Re: [mpls-linux-general] ldp question

[James R. L. <jl...@mi...>]

I trued to send a reponse to this a week ago, but I got a delivery error,
hopefully this one makes it to you.


Date: Fri, 6 Apr 2001 13:37:25 -0500
From: "James R. Leu" <jl...@mi...>
To: Scott Lee <nat...@ya...>
Cc: jl...@mi..., uk...@rz...
Subject: Re: ldp question

Hello,

Sorry for not getting back sooner.  Yon's answer reminded me about this.

On Thu, Apr 05, 2001 at 09:59:49AM -0700, Scott Lee wrote:
> Hi James,
> 
> My name is Scott Lee and I am one of many who
> is interested in Linux MPLS, LDP, transporting layer
> 2 over IP backbone, etc.
> 
> Can  I ask you a quick question?
> 
> When operating in downstream-unsolicited, liberal
> retention mode, 
> independent control mode, do you ever issue Label
> Request Message?

If you (the LSR) do not support label merge and have more then one
upstream neighbor to whom you must propogate an unsolicited
advertisment that you received from downstream, then you will need to
request more labels to satisfy building these LSPs.  Whether you propogate
a mapping and then request or request and then propogate a mapping is
determined by your control mode.

How sane is it to run unsolicited and not support label merge?  It's
not, BUT if your running over ethernet and you and your peer disagree
about distribution mode the RFC specifies that DU will be used.  SO ...
it is very possible that you will be in this situation and have no control
over it.

> According to the MPLS architecture RFC, the above
> mode should lead to the following scheme.
> {pushUnconditional, RequestNever, NoReleaseOnChange,
> noLoopDetection}
> 
> It seems like we never send label request message.
> 
> One more question, when you send label withdraw
> messsage and if you don't get label release message,
> what do you do?

I think Yon brought up a good point that a timer is needed, but it
doesn't seem like the RFC specifies one.  I know I don't handle this
case yet :-)  I'll add it to my list.


> 
> Thanks!
> 
> 
> 
> 
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-- 
James R. Leu

On Thu, Apr 12, 2001 at 03:31:14PM -0700, Scott Lee wrote:
> 
> When operating in downstream-unsolicited, liberal
> retention mode, 
> independent control mode, do you ever issue Label
> Request Message? According to MPLS architecture doc,
> it seems like LDP would never send Label Request msg.
> 
> One more question.
> When you send label withdraw message and you don't get
> label release message, what do you do in that case?
> Should LDP timeout and resend the withdraw message?
> 
> Thanks.
> 
> 
> 
> 
> 
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-- 
James R. Leu