Hi, all

The current immutable-flag draft 
(https://www.ietf.org/archive/id/draft-ma-netmod-immutable-flag-03.txt) defines 
both a YANG extension and a metadata annotation to indicate the immutability of 
data nodes and instances, respectively.

An alternative approach discussed on the list is to update NACM and define a 
"nacm: static-data" YANG extension besides nacm:default-deny-write and 
nacm:default-deny-all.
Authors' considerations on this proposal are following:
*             Immutability is a property of YANG data nodes or instances, while 
NACM is a security feature
*             NACM can be switched off by setting the /nacm/enable-nacm leaf to 
"false"
*             Emergency recovery session will bypass access control enforcement
*             A single YANG extension cannot express instance-level immutability

In the current draft, YANG extension we defined doesn't depend on NACM module, 
but this draft doesn't clarify one point well related to the relation between 
this YANG extension and NACM, i.e., whether using such YANG extension causes 
NACM rule not take effect.
To address ambiguity when both an immutable-flag and "a user-provided NAC rule 
to allow write access" are used, the draft can add the following explicit text:
"When a specific data node or instance is marked as "immutable", NACM
cannot override this to allow create/delete/update access. Servers will
 ignore such NACM rule. For example, if a particular data node is marked
 as 'im:immutable' without the 'exceptions' argument for update, the server
will ignore any user-defined NACM rule to allow update access operation to
 that specific data node."

We plan to integrate this on Oct 19 if there is no objection to this change.
Any thoughts or feedback on this?

Best Regards,
Qiufang
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