[ntp:hackers] NTP protocol version interoperability

Jon Hart Jon_Hart at rapid7.com
Wed Jun 11 16:56:48 UTC 2014


Hello,

I've been doing some research into the NTP protocol recently and came
upon some behavior that made me question what I thought I knew about
NTP.

I've consulted the 5 NTP RFCs for versions 0-4 and while they all (as
applicable) do talk about compatibility with previous versions, I can't
find anything that clarifies exactly how/when the various versions
should be used.  When two hosts A and B are communicating with each
other using NTP and host A sends a message to B using version N, is it
required that B interpret the message as version N?  If/when B responds,
must it also use version N?  If B uses a newer version in the response,
how should A react?  If B uses an older version in the response, how
should A react?

If there is a particular part of the RFCs, other document/etc that
answers this or provides more color, feel free to point me in that
direction.  I've searched and couldn't find what I was looking for.

Thanks!

-jon

--
---------------------
Jon Hart
Senior Security Researcher
Rapid7
http://www.rapid7.com
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Cell:   310-689-8377
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