= DNS on Linux =

'''Domain Name Resolution''' ('''DNS''') on Linux is done in a very similar way to [[BSD/DNS|DNS on BSD]]. It is worth reiterating that [[Bind|DNS was invented for BSD]].

<<TableOfContents>>

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== Name resolution ==



=== Name Service Switch ===

The [[Linux/NsSwitchConf|Name Service Switch (NSS) configuration file]] (`/etc/nsswitch.conf`) defines the order of operations for various services, among them being name resolution.

{{{
hosts: files dns
}}}

Consider instead this configuration, which makes use of libraries and services from the `systemd` project. This will enable some omissions from the hosts file.

{{{
hosts: files mymachines myhostname dns
}}}



=== Hosts ===

The [[Linux/Hosts|hosts file]] (`/etc/hosts`) is a list of addresses and names, especially for local hosts and machines.

{{{
127.0.0.1 localhost
}}}



=== Resolver ===

The [[Linux/ResolvConf|resolver configuration file]] (`/etc/resolv.conf`) is a list of nameservers to query for name resolution. Changes are immediately effective.

If the resolver file is being configured directly, then it should look like:

{{{
nameserver 8.8.8.8
}}}

Services that manipulate the resolver file include:

 * [[Linux/SystemdResolved|systemd-resolved(8)]] and it's userland utility `resolvectl(1)`
 * [[Linux/SystemdResolved#ResolveConf|systemd-resolveconf(8)]]
 * [[OpenResolv|openresolve]] with [[Linux/ResolvConfConf|resolveconf.conf(5)]]
 * [[Dhcpcd|dhcpcd(8)]]
 * [[NetworkManager|NetworkManager(8)]]



=== Utilities ===

 * `drill(1)`, used as `drill NAME @SERVER TYPE`
 * [[Bind/Dig|dig(1)]]

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== Multicast name resolution ==

'''Multicast domain name resolution''' ('''mDNS''') is an expansion of the DNS protocol. An mDNS broadcaster makes use of port 5353 and resolves names in the `.local` domain.

Note that there is also partial/coincidental support for '''link-local multicast name resolution''' ('''LLMNR''') in many of the Linux implementations of mDNS. LLMNR is a similar but deliberately incompatible protocol (using port 5355) and also with a limited scope for features.



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