other than to leave it > > > alone. Howard probably has somewhat more detailed insight here. At > > > present, inconsistent advertisements are accepted and many feel are valid > > > and should not be handled differently from normal announcements. > > > > > > Customers who think that connecting to two providers is generally better > > > than two pops from a single provider and providers who are too about > > > nervous about losing customer revenue to force customers to properly > > > multi-home (PI space/ASN) or not multi-home to different providers at all > > > are likely the cause of this situation. So long as this continues to be > > > the norm, we'll likely see more and more of these type announcements and > > > the likelihood of routers dealing with them differently (dropping for > > > example) will similarly decrease. > > > > > > Hit a route server (say route-server.exodus.net) and do a show ip bgp > >incon > > > and you'll see just how many of these routes we are dealing with. > > > > > > Pete > > > > > > > > > > > > > > > > > > > >snip for brevity< Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=57569&t=57569 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
