dnsmasq

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dnsmasq provides services as a DNS cacher and a DHCP server. As a Domain Name Server (DNS) it can cache DNS queries to improve connection speeds to previously visited sites, and as a DHCP server dnsmasq can be used to provide internal IP addresses and routes to computers on a LAN. Either or both of these services can be implemented. dnsmasq is considered to be lightweight and easy to configure; it is designed for personal computer use or for use on a network with less than 50 computers. It also comes with a PXE server.

Installation

Install dnsmasq.

Configuration

To configure dnsmasq, you need to edit /etc/dnsmasq.conf. The file contains extensive comments explaining its options.

Warning: dnsmasq by default enables its DNS server. If you do not require it, you need to explicitly disable it by setting DNS port to 0:
/etc/dnsmasq.conf
port=0
Tip: To check configuration file(s) syntax, execute:
$ dnsmasq --test

DNS cache setup

To set up dnsmasq as a DNS caching daemon on a single computer edit /etc/dnsmasq.conf and uncomment the listen-address directive, adding in the localhost IP address:

listen-address=127.0.0.1

To use this computer to listen on its LAN IP address for other computers on the network:

listen-address=192.168.1.1    # Example IP

It is recommended that you use a static LAN IP in this case.

Multiple ip address settings:

listen-address=127.0.0.1,192.168.1.1 

DNS addresses file

Merge-arrows-2.pngThis article or section is a candidate for merging with resolv.conf.Merge-arrows-2.png

Notes: Same topic. Also note that most of this can also be done natively in /etc/resolvconf.conf using the name_servers and name_servers_append options. (Discuss in Talk:Dnsmasq#)

After configuring dnsmasq, the DHCP client will need to prepend the localhost address to the known DNS addresses in /etc/resolv.conf. This causes all queries to be sent to dnsmasq before trying to resolve them with an external DNS. After the DHCP client is configured, the network will need to be restarted for changes to take effect.

resolv.conf

One option is a pure resolv.conf configuration. To do this, just make the first nameserver in /etc/resolv.conf point to localhost:

/etc/resolv.conf
nameserver 127.0.0.1
# External nameservers
...

Now DNS queries will be resolved first with dnsmasq, only checking external servers if dnsmasq cannot resolve the query. dhcpcd, unfortunately, tends to overwrite /etc/resolv.conf by default, so if you use DHCP it is a good idea to protect /etc/resolv.conf. To do this, append nohook resolv.conf to the dhcpcd config file:

/etc/dhcpcd.conf
...
nohook resolv.conf

It is also possible to write protect your resolv.conf:

# chattr +i /etc/resolv.conf
More than three nameservers

A limitation in the way Linux handles DNS queries is that there can only be a maximum of three nameservers used in resolv.conf. As a workaround, you can make localhost the only nameserver in resolv.conf, and then create a separate resolv-file for your external nameservers. First, create a new resolv file for dnsmasq:

/etc/resolv.dnsmasq.conf
# Google's nameservers, for example
nameserver 8.8.8.8
nameserver 8.8.4.4

And then edit /etc/dnsmasq.conf to use your new resolv file:

/etc/dnsmasq.conf
...
resolv-file=/etc/resolv.dnsmasq.conf
...

dhcpcd

dhcpcd has the ability to prepend or append nameservers to /etc/resolv.conf by creating (or editing) the /etc/resolv.conf.head and /etc/resolv.conf.tail files respectively:

echo "nameserver 127.0.0.1" > /etc/resolv.conf.head

dhclient

For dhclient, uncomment in /etc/dhclient.conf:

prepend domain-name-servers 127.0.0.1;

NetworkManager

DNS requests can be sped up by caching previous requests locally for subsequent lookup. NetworkManager has a plugin to enable DNS caching using dnsmasq, but it is not enabled in the default configuration.

