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Re: I-D ACTION:draft-ietf-ccamp-inter-domain-pd-path-comp-01.txt

Hi Igor,
Just to reiterate what Adrian said, this ID is only intended to cover the case where you do not have a PCE. 

I do, however, agree with what you say below in "The bottom line".

thanks,
-arthi



The bottom line: when PCE is available one should never consult IP routing
to determine the outgoing border node when one performs per-domain path
computation. If PCE is not available, than in case of IP network, I agree,
there is a value to consult IP routing. This is because in IP world TE
resources are still tightly coupled with IP interfaces. In the non-IP world,
I'd say, consulting IP routing makes much lesser sense: it could give you a
path when no TE path exists or, more importantly, fail the request when one
or more TE paths do exist. I'd suggest in this case rather than consulting
IP (which is as useful IMO as consulting somebody's Outlook address book) to
route the LSP towards any known domain border node and hope that the latter
will crankback the request specifying the proper border node if necessary.



Cheers,

Igor



----- Original Message -----
From: "Adrian Farrel" <adrian@olddog.co.uk>
To: "Igor Bryskin" <ibryskin@movaz.com>; <jpv@cisco.com>; "Arthi Ayyangar"
<arthi@juniper.net>
Cc: <ccamp@ops.ietf.org>
Sent: Friday, October 21, 2005 2:20 PM
Subject: 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.

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