Subject: [netmod] WBEM/CIM v. NETCONF/YANG

From: Jonathan Hansford <[email-masked]>
Date: Wed, 11 Jul 2012 10:15:08 +0100

This will probably be so obvious to most of you, I almost feel like
not sending this, but I just want to confirm something rather
fundamental that only struck me yesterday. 

CIM, as described on the
DMTF web site, "provides a common definition of management information
for systems, networks, applications and services, and allows for vendor
extensions". The CIM Concepts White Paper identifies CIM's goal as "to
model all the various aspects of the managed environment, not just a
single problem space". In other words CIM provides an information model
of the whole system, it is system-centric. In contrast, YANG data models
are intended to be device-centric. Consequently there is typically no
YANG system model and relationships between entities only need to make
sense within the scope of the device being configured. Have I got that
right? 

The reason I ask is that, if that is the case, I am
over-complicating my YANG modules in an attempt to capture system
relationships that are never visible at the device level. 

Jonathan

---

From: Juergen Schoenwaelder <[email-masked]>
Date: Wed, 11 Jul 2012 11:34:25 +0200

> sense within the scope of the device being configured. Have I got that

The word "system" has way too many meanings. I am not even sure the
CIM's usage of system has the meaning you seem to associate with it.

In the telco world, people talk about element managers (managing
elements = devices) and network managers (managing whole networks,
that is a collection of elements = devices and links). While the IETF
work is currently focussed on managing devices, it seems some people
use NETCONF/YANG technology as well to manage whole networks, that is
YANG/NETCONF is used as an interface to a network manager instead of a
device interface. A few IETFs back, we even had a bar bof discussion
about this.

> relationships that are never visible at the device level. 

Not sure what you are doing but it might be a good idea to separate
network-wide data models from device specific data models. For
managing a network, you need to have information about topologies
(likely even at different layers) and only then you can do something
useful. Sure, it would be nice if there were a common (IETF) data
model for this (or at least IP layer topologies) but I assume, if this
happens at all, it will take time.

/js

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: +49 421 200 3587         Campus Ring 1, 28759 Bremen, Germany
Fax:   +49 421 200 3103         <http://www.jacobs-university.de/>

---

From: Jan Lindblad <[email-masked]>
Date: Wed, 11 Jul 2012 11:40:43 +0200

Jonathan,
> This will probably be so obvious to most of you, I almost feel like not sending this, but I just want to confirm something rather fundamental that only struck me yesterday.
> 
> CIM, as described on the DMTF web site, "provides a common definition of management information for systems, networks, applications and services, and allows for vendor extensions". The CIM Concepts White Paper identifies CIM's goal as "to model all the various aspects of the managed environment, not just a single problem space". In other words CIM provides an information model of the whole system, it is system-centric. In contrast, YANG data models are intended to be device-centric. Consequently there is typically no YANG system model and relationships between entities only need to make sense within the scope of the device being configured. Have I got that right?
> 
> The reason I ask is that, if that is the case, I am over-complicating my YANG modules in an attempt to capture system relationships that are never visible at the device level.
> 
If you look at the actual CIM classes, I think you'll find that the DMTF definition of a "system" above is pretty much one machine, e.g. one "server" or desktop machine. Not a cluster or network of machines.

For good and bad, there is a fundamental difference in how the CIM set of classes/data models are treated by DMTF and how YAMs and MIBs are treated by IETF. The CIM model is based on UML, and therefore uses concepts like inheritance heavily. This gives a high cohesion among all the various classes. Therefore DMTF releases the CIM model as one unit, with a version number for the entire model with all 1,100+ classes. This ensures good alignment between models, but is very different from how IETF version handles RFCs separately. Vendor extensions and version handling in the field becomes very tricky business.

