Re: [netmod] question about unprefixed path in leafref

[tom petch <[e-mail]>]

From: netmod <[e-mail]> on behalf of Ladislav Lhotka <[e-mail]>
Sent: 10 February 2022 15:58

"Sterne, Jason (Nokia - CA/Ottawa)" <[e-mail]> writes:

> This immediately made me worried about all such xxx-ref constructs in YANG that I've seen in a few modules.
>
> But looking at IETF interfaces https://datatracker.ietf.org/doc/html/rfc8343 I see that this error is avoided because interface-ref is fully qualified right ?
>

RFC 8407, sec 4.2:

   o  The local module prefix SHOULD be used instead of no prefix in all
      path expressions.

This is particularly important for typedefs that are intended to be used in other modules.

<tp>

I cannot recall which I-D triggered it but this point was hammered home, at least to me, some time back, a year or two perhaps, and I have looked out for it ever since.  It was probably a TEAS I-D that gave different results with different validators.

Tom Petch
Lada

>      typedef interface-ref {
>        type leafref {
>          path "/if:interfaces/if:interface/if:name";
>        }
>        description
>          "This type is used by data models that need to reference
>           interfaces.";
>      }
>
> Jason
>
> From: netmod <[e-mail]> On Behalf Of Jernej Tuljak
> Sent: Wednesday, February 9, 2022 3:47 AM
> To: Fengchong (frank) <frank.fengchong=[e-mail]>; [e-mail]
> Subject: Re: [netmod] question about unprefixed path in leafref
>
>
> On 08/02/2022 03:40, Fengchong (frank) wrote:
> Hi all,
>
> In RFC7950 sec6.4.1 says:
>
>
> o  Names without a namespace prefix belong to the same namespace as
>
>       the identifier of the current node.  Inside a grouping, that
>
>       namespace is affected by where the grouping is used (see
>
>       Section 7.13<https://datatracker.ietf.org/doc/html/rfc7950#section-7.13>).  Inside a typedef, that namespace is affected by
>
>       where the typedef is referenced.  If a typedef is defined and
>
>       referenced within a grouping, the namespace is affected by where
>
>       the grouping is used (see Section 7.13<https://datatracker.ietf.org/doc/html/rfc7950#section-7.13>).
>
> But in module openconfig-aft-network-instance:
>
>   augment "/oc-ni:network-instances/oc-ni:network-instance/" +
>           "oc-ni:afts/oc-ni:next-hops/oc-ni:next-hop/oc-ni:state" {
>
>     description
>       "Add leaves that require referencing of a network instance to the
>       operational state parameters of a next-hop within the AFT for IPv4
>       unicast.";
>
>     uses aft-nexthop-ni-state;
>   }
>
>   grouping aft-nexthop-ni-state {
>     description
>       "Operational state parameters relating to a next-hop which reference a
>       network instance.";
>
>     leaf network-instance {
>       type oc-ni:network-instance-ref;
>       description
>         "The network-instance within which the next-hop should be resolved.
>          When this leaf is unspecified, the next-hop is resolved within
>          the local instance.";
>     }
>   }
>
> The typedef network-instance-ref is defined in module openconfig-network-instance:
>
>   typedef network-instance-ref {
>     type leafref {
>       path "/network-instances/network-instance/config/name";
>     }
>     description
>       "A re-usable type that can be referenced within other
>        modules that references a network instance.";
>   }
>
> The leafref’s path is a unprefixed path.
>
> So, according RFC7950, the typedef network-instance-ref is referenced in leaf network-instance, and the leaf is inside grouping aft-nexthop-ni-state, and this grouping is used in augment "/oc-ni:network-instances/oc-ni:network-instance/" +
>           "oc-ni:afts/oc-ni:next-hops/oc-ni:next-hop/oc-ni:state"
> So the path "/network-instances/network-instance/config/name" ‘s namespace is module openconfig-aft-network-instance’s namespace. But in fact, there is no node called network-instances with namespace: http://openconfig.net/yang/aft/ni.
>
> Is it incorrect?
>
> I try to use pyang to compile it, and no error is reported.
>
> These modules are written in YANG 1.0, therefore RFC6020 applies, not RFC7950. This was one of the cases where RFC6020 was unclear, hence new text you quote from RFC7950. If you change openconfig-network-instance to YANG 1.1, pyang should report an error for that "path" when the "typedef" gets used in openconfig-aft-network-instance.
>
> Jernej
>
>
>
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--
Ladislav Lhotka
Head, CZ.NIC Labs
PGP Key ID: 0xB8F92B08A9F76C67

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