Re: [Netconf] quick comment on NETCONF Light draft

[Juergen Schoenwaelder <[e-mail]>]

On Wed, Jan 18, 2012 at 04:39:10PM -0800, Andy Bierman wrote:
> Hi,
> 
> I was looking over this draft:
> 
> http://www.ietf.org/id/draft-schoenw-netconf-light-01.txt
> 
> I can agree with the problem statement:
> There is a need for a constrained server which supports a limited subset of NETCONF operations.
> 
> I don't agree with the solution, since it is not backward-compatible with
> any version of NETCONF.  A base:1.0 or base:1.1 peer will simply terminate
> the session when a NETCONF Light peer does not advertise either of these capabilities.

And this is correct. A NETCONF Light server does not implement
base:1.0 nor base:1.1 - so announcing it would be bad.
 
> YANG deviations can be used to fully describe the operations subset
> that a server implements, and this is backward-compatible with the
> current version of NETCONF.

There are two concerns with this:

1) YANG says deviations can't be standardized:

   Deviations define the way a device or class of devices deviate from a
   standard.  This means that deviations MUST never be part of a
   published standard, since they are the mechanism for learning how
   implementations vary from the standards.

2) Can we reasonably expect all client implementations, including
   scripts, to handle deviations correctly? If not, announcing the
   base:1.x with deviations will likely lead dumb clients to assume
   the server speaks NETCONF while it does not. By using a different
   capability, it is explicit from the start that the device
   implements NETCONF Lite.

I believe it is more robust to use a different capability + features
than using the NETCONF base:1.1 capability + deviations.

/js

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: [phone]         Campus Ring 1, 28759 Bremen, Germany
Fax:   [phone]         <http://www.jacobs-university.de/>