[time-nuts] Re: NIST NTP servers way off for anyone else?

[Hal Murray]

> Is it ALWAYS there?

No.  You have to ask for it with setsockopt.

> Also cmsg doesn't make it clear what these auxiliary headers might  actually
> be, so that doesn't really leave me able to use this?

The type of the cmsg block will be the same as the option you turned on with 
setsockopt.

If you want a code sample, look in ntpd/ntp_packetstamp.c from ntpsec.
  https://gitlab.com/NTPsec/ntpsec


> What about receive offload?

I would assume that would maintain the same API.

There is also PTP, IEEE-1588 (I think).
I haven't gone down that rathole.


> I've seen cards (ethtool) that support several time options - what are  they
> and how do I use them? 

I'm not sure which options you are referring to.

The usual tangle with timing packets is that the hardware defaults to batching 
interrupts to avoid using lots of CPU cycles getting into and back out of the 
interrupt routine.   coalesce is the buzzword.  That adds a delay between the 
packet arrival and the time the interrupt line goes active.

Other time related options may be referring to PTP support.  The general idea 
with PTP is to have hardware do the timestamping, AND for routers/switches to 
update a slot in the packet when the packet is waiting around on the box.

You can't have boxes on the internet update packets if you are interested in 
security.


-- 
These are my opinions.  I hate spam.