[ntp:questions] Multicast and dynamic interfaces

[Danny Mayer]

barry bouwsma wrote:
> Moin,
> 
> ntp-dev-4.2.5p118, Linux latest-ish.  Also observed with ntp-dev-4.2.5p113
> 
> 
> Should ntpd be able to listen for multicasts on interfaces that
> get added/configured after ntpd starts?
> 
> For example, I just brought up and configured this interface:
> Jul  9 21:12:46 localhost ntpd[3422]: Listening on interface #8 eth3, fe80::200:e8ff:fe00:fe0#123 Enabled
> Jul  9 21:12:46 localhost ntpd[3422]: Listening on interface #9 eth3, 172.27.72.99#123 Enabled
> 
> However I'm not able to get it to hear the multicast data which
> can be heard, no matter how long I wait, unless I restart ntpd,
> like so:
> 
> Jul  9 21:15:42 localhost ntpd[19791]: Listening on interface #3 eth3, fe80::200:e8ff:fe00:fe0#123 Enabled
> Jul  9 21:15:42 localhost ntpd[19791]: Listening on interface #4 lo, 127.0.0.1#123 Enabled
> Jul  9 21:15:42 localhost ntpd[19791]: Listening on interface #5 eth3, 172.27.72.99#123 Enabled
> Jul  9 21:15:43 localhost ntpd[19791]: Listening on interface #6 multicast, 224.0.1.1#123 Enabled
> Jul  9 21:15:43 localhost ntpd[19791]: setsockopt IP_ADD_MEMBERSHIP failure: No Jul  9 21:15:43 localhost ntpd[19791]: Failed to add Multicast Listener 224.0.1.1
> (no big deal that)
> Jul  9 21:15:43 localhost ntpd[19791]: Listening on interface #7 multicast, ff05::101#123 Enabled
> Jul  9 21:15:43 localhost ntpd[19791]: Added Multicast Listener ff05::101 on interface #7 multicast
> 
> 
> And voila, now I can hear and use that multicast data...
>      remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
>  fe80::200:c0ff: .DCFa.           1 m   14   16  200    0.741    1.240   0.008
> 
> 
> Is this a case of missing or non-functioning code, or is this
> something that really isn't possible?

It sounds like a bug, possibly 2 bugs. Please file a bug report. The 
multicast option should reconfigure itself after a change of IP address 
and rebind itself to the new address. If the address has gone away then 
the multicast socket won't be able to receive any multicast packets. Are 
you using DHCP provided addresses or static ones?

Danny