[netmod] extensions and conformance

[Ladislav Lhotka <[e-mail]>]

Hi,

recent discussions show that 6020(bis) text about extensions isn't
sufficiently clear about the scope and semantics of extensions. IMO this
needs to be fixed and so I propose to add the following item to YANG 1.1
issue list. Comments and additional solutions are welcome.

Lada

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* NEW :Yxx: clarify conformance wrt extensions

** Description

   YANG extensions as defined in RFC 6020 have no limits on scope –
   they can possibly modify YANG language, datastore semantics or even
   the NETCONF protocol. However, from the text in RFC 6020 it is
   unclear whether extensions appearing in YANG modules advertised by
   a server are mandatory to implement: "If a YANG compiler does not
   support a particular extension, which appears in a YANG module as
   an unknown-statement (see Section 12), the entire unknown-statement
   MAY be ignored by the compiler."

** Solution Yxx-01
   
   Extensions appearing in the server's model are an integral part of
   the server-client contract. That is, the server MUST implement
   them, and the client SHOULD terminate the session if it doesn't
   implement any of the extensions.

** Solution Yxx-02

   Develop a mechanism for negotiating extensions.

** Solution Yxx-03

   Make extensions optional. This means that extensions won't be
   allowed to change YANG language, NETCONF protocol, and validity of
   datastores and protocol messages.
------------------------------------------------------------------------

-- 
Ladislav Lhotka, CZ.NIC Labs
PGP Key ID: E74E8C0C