Re: [OSPF] [yang-doctors] Yangdoctors last call review of draft-ietf-ospf-yang-09

"Acee Lindem (acee)" <acee@cisco.com> Mon, 22 January 2018 18:42 UTC

Return-Path: <acee@cisco.com>
X-Original-To: ospf@ietfa.amsl.com
Delivered-To: ospf@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id CABD0127599; Mon, 22 Jan 2018 10:42:23 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -14.531
X-Spam-Level:
X-Spam-Status: No, score=-14.531 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, RCVD_IN_DNSWL_HI=-5, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_PASS=-0.001, T_RP_MATCHES_RCVD=-0.01, USER_IN_DEF_DKIM_WL=-7.5] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (1024-bit key) header.d=cisco.com
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id DpNRo3q-pVLh; Mon, 22 Jan 2018 10:42:21 -0800 (PST)
Received: from alln-iport-5.cisco.com (alln-iport-5.cisco.com [173.37.142.92]) (using TLSv1.2 with cipher DHE-RSA-SEED-SHA (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 19EBC127058; Mon, 22 Jan 2018 10:42:10 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=cisco.com; i=@cisco.com; l=13412; q=dns/txt; s=iport; t=1516646530; x=1517856130; h=from:to:cc:subject:date:message-id:references: in-reply-to:content-id:content-transfer-encoding: mime-version; bh=Rc8/uiDLDldJhBmi7/THxqIEm5gtJnkGEu1ZPBOoiZM=; b=Yywh2HXiTNi90fvp1mJC9312HO8g75Wf2rkF+UR6bEYs1sHFB4oE2TVB VBJ2jGn7wRv4TmAdIINguPMfbddwoag2sOTqAVpwVL8rTUNGWGPRXOj0b S489rJ2Bwb4pEYwYmMGZGo9xCDTiGltmwzs8wjVVjZ/aWZwxEOD9AoLOY Y=;
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: A0AfAQDRL2Za/5BdJa1UCRkBAQEBAQEBAQEBAQEHAQEBAQGDQoFaJweDVookjmWBWyeXPoIXCoU7AhqEVlQYAQEBAQEBAQEBayiFJAEFIxFFEAIBCA4KAgImAgICMBUQAgQBDQWKM7UlgieKNgEBAQEBAQEBAQEBAQEBAQEBAQEBAR2BD4M6ghWDaAyCeYMvBIFFFBaDFzGCFCAFkjGRSQKMDYlMghuGH4tlh3KPKAIRGQGBOwEfOYFQbxVnAYF/hFd4iCAsgQaBFwEBAQ
X-IronPort-AV: E=Sophos;i="5.46,397,1511827200"; d="scan'208";a="59498102"
Received: from rcdn-core-8.cisco.com ([173.37.93.144]) by alln-iport-5.cisco.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 22 Jan 2018 18:42:09 +0000
Received: from XCH-RTP-012.cisco.com (xch-rtp-012.cisco.com [64.101.220.152]) by rcdn-core-8.cisco.com (8.14.5/8.14.5) with ESMTP id w0MIg8ZN023325 (version=TLSv1/SSLv3 cipher=AES256-SHA bits=256 verify=FAIL); Mon, 22 Jan 2018 18:42:09 GMT
Received: from xch-rtp-015.cisco.com (64.101.220.155) by XCH-RTP-012.cisco.com (64.101.220.152) with Microsoft SMTP Server (TLS) id 15.0.1320.4; Mon, 22 Jan 2018 13:42:08 -0500
Received: from xch-rtp-015.cisco.com ([64.101.220.155]) by XCH-RTP-015.cisco.com ([64.101.220.155]) with mapi id 15.00.1320.000; Mon, 22 Jan 2018 13:42:07 -0500
From: "Acee Lindem (acee)" <acee@cisco.com>
To: Martin Bjorklund <mbj@tail-f.com>, "lhotka@nic.cz" <lhotka@nic.cz>
CC: "yang-doctors@ietf.org" <yang-doctors@ietf.org>, "draft-ietf-ospf-yang.all@ietf.org" <draft-ietf-ospf-yang.all@ietf.org>, "ietf@ietf.org" <ietf@ietf.org>, "ospf@ietf.org" <ospf@ietf.org>
Thread-Topic: [yang-doctors] Yangdoctors last call review of draft-ietf-ospf-yang-09
Thread-Index: AQHTboUcIbs87wVZj0yzoeuFibmmLKNqkMSAgAEjW4CAAARAAIAAdfEAgAAD/ICAAAyegIABJEgAgBMhLoA=
Date: Mon, 22 Jan 2018 18:42:07 +0000
Message-ID: <2AECD072-7E95-4493-82E1-F83EA32F6F2E@cisco.com>
References: <1515510536.26845.18.camel@nic.cz> <20180109.162311.49506989189385960.mbj@tail-f.com> <1515514101.26845.52.camel@nic.cz> <20180110.103428.251892557297447292.mbj@tail-f.com>
In-Reply-To: <20180110.103428.251892557297447292.mbj@tail-f.com>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
x-ms-exchange-messagesentrepresentingtype: 1
x-ms-exchange-transport-fromentityheader: Hosted
x-originating-ip: [10.116.152.198]
Content-Type: text/plain; charset="utf-8"
Content-ID: <E76353956471A14E99348ACA16EB6F8A@emea.cisco.com>
Content-Transfer-Encoding: base64
MIME-Version: 1.0
Archived-At: <https://mailarchive.ietf.org/arch/msg/ospf/uMu_j835ebYBNFbS0rR6fiMR47o>
Subject: Re: [OSPF] [yang-doctors] Yangdoctors last call review of draft-ietf-ospf-yang-09
X-BeenThere: ospf@ietf.org
X-Mailman-Version: 2.1.22
Precedence: list
List-Id: The Official IETF OSPG WG Mailing List <ospf.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/ospf>, <mailto:ospf-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/ospf/>
List-Post: <mailto:ospf@ietf.org>
List-Help: <mailto:ospf-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ospf>, <mailto:ospf-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 22 Jan 2018 18:42:24 -0000

