Oscar:
Speak as contributor or for software implementers, I would like to thank you to 
initiate this work, a few thoughts on this model design choice:
1.It is not clear to me whether L3NM model is positioned as Network model or 
service model.

l  Service model focus on describing what the service is while network model 
focusing how to realize the service.

l  Service model is used as input to automated control and configuration 
applications while network model is translated or derived from service model 
and is used to describe instantiated L3VPN with various resource allocation 
(e.g., RT,RD, endpoint/attachment point), therefore network model doesn’t need 
to take the same model structure as L3SM model.

2.L3SM describes customer view of L3VPN service and can be used to describe 
multiple sites belonging to multiple VPNs, spanning across multiple domains. 
However L3NM model is described domain controller view of L3VPN service, it 
will be great to allow automated control and configuration applications 
decomposed L3SM with multiple VPNs support into multiple per VPN Network model 
(per VRF or VRF centric), then domain controller can manage VPN service one by 
one, it also will be convenient to allow Domain controller further decompose 
per VPN Network model into various device model or network element models(e.g., 
Network instance model, BESS L3VPN model).

3. If we can model L3NM model as per VPN Network model, describe the 
relationship between VPN service and site/endpoints as parent child 
relationship instead of sibling relationship defined in L3SM model, then cross 
reference(e.g., using leafref) between VPN service and site/endpoint is not 
needed.
Therefore I think taking “Prune and extend” approach make us easily decompose 
abstract view of VPN service from customer perspective spanning multi-domain, 
multi-layer  to domain specific view of VPN service or resource level of VPN.

-Qin
发件人: OPSAWG [mailto:[email protected]] 代表 Oscar González de Dios
发送时间: 2019年5月28日 1:16
收件人: [email protected]
主题: [OPSAWG] Feedback and operators+implementers input for L3NM 
draft-aguado-opsawg-l3sm-l3nm-00

Dear Opsawg colleagues,

     I would like to ask for feedback on an operator-led initiative to build a 
L3VPN Network Yang model (let’s refer to it as L3NM). The first draft is 
available in https://tools.ietf.org/html/draft-aguado-opsawg-l3sm-l3nm-00.

      Please note that the yang model itself is still a work in progress, and 
the first intention is to show the need of having such a model and how it 
related to current initiatives. The starting point of the work is the L3VPN 
Yang model defined in RFC 8299.  More complex deployment scenarios involving 
the  coordination of different VPN instances and different technologies to  
provide end-to-end VPN connectivity is out of scope of this document,  but is 
discussed in 
https://tools.ietf.org/html/draft-evenwu-opsawg-yang-composed-vpn-03 .

    RFC 8309 splits the service models into “Customer Service Model” and 
“Service Delivery Model”. The L3SM Yang model, defined in RFC 8299, is valid 
for the customer to network operator conversation, but if operators want to use 
it for the conversations between the B/OSS (business and operation support 
systems) and the network orchestrator (or controller, depending on the 
terminology used) then the model has some gaps. There are two options:


A)     “Augment” approach. This is the approach shown in version 00. The model 
in RFC 8299 is extended via augmentation to cover the gaps. Still, some 
parameters defined by L3SM may not be necessary for the network version of the 
service model (those more related to the customer, which are mandatory for the 
direct customer interface).

B)      “Prune and extend” approach. This approach will present an easier way 
to ignore and prune unnecessary information defined at L3SM. At the same time, 
any extension can be presented as part of the main module, and not as augments 
of an existing model. However, many content would be similar to L3SM

In the draft you can find a first set of topics covered by the model.  The 
scenarios covered include: the integration of ethernet and encapsulation 
parameters, the extension for transport resources (e.g. RTs and RDs) to be 
orchestrated from the management system, far-end  configuration of PEs not 
managed by the management system and the definition for PE identification. Note 
the end customer does not really care about the internal network resources, 
neither does care exactly which PE is used. Those decisions are taken by the 
operator, that then with the help of the control systems will deploy the 
service.

    We would like to ask input from operators/service providers who might use 
this model and from software implementers who might code the model.

    Best Regards,

                Oscar

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