Subject: Questions about draft-ietf-mpls-lsp-query-09.txt

From: lidefeng <[email-masked]>
Date: Sat, 05 Jul 2003 17:42:56 +0800

In  Section 6.2 of draft-ietf-mpls-lsp-query-09.txt,it states that:
" When the Query message gets to a tunnel, it has to be able to handle
    both the previous label and the tunnel's label. The Query Label TLV
    behaves like a label stack. The previous label is pushed and the
    tunnel label is used. At the end of the tunnel, we need to pop the
    stack and start substituting the lower level labels."

Could you please tell me what do "the previous label" and the "tunnel's
label" signify respectively?An example to clarify this question will be
appreciated  ?Thanks

Sincerely Yours

Defeng Li
Huawei Technologies
+86-10-82882343
[email-masked]

---

From: "David Allan" <[email-masked]>
Date: Tue, 8 Jul 2003 10:41:45 -0400

hi Defeng:

The scenario discussed is when hitting a tunnel ingress, the LSR has a
choice as to whether to expose the tunnel workings (if the tunnel layer also
supports query capability) by continuing the trace at the tunnel layer, or
simply forwarding the trace at the current level.

If the LSR chooses to expose the tunnel, then the Query Label TLV stack
carries the context forward such that the tunnel egress can then
appropriately map back to the original top label.

	R1--------R2- - - - - - R3 - - - - - - -R4-----------R5
		     ==============================

A tunnel connects R2 to R4 via R3 and all LSRs have routable addresses. If
R2 chooses not to expose the tunnel, the trace will transit R1-R2-R4-R5. If
R2 chooses to expose the tunnel, the trace will transit R1-R2-R3-R4-R5. The
Query Label TLV propagated by R2 in the first case only carries the R2-R4
label. In the second case, it would push the R2-R4 label, and carry the
R2-R3 label then replace the label at R3 with the R3-R4 label.

The scenarios whereby LDP is recursive would be P2P PWs and use of
LDP/CR-LDP.

hope this helps
Dave

> -----Original Message-----
> From: lidefeng [mailto:[email-masked]] 
> Sent: Saturday, July 05, 2003 5:43 AM
> To: Ashwood-Smith, Peter [CAR:1A00:EXCH]; Paraschiv, Antonela 
> [BL60:NP30:EXCH]; Allan, David [CAR:NS00:EXCH]
> Cc: [email-masked]
> Subject: Questions about draft-ietf-mpls-lsp-query-09.txt
> 
> 
> In  Section 6.2 of draft-ietf-mpls-lsp-query-09.txt,it states 
> that: " When the Query message gets to a tunnel, it has to be 
> able to handle
> Could you please tell me what do "the previous label" and the 
> "tunnel's label" signify respectively?An example to clarify 
> this question will be appreciated  ?Thanks
> 
> 
> 
> Sincerely Yours
> 
> Defeng Li
> Huawei Technologies
> +86-10-82882343
> [email-masked]
> 
>