Sample NTP Peers, Leap Second 2005

A leap second was inserted into the last minute of 2005. This page contains some graphs showing how various NTP peers of ours behaved during that leap second. I have also collected some other leap second observations.

Well Behaved Peer

The graph below shows a well behaved peer during the leap second. The X-axes shows the number of seconds to the leap second, so the leap second is where X=0. The Y-axes has units of milliseconds and shows the offset, delay and jitter as reported by ntpq -p. All values are small, and the offset is quite smooth apart from occasional jumps that seem to correspond to jumps in the delay (round trip time to the remote machine).

Graph of well behaved peer

We can also zoom in around the leap second to see the detail. The small gap visible just before the leap second is a missing response from that server.

Zoomed in graph of well behaved peer

Non-Leap Second Related Events

There are some peers who behave well, but you can see events that are not leap second related. For example in the following graph we see a shift in round trip time (probably due to a routing change) which results in an adjustment in the offset.

Graph showing routing change

Around the leap second we see the peer is well behaved.

Zoomed Graph showing routing change

Leap Second Spike with Decay

This machine seems to have mishandeled the leap second resulting in a big spike in the offset just after the leap second. This is followed by a step, to correct the clock and then the offset decays to 0 as over time.

Graph of peer with spike

Zooming in, we see this more clearly. I'm not sure why the offset is 0.5s just after the leap second - I would have expected it to be 1.

Zoomed in Graph of peer with spikegraph of well behaved peer

More graphs

There are more graphs of other peers available with brief comments.