Re: [Ntp] Antw: [EXT] Re: Quick review of WGLC for status change for draft-ietf-ntp-update-registries

[Miroslav Lichvar <[e-mail]>]

On Wed, Aug 17, 2022 at 02:30:20AM -0700, Harlan Stenn wrote:
> I believe that's what has already been done.  For the timing modes:
> 
> v2 to v3 changed a variable in the packet header.

So if a v2 server responded to v3 request with v2 data in v3 packet,
the client would get incorrect data?

I thought you said the idea was to add new fields if incompatible
changes are made.

In case you forgot, v2 was not compatible with v1 either.

> v3 to v4 added extension fields.

As Ulrich already explained, that works only for the v3-subset of the
protocol, i.e. the same is if the protocol number didn't change.

A v3 server is not able to respond to a v4 request containing
extension fields, even if it's authenticated with a symmetric key that
the server knows.

> As I have said many times, the design of the timing modes and the packet
> structure allows NTP to reply to packets of lesser, equal, or greater
> version numbers and "it just works".

No, it doesn't. You may think it works, but you just don't see the
whole picture.

> Your NTPv5 work is explicitly breaking that rule, and y'all are apparently
> only recently beginning to see some of the consequences of that choice.

That rule isn't written anywhere and as you just shown, it wasn't
followed anyway. Why should be v4->v5 be different?

> It's not clear to me what or how long it will take for a v5 client to detect
> and remediate an attempt to talk to a v4 server.

If you read the draft, you would know there is no additional delay.

> It's not clear to me what or how long it will take a v4 client to detect and
> remediate an attempt to get time from a v5 server that does not respond to
> the v4 request.

As was said multiple times, a v5-only server cannot respond to v4
requests. The same as a v4-only server following RFC5905 cannot
respond to a v3 request and the same as a v3-only server following
RFC1305 cannot respond to a v2 request.

> > > > Are there any client implementations using the NTPv4 control mode?

> If that is, indeed, what you are asking, then no, I'm not aware of anything.
> But how does that matter?

It gives us an idea how important it is to have it specified.

-- 
Miroslav Lichvar