Re: dntpd

[Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>]

:Matthew Dillon wrote:
:>     I'm going to do some work on dntpd to try to correct two unrelated
:>     issues.  First I'll try to have it detect a bad time source when 
:>     several are available.  Second, I'll have it re-run the DNS lookup
:>     if a server stops responding and I'll have it detect duplicate IPs.
:
:How about taking the median of offsets to all servers which are considered "good"?  Good would be something like "off less than two times the standard deviation" or so.
:
:cheers
:  simon

    I don't think you can quantify the accuracy of a median offset verses
    a statistically good offset returned by a single server, so no. 

    What I did, amoung other things, was add a quorum calculation to the
    code.  Now it chooses the best server and then requires that a quorum
    of servers agree that the offset reported by that server is reasonable.

    There might be a way to algorithmically reduce offset errors (due to
    packet lag) relative to real time given multiple good sources, but I
    haven't researched it.

    Another thing we can do is 'lock' to a particular server as long as
    its accuracy does not deviate from the current best available by too
    much.  I have not coded something like that yet.

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>