[ntp:questions] Linux : ntp-dev-4.2.7p84 : Local clock not getting synced.

Martin Burnicki martin.burnicki at meinberg.de
Mon Jan 3 13:44:04 UTC 2011


Mike S wrote:
> At 02:21 PM 1/2/2011, David Woolley wrote...
>>Arul Kumar Chellappan wrote:
>>>server  ::1
>>>fudge   ::1 stratum 10

The line above tries to fudge the localhost IP address, i.e. the loopback
interface, which indeed makes no sense.

>>These lines don't make sense, and not just because you can't fudge
>>stratum on a server.
> 
> How odd, since the official docs say you can :
> http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver1.html
> 
> "Fudge Factors...stratum number...Specifies the driver stratum, in
> decimal from 0 to 15, with default 3."
> 
> And the FAQ even gives an example:
> http://www.ntp.org/ntpfaq/NTP-s-refclk.htm#Q-LOCAL-CLOCK
> 
> "server 127.127.1.1             # LCL, local clock
> fudge  127.127.1.1 stratum 12   # increase stratum"

The line above fudges the stratum of the "local clock" which is something
different than the localhost IP address. See below.

> If not fudging stratum on a server, then where do you propose it's
> appropriate?

I think this is simply a misunderstanding which I've often seen with people
who are not (yet) very familiar with NTP.

::1 is the IPv6 address for localhost, i.e. the loopback network interface,
the IPv4 equivalent of which is 127.0.0.1. 

Configuring localhost (::1 or 127.0.0.1) using a "server" line in ntp.conf
makes no sense at all.

The IPv4 localhost IP 127.0.0.1 is sometimes confused with the special IP
addresses 127.127.x.y ntpd uses in general to configure hardware reference
clocks, and especially 127.127.1.0 which specifies the so-called local
clock.

The stratum of an NTP node visible on the network is always the stratum of
the selected time source (the system peer) plus 1.

If the system peer is a refclock you can fudge the stratum of the refclock,
and the resulting stratum of the NTP node is the stratum of the refclock
plus 1.

However, if the system peer is another NTP server you can not fudge the
stratum since NTP node's stratum would alsways be the stratum of system
peer, plus 1.

Martin
-- 
Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont
Germany




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