Re: IGP Extensions - CCAMP Milestones

[Mr Xu <[e-mail]>]

I think distributing opaque LSAs for TE router cap across OSPF domain is not a good idea, because this information is concrete and can not aggregated, it will cause too much flooding in an AS. 

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----- Original Message ----- 
From: "dimitri papadimitriou" <[e-mail]>
To: "Igor Bryskin" <[e-mail]>
Cc: <[e-mail]>; "JP Vasseur" <[e-mail]>; "Adrian Farrel" <[e-mail]>; "LE ROUX Jean-Louis RD-CORE-LAN" <[e-mail]>; <[e-mail]>
Sent: Tuesday, November 22, 2005 7:19 AM
Subject: Re: IGP Extensions - CCAMP Milestones


> igor
> 
> Igor Bryskin wrote:
> 
> > Dimitri,
> > 
> > See my reply to JP. Also see below.
> > 
> > ----- Original Message ----- 
> > From: "dimitri papadimitriou" <[e-mail]>
> > To: "JP Vasseur" <[e-mail]>
> > Cc: "Igor Bryskin" <[e-mail]>; <[e-mail]>;
> > "Adrian Farrel" <[e-mail]>; "LE ROUX Jean-Louis RD-CORE-LAN"
> > <[e-mail]>; <[e-mail]>
> > 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 be withdrawn or modified by the LSR that has originated them.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" <[e-mail]>
> >>>>
> >>>>To: "Adrian Farrel" <[e-mail]>
> >>>>
> >>>>Cc: "LE ROUX Jean-Louis RD-CORE-LAN"
> >>>><[e-mail]>;
> >>>>"JP Vasseur" <[e-mail]>; "Dimitri Papadimitriou"
> >>>><[e-mail]>; <[e-mail]>
> >>>>
> >>>>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"
> >>>>>><[e-mail]>
> >>>>>>To: "JP Vasseur" <[e-mail]>; "Dimitri Papadimitriou"
> >>>>>><[e-mail]>; "Dimitri Papadimitriou"
> >>>>>><[e-mail]>
> >>>>>>Cc: <[e-mail]>; <[e-mail]>
> >>>>>>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:[e-mail]]
> >>>>>>>Envoyé : jeudi 17 novembre 2005 16:58
> >>>>>>>À : Dimitri Papadimitriou; Dimitri Papadimitriou
> >>>>>>>Cc : [e-mail]; [e-mail]; 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
> >>>>>>>>>.
> >>>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>>.
> >>>>>>
> >>>>>>
> >>>>>
> >>>
> >>>.
> >>>
> >>
> > 
> > 
> > .
> > 
>