/Jan Lindblad
--
Jan Lindblad, [email-masked], +46 702855728
Principal Solutions Architect, Tail-f Systems, www.tail-f.com

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From: Jonathan Hansford <[email-masked]>
Date: Wed, 11 Jul 2012 10:44:38 +0100

On 11.07.2012 10:34, Juergen Schoenwaelder wrote: 

> On Wed, Jul
11, 2012 at 10:15:08AM +0100, Jonathan Hansford wrote:
>> This will
probably be so obvious to most of you, I almost feel like not sending
this, but I just want to confirm something rather fundamental that only
struck me yesterday. CIM, as described on the DMTF web site, "provides a
common definition of management information for systems, networks,
applications and services, and allows for vendor extensions". The CIM
Concepts White Paper identifies CIM's goal as "to model all the various
aspects of the managed environment, not just a single problem space". In
other words CIM provides an information model of the whole system, it is
system-centric. In contrast, YANG data models are intended to be
device-centric. Consequently there is typically no YANG system model and
relationships between entities only need to make sense within the scope
of the device being configured. Have I got that right?
> The word
"system" has way too many meanings. I am not even sure the
> CIM's usage
of system has the meaning you seem to associate with it.
> In the
telco world, people talk about element managers (managing
> elements =
devices) and network managers (managing whole networks,
> that is a
collection of elements = devices and links). While the IETF
> work is
currently focussed on managing devices, it seems some people
> use
NETCONF/YANG technology as well to manage whole networks, that is
about this.

I'm not sure I understand the client/server model in such a
situation. Does that mean a NETCONF server is on the network manager as
well as having servers on the devices? Or is there a hierarchy of
clients and servers such that the devices are servers to the element
manager clients and the element managers are servers to the network
manager client?

/jh

>> The reason I ask is that, if that is the case,
I am over-complicating my YANG modules in an attempt to capture system
relationships that are never visible at the device level.
> Not sure
what you are doing but it might be a good idea to separate

---

From: Juergen Schoenwaelder <[email-masked]>
Date: Wed, 11 Jul 2012 12:00:36 +0200

> manager clients and the element managers are servers to the network

As far as I understood things, there is a NETCONF server interface to
the piece of software acting as a network manager. And devices might
have their device specific NETCONF server. Whether there are element
managers in-between or not, I have no clue. As said before, in order
to manage the network, you need lots of topology information etc.  The
devices usually don't need this or only a rather small part of it.

/js

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From: "Ersue, Mehmet (NSN - DE/Munich)" <[email-masked]>
Date: Wed, 11 Jul 2012 12:28:09 +0200

> device interface. A few IETFs back, we even had a bar bof discussion

DMTF CIM can be seen as an information model for the IT world, where 
TM Forum SID is an information model for the telecommunication world.
Both are very comprehensive and too big for an implementation. IETF 
traditionally did not provide high level information models, except a
few 
single cases focused on particular technologies, e.g. RFC5102
Information 
Model for IPFIX. 

Yang and MIB modules are rather data models. See RFC3444 "On the 
Difference between Information Models and Data Models".

Mehmet

---

From: Juergen Schoenwaelder <[email-masked]>
Date: Wed, 11 Jul 2012 12:39:50 +0200

On Wed, Jul 11, 2012 at 12:28:09PM +0200, Ersue, Mehmet (NSN - DE/Munich) wrote:
 
> IETF traditionally did not provide high level information models,
> except a few single cases focused on particular technologies,
> e.g. RFC5102 Information Model for IPFIX.

I do not consider RFC5102 to provide an information model. The RFC
title is IMHO an unfortunate misnomer.
 
/js

---

From: "Ersue, Mehmet (NSN - DE/Munich)" <[email-masked]>
Date: Wed, 11 Jul 2012 13:08:10 +0200

> title is IMHO an unfortunate misnomer.

Yeah, this is a bad example. Though, there are not many examples.
May be
http://tools.ietf.org/html/draft-ietf-ipfix-configuration-model-11
is a better one. 

Mehmet

---

From: Martin Bjorklund <[email-masked]>
Date: Sun, 15 Jul 2012 11:27:27 +0200 (CEST)

Juergen Schoenwaelder <[email-masked]> wrote:
> have their device specific NETCONF server.

Here's a paper describing such an implementation:

http://static.usenix.org/events/lisa11/tech/full_papers/Wallin.pdf

/martin