DoIT has three GPS-synched stratum-1 servers.

The service addresses are as follows:

ntp1.doit.wisc.edu (provided by ntp-cssc-8350-1)
   144.92.9.22 (proxied to 146.151.145.52)
   2607:f388::123:1

ntp2.doit.wisc.edu (provided by ntp-animal-226-1-mgmt)
   144.92.20.100
   2607:f388::123:2

ntp3.doit.wisc.edu (provided by ntp-432nm-b3a-1)
   144.92.104.20 (proxied to 128.104.254.244)
   2607:f388::123:3

Deprecated service address:

   128.104.30.17 (deprecated provided by ntp-animal-226-1-mgmt on eth2)

The NTP appliances also have the following addresses. Service should be stable on their IPv4 address as well as the IPv6 service address (in 2607:f388::/64 service block eg. 2607:f388::123:1). In the future we may migrate the service addresses for ntp1.doit.wisc.edu (144.92.9.22) to the real address of the appliance (146.151.145.52) and ntp3.doit.wisc.edu (144.92.104.20) to (128.104.254.244), deprecating the existing service IPv4 addresses, although keeping them active for the foreseeable future as many devices will have those addresses hard-coded in their base OS config. The service names ntp1.doit.wisc.edu, ntp2.doit.wisc.edu and ntp3.doit.wisc.edu should continue to exist even if the IPv4 addresses they point to change in the future.

ntp-cssc-8350-1-mgmt.net.wisc.edu has address 146.151.145.52
ntp-cssc-8350-1-mgmt.net.wisc.edu has IPv6 address 2607:f388:d:1::1001
ntp1.doit.wisc.edu has IPv6 address 2607:f388::123:1

ntp-animal-226-1-mgmt.net.wisc.edu has address 144.92.20.100 (aka ntp2.doit.wisc.edu)
ntp-animal-226-1-mgmt.net.wisc.edu has IPv6 address 2607:f388:d:2::1001
ntp2.doit.wisc.edu has IPv6 address 2607:f388::123:2

ntp-432nm-b3a-1-mgmt.net.wisc.edu has address 128.104.254.244
ntp-432nm-b3a-1-mgmt.net.wisc.edu has IPv6 address 2607:f388:d::1002
ntp3.doit.wisc.edu has IPv6 address 2607:f388::123:3