nanog mailing list archives
Re: Need trusted NTP Sources
From: Andriy Bilous <andriy.bilous () gmail com>
Date: Sun, 9 Feb 2014 22:41:48 +0100
Unfortunately I don't have the book handy. May be I am wrong too. Just checked and 4 looks to be a valid solution for 1 falseticker according to Byzantine Generals' Problem. On Sun, Feb 9, 2014 at 10:03 PM, Saku Ytti <saku () ytti fi> wrote:
On (2014-02-09 21:08 +0100), Andriy Bilous wrote:Best practice is five. =) I don't remember if it's in FAQ on ntp.org orinDavid Mills' book. Your local clock is kind of gullible "push-over" which will "vote" for the "party" providing most reasonable data. The algorithm would filter out insane sources which run too far from the rest and then group sane sources into 2 "parties" - your clock will follow the onewhererunners are closer to each other. That is why uneven number oftrustworthysources at least at start is required. With 2 sources you will blindly follow the one which is closer to your own clock. You're also having the the risk to degrade into this situation when you lose 1 out of 3 sources. Four is again 2:2 and only with five you have a good chance to start disciplining your clock into the right direction at the right pace, sowhen1 source is lost you (most probably) won't run into insanity.I'm having bit difficulties understanding the issue with 4. Is the implication that you have two groups which all agree with each other reasonably well, but do not agree between the groups. Which would mean that 4 cannot handle situation where 2 develop problem where they agree with each other but are wrong. But even in that case, you'd still recover from 1 of them being wrong. So 3 = correct time, no redundancy 4 = correct time, 1 can fail 5 = correct time, 2 can fail and so forth? But not sure here, just stabbing in the dark. For the fun of it, threw email to Mills, if he replies, I'll patch it back here. -- ++ytti
Current thread:
- Re: Need trusted NTP Sources, (continued)
- Re: Need trusted NTP Sources Jared Mauch (Feb 07)
- Re: Need trusted NTP Sources Anthony Williams (Feb 07)
- You need a VLAN to the foot of NIST ITS services - no problem - we got you covered. Re: Need trusted NTP Sources TGLASSEY (Feb 07)
- Re: Need trusted NTP Sources Bryan Seitz (Feb 07)
- Re: Need trusted NTP Sources Majdi S. Abbas (Feb 08)
- Re: Need trusted NTP Sources Jay Ashworth (Feb 08)
- Re: Need trusted NTP Sources Jay Ashworth (Feb 08)
- Re: Need trusted NTP Sources Saku Ytti (Feb 09)
- Re: Need trusted NTP Sources Andriy Bilous (Feb 09)
- Re: Need trusted NTP Sources Saku Ytti (Feb 09)
- Re: Need trusted NTP Sources Andriy Bilous (Feb 09)
- Re: Need trusted NTP Sources Jay Ashworth (Feb 09)
- Re: Need trusted NTP Sources Saku Ytti (Feb 09)
- Re: Need trusted NTP Sources Jay Ashworth (Feb 09)
- Re: Need trusted NTP Sources Saku Ytti (Feb 09)
- Re: Need trusted NTP Sources Lyle Giese (Feb 09)
- Re: Need trusted NTP Sources Jimmy Hess (Feb 09)
- Re: Need trusted NTP Sources Brett Frankenberger (Feb 09)
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- Re: Need trusted NTP Sources Larry Sheldon (Feb 06)
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- Re: Need trusted NTP Sources Larry Sheldon (Feb 06)
- Re: Need trusted NTP Sources Jay Ashworth (Feb 06)