Subject: RE: Question about LDP Receive Label Request

From: "Gray, Eric" <[email-masked]>
Date: Tue, 3 Sep 2002 07:59:10 -0400

Kim,

            See below...

Eric W. Gray

Systems Architect

Celox Networks, Inc.

[email-masked]

508 305 7214

...
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(1) As I know, "Label Request " is only applicable for DoD. But in this
line,       

     it is mentioned as the message is also applicable for Downstream
Unsolicited Independent Control. 

     Is it right?

Label Request is required for DoD and allowed for DU.  Any implementation 
must support handling of Label Requests for both modes.
 
(2) What is "Propagating"?

      Could you tell me the reason why the algorithm check the state, 

     "Has LSR previously received and retained a label  mapping for FEC from
Next Hop?.", 

      and set "Propgating" with "IsPropagating" or "NotPropagating"? What
does it mean?
 
Propagating state might be thought of as indicating - for independent
control
- whether the Label (about to be given) is bound to a downstream Label.
 
(3) As the summary of A.1.1. Recevie Label Request in RFC 3036, the general
procedure of Label Request is as follow:

      - Transmission of a notification ...........

      - Transmission of label mapping .........

      - Transmission of label request ..........

      - Installation of labels ................
      But, in this procedure, the algorithm checks whether the LSR is egress
or the LSR has the labels from the Next Hop.

      As far as I think, it looks like that this procedure must be checked
before Send_Label procedure or Prepare_Label_Mapping_Attributes.

      Why this procedure is performed after Send_Label procedure?

      Is is right?
I need your help.!!
 
It is not likely that you could summarize the steps without over
simplifying.
 
There are many modes to consider and - if it could have been summarized 
as easily as this - it would have been.  :-)
 
If you consider each combination of modes - one at a time - the procedure
you arrive at for each should make sense.  Even then, you need to cover all
of the possible cases (or states) that might exist at the time of receipt of
a
Label Request. You might also look into RFC 3215. These are things you
need to do for yourself.  If you then come up with more specific questions,
you are much more likely to get help.  As it is, you are asking for a simple
explanation of a complex set of instructions that have already been stated 
as simply as possible.
Thanks.

---

From: Carlos Patriawan <[email-masked]>
Date: Tue, 3 Sep 2002 06:57:58 -0700 (PDT)

> - whether the Label (about to be given) is bound to
> a down

Yes, Indeed it's needed by the LSR to avoid receiving
another label for the same FEC when it comes from the
same downstream(next-hop) LSR. This condition should
be prohibited when LSR already has a label value for
the same FEC/next-hop LSR. If the condition is allowed
then ILM table may get confused.

Carlos Patriawan

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