nanog mailing list archives
Re: BGP prefix filter list
From: Matt Corallo <nanog () as397444 net>
Date: Thu, 30 May 2019 13:42:46 -0400
Required or not, I've seen a number of networks doing this. At some point "single global ASN" became a marketable pitch and folks realized they don't actually have to have a single Network to get it. Matt (Oops +nanog, sorry Mel + William)
On May 30, 2019, at 13:10, Mel Beckman <mel () beckman org> wrote: Bill, Are your sure about your Error #2, where you say "Prefixes from the same AS are not required to have direct connectivity to each other and many do not."? From BGP definitions: The AS represents a connected group of one or more blocks of IP addresses, called IP prefixes, that have been assigned to that organization and provides a single routing policy to systems outside the AS. “...a connected group..." implies that all the prefixes in an AS must have direct connectivity to each other (direct meaning within the IGP of the AS). I realize that some AS’s have hot backup facilities that they advertise with heavy prefixing, but in my experience, the backup facility must still be interconnected with the rest of the AS, because prefixing doesn’t guarantee no packets will its that border router. -melOn May 30, 2019, at 9:54 AM, William Herrin <bill () herrin us> wrote:On Thu, May 30, 2019 at 8:30 AM Robert Blayzor <rblayzor.bulk () inoc net> wrote: On 5/24/19 2:22 PM, William Herrin wrote:Get it? I announce the /24 via both so that you can reach me when there is a problem with one or the other. If you drop the /24, you break the Internet when my connection to CenturyLink is inoperable. Good job!It would be dropped only if the origin-as was the same. Your AS and your carriers aggregate announcement would be from two different origin AS. At least that's the gist of it...Hi Robert, Error #1: https://tools.ietf.org/html/rfc6996 section 4. It's permissible to announce to your transits with a private AS which they remove before passing the announcement to the wider Internet. As a result, the announcement from each provider will have that provider's origin AS when you see it even though it's actually from a downstream multihomed customer. Error #2: An AS is an informative handle, not a route. In routing research parlance, an identifier not a locator. Prefixes from the same AS are not required to have direct connectivity to each other and many do not. The origin AS could solve this by disaggregating the announcement and sending no covering route, but that's exactly what you DON'T want them to do. Regards, Bill Herrin -- William Herrin bill () herrin us https://bill.herrin.us/
Current thread:
- Re: BGP prefix filter list, (continued)
- Re: BGP prefix filter list William Herrin (May 30)
- Re: BGP prefix filter list Mel Beckman (May 30)
- Re: BGP prefix filter list William Herrin (May 30)
- Re: BGP prefix filter list Mel Beckman (May 30)
- Re: BGP prefix filter list Thomas Bellman (May 30)
- Re: BGP prefix filter list Mel Beckman (May 30)
- Re: BGP prefix filter list Valdis Klētnieks (May 30)
- Re: BGP prefix filter list Mel Beckman (May 30)
- Re: BGP prefix filter list Thomas Bellman (May 31)
- Re: BGP prefix filter list Valdis Klētnieks (May 30)
- Re: BGP prefix filter list Matt Corallo (May 30)
- Re: BGP prefix filter list Saku Ytti (May 30)
- Re: BGP prefix filter list Robert Blayzor (May 30)
- Re: BGP prefix filter list William Herrin (May 30)
- Re: BGP prefix filter list Robert Blayzor (May 30)
- Re: BGP prefix filter list Robert Blayzor (May 30)
- Re: BGP prefix filter list Brielle (May 15)
- Re: BGP prefix filter list Jon Lewis (May 15)
- Re: BGP prefix filter list Dovid Bender (May 15)