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 <m...@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. > > -mel > > >> On May 30, 2019, at 9:54 AM, William Herrin <b...@herrin.us> wrote: >> >> >> >>> On Thu, May 30, 2019 at 8:30 AM Robert Blayzor <rblayzor.b...@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 >> b...@herrin.us >> https://bill.herrin.us/ >
