nanog mailing list archives
Re: NTP Issues Today
From: "Robert E. Seastrom" <rs () seastrom com>
Date: Wed, 21 Nov 2012 07:20:47 -0500
Blake Dunlap <ikiris () gmail com> writes:
That's what happens when you just follow vendor recommendations blindly. If you do follow that on vm's (which can actually be a good practice), make sure they pull from your own time infrastructure, and not just the world at large, and that those servers behave in a sane fashion with regard to time jumps.
Emphatically disagree on the "pull from your own infrastructure" point. You probably don't have the budget even in a big company for sufficient diversity of sources [*] for your NTP server and even if you do the NTP servers will probably be run by the same person/organization. Mills has called the latter practice out as bad in the past. As Leo pointed out, the key is having a large diverse set so that if a couple of them go nuts they can be voted off the island. If you have a requirement for super low jitter or holdover if you lose network, you're looking at on-site devices with OCXO or Rb frequency standards in them. That doesn't mean you shouldn't be talking to the rest of the world too though. What if your on-site sources go nuts? This happens periodically, say every 10 years or so, because of crappy implementations and worst-current-practices. A re-read of https://groups.google.com/forum/?fromgroups=#!search/mills$20ntp$20byzantine/comp.protocols.time.ntp/TryjqtAd1XM/R0zzzE13Tl8J may prove instructive. (reading list also includes http://www.amazon.com/dp/1439814635/ ) In my experience NTP beats out even DNS for "blatantly wrong configs in the wild that nevertheless seem to work well enough that dilettante tech folks don't notice". I might have replied to this thread yesterday but I was blissfully unaware of any problems: rs@bifrost [8] % ntpq -c peers | egrep -v '(===|remote)' | wc -l 11 rs@bifrost [9] % -r [*] particularly due to shortsighted US federal government choices on LORAN, GOES, WWVB time format, etc
Current thread:
- Re: NTP Issues Today, (continued)
- Re: NTP Issues Today Mike Lyon (Nov 20)
- Re: NTP Issues Today Jared Mauch (Nov 20)
- Picking outside NTP servers (Re: NTP Issues Today) Jay Ashworth (Nov 20)
- Re: Picking outside NTP servers (Re: NTP Issues Today) George Herbert (Nov 20)
- Re: Picking outside NTP servers (Re: NTP Issues Today) Majdi S. Abbas (Nov 20)
- Re: NTP Issues Today Ask Bjørn Hansen (Nov 21)
- Re: NTP Issues Today Jimmy Hess (Nov 20)
- Re: NTP Issues Today Darius Jahandarie (Nov 20)
- Re: NTP Issues Today Blake Dunlap (Nov 20)
- Re: NTP Issues Today George Herbert (Nov 20)
- Re: NTP Issues Today Robert E. Seastrom (Nov 21)
- Re: NTP Issues Today Darius Jahandarie (Nov 20)
- Re: NTP Issues Today Damian Menscher (Nov 20)
- Re: NTP Issues Today Alvaro Pereira (Nov 20)
- RE: NTP Issues Today Chuck Church (Nov 21)
- Re: NTP Issues Today Greg Ihnen (Nov 21)
- Re: NTP Issues Today Clay Haynes (Nov 19)
- Re: NTP Issues Today Ryan Malayter (Nov 21)
- Re: NTP Issues Today Ryan Malayter (Nov 21)