[ntp:questions] unexpected multicast client operation

Steve Kostecke kostecke at ntp.isc.org
Wed Feb 21 22:18:42 UTC 2007

On 2007-02-21, none <none at none1.invalid> wrote:

> I am using the NTPD (v4.1 I think) that comes out of the box with RHEL 3
> and I have multicast set up. What I am seeing confuses me though.
> Every time the server sends the multicast packet the client on the RHEL3
> machine does a client/server NTP transaction back to the server.

What you are seeing is normal. A multicast-client will use temporary
unicast association with the multicast-server to determine the delay.

You can supress this (w/ novolley) but then you will need to determine
the delay manually.

> Isn't the whole purpose of multicast so the clients just all listen
> and not talk to the server ?

No. Multicast association _can_ be used in architectures which only allow
one-way communication.

> I dont have the server listed in the clients config so it is finding the
> server via the multicast message.

If you _did_ have that server explicitly listed in a "client" ntp.conf
that client would bring up a unicast assocciation with the server and
would never bring up the multicast association.

Steve Kostecke <kostecke at ntp.isc.org>
NTP Public Services Project - http://ntp.isc.org/

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