Re: changes in draft-ietf-cbor-network-addresses-05.txt

[Jürgen Schönwälder <[e-mail]>]

On Wed, Jul 28, 2021 at 08:04:16AM +1200, Brian E Carpenter wrote:
> On 26-Jul-21 23:49, tom petch wrote:
> > From: ipv6 <[e-mail]> on behalf of Brian E Carpenter <[e-mail]>
> > Sent: 25 July 2021 00:44
> > 
> > There's an "interesting" issue there, especially for IPv6, which is that the interface ID (or "zone index", per RFC4007) has no meaning outside the host. So it really shouldn't need to be sent on the wire in normal circumstances.
> > 
> > (The conversation around RFC6874bis is slightly relevant.)
> > 
> > <tp>
> > Brian
> > 
> > As I may have said before, the YANG Types RFC6991 provides types for IPv4 and IPv6 addresses both with a zone index.  It also provides no-zone types with a suffix 'no-zone' on the type name.  I see evidence that most authors of YANG modules do not realise that a reference to 'ip-address' per se is a reference to the format that includes the zone and so have specified that format in many if not most cases.  Thus it seems likely that many of the addresses on the wire are in the zone format, even if the zone is rarely present.  With hindsight, it might have been better to have specified 'ip-address' and 'ip-address-zone' rather than ip-address' and io-address-no-zone'.
> 
> Makes sense. The reply I just sent to Christian Amsüss probably applies to YANG too. Sending a zone index to another host is rarely meaningful or useful.
>

YANG was designed for network management purposes and there are quite
some use cases where communicating the zone index is somewhat essential:

- If you want to debug a problem, you likely need to know to which
  link a link-local address belongs.
- If you want to generate statistics for protocols using link-local
  addresses, you likely need to know to which links the link-local
  addresses belongs.
- If you want to configure a service to use a certain link-local
  address on a certain link, you may have to include the proper zone
  index.
- If an IP address is used to index lists, things can fall apart if
  you end up with duplicate link-local addresses on different links.

Whether we should have picked different names for the types may be
debatable but at the end it is the YANG module author's responsibility
to pick the appropriate types.

In other words, network management applications often need to be aware
of zone indexes in order to do the right thing. This is different from
end user applications (that usually have no topological awareness).

/js

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
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