[ntp:questions] NTP request retry?

William Unruh unruh at invalid.ca
Mon Jan 27 20:20:00 UTC 2014

On 2014-01-27, Rob <nomail at example.com> wrote:
> Charles Swiger <cswiger at mac.com> wrote:
>> Hi--
>> On Jan 27, 2014, at 10:10 AM, Rob <nomail at example.com> wrote:
>>> Despite lots of tracing I still cannot really pinpoint the problem.
>>> The only thing I see is that ping has absolutely zero loss and all
>>> usual protocols work fine, but ntp indicates a high loss when there
>>> is no other network activity.
>>> When the network is kept busy, ntp works fine as well.
>>> Very strange.
>> That's odd.  Are the NTP servers and your client subnet-local or remote?
> It is a local network.
> One client is wired (100Mbit ethernet) and the other is WiFi.

And the server? And are they really on the same subnet? Often wifi is a
different subnet than wired. 

>> If they're remote, then ARP probably isn't involved unless you're having
>> issues finding your default gateway.  Set up an /etc/ethers entry [1] for it,
>> or for your subnet-local NTP servers if you have them around, and see whether
>> it makes a difference.
>> Otherwise, tcpdump/wireshark/etc captures should be informative.
> Unfortunately they have not been so far.
> Logs on the client show a request with no reply, logs on the server
> show no request coming in.  It is unclear to me if an outgoing request
> would be shown on the trace when ARP resolution is incomplete.

Sounds like it could be a firewall issue. 
ARP is ONLY used for machines on exactly the same network. 
Note it may also be that there is another machine on the net with the
same IP address, and it is stealing the packets. 

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