Packages automagically modifies /etc/nsswitch.conf
--------------------------------------------------
Previously the base-files package shipped /etc/nsswitch.conf and specified:
hosts: files dns mdns
However, due to bug#351990, this is no longer the case. /etc/nsswitch.conf
is now generated post-installation. Upon installation of nss-mdns, if the
strings 'mdns', 'mdns_minimal', 'mdns4', 'mdns4_minimal', 'mdns6' or
'mdns6_minimal' appear on the hosts line, your /etc/nsswitch.conf file
will not be updated, otherwise it will updated to match the upstream
recommended configuration which usually looks like:
hosts: files mdns4_minimal [NOTFOUND=return] dns
Other possible configurations
-----------------------------
In versions older than 0.10-4 we used this configuration:
hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4
This looks in mDNS whenever a non-link-local address does not have a PTR
(reverse DNS) record in DNS. If the host with that address is local
and available in mDNS, this means it becomes reverse-resolvable, but if
the host with that address is not local, it causes a 5 second delay,
so this is no longer enabled by default. If a local administrator wishes
to reinstate mdns4, they can do so.
Sites with a .local DNS zone
----------------------------
Making nss-mdns authoritative for .local breaks resolution on networks
where .local is a real domain name. To workaround this, avahi-daemon
should be restarted when the DNS settings change (for example via
resolvconf and dhclient hooks) and disable itself when a SOA for the
.local zone is found. This is not currently implemented at the time of
writing, but should soon be.
See also this excellent summary on the upstream website:
<http://avahi.org/wiki/AvahiAndUnicastDotLocal>