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

["Acee Lindem (acee)" <[e-mail]>]

Hi Martin, 
Please see my example of the yangvalidator not working - we can't use these YANG 1.1 functions until this is resolved. 
Thanks,
Acee 

On 1/10/18, 4:36 AM, "Martin Bjorklund" <[e-mail]> 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 <[e-mail]> wrote:
    > On Tue, 2018-01-09 at 16:23 +0100, Martin Bjorklund wrote:
    > > Ladislav Lhotka <[e-mail]> wrote:
    > > > On Tue, 2018-01-09 at 09:06 +0100, Martin Bjorklund wrote:
    > > 
    > > > > Hi,
    > > 
    > > > > 
    > > 
    > > > > Ladislav Lhotka <[e-mail]> 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" <[e-mail]> 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
    >