Description

This library is only needed if /etc/nsswitch.conf specifies 'mdns4' or 'mdns4_minimal' on the 'hosts' line. This is only known to be the case on Debian and Ubuntu systems.
When this library is needed, it is used to resolve host names; so its absence will break most network and Internet applications.

Resolution

To install this library, run one of the following commands as root, or look for the corresponding package names in your favorite package manager:
64-bit Debian 8 : apt-get install libnss-mdns:i386
32-bit Debian or Ubuntu : apt-get install libnss-mdns
64-bit Ubuntu : apt-get install libnss-mdns:i386
32/64-bit Fedora : dnf install nss-mdns.i686
32-bit Mandriva : urpmi nss_mdns
64-bit Mandriva : Not available
32-bit SUSE : zypper install nss-mdns
64-bit SUSE : zypper install nss-mdns-32bit
32-bit Arch : pacman -Syu nss-mdns
64-bit Debian 7 and older : apt-get install lib32nss-mdns
Note that on Debian or Ubuntu (versions earlier than 14.04), should you do attempt to use libnss-mdns:i386, the package manager will warn you that it will replace all of the appropriate 64-bit libraries with the same 32-bit libraries.

Mageia

Mageia 2 and 3 users running the 64 bit version will need to manually download the nss-mdns library and install it via the rpm:
Mageia 3
wget ftp://rpmfind.net/linux/mageia/distrib/3/i586/media/core/release/nss_mdns-0.10-10.mga3.i586.rpm rpm -ihv nss_mdns-0.10-10.mga3.i586.rpm
Mageia 2
wget ftp://rpmfind.net/linux/mageia/distrib/2/i586/media/core/release/nss_mdns-0.10-9.mga1.i586.rpm rpm -ihv nss_mdns-0.10-9.mga1.i586.rpm
The relevant bug report is available here.
with thanks to Dylan Myers for this tip