Hi Martin, Lada, 

In experimenting with this, I get YANGLINT validation errors. I’m not sure what I’m missing but the first argument to derived-from()/derive-from-or-self() is the schema node and the second is the identity – correct?
For example, the following YANG leaf:

identity ospf-protocol {
    base "rt:routing-protocol";
    description "Any version the OSPF protocol";
  }

  identity ospfv2 {
    base "ospf-protocol";
    description "OSPFv2";
  }

  identity ospfv3 {
    base "ospf-protocol";
    description "OSPFv3";
  }

leaf routing-protocol-name {
      type leafref {
        path "/rt:routing/rt:control-plane-protocols/"
           + "rt:control-plane-protocol/rt:name";
      }
      must "derived-from( "
	+ "/rt:routing/rt:control-plane-protocols/"
        + "rt:control-plane-protocol[rt:name=current()]/"
        + "rt:type, ospf:ospf-protocol)";
      description
       "OSPF routing protocol instance name.";
    }

Gives me: 

warn: Schema node "ietf-ospf:ospf-protocol" not found (derived-from( /ietf-routing:routing/ietf-routing:control-plane-protocols/ietf-routing:control-plane-protocol[ietf-routing:name=current()]/ietf-routing:type, ietf-ospf:ospf-protocol) with context node "/ietf-ospf:if-state-change/routing-protocol-name".

Thanks
Acee 

On 1/10/18, 4:36 AM, "Martin Bjorklund" <mbj@tail-f.com> wrote:

    Hi,
    
    I think we can agree that the model in this I-D should use
    derived-from-or-self() instead of string comparison, and conclude this
    discussion here.  I suggest that if we need to further discuss the
    representation of identityrefs, then we start a new thred on the
    NETMOD ML.
    
    
    /martin
    
    
    
