Re: [netmod] A question on the parameter overriding in draft-ietf-isis-yang-isis-cfg

[Juergen Schoenwaelder <[e-mail]>]

Hi,

YANG does not have 'levels'. This seems to be an ISIS specific
question you should ask on the ISIS list.

/js

On Sun, Jun 09, 2019 at 10:35:11AM -0400, Xufeng Liu wrote:
> In Section 2.3. and many other locations, the current IS-IS model applies
> the parameter overriding rule as below:
> 
> [Quote]:
> 
> 2.3 <https://tools.ietf.org/html/draft-ietf-isis-yang-isis-cfg-35#section-2..3>.
> Per-Level Parameters
> 
> 
>    Some parameters allow a per level configuration.  In this case, the
>    parameter is modeled as a container with three configuration
>    locations:
> 
>    o  a top-level container: corresponds to level-1-2, so the
>       configuration applies to both levels.
> 
>    o  a level-1 container: corresponds to level-1 specific parameters.
> 
>    o  a level-2 container: corresponds to level-2 specific parameters.
> 
>                +--rw priority
>                |  +--rw value?     uint8
>                |  +--rw level-1
>                |  |  +--rw value?   uint8
>                |  +--rw level-2
>                |     +--rw value?   uint8
> 
>    Example:
> 
>            <priority>
>                <value>250</value>
>                <level-1>
>                    <value>100</value>
>                </level-1>
>                <level-2>
>                    <value>200</value>
>                </level-2>
>            </priority>
> 
>    An implementation SHOULD prefer a level specific parameter over a
>    level-all parameter.  As example, if the priority is 100 for the
>    level-1, 200 for the level-2 and 250 for the top-level configuration,
>    the implementation should use 100 for the level-1 and 200 for the
>    level-2.
> 
> [End of Quote]
> 
> 
> In the model, all three value leaves above have a default statement
> “default 64”, which brings up my question for the following example:
> 
> 
>            <priority>
>                <value>250</value>
>                <level-1>
>                    <value>100</value>
>                </level-1>
>            </priority>
> 
> 
> The user does not provide a configured value for level-2. According to
> Section 7.6.1. of RFC7950, because the default value is in use, “the server
> MUST operationally behave as if the leaf was present in the data tree with
> the default value as its value”. This means the priority value for level-2
> will be 64 (the default value), so the value 250 can never take effect as
> intended in the above quoted Section 2.3.
> 
> 
> Is my understanding correct?
> 
> 
> Since this is a generic question, I am CC’ing NETMOD WG too.
> 
> 
> Thanks,
> 
> - Xufeng

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