Subject: Re: CR-LDP

From: "Santosh Gupta" <[email-masked]>
Date: Tue, 28 Mar 2000 10:15:39 +0530

Hi Sumit
    The concerned section of CR-LDP draft is as below.
4.7.4. ER-Hop 4: LSPID

The LSPID is used to identify the tunnel ingress point as the next
hop in the ER. This ER-Hop allows for stacking new CR-LSPs within an
already established CR-LSP. It also allows for splicing the CR-LSP
being established with an existing CR-LSP.
If an LSPID Hop is the last ER-Hop in an ER-TLV, than the LSR may
splice the CR-LSP of the incoming Label Request to the CR-LSP that
currently exists with this LSPID. This is useful, for example, at
the point at which a Label Request used for local repair arrives at
the next ER-Hop after the loosely specified CR-LSP segment. Use of
the LSPID Hop in this scenario eliminates the need for ER-Hops to
keep the entire remaining ER-TLV at each LSR that is at either
(upstream or downstream) end of a loosely specified CR-LSP segment
as part of its state information. This is due to the fact that the
upstream LSR needs only to keep the next ER-Hop and the LSPID and
the downstream LSR needs only to keep the LSPID in order for each
end to be able to recognize that the same LSP is being identified.

In this it clearly states that it is not only the Ingress LER and the LSRs in the path of this LSP but other LERs also need to know the LSP-ID of different LSPs. The scenario is something like

                LER1 ------> LSR2-------->LSR3------>LSR4                

                LER2-------->LSR5

there is an LSP setup as shown from LER1 thru LSR2,LSR3, LSR4. Now LER5 receives a ER-TLV which says it has to make an  LSP for which the next hop is LSR3 and the already existing LSP with the LSP-ID is to be used. Now the question is how does LSR5 or LER2 come to know about this particular LSP-ID which actually originated at LER1?

santosh

[email-masked]

----- Original Message ----- 
From: Sumit Garg 
To: 'ashish' 
Sent: Tuesday, March 28, 2000 3:49 A
Subject: RE: CR-LDP

Hi,
 
LSD-ID is a TLV defined by the CR-LDP draft. It is a combination of the LSR-ID and a 2 octect number assigned by the ingress/ initiating LSR. This would typically be an administor assigned/ monitored quantity and thereof known a priori for LSP splicing/ tunneling.
 
The LSPID is propagated to downstream LSRs in the LSP setup request.
 
Regards
Sumit
 
  -----Original Message-----
  From: ashish [mailto:[email-masked]]
  Sent: Monday, March 27, 2000 03:58 AM
  To: [email-masked]
  Subject: CR-LDP

  In CR-LDP draft-03, one of the ER-HOP TLV types contain LSPID field that is used for tunneling thru some existing LSP having that LSPID field.
  This means that that LSPID should be known in advance .
  How is that done.
  Does information regarding each LSP being created each having unique LSPID is propagated to all LSR's.
  Please clarify.