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Re: I-D ACTION:draft-ietf-ccamp-inter-domain-pd-path-comp-01.txt
Hi Igor,
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?
No.
2. Yes, the IP reachability may give us a sub-optimal TE path.
Is this path worse than no path?
No.
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.
Cheers,
Adrian
----- Original Message -----
From: "Igor Bryskin" <ibryskin@movaz.com>
To: <jpv@cisco.com>; "Arthi Ayyangar" <arthi@juniper.net>
Cc: <ccamp@ops.ietf.org>
Sent: Friday, October 21, 2005 4:27 PM
Subject: Re: I-D ACTION:draft-ietf-ccamp-inter-domain-pd-path-comp-01.txt
> Arthi, JP
>
>
>
> 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
> ABR/ASBR).
>
>
>
> 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
can
> 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
the
> 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
not
> suboptimal compared to one from some other ABR/ASBR which knows about
worse
> IP path to the destination and hence will not be reported to the
computing
> 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
may
> ask why not to request explicit path(s) in this case? Several reasons
why
> the PCC wouldn't want to do so:
>
>
>
> a) it could be easier and faster for the PCE to determine domain border
node
> 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
> topology(ies)
>
>
>
> c) it may be desirable to compute and setup services on per-domain
basis,
> for instance, to have each domain take separate care for service
> restoration.
>
>
>
> What do you think?
>
>
>
> Igor
>
>
>
> ----- Original Message -----
>
> From: <Internet-Drafts@ietf.org>
>
> To: <i-d-announce@ietf.org>
>
> Cc: <ccamp@ops.ietf.org>
>
> 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
> directories.
> > 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.
> >
> > A URL for this Internet-Draft is:
> >
>
http://www.ietf.org/internet-drafts/draft-ietf-ccamp-inter-domain-pd-path-comp-01.txt
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