Difference between revisions of "Dnsmasq"

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(NetworkManager: move to NetworkManager#Enable DNS Caching)
(DHCP server: use special address "0.0.0.0", it means "the address of the machine running dnsmasq")
 
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{{Related|unbound}}
 
{{Related|unbound}}
 
{{Related articles end}}
 
{{Related articles end}}
[http://www.thekelleys.org.uk/dnsmasq/doc.html dnsmasq] provides a local [[Wikipedia:Name server|DNS server]], a [[Wikipedia:Dynamic Host Configuration Protocol|DHCP server]] with support for [[Wikipedia:DHCPv6|DHCPv6]] and [[Wikipedia:Preboot Execution Environment|PXE]], and a [[Wikipedia:Trivial File Transfer Protocol|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.
+
[http://www.thekelleys.org.uk/dnsmasq/doc.html dnsmasq] provides a [[Wikipedia:Name server|DNS server]], a [[Wikipedia:Dynamic Host Configuration Protocol|DHCP server]] with support for [[Wikipedia:DHCPv6|DHCPv6]] and [[Wikipedia:Preboot Execution Environment|PXE]], and a [[Wikipedia:Trivial File Transfer Protocol|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 ==
 
== Installation ==
Line 31: Line 31:
 
The network will also need to be restarted so the DHCP client can create a new {{ic|/etc/resolv.conf}}.
 
The network will also need to be restarted so the DHCP client can create a new {{ic|/etc/resolv.conf}}.
  
== Server setup ==
+
== Configuration ==
  
 
To configure dnsmasq, you need to edit {{ic|/etc/dnsmasq.conf}}. The file contains extensive comments explaining its options. For all available options see {{man|8|dnsmasq}}.
 
To configure dnsmasq, you need to edit {{ic|/etc/dnsmasq.conf}}. The file contains extensive comments explaining its options. For all available options see {{man|8|dnsmasq}}.
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{{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 {{ic|0}}:
 
{{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 {{ic|0}}:
  
{{hc|/etc/dnsmasq.conf|2=
+
{{bc|1=port=0}}
port=0
 
}}
 
  
 
}}
 
}}
Line 49: Line 47:
 
}}
 
}}
  
=== Caching DNS server ===
+
=== DNS server ===
  
To set up dnsmasq as a DNS caching daemon on a single computer edit {{ic|/etc/dnsmasq.conf}} and uncomment the {{ic|listen-address}} directive, adding in the localhost IP address:
+
To set up dnsmasq as a DNS caching daemon on a single computer specify a {{ic|listen-address}} directive, adding in the localhost IP address:
  
 
  listen-address=::1,127.0.0.1
 
  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.
+
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=192.168.1.1   # Example IP
+
  listen-address=::1,127.0.0.1,192.168.1.1
  
Set the number of cached domain names with {{ic|1=cache-size=''size''}} (the default is {{ic|150}}) and optionally disable caching of "no such domain" responces with {{ic|no-negcache}}:
+
Set the number of cached domain names with {{ic|1=cache-size=''size''}} (the default is {{ic|150}}):
  
 
  cache-size=1000
 
  cache-size=1000
no-negcache
 
  
To validate [[DNSSEC]] set the option {{ic|dnssec}} and load the DNSSEC trust anchors provided by the {{Pkg|dnsmasq}} package:
+
To validate [[DNSSEC]] load the DNSSEC trust anchors provided by the {{Pkg|dnsmasq}} package and set the option {{ic|dnssec}}:
  
 +
conf-file=/usr/share/dnsmasq/trust-anchors.conf
 
  dnssec
 
  dnssec
  conf-file=/usr/share/dnsmasq/trust-anchors.conf
+
  dnssec-check-unsigned
  
 
See {{man|8|dnsmasq}} for more options you might want to use.
 
See {{man|8|dnsmasq}} for more options you might want to use.
  
==== DNS addresses file ====
+
==== DNS addresses file and forwarding ====
  
{{Merge|resolv.conf|Same topic. Also note that most of this can also be done natively in {{ic|/etc/resolvconf.conf}} using the {{ic|name_servers}} and {{ic|name_servers_append}} options.}}
+
After configuring dnsmasq, you need to add the localhost addresses as the only nameservers in {{ic|/etc/resolv.conf}}. This causes all queries to be sent to dnsmasq.
  
