Re: [OSPF] FW: New Version Notification for draft-ietf-ospf-prefix-link-attr-00.txt

"Acee Lindem (acee)" <acee@cisco.com> Fri, 05 September 2014 12:37 UTC

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From: "Acee Lindem (acee)" <acee@cisco.com>
To: "Peter Psenak (ppsenak)" <ppsenak@cisco.com>, "A. Przygienda" <prz@zeta2.ch>, "ospf@ietf.org" <ospf@ietf.org>
Thread-Topic: [OSPF] FW: New Version Notification for draft-ietf-ospf-prefix-link-attr-00.txt
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Date: Fri, 5 Sep 2014 12:37:15 +0000
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Subject: Re: [OSPF] FW: New Version Notification for draft-ietf-ospf-prefix-link-attr-00.txt
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Hi Tony, Peter, 

I plan to update the draft next week and address some of these
clarifications.

Thanks,
Acee 

On 9/5/14, 4:34 AM, "Peter Psenak (ppsenak)" <ppsenak@cisco.com> wrote:

>Hi Tony,
>
>please see inline:
>
>On 9/4/14 21:02 , A. Przygienda wrote:
>> On 09/04/2014 12:24 AM, Peter Psenak wrote:
>>> Hi Tony,
>>>
>>> please see inline:
>>
>> Hey Peter, same
>>
>>>
>>> On 9/3/14 18:13 , A. Przygienda wrote:
>>>>
>>>>
>>>> It's also wise to add 'if the same extended prefix TLV (i.e. for same
>>>> prefix) is seen twice in same opaque LSA only use the first and force
>>>> people to put all sub-tlvs into a single tlv.
>>>
>>> it's kind of obvious, but we can add a text to be sure.
>>
>> As I see it, the purpose of an RFC is to assure interoperability. If
>> there are two
>> interpretations available of the same packet that will make two
>> solutions not interoperable,
>> the standard has to mandate the correct one.
>
>ok, we will add a text to make it clear.
>
>>
>>>
>>>>
>>>> "OSPFv2 requires functional extension beyond what can readily be done
>>>> with the fixed-format Link State Advertisements (LSAs) as described
>>>> in RFC 2328 [OSPFV2]. This document defines OSPF opaque LSAs based
>>>> on Type-Length-Value (TLV) tuples that can be used to associate
>>>> additional attributes with advertised prefixes or links."
>>>>
>>>> That's strongly suggestive of "you advertise normal LSA and then you
>>>>use
>>>> opaque to 'extend' it" . Extended extends and is not independent from
>>>> original stuff in normal use of English idiom.
>>>
>>> because existing LSA are not extensible, any additional link/prefix
>>> attributes must be advertised in a separate LSAs. We called it
>>> "extended", but it does not mean that existence of the extended LSA
>>> require existence of the base LSA. I had a text in the original SR
>>> draft around that, we can add it here too.
>>
>> yepp, once it spelled out, it's obvious but the first conclusion one
>> jumps to is that they are inter-dependent otherwise.
>
>ok, we will add a text to clarify.
>
>>
>>>
>>>
>>>> .,..
>>>> the area that do not support opaques, an additional text is needed
>>>> saying  "never compute through routers without opaques using
>>>>information
>>>> in opaques that influences reachability or metrics". Actually, it's
>>>> worse since if a router without opaques forwards through a router
>>>> advertising opaques influencing metrics (for sake or simplicity), you
>>>> cannot start using opaques to keep on forwarding.  In case that all
>>>> doesn't parse, I can do a simple looping example.
>>>
>>> we are not advertising any metrics in the extended LSAs, so I do not
>>> see why we would have to deal with that case here. If one day someone
>>> wants to do that, then it would have to be covered in a separate draft
>>> and we would deal with it at that time.
>>
>> agreed here. you're correct. That would be overspecification in this
>>draft
>>
>>>
>>>> OK, I still don't understand 'WHICH flooding scope', the  type-3 vs.
>>>> type-5 one or the 'opaque flodding scope one'.  I think you mean 'all
>>>> prefixes in the same opaque must have the same OSPF-route-type
>>>> [0+unevens]'  but the text is really hard to parse here.
>>>>
>>>> Acee, you mean remove the restriction ?  I see how some
>>>>implementations
>>>> may benefit from cramming all type-3 into the same opaque but I would
>>>> also suggest to not restrict this and remove the text.
>>>
>>> the restriction can not be removed. All the Extended Prefix TLVs that
>>> you put in a singe Extended Prefix LSA will only use a flooding scope
>>> of the Extended LSA itself.
>>
>> I still think it's not clear what the original paragraph means.
>
>prefixes can have different flooding scope. Today intra-area and
>inter-area prefixes have area flooding scope and external prefixes have
>domain wide flooding scope. You can not mix prefixes of different
>flooding scope in a single Extended Prefix LSA, because Extended Prefix
>LSA can only have a single flooding scope.
>
>>
>>>
>>>> yes, and again, I think 'extended' is an ill chosen name maybe if
>>>>that's
>>>> the intention of the draft.
>>>>
>>>> BTW, what is the plan if all the TLVs blow out the MTU of the opaque ?
>>>
>>> you can generate many Extended Prefix or Extended Link LSAs, so there
>>> is no issue.
>>
>> ack
>>
>>>
>>>> I'm missing something ?   RFC5250 is not describing how the instance
>>>> (they call it Opaque ID) is supposed to be generated (it references
>>>> appendix A referencing section 7 which has nothing in it about this).
>>>> I'm divining the instance allows to have multiple opaques of the same
>>>> type which leads to bunch interesting discussions
>>>>        * what happens when the MTU gets blown & TLVs are shifted into
>>>> next 'fragment' in ISIS speak [with all the restrictions how the TLVs
>>>> can migrate between fragments, ISIS guys suffered this one [as did
>>>>PNNI]
>>>> @ length & will surely lend a helping hand in such a case].
>>>
>>> TLVs can come and go and move from one Extended Opaque LSA to the
>>> other. Implementation needs to track these changes and deal with them.
>>
>> I would let the ISIS guys chime in here. They have tons experience with
>> TLVs sliding fragments and what kind of implementation/operation pain
>> that can cause.
>>
>>>
>>>
>>>>        * what happens if the same extended prefix TLV shows up twice
>>>>in
>>>> two different opaques of same type ?  You use the one that is in lower
>>>> opaque ID ?
>>>
>>> I would call it a bug on the originator side.
>>
>> yes, but still, the draft should mandate what the desired behavior is @
>> this point in time otherwise some will use the lower ID, some higher and
>> some none of the above & the implementations will not interop ?
>
>ok, we will add a tiebreaker there.
>
>thanks,
>Peter
>>
>> --- tony
>>
>> _______________________________________________
>> OSPF mailing list
>> OSPF@ietf.org
>> https://www.ietf.org/mailman/listinfo/ospf
>> .
>>
>
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