Re: [Ntp] Antw: Re: Calls for Adoption -- NTP Extension Field drafts -- Four separate drafts

[Daniel Franke <[e-mail]>]

On Mon, Sep 9, 2019 at 12:08 PM Salz, Rich <[e-mail]> wrote:
>
> >    It can't.  There are fields in a NTP v3 reply that are copied from the request
>     packet.  The v3 only system doesn't know how to find them in a v4 packet.
>
> So that could be a signal to the sender that the receiver does not know the version, right?

The only thing that would really paint us into a corner would be if
there were a lot of v4 servers out there that reply to v5 packets with
something structured like a v4 packet but with a 5 in the version
field. That would create a big mess for the client to figure out
whether what it's getting back a response from a correct v5 server or
a broken v4 server. As long as v4 servers never put any version higher
than 4 in their replies, then a v5 client can interpret any v4
response as an error signal no matter whether that was what the server
intended. But it's really silly for a v4 server to attempt to reply to
a v5 request with anything but an error.

I propose we just avoid this situation entirely by making NTS a
mandatory part of v5. NTPv5 gets a separate NTS Next Protocol code
from NTPv4, so version negotiation happens during NTS-KE. And then no
correct client will ever emit a v5 time packet without already knowing
that the server supports v5.