[ntp:questions] Choice of local reference clock seems to affect synchronization on a leaf node

Nathan Kitchen nkitchen at aristanetworks.com
Fri Nov 4 23:27:36 UTC 2011

I'm curious about some behavior that I'm observing on a host running
ntpd as a client. As I understand it, configuring a local reference
clock--either an undisciplined local clock or orphan mode--shouldn't
help me, but I see different behavior when I do have one. In
particular, when I'm synchronizing after correcting a very large
offset, I synchronize about 2x faster in orphan mode than with no
local clock, and with an undisciplined local clock I don't even fix
the offset.

I'm curious about whether this difference should be expected.

I'm using the following configuration in all cases:

   driftfile /persist/local/ntp.drift
   server iburst

My three different configurations for local clocks are the following:

1. No additional commands

2. tos orphan 10

3. server
    fudge stratum 10

In all three cases, my test has these steps:

1. Stop ntpd.
2. Set the clock to 2000-1-1 00:00:00 (that is, more than 10 years ago).
3. Run ntpd -g.
4. Check that the 11-year offset is corrected.
5. Wait for synchronization to the time server.

With either configuration #1 (no local clock) or #2 (orphan mode), the
offset is corrected quickly: 4 and 13 seconds, respectively. With
configuration #3 (undisciplined local clock), it fails to be corrected
within 60 seconds.

After the offset is corrected, configuration #1 takes 921 seconds to
synchronize to the server. Configuration #2 takes 472.

Can you provide any insight?

-- Nathan

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