[ntp:hackers] Broadcast/multicast commands

Danny Mayer mayer at ntp.isc.org
Fri Dec 7 20:01:44 GMT 2007


Dave,

Sorry, I overreacted. However the multicastclient will have to remain
there for a while as people use it.

Yes, you can tell from the IP address if it is a broadcast, multicast or
any other address. I believe we flag the address as an error in the
multicastclient case if it is not a multicast address.

There's a dirty little secret with the novolley parameter of
broadcastclient. It turns out that you can put absolutely anything after
the broadcastclient option and it will assume that you meant 'novolley'
so an IP address there will just say novolley on broadcastclient. It's
bad code. The other part of this is that broadcast gets ALL broadcast on
the (no)wire(s) and the destination broadcast address doesn't matter.
That's the way that broadcast works so there is not much point in
putting in a specific address except to identify it. It will receive
*all* broadcast packets. Multicast on the other hand will only accept
packets sent to the multicast address specified and this makes a big
difference in how it's handled at the IP socket level. When it bubbles
up to ntpd it doesn't matter so much since you are really looking at the
payload at that point rather than how it got there.

Does this all make some kind of sense?

Danny

David L. Mills wrote:
> Danny,
> 
> The message was a trial ballon; I have no intention to cut code.
> 
> I want the novolley option to go away in any case. I had assumed you 
> could tell from the address whether it was a IPv4 broadcast or multicast 
> or IPv6 broadcast. At least the broadcast command can do that.
> 
> Dave


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