The MPLS WG Archive

[Curtis Villamizar <curtis@fictitious.org>]

In message <0536FC9B908BEC4597EE721BE6A35389014CFD04@i2km07-ukbr.domain1.system
host.net>, neil.2.harrison@bt.com writes:
> Dave,  please see below.
> 
> regards, Neil
> 
> > -----Original Message-----
> > From: David Allan [mailto:dallan@nortelnetworks.com]
> > Sent: 11 December 2002 23:44
> > To: curtis@fictitious.org
> > Cc: curtis@fictitious.org; mpls@UU.NET
> > Subject: RE: draft-ietf-mpls-lsp-ping-01.txt - ECMP considerations 
> > 
> > 
> > Curtis:
> > 
> > I'm FAR from throwing my hands up in the air..... ;-) Just 
> > trying to move
> > the mountain (and some thinking). 
> > 
> > If I did not make it clear, for figuring out what went wrong 
> > once yoou know
> > somthing is wrong,
> NH=> This is an important point.  The discussion would have a far clearer
> basis for comment/analysis if we first identified/agreed all the failure
> conditions we want to detect, and the consequent actions that must be
> activated on such.  Discussing nuances of ECMP and the rights/wrongs of the
> LSP-Ping protocol without having this clear separation of (i) detection and
> (ii) diagnostics as a bsis for discussion is not very helpful IMO.
> <snipped to end>


OK.  I think the following summarizes the intent.

   MPLS-ping is intended to detect forwarding faults in an MPLS LSP
   and isolate the fault to the LSR at which traffic stops flowing.
   No attempt is made to determine that cause of the fault or diagnose
   problems any further.  Since MPLS-ping "echo request" packets are
   injected no further upstream than the ingress LSR, faults at the
   ingress related to classifying and directing packets and
   encapsulating them for placement in the LSP are not detected.
   Since the MPLS-ping "echo request" packets are extracted no further
   downstream than the egress LSR, faults at the egress in
   decapsulating and directing traffic further are not detected.
   Persistent faults in transiting the LSP, regardless of their cause,
   can be detected and isolated to one or two LSR.

The document doesn't explicitly state what I have above but it only
talks about detection and isolation.  For example:

   There are two parts to this
   document: information carried in an MPLS "echo request" and "echo
   reply" for the purposes of fault detection and isolation; and
   mechanisms for reliably sending the echo reply.

If Kireeti adds this to the document we don't need to enumerate all
possible faults before getting started.  I personally think it is
obvious enough that it doesn't need to be stated but it won't hurt to
add it.  If this doesn't satisfy you, please explain in greater detail
what you would like to see discussed or in the document.

Curtis