[ntp:questions] Multicast question

Martin Burnicki martin.burnicki at meinberg.de
Fri Feb 29 14:43:38 UTC 2008

Danny Mayer wrote:

> Martin Burnicki wrote:
>> Danny Mayer wrote:
>>> John Vossler wrote:
>> [...]
>>>> 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.
>> If ntpd has been configured to send multicasts, shouldn't it by default
>> send multicasts on every interface it actually uses?
>> I had expected ntpd would already do so.
> How could you do that? You have one packet that you are sending out. It
> can only go out on exactly one interface. You can only choose which
> interface to use, you cannot select more than one.

I'd expect that either the kernel routed multicast packets to all interfaces
(isn't that what routers do with multicasts, contrarily to broadcasts?), or
the application would send an individual packet on each interface.

Anyway, if I have a server with several interfaces I'd expect those
multicasts to appear on every single subnet connected to one of those

Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont

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