I think you have to set the context of this I-D carefully, and then
understand the limited scope that is additionally proposed.
The context of the I-D is limited to the per-domain computation case.
Hence, consulting an external PCE is out of scope. This is not to say that
it is not valid to consult a PCE (in fact, you might expect JP and me to
support that technique), but this I-D is demonstrating what we can do and
how we can solve the problem without using PCE.
With respect to the use of the IP reachability, you may recall that I
raised this concern in Paris and on the list. The conclusion was that if
you have no other way of determining an exit router for your domain, then
attempting to use the IP reachability is no worse than giving up, and may
be much better.
In the cases you raise:
1. Yes, an interface address may be unreachable.
Do we lose anything by consulting IP reachability in this case?
2. Yes, the IP reachability may give us a sub-optimal TE path.
Is this path worse than no path?
So I asked the authors to be clear that what they are suggesting has
limitations, and should not be applied in some specific cases. I haven't
looked at the text yet, but I hope they have covered this.
----- Original Message -----
From: "Igor Bryskin" <email@example.com>
To: <firstname.lastname@example.org>; "Arthi Ayyangar" <email@example.com>
Sent: Friday, October 21, 2005 4:27 PM
Subject: Re: I-D ACTION:draft-ietf-ccamp-inter-domain-pd-path-comp-01.txt
I have a problem with the auto-discovery mechanism you described in the
draft (one that is based on query to IGP or BGP to determine outgoing
1. Destination ID must be network unique but it does not have to be IP
routable, for example, it could be a numbered link ID.
2. Even in case when destination is IP address, the path computing node
only obtain the ID of an ABR or ASBR that advertises IP route to the
destination, which would be one that knows about the shortest IP path to
destination. However, it does not mean that properly constrained TE path
from this ABR/ASBR to the destination or the next ABR/ASBR exist, or is
suboptimal compared to one from some other ABR/ASBR which knows about
IP path to the destination and hence will not be reported to the
entity by the routing sub-system.
I wonder why not to use the remote PCE service for this purpose. For
instance a PCC may ask a PCE to determine either the ID of the outgoing
domain border node or entire path in terms of domain border nodes. You
ask why not to request explicit path(s) in this case? Several reasons
the PCC wouldn't want to do so:
a) it could be easier and faster for the PCE to determine domain border
in direction towards the destination rather than explicit path(s). For
instance, the latter may require cooperation of other PCEs;
b) security considerations - PCE may not want to reveal remote domain
c) it may be desirable to compute and setup services on per-domain
for instance, to have each domain take separate care for service
What do you think?
----- Original Message -----
Sent: Thursday, October 20, 2005 6:50 PM
Subject: I-D ACTION:draft-ietf-ccamp-inter-domain-pd-path-comp-01.txt
A New Internet-Draft is available from the on-line Internet-Drafts
This draft is a work item of the Common Control and Measurement Plane
Working Group of the IETF.
Title : A Per-domain path computation method for establishing
Inter-domain Traffic Engineering (TE) Label
Switched Paths (LSPs)
Author(s) : J. Vasseur, et al.
Filename : draft-ietf-ccamp-inter-domain-pd-path-comp-01.txt
Pages : 18
Date : 2005-10-20
This document specifies a per-domain path computation technique for
establishing inter-domain Traffic Engineering (TE) Multiprotocol Label
Switching (MPLS) and Generalized MPLS (GMPLS) Label Switched Paths
(LSPs). In this document a domain refers to a collection of network
elements within a common sphere of address management or path
computational responsibility such as IGP areas and Autonomous Systems.
Per-domain computation applies where the full path of an inter-domain
TE LSP cannot be or is not determined at the ingress node of the TE
LSP, and is not signaled across domain boundaries. This is most likely
to arise owing to TE visibility limitations. The signaling message
indicates the destination and nodes up to the next domain boundary. It
may also indicate further domain boundaries or domain identifiers. The
path through each domain, possibly including the choice of exit point
from the domain, must be determined within the domain.
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