Subject: RE: MPLS domain - AS

From: Lane Patterson <[email-masked]>
Date: Tue, 30 May 2000 17:21:44 -0700

The proposed application of MPLS across public exchange point switches/LSRs
(for example http://www.nanog.org/mtg-0002/feldman.html) is an example that
stretches the definition of "administrative domain".  In this case, the
administrative domain is not the AS, it is the common practices and
coordination necessary by exchange point participants.

The primary motivation for this is to provide higher-speed and layer-2
agnostic interfaces as a means of public peering, although there is little
if any operational experience in this area.

The implementation is likely two-hop [IXP LSR, peer LER/LSR] explicit route
LSPs using signalling and static routes, no IGP.

Regards,
-Lane

-----Original Message-----
From: Jeremy Lawrence [mailto:[email-masked]]
Sent: Friday, May 26, 2000 8:22 PM
To: [email-masked]
Cc: [email-masked]
Subject: RE: MPLS domain - AS

Someone else has privately pointed out that Brijesh and I are in
violent agreement on this issue. :-)

This is not quite true: we are generally in agreement, apart from
one detail. Comments inline...

At 10:25 05/26/2000 -0400, Brijesh Kumar wrote:
>In his last mail, Jeremy Lawrence writes
>
> > At 16:16 05/25/2000 +0530, Naveen Seth wrote:
> > >Hi,
> > >The definition of MPLS domain in the
> > draft-ietf-mpls-arch-06.txt says that the MPLS nodes are in
> > one routing or administrative domain.
> > >
> > >1. Does it imply that we cannot have 2 AS(Autonomous System)
> > within the same MPLS domain?
> >
> > This is possible only under very restricted circumstances. Consider
> > the ASBRs of two adjacent ASes. If either or both ASBRs summarize
> > eBGP routes before distributing them into their IGP, or if there is
> > any other set-up where the IGP routes cover a set of FECs which
> > differs from that of the eBGP routes (and this would almost always
> > be the case), then the ASBRs cannot forward traffic based on the
> > top-level label. A similar argument applies to TE tunnels. Some
> > traffic usually will be either IP forwarded by the ASBR, or
>
>Well... This is inconsistent with the MPLS Arch document.

No, it is consistent but unlikely - see below.

>A MPLS domain is defined in MPLS architecture document as "a contiguous set
>of nodes which operate MPLS routing and forwarding and WHICH ARE IN *ONE
>ROUTING OR ADMINISTRATIVE DOMAIN*".
>
>This means that a MPLS Domain, at most, can cover one Administrative
Domain.

Agreed.

>Any other implementation (i.e., an MPLS domain being defined as part of two
>administrative domain) is not in line with this definition.

Agreed.

It is possible for two ASes to be in the same administrative domain.
There are a small number of large SP networks which consist of more
than one registered AS, and there are probably many more which use
private ASes. In the unlikely case that an MPLS domain does extend
across two ASes, the two ASes must have tightly coordinated routing,
which would require that they are in the same administrative domain
(at least in effect).

Regards,

Jeremy

---

From: Jeremy Lawrence <[email-masked]>
Date: Wed, 31 May 2000 15:41:40 +1000

Another example (thanks to Rob Raszuk) is with the multi-provider
application of BGP+MPLS VPNs: section 10 of
http://www.ietf.org/internet-drafts/draft-rosen-rfc2547bis-01.txt

As described earlier, there are usually no *top-level* LSPs
established across the two (or more) provider ASes involved, so
it can be argued that
1. the two ASes are separate administrative domains.
However there are some LSPs established across the two ASes, at
a lower level in the label stack. So, it can be argued that
2. the two ASes are the same administrative domain, in so far
    as the two providers agree to allow lower-level LSPs to
    be established across the two ASes

I think that (1) and (2) are both true, which implies that
different definitions of the boundary of the administrative
domains can exist with respect to different levels in the label
stack. It is also (in hindsight) obvious that different MPLS
domain boundaries can exist with respect to different levels of the
label stack. 

Jeremy