[ntp:questions] Re: NTP over multicast sat link with no return channel

Danny Mayer mayer at ntp.isc.org
Tue Apr 11 02:32:12 UTC 2006


juliansomers at googlemail.com wrote:
> Thanks for the replies,
> 
> I think I now have the server sending the multicast correctly, using
> this:
>  broadcast 229.1.1.8 ttl 2
> 
> I see the packets coming over the satellite using tcpdump:
>  22:50:05.750313 IP 192.168.1.2.123 > 229.1.1.8.123: NTPv4 bcast, strat
> 3, poll 6, prec -20
> 
> Im running ntpd on the client with this config:
> driftfile       /var/lib/ntp/ntp.drift
> restrict default nomodify nopeer
> restrict 127.0.0.1
> multicastclient 229.1.1.8
> disable auth
> 
> It seems that ntpd is listening to the multicast:
> root # netstat -na | grep 229.1.1.8
> udp        0      0 229.1.1.8:123           0.0.0.0:*
> 
> but I don't see the peer come up on he client when I go:
> root # ntpq -pn
> No association ID's returned
> 
> Should I see it as a peer?
> 

You should give it long enough. Broadcast/Multicast packets are sent
every 64 seconds and that never changes, unlike regular associations.
What version of ntp are you running? You need to use a recent version as
earlier versions were badly broken in multiple places.

> I did not expect to see 229.1.1.8 on the server as a peer:
> water root # ntpq -pn
>      remote           refid      st t when poll reach   delay   offset
> jitter
> ==============================================================================
>>  229.1.1.8       .MCST.          16 u    -   64    0    0.000    0.000
> 4000.00
> 
> Does this look correct?
> 

Yes, that's normal.

> Danny, you said,
>> You can disable auth in the client by adding disable auth to the config
>> file. You would need to do it for your case.
> does this mean that if I disable auth, the client will not try to
> contact the server for authentication, and so there is not a need for
> novolley?
> 

You cannot specify novolley for multicast, it's not supported.

> many thanks for your time,
> 
> Julian

Danny



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