[ntp:questions] Multicast question

Danny Mayer mayer at ntp.isc.org
Fri Feb 29 05:05:00 UTC 2008

John Vossler wrote:

> Danny,
> You are correct, I am talking about outgoing multicast intended for 
> client systems in our environment.
> I not certain I completely understand what you mean about associating 
> interfaces with multicast addresses.  It seems like you are inferring 
> that I would need to define a unique multicast address for each 
> interface on the NTP server.  Am I understanding this correctly?


> My original intent was to have the NTP server multicast on all 
> 12 interfaces, and have the clients all listen for the same multicast 
> address.

I don't believe it can be done that way but I'd have to check the 
multicast protocol to be sure. As far as I know you have to send out 
multiple packets, one for each interface, and you have to do that 
explicitly. You certainly cannot do that today in NTP since it only uses 
one interface to send out to the multicast address.

> My ntp.conf file on the server just has the single broadcast line 
> "broadcast ttl 4"  it does not appear to attached to any 
> specific interface; thus your comment about adding a parameter.

Correct. That does not exist today.

> My initial reaction to this issue was to determine if there was an OS 
> (Solaris) directive to include the multicast for other interfaces in the 
> group as reported by "netstat -g".  Or a method to specify the multicast 
> interfaces in the ntp.conf file (apparently not, or not easily).

No, and certainly it has not been implemented in NTP.

> Is it possible to accomplish what I intended?  Or is there a method to 
> specify the single interface that ntp is multicasting on?  I might be 
> able to get the environment in sync if I could multicast on just ce3 
> instead of bge0; the interface it is using currently.

We'd have to add that to the code. It does not exist today. Please 
submit a bug report for an enhancement to add the option so it won't get 

> One note.  I am running the ntp code shipped with Solaris 10 which is v3.
> John

We cannot do anything with V3 and we would certainly not touch that 
code. V3 was retired a long time ago. Upgrade to V42.4 at least, you 
won't be sorry.


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