[ntp:questions] NTP Broadcast/Multicast Benefits

Danny Mayer mayer at gis.net
Thu Aug 4 17:08:30 UTC 2005

Matt Kinard wrote:
> Howdy guys!
>    I was wondering if anyone could enumerate on the reasons why one
> would want to configure an ntp in a broadcast/multi-cast mode.  Do we
> see siginifcant network performance issues in client/server mode?  I
> know that the management of the NTP configuration could be simplified if
> the bc/mc mode is used, but are there any other benefits?  What about
> drawbacks?

The best configuration is with multicast rather than broadcast. With 
broadcast a packet gets sent out to everyone, while with multicast it 
only gets sent to those systems that request to join the multicast 
group. If EVERY node in the network is requesting it it may be simpler 
to just do broadcast, though that restricts you to IPv4 only.  With 
broadcast/multicast packets are sent every 64 seconds. With client 
server, the client makes requests based on whether or not it's 
synchronized and settled down (or it has lost the connection) and can be 
anything from 64 seconds to 1024 seconds.  These are small packets so 
the traffic only gets high if a lot of nodes are requesting the service. 
At that point, multicast and broadcast are far better.

> Thanks all!
> Matt
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