[Dnsmasq-discuss] Multicast dns

Simon Kelley simon at thekelleys.org.uk
Wed Apr 25 12:22:12 BST 2007

Tom Fanning wrote:
> <snip>
>> Not at all, It's a reasonable suggestion that dnsmasq should be
>> configurable to listen for mDNS and reply to everything: Even with the
>> nsswitch.conf fix, that has to be fixed on every new Ubuntu Feisty
>> install, a dnsmasq configuration tweak would do it for  a whole network
>> and if mDNS was not otherwise in use, nothing is lost.
>> OTOH, against doing this is that it breaks "real mDNS" so it's  a bug
>> to
>> fix another bug. Also it's possibly bloat for dnsmasq and of minor real
>> world use for most people. A judgement call, like most possible
>> enhancements.

I did some experimental hacking last night, and it looks like adding
mDNS support is a non-starter. Despite being billed as "DNS just
multicast" mDNS is in fact subtly different.

I made dnsmasq listen for and reply to multicast queries, and had it
reply to .local queries multicast by Avahi on an Ubuntu Feisty system.
The replies were rejected by Avahi, and on further reading it turns out
that mDNS replies must not include the "question" section which is
included in normal DNS replies. The presence of this section was enough
to spook Avahi.

The way dnsmasq is implemented makes it almost impossible to reliably
generate replies without a question section, so the whole plan is broken.

Sorry: editing nsswitch.conf or avoiding .local are the best I can offer.

There's a great quote in the draft standard:

   Note also that the special treatment of names ending in ".local." has
   been implemented in Macintosh computers since the days of Mac OS 9,
   and continues today in Mac OS X. There are also implementations for
   Linux and other platforms [dotlocal]. Operators setting up private
   internal networks ("intranets") are advised that their lives may be
   easier if they avoid using the suffix ".local." in names in their
   private internal DNS server. Alternative possibilities include:




More information about the Dnsmasq-discuss mailing list