Make sure dnsmasq has been installed, but has been disabled. Then, edit /etc/NetworkManager/NetworkManager.conf and change the dns in the [main] section:

/etc/NetworkManager/NetworkManager.conf
[main]
...
dns=dnsmasq

Now restart NetworkManager or reboot. NetworkManager will automatically start dnsmasq and add 127.0.0.1 to /etc/resolv.conf. The actual DNS servers can be found in /run/NetworkManager/dnsmasq.conf. You can verify dnsmasq is being used by doing the same DNS lookup twice with $ dig example.com that can be installed with bind-tools and verifying the server and query times.

Usage with libvirt

Network-manager think if there is one running libvirt that he run this before. To fix conflicts between other dnsmasq, eg: used in libvirt, you must run it externally.

We do not want change our resolv.conf automaticly.

/etc/NetworkManager/NetworkManager.conf
[main]
...
dns=none

We put it manually here.

/etc/resolv.conf.head
nameserver 127.0.0.1

The interface to bind and bind it even if there is second dnsmasq runned on computer.

/etc/NetworkManager/dnsmasq.d/bind-interface.conf
interface=lo
bind-interface

This start service if interface is up. This service can start only once before stop which will be initiate by systemd on restart/shutdown.

/etc/NetworkManager/dispatcher.d/10_dnsmasq
#!/bin/sh
if [ -n "$2" ] && [ "$2" = "up" ]; then # $INTERFACE is up
	systemctl start NetworkManager-dnsmasq.service
fi

Systemd service.

/etc/systemd/system/NetworkManager-dnsmasq.service
[Unit]
Description=A lightweight DHCP and caching DNS server
After=network.target
Documentation=man:dnsmasq(8)

[Service]
Type=dbus
BusName=uk.org.thekelleys.dnsmasq
ExecStartPre=/usr/bin/dnsmasq --test
ExecStart=/usr/bin/dnsmasq -k --enable-dbus --user=dnsmasq --pid-file --conf-dir=/etc/NetworkManager/dnsmasq.d/
ExecReload=/bin/kill -HUP $MAINPID

Custom configuration

Custom configurations can be created for dnsmasq by creating configuration files in /etc/NetworkManager/dnsmasq.d/. For example, to change the size of the DNS cache (which is stored in RAM):

/etc/NetworkManager/dnsmasq.d/cache.conf
cache-size=1000

IPv6

Enabling dnsmasq in NetworkManager may break IPv6-only DNS lookups (i.e. dig -6 [hostname]) which would otherwise work. In order to resolve this, creating the following file will configure dnsmasq to also listen to the IPv6 loopback:

/etc/NetworkManager/dnsmasq.d/ipv6_listen.conf
listen-address=::1

In addition, dnsmasq also does not prioritize upstream IPv6 DNS. Unfortunately NetworkManager does not do this (Ubuntu Bug). A workaround would be to disable IPv4 DNS in the NetworkManager config, assuming one exists

Other methods

Another option is in NetworkManagers' settings (usually by right-clicking the applet) and entering settings manually. Setting up will depending on the type of front-end used; the process usually involves right-clicking on the applet, editing (or creating) a profile, and then choosing DHCP type as 'Automatic (specify addresses).' The DNS addresses will need to be entered and are usually in this form: 127.0.0.1, DNS-server-one, ....

Test

To do a lookup speed test choose a website that has not been visited since dnsmasq has been started (dig is part of the bind-tools package):

$ dig archlinux.org | grep "Query time"

Running the command again will use the cached DNS IP and result in a faster lookup time if dnsmasq is setup correctly:

$ dig archlinux.org | grep "Query time"
;; Query time: 18 msec
$ dig archlinux.org | grep "Query time"
;; Query time: 2 msec

DHCP server setup

By default dnsmasq has the DHCP functionality turned off, if you want to use it you must turn it on in (/etc/dnsmasq.conf). Here are the important settings:

# Only listen to routers' LAN NIC.  Doing so opens up tcp/udp port 53 to
# localhost and udp port 67 to world:
interface=<LAN-NIC>

# dnsmasq will open tcp/udp port 53 and udp port 67 to world to help with
# dynamic interfaces (assigning dynamic ips). Dnsmasq will discard world
# requests to them, but the paranoid might like to close them and let the 
# kernel handle them:
bind-interfaces

# Dynamic range of IPs to make available to LAN pc
dhcp-range=192.168.111.50,192.168.111.100,12h

# If you’d like to have dnsmasq assign static IPs, bind the LAN computer's
# NIC MAC address:
dhcp-host=aa:bb:cc:dd:ee:ff,192.168.111.50

Test

From a computer that is connected to the one with dnsmasq on it, configure it to use DHCP for automatic IP address assignment, then attempt to log into the network normally.

