Re: [Netconf] Advertisement of imported features

Muly Ilan <muly_i@rad.com> Tue, 08 January 2019 20:39 UTC

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From: Muly Ilan <muly_i@rad.com>
To: Martin Bjorklund <mbj@tail-f.com>
CC: "netconf@ietf.org" <netconf@ietf.org>
Thread-Topic: [Netconf] Advertisement of imported features
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Date: Tue, 8 Jan 2019 20:39:37 +0000
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Subject: Re: [Netconf] Advertisement of imported features
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Hi Martin,


-----Original Message-----
From: Martin Bjorklund [mailto:mbj@tail-f.com] 
Sent: 08/01/2019 22:18
To: Muly Ilan
Cc: netconf@ietf.org
Subject: Re: [Netconf] Advertisement of imported features

Hi,

Muly Ilan <muly_i@rad.com> wrote:
> Hi,
> 
> Not sure whether import of features from one module to the other is
> fully supported by YANG and NETCONF.
> 
> For example, with these modules:
> 
> module alpha {
>   namespace "https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fexample.com%2Falpha&amp;data=01%7C01%7Cmuly_i%40rad.com%7C5b4c4319f5f2434a332408d675a6599c%7Cf9047108cc2c4e4897a343fad1b3bf9d%7C1&amp;sdata=QEesCuMPU6YgQYnpuhAidhLe7nq2ywAV2BjKPn%2BHcV8%3D&amp;reserved=0";
>   prefix "a";
> 
>   feature a-feature;
> 
>   leaf aoo {
>     if-feature a-feature;
>     type string;
>   }
> 
>   leaf a2 {
>     type string;
>   }
> 
> }
> 
> 
> module beta {
>   namespace "https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fexample.com%2Fbeta&amp;data=01%7C01%7Cmuly_i%40rad.com%7C5b4c4319f5f2434a332408d675a6599c%7Cf9047108cc2c4e4897a343fad1b3bf9d%7C1&amp;sdata=8GyM2bkXE0E0YbSfFWYgxRZUsiRFnN%2BPEzpaKX0fX8M%3D&amp;reserved=0";
>   prefix "b";
> 
>   import alpha {
>     prefix a;
>   }
> 
>   leaf boo {
>     if-feature a:a-feature;
>     type string;
>   }
> 
>   leaf b2 {
>     type string;
>   }
> 
> }
> 
> The intension is re-use of the feature "a-feature" in the importing
> module "beta".

The statement

  if-feature a:a-feature;

means that the boo leaf if valid if the "a-feature" in module "a" is
supported in the server.

> Now, how should a server advertise the support of "a-feature" in
> module "beta"?

It doesnt; it should advertise module "alpha" with "a-feature", and
"beta" w/o any features.

[Muly Ilan]
This was what I initially thought.
But it didn't work with NSO version 4.7 (the leaf "boo" in module "beta" was not available).

Then I carefully read, again, section 5.6.4.2 of RFC 6020:

"
Servers indicate the names of supported features via the <hello>
message. In <hello> messages, the features are encoded in the
"features" parameter within the URI. The value of this parameter is
a comma-separated list of feature names that the device supports for
the specific module.
"

My understanding of the last sentence is that per module, feature support should be declared.
In this example "a-feature" is supported by both modules.


> 
> 1.      YANG 1.0
> According to section 5.6.4 of RFC6020 the NETCONF <hello> message is
> used.
> So, I assume the <hello> should contain the following:
> <capability>
>   https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fexample.com%2Fbeta%3Fmodule%3Dbeta%26features%3Da%3Aa-feature&amp;data=01%7C01%7Cmuly_i%40rad.com%7C5b4c4319f5f2434a332408d675a6599c%7Cf9047108cc2c4e4897a343fad1b3bf9d%7C1&amp;sdata=rDlo2oLhLyQGP6rihXuPCWCXbMHFPiL74ULx9X6401E%3D&amp;reserved=0
> </capability>
> 
> Is the above a valid capability?

No.  It should be:

 <capability>
   https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fexample.com%2Falhpa%3Fmodule%3Dalpha%26features%3Da%3Aa-feature&amp;data=01%7C01%7Cmuly_i%40rad.com%7C5b4c4319f5f2434a332408d675a6599c%7Cf9047108cc2c4e4897a343fad1b3bf9d%7C1&amp;sdata=AXq7oIC7VNUlUtAAGQdAI%2B3%2FpKpQqUF03Y9r2mCTGlg%3D&amp;reserved=0
 </capability>
 <capability>
   https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fexample.com%2Fbeta%3Fmodule%3Dbeta&amp;data=01%7C01%7Cmuly_i%40rad.com%7C5b4c4319f5f2434a332408d675a6599c%7Cf9047108cc2c4e4897a343fad1b3bf9d%7C1&amp;sdata=PrczrfDxzOypK5VASbbDtrJrdYLYlg5pCfgprSRuIBw%3D&amp;reserved=0
 </capability>

> 2.      YANG 1.1
> According to section 5.6.4 of RFC7950 the "ietf-yang-library" defined
> in RFC7895 must be implemented.
> 
> The relevant node definition from RFC7895:
> 
>        leaf-list feature {
>          type yang:yang-identifier;
>          description
>            "List of all YANG feature names from this module that are
>             supported by the server, regardless whether they are defined
>             in the module or any included submodule.";
>        }
> 
> But the pattern of the typedef "yang:yang-identifier" does not permit
> a prefix.
> 
> Can this be fixed in draft-ietf-netconf-rfc7895bis ?

As per above, this is not needed.


/martin

> 
> 
> Regards,
> 
> Muly
> 
> 


[Muly Ilan] 
Best,

Muly