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Re: IGP Extensions - CCAMP Milestones

igor

Igor Bryskin wrote:


Dimitri,

See my reply to JP. Also see below.
----- Original Message ----- From: "dimitri papadimitriou" <dpapadimitriou@psg.com> 
To: "JP Vasseur" <jvasseur@cisco.com>
Cc: "Igor Bryskin" <ibryskin@movaz.com>; <dimitri.papadimitriou@alcatel.be>;
"Adrian Farrel" <adrian@olddog.co.uk>; "LE ROUX Jean-Louis RD-CORE-LAN"
<jeanlouis.leroux@francetelecom.com>; <ccamp@ops.ietf.org>
Sent: Sunday, November 20, 2005 2:40 PM
Subject: Re: IGP Extensions - CCAMP Milestones




hi jp,

indeed, i don't really understand the issue brought up by igor;

in the present case, one should also underline that, the information
distributed across the OSPF domain using opaque LSAs, is *indirectly*
used by e.g. TE applications (note: RFC2370 allows for this information
to be used directly by OSPF but i think we're not discussing this
alternative)

this means that these e.g. TE applications can in case of control engine
failure detect this failure and trigger any necessary action in order to
avoid the behaviour described by igor



IB>> Two points here:

a) all TE LSAs are of the area scope;
you are confusing TE LSAs (opaque type 1, area-scope) applicability with the broader context of e.g. TE applications (see initial statement) that can make use of RI LSAs for inst. 


b) A TE application can detect a control engine failure only within one
area. 

this is not correct, as by definition, application dependent;

thanks,
- dimitri.


It does not help for LSRs located outside of this area because no LSR
(including ABR) is allowed to withdraw somebody else's LSAs - the LSAs could
be withdrawn or modified by the LSR that has originated them.
Igor 



thanks,
- dimitri.

JP Vasseur wrote:


Hi Igor,

On Nov 19, 2005, at 11:16 AM, Igor Bryskin wrote:



Hi everybody,



I'd like to note that although the AS scope flooding is allowed for
opaque
LSAs, in my experience it does not work.



So your experience is different than the one of many people ...  Opaque
LSA have been
used for quite a few years without any problem. See RFC2370 (July 1998)



Imagine that some routing
controller advertises an AS scope LSA and goes out of service  quickly
after
that. Controllers outside of the area that the dead controller
belongs to
have no way of detecting its death and, therefore, will keep using the
advertising for another 90 min before the LSA times out.



I guess that you mean 60 min (Maxage=60mn, Architectural Constant) -
See RFC2328, but this is not the point, see below.



Note that the
controllers located within the same area do not have such a problem
because
they can always verify the validity of the advertising by trying to
locate a
sequence of active adjacencies interconnecting each of them with the
advertising controller. If they find at least one such a sequence, the
advertising is valid (otherwise, it would be withdrawn); on the  other
hand,
if no such sequences exist, than advertising is likely to be stale
and hence
could not be trusted. The conclusion is that opaque LSAs should  never


be


flooded within AS, rather, within a single area, and, if there is a
need for
the information to be propagated beyond the area boundaries, ABRs
must relay
the advertising into other areas (by originating new area-scope
LSAs). Note
also that as far as I remember OSPF itself never uses AS scope
advertisings
for its own needs. For example, an ASBR does not distribute  external
routes
learned by BGP from other ASs using AS scope LSAs, rather, the  routes
are
advertised within a single area and ABRs relay the advertisings  into
other
areas.



This is not correct. External routes are redistributed with LSA Type  5
which are
flooded across the entire domain except in stub-area (not generated by
the ABR as type 3 as you mention).

Anyway, back to the point, one cannot say of course that "Opaque LSA
Type 11 does not work". There are suitable to some application, this is
all. You can perfectly reply on an opaque LSA Type 11 to learn the
capability of a router which does not reside in the local area and rely
on another mechanism to detect its liveness. There are several such
examples.

Hope this helps.

JP.






The bottom line is that the TLVs described in the draft should be  of


the


area scope (just like TE LSAs), and hence it is not all that important
whether we use new high level TLVs or sub-TLVs of the TE router cap


TLV.




Igor





----- Original Message -----

From: "dimitri papadimitriou" <dpapadimitriou@psg.com>

To: "Adrian Farrel" <adrian@olddog.co.uk>

Cc: "LE ROUX Jean-Louis RD-CORE-LAN"
<jeanlouis.leroux@francetelecom.com>;
"JP Vasseur" <jvasseur@cisco.com>; "Dimitri Papadimitriou"
<dimitri.papadimitriou@alcatel.be>; <ccamp@ops.ietf.org>

Sent: Friday, November 18, 2005 10:57 AM

Subject: Re: IGP Extensions - CCAMP Milestones






adrian

i think JL's reply did partially translate the initial concern

in brief, there are three well identified TE applications that could
make use of the TE node cap TLVs on both intra and inter-area basis:
- LSP Stitching edge node capability
- Edge nodes connecting/being P2MP TE egresses
- TE auto-mesh

hence, the question on why keeping separated TLVs as part of the


router


capability and not consider these as sub-TLVs of the TE router cap


TLV


this would
1) provide a logical grouping of TE sub-TLVs as part of the same  TLV
and
2) leave the flexibility of flooding scope on a per application


 need -


note: that the path computation specific sub-TLVs could still be
restricted with their current area-scope

hope this clarifies the issue,

thanks,
- dimitri.

