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Re: IGP Extensions - CCAMP Milestones
Hi JP,
See in-line.
Cheers,
Igor
----- Original Message -----
From: "JP Vasseur" <jvasseur@cisco.com>
To: "Igor Bryskin" <ibryskin@movaz.com>
Cc: <dpapadimitriou@psg.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 9:57 AM
Subject: Re: IGP Extensions - CCAMP Milestones
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 advertising is valid (otherwise, it would be withdrawn); on the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).
IB>> True, that what is written in RFC2328. And my contention here is that
if an ASBR advertises LSAs type 5 and dies after that, than OSPF speakers
outside of the ASBR's area have good likelihood to use stale external routes
for a considerable period of time. There is no remedy to that (OSPF speakers
do not use Keep Alive protocol :=). This, however, could be fixed by
avoiding using of AS scope flooding, and that's exactly the reason why some
OSPF applications that I know of do just that. But this is the discussion
for OSPF WG, I suggest not argue about that. See below.
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.
IB>> Let's stick to your example. Why is it better to flood router
capability LSAs across an AS, rather than flood them within a single area
and have ABRs relay the advertisings into other areas by originating their
own LSAs? Yes, the AS-scope flooding is simpler. But what I am suggesting
has the following advantages:
a) Advertisings of a crashed LSR could be withdrawn from use by all AS
LSRs immediately after the crash;
b) Advertisings could be summarized by an ABR providing scalability
improvements;
c) What is more important that policies could be applied on ABRs wrt to
what information is leaked to external areas. Regretfully, you keep
forgetting about the policy aspects, but in the context of AS-scope flooding
how can you enforce that an LSR capabilities are advertised into some areas,
not advertised into some other areas, and advertised in a modified way into
the third set of areas?
Igor
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
>>>>>> .
>>>>>>
>>>>>
>>>>>
>>>
>>>
>>>
>>>
>>> .
>>>
>>>
>>
>