    Ladislav Lhotka <lhotka@nic.cz> wrote:
    > On Tue, 2018-01-09 at 16:23 +0100, Martin Bjorklund wrote:
    > > Ladislav Lhotka <lhotka@nic.cz> wrote:
    > > > On Tue, 2018-01-09 at 09:06 +0100, Martin Bjorklund wrote:
    > > 
    > > > > Hi,
    > > 
    > > > > 
    > > 
    > > > > Ladislav Lhotka <lhotka@nic.cz> wrote:
    > > 
    > > > > > Hi Acee,
    > > 
    > > > > 
    > > 
    > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > please see inline.
    > > 
    > > > > 
    > > 
    > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > On Mon, 2018-01-08 at 19:28 +0000, Acee Lindem (acee) wrote:
    > > 
    > > > > 
    > > 
    > > > > > > Hi Lada,
    > > 
    > > > > 
    > > 
    > > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > > Apologies for the delay. We somewhat got hung up on 4 and 6. See
    > > inline.
    > > 
    > > > > 
    > > 
    > > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > > On 12/6/17, 6:26 AM, "Ladislav Lhotka" <lhotka@nic.cz> wrote:
    > > 
    > > > > 
    > > 
    > > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > > > Reviewer: Ladislav Lhotka
    > > 
    > > > > 
    > > 
    > > > > > > > Review result: Ready with Issues
    > > 
    > > > > 
    > > 
    > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > ...
    > > 
    > > > > 
    > > 
    > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > > > 3. Maybe the draft could mention that implementations should supply
    > > a
    > > 
    > > > > 
    > > 
    > > > > > > >   default routing domain as a system-controlled resource.
    > > 
    > > > > 
    > > 
    > > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > > Isn’t this more of an RFC8022BIS statement? I guess we could state
    > > this as
    > > 
    > > > > 
    > > 
    > > > > > > an assumption.
    > > 
    > > > > 
    > > 
    > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > Probably, but it is not a YANG issue, so I'd leave it to you routing
    > > folks
    > > 
    > > > > to
    > > 
    > > > > 
    > > 
    > > > > > decide.
    > > 
    > > > > 
    > > 
    > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > >  
    > > 
    > > > > 
    > > 
    > > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > > > 4. In "when" expressions, the module uses literal strings for
    > > 
    > > > > 
    > > 
    > > > > > > >   identities. This is known to be problematic, the XPath functions
    > > 
    > > > > 
    > > 
    > > > > > > >   derived-from() or derived-from-or-self() should be used instead.
    > > 
    > > > > 
    > > 
    > > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > > Why is this problematic? Is it because the types can be extended?
    > > 
    > > > > 
    > > 
    > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > That's one reason: derived identities should often also satisfy the
    > > 
    > > > > constraint.
    > > 
    > > > > 
    > > 
    > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > But the more serious problem is that things like
    > > 
    > > > > 
    > > 
    > > > > > 
    > > 
    > > > > 
    > > 
    > > > > >     when "../../../../../../../rt:type = 'ospf:ospfv3'"
    > > 
    > > > > 
    > > 
    > > > > > 
    > > 
    > > > > 
    > > 
    > > > > > rely on plain string comparison that depends od the actual prefix used
    > > for
    > > 
    > > > > the
    > > 
    > > > > 
    > > 
    > > > > > "rt:type" value. For one, according to RFC 7951 the JSON encoding of
    > > this
    > > 
    > > > > value
    > > 
    > > > > 
    > > 
    > > > > > would be "ietf-ospf:ospfv3" so the above expression is always false. 
    > > 
    > > > > 
    > > 
    > > > > 
    > > 
    > > > > This is not correct; the when expression is not evaluated on the JSON
    > > 
    > > > > encoding.  See the last paragraph of section 9.10.3 in RFC 7950:
    > > 
    > > > > 
    > > 
    > > > >    The string value of a node of type "identityref" in a "must" or
    > > 
    > > > >    "when" XPath expression is the referred identity's qualified name
    > > 
    > > > >    with the prefix present.  If the referred identity is defined in an
    > > 
    > > > >    imported module, the prefix in the string value is the prefix defined
    > > 
    > > > >    in the corresponding "import" statement.  Otherwise, the prefix in
    > > 
    > > > >    the string value is the prefix for the current module.
    > > 
    > > > 
    > > 
    > > > This is weird, to say the least. The leafref instance may have an identity
    > > value
    > > 
    > > > that is defined in a module that (has to be implemented by the server but)
    > > 
    > > > needn't be imported in the module that contains the XPath expression. So I
    > > don't
    > > 
    > > > know what 'corresponding "import" statement' this paragraph is talking
    > > about.
    > > 
    > > 
    > > It has to import the module in order to give a prefix, which then can
    > > be used in the XPath expression.
    > 
    > In the XPath expression above, do you mean the "rt" prefix of "rt:type"? If so,
    > it is irrelevant for the string comparison, what's important is the *value* of
    > the "rt:type" instance, which can be an identity defined in a module that
    > needn't be imported by ietf-routing, ietf-ospf or whatever. Sec. 9.10.2:
    > 
    >    On a particular server, the valid values are further restricted to the set of
    >      identities defined in the modules implemented by the server.
    > 
    > > 
    > > > Also, potentially there can be a collision in prefixes and then this also
    > > breaks
    > > 
    > > > down.
    > > 
    > > 
    > > No, two modules cannot be imported with the same prefix.
    > 
    > I have to disagree. An identity derived from the "ietf-routing:control-protocol-
    > type" base identity can be defined in a module that is not imported anywhere. If
    > a server declares such a module as implemented, then "rt:type" may have this
    > value per sec. 9.10.2.
    > 
    > And, consequently, there may be two different modules with conflicting prefixes
    > defining identities that are derived from "ietf-routing:control-protocol-type". 
    > 
    > > 
    > > > A moral of the namespace/prefix story in XML was that relying of namespace
    > > 
    > > > prefixes having a particular value is a really bad idea. I know that the
    > > cited
    > > 
    > > > paragraph was intended to make such XPath string comparisons more
    > > deterministic,
    > > 
    > > > but it is also problematic and should be avoided if possible.
    > > 
    > > 
    > > Note that this prefix is under the control of the module designer
    > > writing the XPath expression.  The same identityref value might use a
    > 
    > No, it is not. The prefixes appear in instance data.
    > 
    > Lada
    > 
    > > different prefix in some other module.
    > > 
    > > 
    > > /martin
    > > 
    > > 
    > > 
    > > > 
    > > 
    > > > Lada
    > > 
    > > > 
    > > 
    > > > > 
    > > 
    > > > > So the equality test of the identityref is correct.
    > > 
    > > > > 
    > > 
    > > > > However, I agree that in most cases 'derived-from-or-self' should be
    > > 
    > > > > used, in order to handle derived identities.
    > > 
    > > > > 
    > > 
    > > > > 
    > > 
    > > > > /martin
    > > 
    > > > -- 
    > > 
    > > > Ladislav Lhotka
    > > 
    > > > Head, CZ.NIC Labs
    > > 
    > > > PGP Key ID: 0xB8F92B08A9F76C67
    > > 
    > > > 
    > > 
    > -- 
    > Ladislav Lhotka
    > Head, CZ.NIC Labs
    > PGP Key ID: 0xB8F92B08A9F76C67
    >