[Ntp] Suggestion for additional draft identification requirements

[David Venhoek <[e-mail]>]

Hi All,

To ensure that different drafts/the final version of the NTPv5 spec
won't step on each others toes when deployed side-by-side I suggest we
strengthen the requirements around draft specification a bit.

This isn't a problem yet as there are very few implementations yet,
but for NTPD-rs we are now planning to include an implementation of
the latest draft in the next version (though still behind a feature
flag) and whilst implementing the issues here came up as potential
problems.

The patch below is also available as a PR on github at
https://github.com/mlichvar/draft-ntp-ntpv5/pull/8

Kind Regards,
David Venhoek

diff --git a/ntp-ntpv5.xml b/ntp-ntpv5.xml
index bec2ff0..190ab3b 100644
--- a/ntp-ntpv5.xml
+++ b/ntp-ntpv5.xml
@@ -413,6 +413,15 @@
           string. If the server string is longer than the client string, the
           server MUST truncate it to the length of the client string.</t>

+        <t>A server SHOULD NOT respond to requests with a draft
identification it does not
+          recognize, and SHOULD respond with a response according to
the same draft specification
+          as given by the client.</t>
+
+        <t>A server implementing a draft of this specification MUST
NOT respond to NTPv5
+          negotiation in NTPv4 unless this extension field is
present. A client implementing
+          the draft SHOULD include a Draft Identificiation Extension
Field during NTPv5
+          negotiation.</t>
+
         <t>Note: the content of this field MUST NOT be null terminated</t>
       </section>