Re: [netmod] [netconf] RE: pls clarify get operation

Qin Wu <> Sat, 29 June 2019 08:05 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id DD93E120142; Sat, 29 Jun 2019 01:05:21 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -4.2
X-Spam-Status: No, score=-4.2 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_MED=-2.3, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id sN2pfCqSboY1; Sat, 29 Jun 2019 01:05:18 -0700 (PDT)
Received: from ( []) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 027E5120033; Sat, 29 Jun 2019 01:05:18 -0700 (PDT)
Received: from (unknown []) by Forcepoint Email with ESMTP id C95A057C775FCF480282; Sat, 29 Jun 2019 09:05:15 +0100 (IST)
Received: from ( by ( with Microsoft SMTP Server (TLS) id 14.3.408.0; Sat, 29 Jun 2019 09:05:14 +0100
Received: from ( by ( with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1713.5; Sat, 29 Jun 2019 09:05:14 +0100
Received: from ( by ( with Microsoft SMTP Server (version=TLS1_0, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.1.1713.5 via Frontend Transport; Sat, 29 Jun 2019 09:05:13 +0100
Received: from ([]) by ([]) with mapi id 14.03.0415.000; Sat, 29 Jun 2019 16:05:05 +0800
From: Qin Wu <>
To: Andy Bierman <>, "Fengchong (frank)" <>
CC: "" <>, "Zhangwei (SS)" <>, Yangang <>, "" <>
Thread-Topic: [netmod] [netconf] RE: pls clarify get operation
Thread-Index: AdUuUEFywS+0G73ZTDqYU19dt7I5WA==
Date: Sat, 29 Jun 2019 08:05:05 +0000
Message-ID: <>
Accept-Language: zh-CN, en-US
Content-Language: zh-CN
X-MS-Has-Attach: yes
x-originating-ip: []
Content-Type: multipart/mixed; boundary="_004_B8F9A780D330094D99AF023C5877DABAA49BA669nkgeml513mbxchi_"
MIME-Version: 1.0
X-CFilter-Loop: Reflected
Archived-At: <>
Subject: Re: [netmod] [netconf] RE: pls clarify get operation
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: NETMOD WG list <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Sat, 29 Jun 2019 08:05:22 -0000

Agree with Andy, Jurgen, Rob.
If my understanding is correct, Frank’s intention is not proposed to fall back to single datastore, split tree. His concern is how Does the non-NMDA client talk with NMDA compliant devices, suppose large amount of devices support NMDA.
Does the device need to support both NMDA model and non-NMDA model? Is this common case or corner case in real deployment senario.
suggestions or guidelines defined in NMDA architecture and NMDA guideline(/rfc8407#section-4.23.3) seem to only assume NMDA client only talks with NMDA server, non-NMDA client only talks with non-NMDA server.

发件人: netmod [] 代表 Andy Bierman
发送时间: 2019年6月28日 23:05
收件人: Fengchong (frank) <>
抄送:; Zhangwei (SS) <>om>; Yangang <>om>;
主题: Re: [netmod] [netconf] 答复: pls clarify get operation

On Fri, Jun 28, 2019 at 7:09 AM Fengchong (frank) <<>> wrote:
Hi Rob,
    I think IETF solution: migrate to NMDA is unrealistic. The cost of migration to NMDA is too expensive, If the entire industry migrates to NMDA, the time will be long.
    This will delay the deployment of the IETF model in the industry.
    Anyway, even if vendor implements NMDA, the network manager/ controller or client tools may not support NMDA client.
    A non-NMDA client only support get/get-config, it still has no way to retrieve system-controlled data.

Although it would have been possible to augment the existing <get> operation, it is much cleaner
to create a new operation instead. (From standards and implementation POV).

There is a significant amount of work needed to support NMDA in a server.
This effort would be the same whether <get> or <get-data> was used.
The protocol work is the tip of the iceberg.  Updating all the instrumentation callbacks to
return operational values is the real work -- and exactly the same no matter what protocol
solution is used. Client complexity is mostly related to the new YANG library.

Starting over on a new solution would only take longer to deploy.


    Generation config false copy for IETF YANG model is not reasonable, because published IETF standard YANG should not be changed, moreover, this is not friendly to the client or the server.
发件人: Rob Wilton (rwilton) [<>]
发送时间: 2019年6月28日 17:18
收件人: Fengchong (frank) <<>>; Juergen Schoenwaelder <<>>
抄送:<>;<>; Zhangwei (SS) <<>>
主题: RE: [netmod] pls clarify get operation

Hi Frank,

You can't just change definitions in RFCs.  It breaks all existing clients/servers.  Besides, what you suggest doesn't really work (path clashes between configuration and operational state), unless you return two trees ... which starts to look extremely similar to the NMDA architecture ...

IETF has already explored this problem and there is already a published IETF solution to the problem that you describe: Migrate to NMDA.  The NMDA architecture has many other benefits as well (E.g. allows for templating, inactive configuration, dynamic configuration, consistent OIR handling).


