Re: [Isis-wg] latest update of draft-ietf-isis-segment-routing-extensions

[Pushpasis Sarkar <[e-mail]>]

Hi Stefano,

As much I understand the LDP mapping server functionality the
Label-Binding TLV shall be used to map a SR Node-SID-Index with a FEC
originated by SR-incapable node.

Now in regular SPRING domain a SR-capable node does not generate one
Node-SID-Index for a given node address (loopback) per topology. The index
is still one for the address across all topologies. Do you suggest that
there should be a Node-SID-Index configured for every topology? If not,
then I don¹t see a need of mapping different node-sid-index for the same
prefix under different topology.

Thanks
-Pushpasis

On 5/21/15, 10:13 PM, "Stefano Previdi (sprevidi)" <[e-mail]>
wrote:

>Hi Hannes,
>
>On May 21, 2015, at 4:34 PM, Hannes Gredler <[e-mail]> wrote:
>> hi stefano,
>> 
>> On Thu, May 21, 2015 at 01:55:07PM +0000, Stefano Previdi (sprevidi)
>>wrote:
>> | [... ]
>> | SP> Can you clarify in a new thread what is your problem in making
>>the Binding TLV _not_ MT aware in ISIS ?
>> 
>> very simple explanation:
>> 
>> Binding TLV only carries non-IP (e.g. MPLS labels, SRGB Indexes)
>>information
>>   at no point it carries information which directly affects IP
>>forwarding state.
>
>
>it propagates information about paths that are useable in a topology.
>
>
>> in contrast all exisiting MT TLVs carry information which have direct
>>relevance
>>   to the generation of IP forwarding state (e.g.
>>     -MT-ISREACH affects metrics for IP routes,
>>     -MT-IPREACH affects advertisment and metrics for IP routes).
>> 
>> what is not clear to me:
>> why do we need to augment non-IP advertisments with extensions
>> that are only relevant for IP path construction. -
>> the intersection between the two seems zero to me.
>
>
>ok, let's try to clarify the point then.
>
>ISIS is used to propagate information pertaining to prefixes and
>topology. This information has been contextualized with the introduction
>of MT-ISIS. This resulted into adding a MT-ID to each piece of topology
>advertised by ISIS, including prefixes and adjacencies.
>
>SR introduced the Binding TLV which is also a piece of topology since it
>represents a useable path in the topology.
>
>Therefore, it makes sense to me to add a MT-ID to the Binding TLV.
>
>Note also that the Binding TLV is used by the Mapping Server. There too,
>the information propagated by the Mapping Server MAY be related to a
>topology. An example is the deployment of IPv6 using MT-ISIS where all
>IPv6 information (prefixes, adjacencies) are advertised within topology
>ID 2. It wouldn't make sense to advertise IPv6/SID mappings without any
>topology identifier.
>
>Therefore, to me, it is straightforward to enhance the Binding TLV with
>MT capability.
>
>
>> | SP> Also, would you also suggest to make it _not_ MT aware in OSPF ?
>>In such case we have to change the OSPF spec.
>> 
>> same reasoning here: in case its not clear what/how to use MT in the
>>binding TLV for, we should remove it.
>
>
>well, it looks to me the ospf wg clearly understood and acknowledged the
>need of the MT-ID and I believe we did the right thing there.
>
>Now, I'd be interested to know other people opinion on this (from both
>isis and spring wg's).
>
>s.
>
>
>> 
>> /hannes
>> 
>> | On May 21, 2015, at 3:26 PM, Hannes Gredler <[e-mail]>
>>wrote:
>> | 
>> | > hi stefano,
>> | > 
>> | > On Thu, May 21, 2015 at 10:14:20AM +0000, Stefano Previdi
>>(sprevidi) wrote:
>> | > [ ... ]
>> | > | > | SP> why not creating a new thread explaining the issue and
>>including isis and spring wg ?
>> | > | > 
>> | > | > HG> thats a good suggestion  - please do it ! -
>> | > | > HG> we need to be clear on the protocol requirements *before*
>>adding
>> | > | > HG> protocol extensions.
>> | > | 
>> | > | SP> well, we agreed already at multiple occasions (last one was
>>during the meeting in Dallas
>> | > | SP> where you and me agreed to add MT support to the Binding TLV)
>>so we're inline with the process, right ?
>> | > 
>> | > again this is meant as a friendly reminder to document (e.g. in
>>some of the SPRING documents
>> | > where you have the pen) how you want to intend to use the MT
>>extensions for the binding TLV.
>> | > 
>> | > its not yet clear to me and i'd like to get an answer on this
>>before progressing the
>> | > protocol extensions in the ISIS and OSPF working groups.
>> | > 
>> | > /hannes
>> | 
>
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