Re: [OSPF] Poll for WG adoption of draft-hegde-ospf-node-admin-tag

Peter Psenak <ppsenak@cisco.com> Wed, 03 September 2014 12:19 UTC

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Date: Wed, 03 Sep 2014 14:19:12 +0200
From: Peter Psenak <ppsenak@cisco.com>
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Subject: Re: [OSPF] Poll for WG adoption of draft-hegde-ospf-node-admin-tag
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Hi Bruno,

On 9/3/14 14:09 , bruno.decraene@orange.com wrote:
> Hi Peter,
>
>> From: Peter Psenak [mailto:ppsenak@cisco.com] > Sent: Wednesday, September 03, 2014 12:32 PM
>>
>> Hi Bruno,
>>
>> On 9/3/14 12:25 , bruno.decraene@orange.com wrote:
>>> Hi Peter, Rob,
>>>
>>> +1 on Rob's comment regarding the use of admin tag for expressing
>>> +operator policy (rather than spec/feature capability)
>>>
>>> 1 point in lined below
>>>
>>>> From: Peter Psenak > Sent: Wednesday, September 03, 2014 10:21 AM
>>>>
>>>> Hi Rob,
>>>>
>>>> On 9/3/14 10:16 , Rob Shakir wrote:
>>>>> Hi Peter,
>>>>>
>>>>> On 3 Sep 2014, at 09:13, Peter Psenak <ppsenak@cisco.com> wrote:
>>>>>
>>>>>>> As per the above, I do not think that this mechanism replaces any
>>>> capability, it just gives an operator a means to be more granular
>>>> than the binary "supported"/"not supported" view that a flag
>>>> indicating capabilities does.
>>>>>>
>>>>>> I understand. My point was that admin tags should not be used in
>>>>>> cases
>>>> where only a binary capability is signaled.
>>>>>
>>>>> ACK, I completely agree. Perhaps we should add something into the
>> draft that the admin-tag should not be used for such a purpose.
>>>
>>>> I would certainly appreciate that.
>>>
>>> I agree as a general rule. Yet IMHO we should not kill this possibility. In
>> particular for feature allowing incremental deployment & interaction with
>> non-compliant nodes.
>>> One example would have been Remote LFA (RLFA):
>>> - the PLR (FRR node) needs to be RLFA compliant. Therefore (potential)
>> communication between PLR regarding their capabilities can be done using
>> IANA/implemented code point.
>>> - the PQ node (Merge Point) does not need to be RLFA compliant. And we
>> should keep this property to ease incremental deployment. Therefore
>> communication between PQ and PLR regarding PQ capabilities should/may
>> be done using node tag.  RLFA spec could have defined an IANA registered
>> node tag to be used by PQ (configured by the network operator) to exclude
>> them as PQ candidate. e.g. for PQ node not accepting T-LDP session or nodes
>> which should not be used as PQ per policy.
>>
>> why is "IANA registered node tag" any better then IANA registered capability
>> bit in the above case?
>
> We need the value to be able to be set/cleared by configuration (by the network operator) in order to allow for PQ node not compliant with RLFA to advertise it.
> Node-admin tag clear matches this requirement.
> I assumed that the capability bits were controlled by the software and not by the network operator and hence could not be used. However, I realize that this is an assumption that may be incorrect as I'm not familiar with OSPF implementations (as we are mostly using ISIS). If all OSPF implementations allow the network operator to control any bits (or at least the non allocated/supported ones) I think I agree that such bit could equally be used. However, after quickly reading the RFC, I'm not seeing that those bits MUST/SHOULD be configurable by configuration. Hence we can't really guaranty that any (future) implementation would allow this.

RFC4970 does not pose any restrictions on setting of a capability bits 
in OSPF Router Informational Capabilities TLV. Some bits may be set 
based on the software capabilities of the originator but others may be 
set based on the configuration and willingness of the originator to 
perform certain functionality. The flexibility is there.

thanks,
Peter

>
>   Thanks,
> Bruno
>> thanks,
>> Peter
>>
>>
>>
>>>
>>> Thanks,
>>> Bruno
>>>
>>>>
>>>> thanks,
>>>> Peter
>>>>
>>>>>
>>>>> Cheers,
>>>>> r.
>>>>>
>>>>
>>>> _______________________________________________
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>>>> OSPF@ietf.org
>>>> https://www.ietf.org/mailman/listinfo/ospf
>>>
>>>
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