[ntp:hackers] smearing the leap second

Harlan Stenn stenn at ntp.org
Wed Jun 24 15:07:15 UTC 2015


Danny Mayer writes:
> On 6/23/2015 10:53 PM, Harlan Stenn wrote:
> > Danny Mayer writes:
> >> I've been following this thread with interest and I have the following
> >> comments.
> >>
> >> 1) Stealing bits is wrong. That not a moral judgement but an
> >> architectural one. Whether you get them from the RefID or the fuzz bits
> >> of the timestamps you are not going to get what you want. If you take it
> >> from the RefID then the reference information will be incorrect and
> >> you've lost loop detection. Moreover it won't be usable unless it's a
> >> stratum 1 server and then you lose the information about the RefClock.
> >> If you take it from the fuzz bits you lose the purpose of those bits.
> >> There's actually a specific purpose to them. I don't remember all the
> >> details but they are important.
> > 
> > It is possible to convey the smear  offset value in an extension field.
> > 
> > The only instances of NTP that will know what to do with this are "new"
> > instances of NTP.
> > 
> > What happens with the tens of millions (could be 100M, not sure) that
> > don't know about this?
> > 
> 
> There is actually nothing you can do about this. ...

We disagree.  If the servers send smeared time with no leap indication
old clients will do the right thing.

> ...
>
> >> 5) If an NTPv4 system receives an NTPv5 packet what does it do with the
> >> packet? Is is supposed to drop it, or respond with an NTPv4 packet but
> >> how will it interpret the contents of the NTPv5 packet? Will it think it
> >> has an unknown extension field?
> > 
> > Why would an NTPv4 client ask for a v5 packet?
> > 
> > Why would a v5 server send a v5 response to a v4 request?
> 
> You misunderstood. What I'm trying to say is that there will eventually
> be NTPv5 servers out there. They won't know if the servers that they are
> contacting are NTPv4 or NTPv5. If the NTPv4 server gets a v5 packet what
> does it do? What should it do?

What we've always done.  Send back a v4 response, the highest version of
the protocol the v4 server understands.

H


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