[ntp:questions] multicast - wrong interface

Richard B. gilbert rgilbert88 at comcast.net
Sat Feb 17 16:26:37 UTC 2007


Martin wrote:
> Hello !
> 
> My NTP server sends all multicast traffic from eth0 and I don't
> know how to configure it to send it to the LAN connected via eth2.
> The details are below. Could you please give me some
> hints or help ?
> 
> Thank you
> 
> 	Martin
> 
> - - - - - -
> 
> In the ntp.conf there is:
> 	broadcast 224.0.1.1 key 145 ttl 3
> 
> and the linux kernel has a route for class D addresses, it uses eth2:
> 	Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
> 	224.0.0.0       *               240.0.0.0       U     0      0        0 eth2
> 
> but the output from ntp -D2 shows, that NTP has chosen eth0 (fd #18) and
> not eth2 (verified with tcpdump):
> 	created interface #2: fd=18, bfd=-1, name=eth0, flags=0x19, scope=0, 
> ifindex=0, sin=217.XX.XXX.XX, bcast=217.XX.XXX.223,, mask=255.255.255.224, 
> Enabled:
> 	......
> 	created interface #3: fd=19, bfd=-1, name=eth2, flags=0x19, scope=0, 
> ifindex=0, sin=192.168.XX.XX, bcast=192.168.XX.255,, mask=255.255.255.0, 
> Enabled:
> 	......
> 	MCAST   ***** sendpkt(fd=18 dst=224.0.1.1, src=217.XX.XXX.XX, ttl=96, len=68)
> 
> (BTW, why is ttl=96 and not 3 ? But that's not the problem.)
> 
> 
> 
> 
> 
> 
> 
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> 

Try going with the flow.  If ntpd wants to multicast via eth0, then 
connect eth0 to the network you want to multicast to.  Reassign another 
interface to do whatever eth0 was doing.

It may be a lot of work but you'll get much faster results than you 
would by waiting for a major redesign of ntpd networking.

Alternatively, you could try hacking the code yourself and contributing 
any solution you find.




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