16-bit ASN kludge

Sat Dec 4 02:09:48 UTC 2004

I think all the meaningful parties have already pretty much agreed on
32bit ASNs in BGP4.  I think that will be coded in the routers well before
any attribute-based thing for 32bit ASNs is.  As such, I don't see much
point to kludging this instead of just going for it assuming a 32bit world.

Owen

--On Saturday, December 4, 2004 0:30 +0000 "Edward B. Dreger" 
<eddy+public+spam at noc.everquick.net> wrote:

> OD> Date: Fri, 03 Dec 2004 14:45:17 -0800
> OD> From: Owen DeLong <owen at delong.com>
>
> OD> I think the original proposal was to still go with 32 bit ASNs, but,
> adapt OD> a range of 32 bit ASNs for the assignment to "NON-TRANSIT" ASNs
> leaving OD> the entire 16 bit range reserved for "TRANSIT" ASNs.
>
> Correct.  BGP would still carry traditional 16-bit ASNs, which would be
> used strictly by transit networks.  Leaf ASes would use the "new" 32-bit
> ASNs, which would be carried as BGP attributes.
>
> It's similar to a transit provider with a downstream connected to
> multiple POPs:  $transit_provider assigns all downstreams a private AS,
> which is stripped from outbound advertisements.
>
>
> OD> I think there's merit to the idea, but, I think that it could use some
> OD> refinement.  I agree there will be many more non-transit than transit
> ASNs
>
> No disagreement re needing refinement.  I lack the clout to push BGPv8
> on the world. ;-)
>
>
> OD> (non-transit is an ASN that does not provide transit, transit is an
> OD> ASN that provides transit).
> OD>
> OD> I think it would make more sense to put the boundary somewhere around
> 12 OD> bits or so.  If we reserved the first meg 1024k ASNs for transit
> providers OD> (excepting the Private ASN reservation already in place),
> and, allowed the OD> remaining ASNs to be assigned to non-transit ASNs,
> this functionality could OD> be implemented relatively easily with
> maximum backward compatibility.
>
> Part of the kludge intent was to create something that standard routers
> would carry.  Hence 16-bit traditional ASNs, with extended information
> as an attribute.  It certainly would be possible to reserve 2^20 "new"
> ASNs, though, for when BGP5 (or whatever) had native 32-bit support.
>
>
> Eddy
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