Re: About that horrible polluting mDNS stuff?

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Mon, 29 Nov 2010 09:02:36 +0200
    From:        Alan Barrett <apb%cequrux.com@localhost>
    Message-ID:  <20101129070236.GA8510%apb-laptoy.apb.alt.za@localhost>

  | The problem is more like: ntpd emits unwanted packets,

Does it really?   As best I can tell, it makes a connection request
to 127.0.0.1 which could only just barely be described as "emits
unwanted packets" (ie: you're never going to be able to see the things).
Those are to the the mdns daemon, if it isn't running, the connection
attempt fails (a single SYN to 127.0.0.1) and it goes away and tries
again later (in case mdnsd starts later, I presume).

I'm not sure what paranoid network admins there are around that care
about packets to 127.0.0.1 - or why, but I suppose it is possible...

  | so there should be a global way of disabling mdns.

As was mentioned earlier, that is just not running mdnsd.   If it weren't
for the unfortunate syslog messages from ntpd, no-one would ever have known
anything different was happening, or trying to happen.  No-one would ever
have cared either (or no more than we all care about all the unknown code
that all of the larger sub-systems are executing.)

Don't any of you kind of think that the very concept of configuration options
for the system that is supposed to be zero configuration networking is just a
little beyond weird???   Or would be if we had them.

Lastly, for the ultra paranoid of you all you really can't handle ntpd
making a connection attempt to 127.0.0.1 (which its default config tries
a whole 5 times), there is NOT no way to disable it, you can set the
mdnstries option in ntpd,conf to control the number of attempts, and if
it is 0, no attempts will be made (and nor will you see any syslog messages,
even without changing their priorities to move them into debug noise land).
(The complete.conf file (in the sources, I don't think it is installed
anywhere) - the one that shows all of the possible options - shows this
option set to its default value of 5.)

As best I can tell, this is documented exactly as well as all of the rest
of ntpd.conf (ie: un).

The hysteria all this has generated has been truly amazing.  Next time,
someone please just go read the source.   That's why we have it.  It
isn't a difficult task.

kre

ps: I'm actually assuming that ntpd is compiled to use 127.0.0.1 to
communicate with mdnsd, the alternative is for it to use a unix domain
socket, which is even less like "emits packets"...