Default configuration for /etc/nsswitch.conf -------------------------------------------- On first installation of libnss-mdns, /etc/nsswitch.conf is modified for the upstream-recommended configuration, which usually looks like: hosts: files mdns4_minimal [NOTFOUND=return] dns If you also have systemd's libnss-resolve enabled, mDNS resolution will be configured to occur before that (higher priority): hosts: files mdns4_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] dns If any of 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 modified. Enabling IPv6 name resolution ----------------------------- Sites where IPv6 is extensively used might prefer to replace mdns4_minimal with mdns_minimal, like this: hosts: files mdns_minimal [NOTFOUND=return] dns This works well for modern software that uses getaddrinfo() with address family AF_UNSPEC. However, some programs implement IPv6 support by making an IPv6-only name resolution attempt (with AF_INET6), then falling back to IPv4-only (AF_INET) if that fails. Failed mDNS name resolution attempts take several seconds, so this configuration will make those programs slow when contacting IPv4-only hosts in the .local zone. See for more information. Falling back to mDNS for names outside .local --------------------------------------------- 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 work around this, nss-mdns implements the heuristic described in : it looks up the SOA record for the .local zone, and disables itself automatically if that record is found.