-----Original Message-----
From: Fengchong (frank) <<>>
Sent: 28 June 2019 10:07
To: Juergen Schoenwaelder <<>>; Rob Wilton (rwilton) <<>>
Cc:<>;<>; Zhangwei (SS) <<>>
Subject: 答复: [netmod] pls clarify get operation

Should we change the definition of get operation? Like this, get operation can retrieve all running operational data including running configuration, system configuration.
Otherwise, we have no way to get the information of system-controlled data according a NMDA-style YANG module(because has no config false copy ) unless we implement NMDA.
发件人: Juergen Schoenwaelder [<>]
发送时间: 2019年6月28日 16:50
收件人: Rob Wilton (rwilton) <<>>
抄送: Fengchong (frank) <<>>;<>;<>; Zhangwei (SS) <<>>
主题: Re: [netmod] pls clarify get operation

Yes, both the NETCONF <get> operation and the RESTCONF GET on the unified view of the underlying datastores have limitations and a solution in situations where these limitations hurt is to move towards NMDA.


On Fri, Jun 28, 2019 at 08:38:38AM +0000, Rob Wilton (rwilton) wrote:
> Hi Frank,
> Pre NMDA:
>   *   You have a the <running> datastore, along with some others like <candidate> and <startup> that you can ignore for the purposes of this discussion.
>   *   The <running> datastore can only contains data for schema nodes that are marked as “config true” in YANG (i.e. “rw” in your tree output below).
>   *   The system may also have some operational state data that is marked as “config false” in YANG (i.e. “ro” in your tree output below).
> The NETCONF <get-config> operation returns the contents of the <running> datastore.
> The NETCONF <get> operation returns the contents of the <running> datastore combined with all the operational state as well.  Filters can be applied to return a subset of the data.
> Regarding your question about user created configuration vs system created configuration, it depends on whether the devices instantiates the configuration in <running> or not.  If it does, then it would be returned in <get> and <get-config> operations.  If it doesn’t then it would not.  Different vendors/devices will likely implement this in different ways.
> Generally, I think that <running> should only contain the configuration explicitly configured by the operator’s systems.  But this means that there isn’t a clean way to represent system created configuration or applied configuration, unless you make a config false copy of every config true node in YANG.  This is approach that was taken by the original IETF YANG models (e.g. RFC 7223) before they were superseded by NMDA, and also the OpenConfig YANG models (but using a different structure – which also struggles to cleanly represent system created configuration data).
> The NMDA architecture was written to solve this problem in a clean way without requiring duplication in the YANG data models.
> Hopefully this helps clarify.
> Thanks,
> Rob
> From: netmod <<>> On Behalf Of Fengchong (frank)
> Sent: 28 June 2019 04:29
> To:<>;<>
> Cc: Zhangwei (SS) <<>>
> Subject: [netmod] 答复: pls clarify get operation
> Hi all,
>      Pls clarify this question. I have been confused for a long time.
> ________________________________
> 华为技术有限公司 Huawei Technologies Co., Ltd.
> [Company_logo]
> 个人签名:冯冲
> 手  机:13776612983
> 电子邮件<><<>>
> 公司网址<><>
> ________________________________
>  本邮件及其附件含有华为公司的保密信息,仅限于发送给上面地址中列出的个人或群组。禁
> 止任何其他人以任何形式使用(包括但不限于全部或部分地泄露、复制、或散发)本邮件中
> 的信息。如果您错收了本邮件,请您立即电话或邮件通知发件人并删除本邮件!
> This e-mail and its attachments contain confidential information from
> HUAWEI, which is intended only for the person or entity whose address
> is listed above. Any use of the information contained herein in any
> way (including, but not limited to, total or partial disclosure,
> reproduction, or dissemination) by persons other than the intended
> recipient(s) is prohibited. If you receive this e-mail in error,
> please notify the sender by phone or email immediately and delete it!
> 发件人: Fengchong (frank)
> 发送时间: 2019年6月27日 9:59
> 收件人: '<>' <<><<>>>;
> 抄送: Yangshouchuan
> <<><<>>>; Zhangwei
> (SS) <<><<>>>
> 主题: pls clarify get operation
> Hi all,
> In RFC6241, get operation is defined as:
> 7.7<>.7>.  <get>
>    Description:  Retrieve running configuration and device state
>       information.
> This description is too simply, so I think it should be clarified.
> The case is: a data node modelled by one yang can be configured by user, but also can be created/modified by system or other protocols. If client issues get operation to retrieve this node,
>           The data is created/modified by system or other protocols SHOULD be returned?
>           For example:
>           Rib can be configured by user and also can be created by routing protocols. In RFC 8349, the rib list is defined as:
>       +--rw ribs
>          +--rw rib* [name]
>             +--rw name              string
>             +--rw address-family?   identityref
>             +--ro default-rib?      boolean {multiple-ribs}?
>             +--ro routes
>             |  +--ro route*
>             |        ...
>             +---x active-route
>             |  +---w input
>             |  |  +---w v4ur:destination-address?   inet:ipv4-address
>             |  |  +---w v6ur:destination-address?   inet:ipv6-address
>             |  +--ro output
>             |        ...
>             +--rw description?      string
>        If client issued get operation to retrieve ribs from non-NMDA device, rib instance created by routing protocols should be returned?
>        Another associated question: If client issued get-config operation from non-NMDA device, only user-controlled rib instance should be returned?

> _______________________________________________
> netmod mailing list

Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
Fax:   +49 421 200 3103         <>
netconf mailing list<>