Subject: Explicit route operations in RSVP

From: "Abes, Andi" <[email-masked]>
Date: Wed, 12 Jan 2000 13:59:01 -0500

Hi again,

I guess the original question was kind of cryptic....

The draft-ietf-mpls-rsvp-lsp-tunnel-04 draft contains
an operation sub-object in the Explict route.

This is part of the Path message traveling from the 
Sender (ingress) of the "to be setup" tunnel
towards the Reciver (egress).

Section 4.3.4.1. 3) says: 
 " If the subobject
   is an operation subobject, the node pops the subobject from the
   EXPLICIT ROUTE object , records the subobject, and continues
   processing with step 2, above. "

This leaves me with the following questions:

What are the processing rules for this sub-object ?
  
In what scenario will this option be used ?

TIA,
Andi

-----Original Message-----
From: Abes, Andi [mailto:[email-masked]]
Sent: Monday, January 10, 2000 2:42 PM
To: MPLS mailing list
Subject: MPLS termination action sub-object in ERO for RSVP

hi,

I'm a little confused about the use of the LSP termination sub-object in the
explicit route 
object and the allocation of multi-level labels using RSVP.

1. Who decides to allocate a higher level label ? 
  a. the egress point ? - this will help it identify the ultimate
destination assuming the LSP
     is part of a tunnel.
  b. An intermediate node that performed a merge - this will allow the
various flows to be uniquely 
     identified using the second level label ? in this case how will the
upper label be negotiated 
     with the next hop ? 
  c. Any other contenders ?

2. How is the "LSP Termination" object is used ?
   Since it can only appear as part of an ERO, and hence only from the
ingress - what 
   is the expected treatment by the receiving node - the one identified in
the ERO ?
   Is it expected that the receiving node realize it has to assign more than
the top label ?
   is it some kind of "penultimate-hop-pop" mechanism ?

Thanx,
Andi.

---

From: Yakov Rekhter <[email-masked]>
Date: Fri, 14 Jan 2000 11:43:57 -0800

Andi,

> In what scenario will this option be used ?

When setting up an LSP within another LSP.

Here is an example where this sub-object could be useful.
Consider the following topology:

   A---B----C----D----E-----F

Assume that A sends a Path message with ERO = (B, E, F).  When this
message arrives at B, B wants to route it along C and D. One way to do
this is just to expand the ERO to (B, C, D, E, F). For this you don't
need the label termination sub-object.

An alternative is for B to expand this ERO to (B, C, D, lto, E, F)
(where "lto" is the label termination sub-object). When D gets a label
L1 from E (this label will be carried in the Resv message from E to D),
D would use it as the outgoing label for the LSP.  D then allocates its
own label, L2, for that LSP.  In the Label Object that D sends to C (in
the Resv message) D will put not just L2, but <Implicit-Null, L2>.  When
C receives this Resv message, C allocates its own label, L3, and sends
<L3, L2> in the Label Object to B. B at this point allocates its own
label, L4, and sends *just* L4 in the Label Object to A (as it was
B who inserted lto in the first place).

When A sends a packet over the LSP, A puts L4 on the packet. B
replaces A4 with L2 and pushes L3 onto the stack. C pops the
stack and sends the packet with just L2 to D. D replaces L2 with
L1....

I don't think that the current text reflects what I described above...

Yakov.