Subject: MPLS-TE-MIB Report 3/3: Specific Questions and Comments

From: "Zhu, Rupert" <[email-masked]>
Date: Mon, 11 Nov 2002 19:10:09 -0600

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MPLS-TE-MIB Report 3/3: Specific Questions and Comments

Below is a list of questions and comments on mplsTunnelTable.
Some of the questions may simply reflect my own confusions.

The quoted MIB text is indented.  My question/comment
is inserted right after each segment of quoted text.

----------------------------------------------------
        OBJECT: mplsTunnelEntry
        DESCRIPTION:
                "An entry in this table represents an MPLS tunnel.

COMMENT: Incorrect.  An entry only represents a tunnel instance.
A set of entries (rows), collectively, represent a tunnel.

----------------------------------------------------
        OBJECT: mplsTunnelIndexIndex
        DESCRIPTION: 
            "Uniquely identifies this row."

COMMENT: Incorrect.  This field alone identifies a tunnel that corresponds
to a set of rows.  You need all fields in INDEX clause together to
identify a row.

COMMENT: The naming "....IndexIndex" looks a bit odd.

----------------------------------------------------
        OBJECT: mplsTunnelInstance
        DESCRIPTION:
            "Uniquely identifies an instance of a tunnel.  ......

COMMENT: Good by itself, but in contradiction with next two fields.

----------------------------------------------------
        OBJECT: mplsTunnelIngressLSRId
        DESCRIPTION: 
            "The purpose of this object is to uniquely identity a
            tunnel within a network.  ......

COMMENT: Confusing.  This field alone neither uniquely identify a tunnel
nor a tunnel instance.

----------------------------------------------------
        OBJECT: mplsTunnelEgressLSRId
        DESCRIPTION: 
            "Specifies the egress LSR ID."

QUESTION: Is this in relation to tunnel or tunnel instance?

----------------------------------------------------
        OBJECT: mplsTunnelSignallingProto
        DESCRIPTION: 
            "The signalling protocol, if any, which was used to
              setup this tunnel."

COMMENT: Please substitute "tunnel" with "tunnel instance".
(There are quite a few similar ambiguities in this table.
Please do the same substitution.)

COMMENT: The ENUM range of this field is a subset of ENUM range of
mplsTunnelOwner field.  Therefore this field becomes redundant
and unnecessary because it may be derived from another field.

----------------------------------------------------
        OBJECT: mplsTunnelResourcePointer
        DESCRIPTION: 
              ............
              By having the same value of this object, two or
              more segments can indicate resource sharing."

COMMENT: This resource-sharing semantics is very unusual and may
cause confusions.

    SCENARIO 1: Same Tunnel
    If two tunnel instances on two different interfaces (of the same
    node) point to the same resource, how to enforce resource sharing?

    SCENARIO 2: Different Tunnels
    If two tunnel instances of different tunnels point to the same
    resource, how can they share resource?

----------------------------------------------------
           INDEX {
              mplsTunnelIndexIndex,
              mplsTunnelInstance,
              mplsTunnelIngressLSRId,
              mplsTunnelEgressLSRId
   }

COMMENT: I have a hard time to understand why the INDEX
clause consists of 4 fields.  By definition, INDEX of a MIB table
should be a minimal subset of fields that uniquely identify a row.
Now we have

a) mplsTunnelIndex uniquely identifies a tunnel;
b) mplsTunnelIndex and mplsTunnelInstance together uniquely
   identify a tunnel instance (i.e., a row).

So these two fields are sufficient to uniquely identify a row.
Why bother to add two extra fields in the INDEX clause?

QUESTION: What's the relationship between the 4 INDEX fields?
Can there be two rows that have identical value in the first two
fields but different values in the last two fields?

QUESTION: Since only point-to-point tunnels are supported, all tunnel
instances of a tunnel should have the same head LSR and tail LSRs,
therefore, same IngressLSRId and EgressLSRId.

I may have missed something here.  It would be helpful to readers
if a clarification on INDEX clause could be added.

----------------------------------------------------
General Suggestions:

1. Please make it crystal clear that a (logical) tunnel is represented
   by a set of rows rather than a single row.

2. Please use accurate terminology to distinguish (logical) tunnel
   from tunnel instance in the DESCRIPTION clause of every object.
   For example, replace "tunnel" with "tunnel instance" when appropriate.

Thanks for your attention.

Rupert Zhu
System Engineering
Santera Systems Inc
3605 E. Plano Parkway
Plano, TX 75074
Phone: 972-461-6383