Subject: Draft IETF MPLS TE MIB 05 usage question: Tunnel Table

From: "Dave Danenberg" <[email-masked]>
Date: Wed, 7 Feb 2001 13:27:24 -0500

Question on the Tunnel Instance.

By description, the Tunnel Table provides for multiple tunnel instances - in
the case where you have backup or parallel tunnels. When using multiple
instances, I would think the TunnelIndex would stay the same value while the
TunnelInstance increments (1, 2, and so on). The reason I'm not sure that
this is right is the description under mplsTunnelIndexNext which says:

"This object contains the next appropriate value to be used for
mplsTunnelIndex when creating entries in mplsTunnelTable."

To better describe my understanding, it would say:

"This object contains the next appropriate value to be used for
mplsTunnelIndex when creating an entry (or, in the case of multiple
instances, a set of entries ) in the mplsTunnelTable."

Help?
Thanx, Dave

Dave Danenberg
VP of Engineering
Litchfield Communications Inc.
www.litchfieldcomm.com

Princeton Building East
76 Westbury Park Rd
Watertown CT 06795 USA

Tel: (860) 945 1573 x3180
Fax: (860) 945 1578

---

From: "Thomas D. Nadeau" <[email-masked]>
Date: Wed, 07 Feb 2001 20:23:55 -0500

>By description, the Tunnel Table provides for multiple tunnel instances - 
>in the case where you have backup or parallel tunnels. When using multiple 
>instances, I would think the TunnelIndex would stay the same value while 
>the TunnelInstance increments (1, 2, and so on). The reason I'm not sure 
>that this is right is the description under mplsTunnelIndexNext which says:

         Correct.

>instances, a set of entries ) in the mplsTunnelTable."

         This is a good point. It is possible that one would want
to manually configure a tunnel instance. We will modify the
text a bit to make this clearer.

         --Tom

---

From: "Choudhury, Sanjaya" <[email-masked]>
Date: Mon, 12 Feb 2001 10:40:58 -0500

Hi Tom! This is a follow-up question based on your reply.
In your reply, you pointed-out "the XCindex notes the 
"group" of LSPs used for the tunnel". 

If this was the main reason for having the mplsXCIndex in
the mplsXCTable, then I might have mis-interpreted the MIB
definitions related to the mplsXCTable. I will appreciate,
if you can clarify the following.

Given the following context:
---------------------------
(1) mplsLspId is not a part of the index into the mplsXCTable
and is optional for implementation [LSR-MIB mplsXCTable 
definition and conformance statements]

(1) "It supports point-to-point, point-to-multipoint and
multipoint-to-point connections" [mplsXCTable description,
in LSR-MIB]

(2) "mplsTunnelTable does not define the in and out segments
   forming the tunnel.  Instead, these are defined by creating
   rows in the in-segment and out-segment tables, defining
   relationships in the cross-connect table and referring to
   these rows in the mplsTunnelTable using a cross-connect
   index, mplsTunnelXCIndex. These segment and cross-connect
   related objects are defined in LSRMIB." [MPLS-TE-MIB Section
   6.1]

(3)"Uniquely identifies an instance of a tunnel. It is
    useful to identify multiple instances of tunnels
    for the purposes of backup and parallel tunnels." [Description
    of mplsTunnelInstance in MPLS-TE-MIB]

I interpreted the following statement:
-------------------------------------
"-cross-connect index mplsXCIndex that uniquely identifies
  a group of cross-connect entries" [Description in the   
  mplsXCEntry]

as:
---
(a) cross-connect index mplsXCINdex uniquely identifies a group of 
    cross-connects entries, that belong to the __same LSP___.
    [NOT a group of independent LSPs, as you pointed out in your
    reply.] 

(b) The main (and only) reason for having the mplsXCIndex, is to 
    represent a LSP (inside the switch)with different cast types: 
    point-to-point point-to-multipoint and multipoint-to-point.
   
(c) mplsTunnelXCPointer is used to associated a particular LSP 
    with the mpls tunnel defined in the mplsTunnelTable.

(d) Parallel tunnels are abstracted in mplsTunnelTable using the
    mplsTunnelIndex and mplsTunnelInstance.

Please correct me, if I mis-interpreted the MIB. 

Thanks,
sanjay	

-----Original Message-----
From: Thomas D. Nadeau [mailto:[email-masked]]
Sent: Friday, February 09, 2001 10:41 PM
To: Filipe Miguel Sousa; [email-masked]
Subject: Re: Draft IETF MPLS TE MIB 05 usage question: Tunnel Table

>Question about the mplsTunnelXcPointer Object.
>
>Can someone clarify me on this issue?
>
>In the MPLS TE MIB the mplsTunnelTable as the
>mplsTunnelXcpointer. This object points to a row in the mplsXCTable
>in the MPLS LSR MIB. My question is how the MPLS TE MIB as all
>the XCsegments used by this tunnel if this pointer only points to
>one row in a specif mib?

         I think that you could be asking two things above, so
I will try to answer both questions. First, the XCindex is
the major index for associated cross-connects on that
particular LSR in the LSR MIB. If there are parallel links
for example, then the XCindex notes the "group" of
LSPs used for the tunnel. If you are asking why the totality
of cross-connects (i.e.: throughout the network) is not
available at the head-end LSR, then this is simple: because
you need to go hop-by-hop checking the LSR MIB along the
way.

         --Tom

---

From: "Thomas D. Nadeau" <[email-masked]>
Date: Wed, 14 Feb 2001 09:27:26 -0500

Comments inline.

>"group" of LSPs used for the tunnel".

         It may denote a group of associated LSPs. It depends
on how you want to implement tunnels and LSPs. See below
for more information.

>Given the following context:

         The LSR MIB exists at all points along an LSP and
identifies the local in-out label swapping for any
particular hop of the LSP. Remember that a tunnel
exists only if at least one LSP which has been signaled
to carry the traffic for that tunnel. To that end, if the
XC pointer in the tunnel entry does not point to anything,
then no LSP exists. What may be confusing is that
each tunnel instance has one LSP per instance and that
it *may* be convenient to associate a "group" of LSPs
in the LSR MIB together using this primary index, but that is
not mandatory. This is not necessarily mandatory, since you
can have distinct XCindexes for each underlying LSP as well.

>     point-to-point point-to-multipoint and multipoint-to-point.

         The main point for the XCindex is to represent the
cross-connection between some set of incoming labels to
some set of outgoing labels.

>     with the mpls tunnel defined in the mplsTunnelTable.

         Yes.

>     mplsTunnelIndex and mplsTunnelInstance.

         Yes, but as I mentioned above, each instance needs its
own LSP.

         --Tom