Re: [44net] Strange Broadcasts... - 44net

12 Jun 2015

...
  Subject:
 Re: [44net] Strange Broadcasts...
 From:
 Jeroen Massar &lt;jeroen(a)massar.ch&gt;
 Date:
 06/11/2015 09:03 PM

 To:
 AMPRNet working group &lt;44net(a)hamradio.ucsd.edu&gt;

 Forget about this; it's just syntax. Who cares
if we have to have
hundreds of P2P interfaces instead of a single P2MP?  ntpd cares about it and also
the Linux and FreeBSD kernels.

 ISC ntpd listens on each interface automatically, hence after ~200
 interfaces it breaks as it runs out of file descriptors (each interface
 gets a separate socket as it uses it that way to be able to properly
 select the interface to reply to packets on that interface). 
I know about that problem!  Silly ntpd listens on a separate socket for every address,
instead of just listening on a wildcard socket.  It caused havoc on our gateway because
it has over 200 addresses assigned to a dummy0 interface, used by an EchoLink proxy
farm running on the machine.

Fortunately in recent versions of ntpd it can be solved by config like this:

interface ignore all
interface listen lo
interface listen eth1
interface listen tun0
interface listen tunl0

i.e. you can direct ntpd what interfaces to watch and to ignore the rest.

I think it would be better when it listened on 0.0.0.0 instead (of course you CAN set
the source address of outgoing packets on a wildcard socket, at least in Linux you can),
but I saw there already has been a heated debate about that on the mailinglist so I chose
not to suggest that and use the abovementioned workaround.

Rob