dnsmasq
dnsmasq provides a DNS server, a DHCP server with support for DHCPv6 and PXE, and a TFTP server. It is designed to be lightweight and have a small footprint, suitable for resource constrained routers and firewalls. dnsmasq can also be configured to cache DNS queries for improved DNS lookup speeds to previously visited sites.
Installation
Start the daemon
Start/enable dnsmasq.service
.
To see if dnsmasq started properly, check the system's journal:
$ journalctl -u dnsmasq.service
The network will also need to be restarted so the DHCP client can create a new /etc/resolv.conf
.
Configuration
To configure dnsmasq, edit /etc/dnsmasq.conf
. The file contains comments explaining the options. For all available options see dnsmasq(8).
0
:
port=0
$ dnsmasq --test
DNS server
To set up dnsmasq as a DNS caching daemon on a single computer specify a listen-address
directive, adding in the localhost IP address:
listen-address=::1,127.0.0.1
To use this computer to listen on its LAN IP address for other computers on the network. It is recommended that you use a static LAN IP in this case. E.g.:
listen-address=::1,127.0.0.1,192.168.1.1
Set the number of cached domain names with cache-size=size
(the default is 150
):
cache-size=1000
To validate DNSSEC load the DNSSEC trust anchors provided by the dnsmasq package and set the option dnssec
:
conf-file=/usr/share/dnsmasq/trust-anchors.conf dnssec
See dnsmasq(8) for more options you might want to use.
DNS addresses file and forwarding
After configuring dnsmasq, you need to add the localhost addresses as the only nameservers in /etc/resolv.conf
. This causes all queries to be sent to dnsmasq.
Since dnsmasq is a stub resolver not a recursive resolver you must set up forwarding to an external DNS server. This can be done automatically by using openresolv or by manually specifying the DNS server address in dnsmasq's configuration.
openresolv
If your network manager supports resolvconf, instead of directly altering /etc/resolv.conf
, you can use openresolv to generate configuration files for dnsmasq. [1]
Edit /etc/resolvconf.conf
and add the loopback addresses as name servers, and configure openresolv to write out dnsmasq configuration:
/etc/resolvconf.conf
# Use the local name server name_servers="::1 127.0.0.1" # Write out dnsmasq extended configuration and resolv files dnsmasq_conf=/etc/dnsmasq-conf.conf dnsmasq_resolv=/etc/dnsmasq-resolv.conf
Run resolvconf -u
so that the configuration files get created. If the files do not exist dnsmasq.service
will fail to start.
Edit dnsmasq's configuration file to use openresolv's generated configuration:
# Read configuration generated by openresolv conf-file=/etc/dnsmasq-conf.conf resolv-file=/etc/dnsmasq-resolv.conf
Manual forwarding
First you must set localhost addresses as the only nameservers in /etc/resolv.conf
:
/etc/resolv.conf
nameserver ::1 nameserver 127.0.0.1
Make sure to protect /etc/resolv.conf
from modification as described in Domain name resolution#Overwriting of /etc/resolv.conf.
The upstream DNS server addresses must then be specified in dnsmasq's configuration file as server=server_address
. Also add no-resolv
so dnsmasq does not needlessly read /etc/resolv.conf
which only contains the localhost addresses of itself.
no-resolv # Google's nameservers, for example server=8.8.8.8 server=8.8.4.4
Now DNS queries will be resolved with dnsmasq, only checking external servers if it cannot answer the query from its cache.
Adding a custom domain
It is possible to add a custom domain to hosts in your (local) network:
local=/lan/ domain=lan
In this example it is possible to ping a host/device (e.g. defined in your /etc/hosts
file) as hostname.lan
.
Uncomment expand-hosts
to add the custom domain to hosts entries:
expand-hosts
Without this setting, you will have to add the domain to entries of /etc/hosts
.
Test
To do a lookup speed test choose a website that has not been visited since dnsmasq has been started (drill is part of the ldns package):
$ drill 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:
$ drill archlinux.org | grep "Query time"
;; Query time: 18 msec
$ drill archlinux.org | grep "Query time"
;; Query time: 2 msec
To test if DNSSEC validation is working see DNSSEC#Testing.
DHCP server
By default dnsmasq has the DHCP functionality turned off, if you want to use it you must turn it on. 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 # Optionally set a domain name domain=example.com # Set default gateway dhcp-option=3,0.0.0.0 # Set DNS servers to announce dhcp-option=6,0.0.0.0 # If your dnsmasq server is also doing the routing for your network, # you can use option 121 to push a static route out. # x.x.x.x is the destination LAN, yy is the CIDR notation (usually /24), # and z.z.z.z is the host which will do the routing. dhcp-option=121,x.x.x.x/yy,z.z.z.z # Dynamic range of IPs to make available to LAN PC and the lease time. # Ideally set the lease time to 5m only at first to test everything works okay before you set long-lasting records. dhcp-range=192.168.111.50,192.168.111.100,12h # Provide IPv6 DHCP leases through Router Advertisements (RAs) for aaaa:bbbb:cccc:dddd::/64 subnet dhcp-range=aaaa:bbbb:cccc:dddd::,ra-only,infinite # If you’d like to have dnsmasq assign static IPs to some clients, bind the LAN computers # NIC MAC addresses: dhcp-host=aa:bb:cc:dd:ee:ff,192.168.111.50 dhcp-host=aa:bb:cc:ff:dd:ee,192.168.111.51
See dnsmasq(8) for more options.
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.
If you inspect the /var/lib/misc/dnsmasq.leases
file on the server, you should be able to see the lease.
TFTP server
dnsmasq has built-in TFTP server.
To use it, create a directory for TFTP root (e.g. /srv/tftp
) to put transferable files in.
For increased security it is advised to use dnsmasq's TFTP secure mode. In secure mode only files owned by the dnsmasq
user will be served over TFTP. You will need to chown TFTP root and all files in it to dnsmasq
user to use this feature.
Enable TFTP:
enable-tftp tftp-root=/srv/tftp tftp-secure
See dnsmasq(8) for more options.
PXE server
PXE requires DHCP and TFTP servers, both functions can be provided by dnsmasq.
interface=enp0s0 bind-dynamic dhcp-range=192.168.0.1,proxy
- set up #TFTP server and #DHCP server
- copy and configure a PXE compatible bootloader (e.g. PXELINUX) on TFTP root
- enable PXE in
/etc/dnsmasq.conf
:
- file paths are relative to TFTP root
- if the file has a
.0
suffix, you must exclude the suffix inpxe-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"
pxe-service
does not 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"
See dnsmasq(8) for more options.
The rest is up to the bootloader.
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>
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
Domain blacklisting
To blacklist domains, i.e. answer queries for them with NXDOMAIN, use the address
option without specifying the IP address:
address=/blacklisted.example/ address=/another.blacklisted.example/
For ease of use place the blacklist in a separate file, e.g. /etc/dnsmasq.d/blacklist.conf
and load it from /etc/dnsmasq.conf
with conf-file=/etc/dnsmasq.d/blacklist.conf
or conf-dir=/etc/dnsmasq.d/,*.conf
.