Why are some pool servers advertising leap second?


#1

First, a big thank you to all pool operators! I recently discovered ntppool and will be adding a server soon.

While playing around with some of the results of querying pool servers I noticed something I was not expecting. I have seen a small number of servers advertise a leap second. For example the following servers are currently advertising a leap second:

pool server			reference_clock_identifier_ip
45.79.109.111		127.67.113.92
207.210.46.249		139.41.49.38
199.241.184.162		130.207.244.240
45.79.109.111		216.218.254.202
185.68.101.2		31.28.161.68
199.241.184.162		209.51.161.238
185.68.101.249		31.28.161.68
45.79.109.111		216.218.254.202
207.210.46.249		139.41.49.38
207.210.46.249		139.41.49.38
199.223.248.101		209.51.161.238

Can somebody explain this to me? Why do they think they should be advertising a leap second?

To be clear I am not seeing an issue with these pool servers, I am merely curious and want to understand how / why this is happening.

Thanks!


#2

When multiple ntp servers are mutually pooled, they may keep exchanging the leap second with each other because a majority vote system is in place to decide when to use the leap second. I had one of my servers in such a loop a few years ago.

Also in 2007 a bug appeared in the ntpd server which prohibited the leap second from clearing, but this has been fixed in 2012. You may want to check if the servers you mentioned use a server version from this period.


#3

Thanks for the reply @lammert

I just spot checked and they are all reporting version 3 so I am guessing that I am not seeing the bug that prohibited the leap second from clearing.

Interesting idea about the mutually pooled. I will try and explore that idea.

Thanks!


#4

Ugh, nice find. The system actually knows this, but doesn’t do anything about it. It’d not be terribly hard to add, in particular if it keeps an updated (and parsed) version of the leap second data around.

http://www.pool.ntp.org/scores/207.210.46.249/log?limit=50

(see the last column)