NTP users are strongly urged to take immediate action to ensure that their NTP daemons are not susceptible to being used in distributed denial-of-service (DDoS) attacks. Please also take this opportunity to defeat denial-of-service attacks by implementing Ingress and Egress filtering through BCP38.

ntp-4.2.8p15 was released on 23 June 2020. It addresses 1 medium-severity security issue in ntpd, and provides 13 non-security bugfixes over 4.2.8p13.

Please see the NTP Security Notice for vulnerability and mitigation details.

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Are you using Autokey in production? If so, please contact Harlan - he's got some questions for you.

6.1.9. Configuring Local Refclocks

A Local Refclock should be configured on a machine if you want that machine to serve time to other machines even if there is no "proper" refclock available.

If you are interested in keeping the clocks on your machines synchronized to each other, it may be better to use orphan mode than a local refclock.

If a machine is "visible" on the internet and is using a local refclock, the stratum of the local refclock should not be lower than, say, 8, as it would be Bad to have machines outside your network believing your unsychronized local clock.

Old-style local backup servers

If you cannot use orphan mode to provide synchronized time should your NTP network become disconnected from real sources of time, this old-style approach may work.

Find your two the "best" machines in your set of servers and configure the best one's local refclock at no better than 2 stratum levels below the worst stratum where the machine would ordinarily run. You then configure the local refclock of your second best machine in your set of servers at 2 stratum levels worse than that.

For example, if ServerA is the "best" and ServerB is the "second best" server in your local time server pool and these servers do not serve time to machines outside your network and they ordinarily synchronize with machines that, at worst case, are at stratum 3 then you should configure ServerA's local refclock at stratum 5 and ServerB's local refclock at stratum 7.