Adrian Farrel wrote:




If I understand the question it is...

In draft-ietf-ospf-cap-07.txt introduces the OSPF router
information LSA
and states that this LSA may have type 9, 10 or 11 scope.

In draft-vasseur-ccamp-te-node-cap-01.txt a new TLV (TE Node
Capability
Descriptor) is added to the OSPF router information LSA. This TLV
(when
generated) MUST be advertised with type 10 scope. JL has given the



reason



why this is limited to type 10. This reason is, of course, open for
discussion as he says.

In draft-vasseur-ccamp-automesh-02.txt a new TLV (TE-MESH-GROUP) is



added



to the OSPF router information LSA. It states that the LSA may be
advertised with type 10 or type 11 scope. JP has given a reason  why
you
might want type 11 in addition to type 10. This reason is, of


course,


open



for discussion.

An interesting feature is that a router advertising an AS-wide mesh



group



*and* a TE router capability may require that two OSPF router



information



LSAs are advertised by the router.

The language in draft-ietf-ospf-cap-07.txt leans towards a router



sending



*an* OSPF router information LSA. But nowhere does it say that the



router



cannot send more than one and in section 2.5 we find...
 The originating router MAY advertise
  multiple RI LSAs as long as the flooding scopes differ.

Hope this answers the point.

Adrian
----- Original Message -----
From: "LE ROUX Jean-Louis RD-CORE-LAN"
<jeanlouis.leroux@francetelecom.com>
To: "JP Vasseur" <jvasseur@cisco.com>; "Dimitri Papadimitriou"
<dpapadimitriou@psg.com>; "Dimitri Papadimitriou"
<dimitri.papadimitriou@alcatel.be>
Cc: <adrian@olddog.co.uk>; <ccamp@ops.ietf.org>
Sent: Thursday, November 17, 2005 6:47 PM
Subject: RE: IGP Extensions - CCAMP Milestones


Hi Dimitri,

Thanks for the comment.

As just explained by JP, the TE Node Cap TLV carries topology


related


parameters used as constraints in path computation. The leaking  of
such
info across areas sounds useless as LSR TE visibility is limited  to
one
area anyway...
But this is, of course, open to discussions. By the way, do you
have any
application in mind where such leaking would be useful?

Regards,

JL










-----Message d'origine-----
De : JP Vasseur [mailto:jvasseur@cisco.com]
Envoyé : jeudi 17 novembre 2005 16:58
À : Dimitri Papadimitriou; Dimitri Papadimitriou
Cc : zzx-adrian@olddog.co.uk; ccamp@ops.ietf.org; LE ROUX
Jean-Louis RD-CORE-LAN
Objet : Re: IGP Extensions - CCAMP Milestones

Hi dimitri,

On Nov 16, 2005, at 6:30 PM, dimitri papadimitriou wrote:





adrian,

could you explain the reasoning for having a TE specific TLV in


the


auto-mesh document with area and AS-wide flooding scope



while the TE




router cap TLV is restricted to an area flooding scope ?
shouldn't be one way or the other i.e. either restrict all TE info
area-local or allow for TE router cap TLV with AS-wide



flooding scope




?

note: there is nothing in the TE router cap TLV that would impact
scaling more than the TE auto-mesh TLV does




I guess that the reason for allowing both intra and inter-area
flooding scopes for automesh is obvious (we need to have TE LSP


mesh


within areas and spanning multiple areas).

So your question is probably why don't we allow the TE router
cap TLV
to be flooded across the domain ? As far as I can remember JL
already
answered this question ... JL, could you forward your email again ?

In the meantime, I can answer it: the reason is that such TE node
capabilities are used for TE LSP computation which cannot take into
account nodes that do not reside in the node's area.

Thanks.

JP.





thanks,
- dimitri.

Adrian Farrel wrote:






Hi,
We have two immediate milestones to address:
Oct 05  First version WG I-D for Advertising TE Node Capabilities
in ISIS
and OSPF
Oct 05  First version WG I-D for Automatic discovery of



MPLS-TE mesh




membership
There are two personal submissions which address these topics:
draft-vasseur-ccamp-te-node-cap-01.txt
draft-vasseur-ccamp-automesh-02.txt
I propose that we move these into the WG and then kick the tires
thoroughly.
Opinions please.
Thanks,
Adrian
.








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