Re: [OSPF] draft-ietf-ospf-yang-03 questions and doubts

[t.petch <[e-mail]>]

----- Original Message -----
From: "Alan Davey" <[e-mail]>
To: "Derek Man-Kit Yeung (myeung)" <[e-mail]>;
<[e-mail]>
Cc: "OSPF WG List" <[e-mail]>
Sent: Wednesday, May 11, 2016 5:40 PM

Hi Derek

A question about the key for OSPF interfaces in the Yang draft.  Please
let me know what you think.

The background is that the Management Information Base definitions
define indices for OSPF interfaces as follows.


-          For OSPFv2, RFC 4750 defines the index as ospfIfIpAddress,
ospfAddressLessIf.

-          For OSPFv3, RFC 5643 defines the index as ospfv3IfIndex,
ospfv3IfInstId.

However, in the OSPF Yang draft, the key is defined as "interface",
which I believe is a name of the interface.

How does "interface" map to the indices defined in RFCs 4750 and 5643?

<tp>

It doesn't (IMHO).  You have two lists of interfaces in this I-D

container interfaces { description "All interfaces."; list interface {
key "interface";
description "List of OSPF interfaces.";

container interfaces { description "All interfaces in the area.";  list
interface { key "interface";
description "List of OSPF interfaces.";

both keyed on 'interface' (which is two separate lists so two separate
'interface' leaf, different sets of key objects.).

Both are defined as

     type if:interface-ref;

and the if: harks back to
     import ietf-interfaces {prefix "if";
and ietf-interfaces is in RFC7223 where interface-ref is defined as
"   An interface is identified by its name, which is unique within the
   server.  This property is captured in the "interface-ref" and
   "interface-state-ref" typedefs, which other YANG modules SHOULD use
   when they need to reference a configured interface or operationally
   used interface, respectively."

So both lists are keyed on a name which is unique within the server and
can be anything, such as 'lan0' or 'fast-ethernet-23/7' or
'hotplug23/6/15' or... It all depends; names may be dictated by the
hardware with no choice, or they may be dictated by the software to
compliant hardware or ...

Underlying this is the thought that we have no good definition of an
interface, one that works across all protocols and other aspects of a
configuration; an interface is like a blob of jelly and pinning it down
to be a name is about as good a grasp of it as we will get (IMO).

Tom Petch

Thanks
Alan