Re: [mpls] Alvaro Retana's Discuss on draft-ietf-mpls-rsvp-shared-labels-07: (with DISCUSS and COMMENT)

[Alvaro Retana <[e-mail]>]

On January 25, 2019 at 6:17:42 PM, Vishnu Pavan Beeram (
[e-mail]) wrote:

Pavan:


...

On Wed, Jan 23, 2019 at 4:52 PM Alvaro Retana <[e-mail]>
wrote:

Snipped..

> These are fine examples, and they would satisfy the point above.
>>>
>>> However, they raise an additional one.  rfc8491 has a very specific
>>> definition of what the Base MPLS Imposition MSD is, but that definition may
>>> not match what is discussed here.  The intent may be the same, but the text
>>> is different, and given the extensive discussion prior to the publication
>>> of rfc8491, I want to make sure that we are in fact talking about the same
>>> thing: "label stack depth push limit” doesn’t directly map to "the total
>>> number of MPLS labels that can be imposed, including all
>>> service/transport/special labels” [rfc8491].  I note that this document
>>> specifically mentions just transport labels.
>>>
>>> If the definition of the BMI-MSD is what is expected in this document,
>>> please explicitly say so.  If not, then I think that we would need to
>>> define a new MSD-Type for the suggestions above to be applicable.
>>>
>> [Pavan] The “label stack depth push limit” is the same as what is
>> referred to as the BMI-MSD in RFC8491. We will make that explicit.
>>
>
> I see no place in the text where the relationship to the BMI-MSD is
> explicitly made.
>
> I see the text (in parenthesis) that you added in §5.3: "label stack depth
> push limit (number of MPLS labels that can be imposed)”, but that doesn’t
> make reference to either the BMI-MSD or rfc8491.  Also, the text added is
> not the complete definition.
>

Please see if the following changes address the concern.
**
In Section 5.2

OLD:

   In order to accurately pick
   the delegation hops, the ingress needs to be aware of the label stack
   depth push limit (number of MPLS labels that can be imposed) of each
   of the transit LSRs prior to initiating the signaling sequence.
   ...
   An example of such a mechanism is specified in [RFC8491].

NEW:
   In order to accurately pick
   the delegation hops, the ingress needs to be aware of the label stack
   depth push limit (total number of MPLS labels that can be imposed,
   including all service/transport/special labels) of each of the
   transit LSRs prior to initiating the signaling sequence.
   ...
   An example of such a mechanism is specified in [RFC8491] (BMI-MSD
   advertisement).
**

>> All this would make rfc8491 a Normative reference.

Would it? Please note that the “explicit delegation” can be implemented
without needing to implement any of the standard BMI-MSD learning
technologies. The RFC8491 mechanism is just one option. As stated earlier,
an implementation may choose to employ any of the following mechanisms
besides RFC8491 —  OSPF (RFC8476), BGP-LS
(draft-ietf-idr-bgp-ls-segment-routing-msd), PCEP
(draft-ietf-pce-segment-routing), local config (just set a global limit),
netconf/restconf/grpc using the data-model specified in
draft-ietf-teas-yang-sr-te-topo.

I would have preferred if a Normative reference was made to BMI-MSD to
avoid any confusion (vs copying the definition here).  That’s were I think
that rfc8491 would be Normative; not in the mechanism, but in the
definition.

In any case, I guess the way you wrote it above is ok as well.  I’ll clear
the DISCUSS when you publish an update.

Thanks!!

Alvaro.