Subject: RE: Label Mapping mesage !!

From: Bhupesh Bajaj <[email-masked]>
Date: Mon, 14 May 2001 14:10:35 +0500

hi...
as specified in RFC 3031..in section 3.14 "scope and uniqueness....."

"A given LSR Rd may bind label L to FEC F1, and distribute that
   binding to label distribution peer Ru1.  Rd may also bind label L to
   FEC F2, and distribute that binding to label distribution peer Ru2.
   IF (AND ONLY IF) RD CAN TELL, WHEN IT RECEIVES A PACKET WHOSE TOP
   LABEL IS L, WHETHER THE LABEL WAS PUT THERE BY RU1 OR BY RU2, THEN
   THE ARCHITECTURE DOES NOT REQUIRE THAT F1 == F2.  In such cases, we
   may say that Rd is using a different "label space" for the labels it
   distributes to Ru1 than for the labels it distributes to Ru2."

it gets clear that the the Rd may specify the same label BUT the label space
used for the Ru1 and Ru2 will be different.

or in other words , if its using Per Platform Label space, the Rd MUST not 
specify the Same Label for different FEC's possibly belonging to different
Ru's.

Correct me If i am wrong

thanks and regards
bhupesh

-----Original Message-----
From: Manoj Dutta [mailto:[email-masked]]
Sent: Monday, May 14, 2001 1:20 PM
To: [email-masked]
Subject: Label Mapping mesage !!

hi,

Is is possible for a given LSR Rd to distribute the same label mapping
for more than one fec elements to another LSR Ru while using platform
wide label space only. If so, then what are the possible scenarios.

thanks
manoj

---

From: Shantnu Sharma <[email-masked]>
Date: Mon, 14 May 2001 07:59:50 -0400

Greetings!

Bhupesh,

Your statement is correct. If you have platform wide label space you cannot
advertise the same label for different FECs.

Thanks
Shantnu

Bhupesh Bajaj wrote:

> -------
> The MPLS-OPS Mailing List
> Subscribe/Unsubscribe:  http://www.mplsrc.com/mplsops.shtml
> Archive: http://www.mplsrc.com/mpls-ops_archive.shtml

--
***************************************************************
        I am prepared to die, but there is no cause
        for which I am prepared to kill.
        - Mohandas Karamchand GANDHI

---

From: Eric Gray <[email-masked]>
Date: Mon, 14 May 2001 15:25:54 -0400

Shantnu,

    I disagree.

    An unfortunate artifact of the choice to use the term 'label
space' is that it can be confusing.  While implementations may
choose to actually use distinct labels in each 'label space',
this is NOT a requirement.  In fact, the quote below is trying
to make this very point - i.e. the exact same label can mean
different things in a different 'label space'.  For this very
reason, I had tried early on to get the term changed to 'label
context', but I was unsuccessful.

    Because the same label can come from different 'label spaces',
it is quite possible to use the same label with different peers
- irrespective of whether or not the per-platform, or interface
specific 'label space' is used.  The 'label space', therefore, is
orthogonal to the issue of supporting multiple FECs using a single
label.

    The section to which Bhupesh refers, is attempting to describe
the implications of using the same label in different ways - and
specifically when this may be allowed.  It is not attempting to
describe the situation in which the same label accomodates multiple
FECs in the same way.  You may want to note that section 3.14, as a
whole, is somewhat misleading.  It seems to imply that there is some
difficulty in being able to determine what peer sent a labeled
packet except in the case where peers are connected by point to
point links.  In general, however, it is only difficult to determine
what peer sent a labeled packet when the label is received on an LSP
for which the ingress is unknown (either because the LSP is a merged
LSP or because the local LSR issued either an implicit NULL label to
the immediate upstream LSR).  This is common behavior, but - by no
means - the only way to tunnel labeled packets.

    It is worth noting that - if a downstream LSR 'Rd' has issued an
implicit NULL label to an upstream LSR 'Ru' and the upstream LSR
performs PHP for a labeled packet where the label is not the bottom
of the stack - it is technically 'violating' the MPLS encapsulation
specification (the implicit NULL labels are for IPv4 and IPv6 packets,
and not for MPLS labeled packets).  However, I believe that this is a
common 'violation'. In the event that this is being done, however, it
will be impossible for the LSR to determine which peer sent a labeled
packet even over a point-to-point link.

--
Eric Gray

You wrote:

>
> Greetings!
>
> Bhupesh,
>
> Your statement is correct. If you have platform wide label space you
> cannot advertise the same label for different FECs.
>
> Thanks
> Shantnu
>
>
> Bhupesh Bajaj wrote:
>
>> hi...