[Nottingham] "ntpq -p" displayed flags

Camilo Mesias camilo at mesias.co.uk
Fri Jan 27 21:27:10 UTC 2012


On Fri, Jan 27, 2012 at 9:07 PM, Martin <martin at ml1.co.uk> wrote:
> Is that hardware timestamping in the NIC or network switches and
> inserted directly into the data packets?
> As in... Special hardware is required?

It's timestamping in the NIC (strictly speaking in the PHY). The
timestamp can be appended to the packet or provided in a special
register that the driver has to read explicitly. It's special hardware
but I think it's becoming more common and might eventually be in most

Network kit can timestamp on the way in and out, in a way that removes
the delay effect of processing within the switch/router.

You can run PTP without hardware timestamping but it might not
synchronise if the errors introduced are too great, also it will
struggle to work through a router for the same reason.


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