Subject: MPLS for UDLR

From: "Robert Schellhase" <[email-masked]>
Date: Tue, 28 Nov 2000 11:48:50 -0500

I am looking for ways to implement certain traffic engineering and QoS
features over satellite links using MPLS.

Does any router support Unidirectional Link Routing (UDLR) using MPLS as the
tunneling encapsulation? I have tried this with Cisco 7200 and 7500 series
boxes (with latest T-train IOS) without success. It seems that UDLR is able
to use only GRE tunnels. In my view, MPLS would be ideally suited to this
purpose because it is lightweight (only 4 bytes) and satellite bandwidth
tends to be scarce.

In general, I have had trouble getting MPLS TE tunnels to work when the
physical interfaces for send and receive are different. This may be more of
a problem with OSPF than with the tunnel mechansim itself. Any thoughts?

---

From: Nhat Thanh Hoang <[email-masked]>
Date: Thu, 30 Nov 2000 07:28:18 +0100

Hi, Alexander

As I know RSVP for traffic engineering that uses in MPLS context is
unidirectinal, which means you need to configure at least two
constraint-based LSPs (ingress--->egress and ingress<---egress), if you want
a bidirectional path.

/Nhat Thanh
Telia Research AB

-----Original Message-----
From: Alexander Marhold [mailto:[email-masked]]
Sent: den 30 november 2000 07:00
To: eduard metz; [email-masked]
Cc: [email-masked]
Subject: RE: MPLS for UDLR

As I have seen no other answers my assumption on that

LSP is unidirectional, but RSVP is not,
RSVP tries to send the PATH message using the ERO ( Path information ) in
the reverse direction. This fails on an UDLR.
For me it seems that RSVP would need additional information (maybe even an
extension)to successfully take care of that problem.

IMHO this is a general RSVP problem and thus maybe an issue for the
corresponding IETF WG's dealing with RSVP.

But maybe someone more knowledgeable can shed some light on that

regards
Alexander

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On Behalf Of eduard
> metz
> Sent: Wednesday, November 29, 2000 12:16 PM
> To: [email-masked]
> Cc: [email-masked]
> Subject: RE: MPLS for UDLR
>
>
>
> Hi Robert,
>
> interesting issue, since MPLS LSP are basically uni-directional I
> think this
> should work (although I'm not really in to UDLR ...).
>
> You may want to redirect your question to [email-masked], as it
> concerns some implementation specific issues. You probably will get better
> feedback on that list ...
>
> cheers, Eduard
>
> -----------------------
>
> ____________________________________________________________________
> Get free email and a permanent address at http://www.netaddress.com/?N=1
>

---

From: "Robert Schellhase" <[email-masked]>
Date: Thu, 30 Nov 2000 09:57:44 -0500

Thanks for the RSVP insights. They improve my overall understanding of
what's happening.

UDLR is supposed to fix the problem of receiving on one interface while
sending on another, by combining the two physical paths into a single
logical interface. So it sounds like we are saying that since MPLS uses RSVP
to build its tunnels, but RSVP needs bi-directional interfaces to get its
job done, and therein lies the problem.

Am I reading this correctly? Does anyone else have thoughts, or a possible
workaround idea?

Best regards,
Robert

-----Original Message-----
From: Alexander Marhold [mailto:[email-masked]]
Sent: Thursday, November 30, 2000 2:07 AM
To: Nhat Thanh Hoang; [email-masked]; eduard metz;
[email-masked]

> unidirectional, which means you need to configure at least two

Sorry for not being clear enough:
Of course you are right  the tunnel which is set up by RSVP is
unidirectional (this is what we tell RSVP when starting the RESV message).

What I wanted to express is:
That the messages itself, RSVP is sending forward (RESV) and backwards
(PATH) to set up the path are assumed to go over the same links in forward
and reverse direction. In the UDLR case those links forward and reverse are
different.

And I think that exactly that is the problem in the UDLR case.

with best regards
Alexander