[ntp:questions] Re: Sufficient # servers to sync to

Brad Knowles brad at stop.mail-abuse.org
Sat Mar 19 10:08:14 UTC 2005

At 9:31 PM -0800 2005-03-18, David Schwartz wrote:

>  "David L. Mills" <mills at udel.edu> wrote in message
>  news:d1g1af$o27$1 at dewey.udel.edu...
>>  When I say "vote", what I mean is that a majority vote among three of the
>>  four servers is possible in order to declare the fourth a traitor. All
>>  this says is the three servers are truechimers and the fourt is a
>>  falseticker. The "vote" is not for the winner, it's for the loser.
>      Certainly the same would be true for three servers if one were way off
>  and the other two were in agreement. The two accurate ones would vote for
>  the one that's off to lose. Whoever the one that was off voted for, it would
>  only have one vote to the screwed up server's two votes.

	Read those numbers again.  The Byzantine Agreement algorithms 
don't work with less than four servers.  You need to have three 
servers left over after everyone else has been voted off, if you're 
going to have one high, one low, and one in-between.

Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

   SAGE member since 1995.  See <http://www.sage.org/> for more info.

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