TFTP server setup

Create a directory for TFTP root (e.g. /srv/tftp) to put transferable files in.

To use dnsmasq's TFTP secure mode chown TFTP root and all files in it to dnsmasq user.

Enable TFTP in dnsmasq.conf

/etc/dnsmasq.conf
enable-tftp
tftp-root=/srv/tftp
tftp-secure

PXE setup

PXE requires DHCP and TFTP servers, both functions can be provided by dnsmasq.

Tip: dnsmasq can add PXE booting options to a network with an already running DHCP server:
/etc/dnsmasq.conf
interface=enp0s0
bind-dynamic
dhcp-range=192.168.0.1,proxy
  1. set up TFTP server and DHCP server
  2. copy and configure a PXE compatible bootloader (e.g. PXELINUX) on TFTP root
  3. enable PXE in /etc/dnsmasq.conf:
Note:
  • file paths are relative to TFTP root
  • if the file has a .0 suffix, you must exclude the suffix in pxe-service options

To simply send one file:

dhcp-boot=lpxelinux.0

To send a file depending on client architecture:

pxe-service=x86PC, "PXELINUX (BIOS)", "bios/lpxelinux"
pxe-service=X86-64_EFI, "PXELINUX (EFI)", "efi64/syslinux.efi"
Note: In case pxe-service doesn't work (especially for UEFI-based clients), combination of dhcp-match and dhcp-boot can be used. See RFC4578 for more client-arch numbers for use with dhcp boot protocol.
dhcp-match=set:efi-x86_64,option:client-arch,7
dhcp-match=set:efi-x86_64,option:client-arch,9
dhcp-match=set:efi-x86,option:client-arch,6
dhcp-match=set:bios,option:client-arch,0
dhcp-boot=tag:efi-x86_64,"efi64/syslinux.efi"
dhcp-boot=tag:efi-x86,"efi32/syslinux.efi"
dhcp-boot=tag:bios,"bios/lpxelinux.0"


The rest is up to the bootloader.

Start the daemon

Start/enable dnsmasq.service.

To see if dnsmasq started properly, check the system's journal:

$ journalctl -u dnsmasq

The network will also need to be restarted so the DHCP client can create a new /etc/resolv.conf.

Tips and tricks

Prevent OpenDNS redirecting Google queries

To prevent OpenDNS from redirecting all Google queries to their own search server, add to /etc/dnsmasq.conf:

server=/www.google.com/<ISP DNS IP>

View leases

$ cat /var/lib/misc/dnsmasq.leases

Adding a custom domain

It is possible to add a custom domain to hosts in your (local) network:

local=/home.lan/
domain=home.lan

In this example it is possible to ping a host/device (e.g. defined in your hosts file) as hostname.home.lan.

Uncomment expand-hosts to add the custom domain to hosts entries:

expand-hosts

Without this setting, you'll have to add the domain to entries of /etc/hosts.

Override addresses

In some cases, such as when operating a captive portal, it can be useful to resolve specific domains names to a hard-coded set of addresses. This is done with the address config:

address=/example.com/1.2.3.4

Furthermore, it's possible to return a specific address for all domain names that are not answered from /etc/hosts or DHCP by using a special wildcard:

address=/#/1.2.3.4

More than one instance

If we want two or more dnsmasq servers works per interface(s).

Static

To do this staticly, server per interface, use interface and bind-interface options. This enforce start second dnsmasq.

Dynamic

In this case we can exclude per interface and bind any others:

except-interface=lo
bind-dynamic
Note: This is default in libvirt.

See also