[ntp:questions] Issues w/ 4.2.0a, multicast, and porting 4.2.2 to Fedora Core

Danny Mayer mayer at ntp.isc.org
Mon Sep 4 02:33:46 UTC 2006

Philip Prindeville wrote:
> Hi.
> I haven't poked around the guts of NTP in about 12 years, so I'm a little
> rusty... (since 2.3???)
> I'm running Linux FC3 and FC5 on a variety of PC machines, with NTP set
> up as a multicast client.

No you haven't, see below.

> I'm using the distro RPM 4.2.0.a.20040617.  I
> have
> various Cisco routers set up to chime multicast running 12.2(20) to
> 12.4(9)T.

You need to use 4.2.2 as there were a large number of fixes to get
multicast working properly.

> And I'd like to build myself an RPM binary of 4.2.2, but the sources don't
> build cleanly on Fedora Core 5... and Fedora distros seem to like to have
> a certain number of patches applied, like not running as root.

I cannot imagine why it would not build. What are the errors you get
during the build?

> Anyway, I noticed the following.  When I configure an FC5 machine with:
> ...
> multicastclient                 # listen on default

This is invalid. multicastclient requires an address, in this case You should be seeing an error message in syslog.

> restrict mask nomodify notrap
> restrict mask nomodify notrap
> # Undisciplined Local Clock. This is a fake driver intended for backup
> # and when no outside source of synchronized time is available.
> server     # local clock
> fudge stratum 10

You don't need these lines unless you are providing ntp service to other

> And run ntpd with the arguments:
>  ntpd -A -m -u ntp:ntp -p /var/run/ntpd.pid -g

As near as I can figure out -m is not a  valid option.

> that I notice it doesn't sync up with the multicast source... Rather it
> discovers
> the multicast server, and then starts to use it as a unicast server:
> # ntpq -n -c peer
>      remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
>     LOCAL(0)        10 l   34   64  377    0.000    0.000   0.001
> *   2 u    4 1024  377    1.190    0.321   0.024
> in our environment, this doesn't scale well.  We have thousands of desktops,
> and we're running QoS, so we end up generating a lot of EF traffic.  Not good.

See above.

> I've attached packet traces below.
> Is there a reason that ntpd isn't just synchronizing with the mulicast packets
> instead?

See above. I see nothing to indicate that it's listening for multicast
packets. If you build and run debug does it show the multicast interface
being set up?


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