North American Network Operators Group

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Re: 16-bit ASN kludge

  • From: Edward B. Dreger
  • Date: Fri Dec 03 19:34:55 2004

OD> Date: Fri, 03 Dec 2004 14:45:17 -0800
OD> From: Owen DeLong <[email protected]>

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> 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.

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