Difference between revisions of "Domain name resolution"
(→OpenNIC: the Worldwide Anycast servers are probably a better default)
(→OpenNIC: added IPv6 addresses)
|Line 54:||Line 54:|
=== OpenDNS ===
=== OpenDNS ===
Revision as of 23:37, 16 December 2016
The configuration file for DNS resolvers is
/etc/resolv.conf. From its man page:
- The resolver is a set of routines in the C library that provide access to the Internet Domain Name System (DNS). The resolver configuration file contains information that is read by the resolver routines the first time they are invoked by a process. The file is designed to be human readable and contains a list of keywords with values that provide various types of resolver information.
- If this file does not exist, only the name server on the local machine will be queried; the domain name is determined from the hostname and the domain search path is constructed from the domain name.
- 1 DNS in Linux
- 2 Alternative DNS servers
- 3 Preserve DNS settings
- 4 Tips and tricks
DNS in Linux
Your ISP (usually) provides working DNS servers, and a router may also add an extra DNS server in case you have your own cache server. Switching between DNS servers does not represent a problem for Windows users, because if a DNS server is slow or does not work it will immediately switch to a better one. However, Linux usually takes longer to timeout, which could be the reason why you are getting a delay.
Use drill (provided by package
$ drill www5.yahoo.com
You can also specify a specific nameserver's ip address, bypassing the settings in your
$ drill @ip.of.name.server www5.yahoo.com
For example to test Google's name servers:
$ drill @126.96.36.199 www5.yahoo.com
To test a local name server (such as unbound) do:
$ drill @127.0.0.1 www5.yahoo.com
Alternative DNS servers
To use alternative DNS servers, edit
/etc/resolv.conf and add them to the top of the file so they are used first, optionally removing or commenting out already listed servers. Currently, you may include a maximum of three
/etc/resolv.conftake effect immediately.
nameserverto the actual DNS server but to
127.0.0.1. See the article for the program you are using for DNS caching.
OpenNIC provides free uncensored nameservers with additional features.
# OpenNIC IPv4 nameservers (Worldwide Anycast) nameserver 188.8.131.52 nameserver 184.108.40.206
# OpenNIC IPv6 nameservers (Worldwide Anycast) nameserver 2a05:dfc7:5::53 nameserver 2a05:dfc7:5::5353
OpenDNS provides free alternative nameservers:
# OpenDNS IPv4 nameservers nameserver 220.127.116.11 nameserver 18.104.22.168
# OpenDNS IPv6 nameservers nameserver 2620:0:ccc::2 nameserver 2620:0:ccd::2
Google's nameservers can be used as an alternative:
# Google IPv4 nameservers nameserver 22.214.171.124 nameserver 126.96.36.199
# Google IPv6 nameservers nameserver 2001:4860:4860::8888 nameserver 2001:4860:4860::8844
Comodo provides another IPv4 set, with optional (non-free) web-filtering. Implied in this feature is that the service hijacks the queries.
# Comodo nameservers nameserver 188.8.131.52 nameserver 184.108.40.206
Yandex.DNS have three options:
# Basic Yandex.DNS - Quick and reliable DNS nameserver 220.127.116.11 # Preferred IPv4 DNS nameserver 18.104.22.168 # Alternate IPv4 DNS nameserver 2a02:6b8::feed:0ff # Preferred IPv6 DNS nameserver 2a02:6b8:0:1::feed:0ff # Alternate IPv6 DNS
# Safe Yandex.DNS - Protection from virus and fraudulent content nameserver 22.214.171.124 # Preferred IPv4 DNS nameserver 126.96.36.199 # Alternate IPv4 DNS nameserver 2a02:6b8::feed:bad # Preferred IPv6 DNS nameserver 2a02:6b8:0:1::feed:bad # Alternate IPv6 DNS
# Family Yandex.DNS - Without adult content nameserver 188.8.131.52 # Preferred IPv4 DNS nameserver 184.108.40.206 # Alternate IPv4 DNS nameserver 2a02:6b8::feed:a11 # Preferred IPv6 DNS nameserver 2a02:6b8:0:1::feed:a11 # Alternate IPv6 DNS
Yandex.DNS' speed is the same in all three modes. In "Basic" mode, there is no traffic filtering. In "Safe" mode, protection from infected and fraudulent sites is provided. "Family" mode enables protection from dangerous sites and blocks sites with adult content.
UncensoredDNS is a free uncensored DNS resolver who also answers queries on port 5353 if you are behind a firewall blocking outgoing port 53.
# censurfridns.dk IPv4 nameservers nameserver 220.127.116.11 ## anycast.censurfridns.dk nameserver 18.104.22.168 ## ns1.censurfridns.dk
# censurfridns.dk IPv6 nameservers nameserver 2001:67c:28a4:: ## anycast.censurfridns.dk nameserver 2002:d596:2a92:1:71:53:: ## ns1.censurfridns.dk
Preserve DNS settings
dhcpcd, netctl, NetworkManager, and various other processes can overwrite
/etc/resolv.conf. This is usually desirable behavior, but sometimes DNS settings need to be set manually (e.g. when using a static IP address). There are several ways to accomplish this.
- If you are using dhcpcd, see #Modify the dhcpcd config below.
- If you are using netctl and static IP address assignment, do not use the
DNS*options in your profile, otherwise resolvconf is called and
To stop NetworkManager from modifying
/etc/NetworkManager/NetworkManager.conf and add the following in the
/etc/resolv.conf might be a broken symlink that you will need to remove after doing that. Then, just create a new
provides a utility resolvconf, which is a framework for managing multiple DNS configurations. See
man 8 resolvconf and
man 5 resolvconf.conf for more information.
The configuration is done in
/etc/resolvconf.conf and running
resolvconf -u will generate
Modify the dhcpcd config
dhcpcd's configuration file may be edited to prevent the dhcpcd daemon from overwriting
/etc/resolv.conf. To do this, add the following to the last section of
Alternatively, you can create a file called
/etc/resolv.conf.head containing your DNS servers. dhcpcd will prepend this file to the beginning of
Or you can configure dhcpcd to use the same DNS servers every time. To do this, add the following line at the end of your
static domain_name_servers=22.214.171.124 126.96.36.199
Another way to protect your
/etc/resolv.conf from being modified by anything is setting the immutable (write-protection) attribute:
# chattr +i /etc/resolv.conf
Use timeout option to reduce hostname lookup time
If you are confronted with a very long hostname lookup (may it be in pacman or while browsing), it often helps to define a small timeout after which an alternative nameserver is used. To do so, put the following in
Tips and tricks
Local domain names
If you want to be able to use the hostname of local machine names without the fully qualified domain names, then add a line to
resolv.conf with the local domain such as:
That way you can refer to local hosts such as
mainmachine1.example.com as simply
mainmachine1 when using the ssh command, but the drill command still requires the fully qualified domain names in order to perform lookups.