After configuring dnsmasq, the DHCP client will need to prepend the localhost address to the known DNS addresses in {{ic|/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.
+
Since dnsmasq is not a recursive DNS server 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 =====
 
===== openresolv =====
  
If your network manager supports [[openresolv]], instead of directly altering {{ic|/etc/resolv.conf}}, you can use ''openresolv'' to generate configuration files for dnsmasq. [https://roy.marples.name/projects/openresolv/config]
+
If your network manager supports ''resolvconf'', instead of directly altering {{ic|/etc/resolv.conf}}, you can use [[openresolv]] to generate configuration files for dnsmasq. [https://roy.marples.name/projects/openresolv/config]
  
 
Edit {{ic|/etc/resolvconf.conf}} and add the loopback addresses as name servers, and configure openresolv to write out dnsmasq configuration:
 
Edit {{ic|/etc/resolvconf.conf}} and add the loopback addresses as name servers, and configure openresolv to write out dnsmasq configuration:
Line 100: Line 98:
 
  resolv-file=/etc/dnsmasq-resolv.conf
 
  resolv-file=/etc/dnsmasq-resolv.conf
  
===== resolv.conf =====
+
===== Manual forwarding =====
  
One option is a pure {{ic|resolv.conf}} configuration. To do this, just make the first nameserver in {{ic|/etc/resolv.conf}} point to localhost:
+
First you must set localhost addresses as the only nameservers in {{ic|/etc/resolv.conf}}:
  
 
{{hc|/etc/resolv.conf|
 
{{hc|/etc/resolv.conf|
 +
nameserver ::1
 
nameserver 127.0.0.1
 
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. {{Pkg|dhcpcd}}, unfortunately, tends to overwrite {{ic|/etc/resolv.conf}} by default, so if you use DHCP it is a good idea to protect {{ic|/etc/resolv.conf}}. To do this, append {{ic|nohook resolv.conf}} to the dhcpcd config file:
 
 
{{hc|/etc/dhcpcd.conf|
 
...
 
nohook resolv.conf
 
 
}}
 
}}
  
It is also possible to write protect your resolv.conf:
+
See [[Domain name resolution#Overwriting of /etc/resolv.conf]] on how to protect {{ic|/etc/resolv.conf}} from modification.
 
 
# chattr +i /etc/resolv.conf
 
  
====== More than three nameservers ======
+
The upstream DNS server addresses must then be specified in dnsmasq's configuration file as {{ic|1=server=''server_address''}}. Also add {{ic|no-resolv}} so dnsmasq does not needlessly read {{ic|/etc/resolv.conf}} which only contains the localhost addresses of itself.
  
A limitation in the way Linux handles DNS queries is that there can only be a maximum of three nameservers used in {{ic|resolv.conf}}. As a workaround, you can make localhost the only nameserver in {{ic|resolv.conf}}, and then create a separate {{ic|resolv-file}} for your external nameservers. First, create a new resolv file for dnsmasq:
+
{{bc|1=
 +
no-resolv
  
{{hc|/etc/resolv.dnsmasq.conf|
 
 
# Google's nameservers, for example
 
# Google's nameservers, for example
nameserver 8.8.8.8
+
server=8.8.8.8
nameserver 8.8.4.4
+
server=8.8.4.4
 
}}
 
}}
  
And then edit {{ic|/etc/dnsmasq.conf}} to use your new resolv file:
+
Now DNS queries will be resolved with dnsmasq, only checking external servers if it cannot answer the query from its cache.
  
{{hc|/etc/dnsmasq.conf|
+
==== Adding a custom domain ====
...
 
resolv-file=/etc/resolv.dnsmasq.conf
 
...
 
}}
 
  
===== dhcpcd =====
+
It is possible to add a custom domain to hosts in your (local) network:
  
{{Remove|dhcpcd supports [[#openresolv]].}}
+
local=/lan/
 +
domain=lan
  
[[dhcpcd]] has the ability to prepend or append nameservers to {{ic|/etc/resolv.conf}} by creating (or editing) the {{ic|/etc/resolv.conf.head}} and {{ic|/etc/resolv.conf.tail}} files respectively:
+
In this example it is possible to ping a host/device (e.g. defined in your {{ic|/etc/hosts}} file) as {{ic|''hostname''.lan}}.
  
echo "nameserver 127.0.0.1" > /etc/resolv.conf.head
+
Uncomment {{ic|expand-hosts}} to add the custom domain to hosts entries:
  
===== dhclient =====
+
expand-hosts
  
For {{Pkg|dhclient}}, uncomment in {{ic|/etc/dhclient.conf}}:
+
Without this setting, you will have to add the domain to entries of {{ic|/etc/hosts}}.
 
 
prepend domain-name-servers 127.0.0.1;
 
  
 
==== Test ====
 
==== Test ====
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To test if DNSSEC validation is working see [[DNSSEC#Testing]].
 
To test if DNSSEC validation is working see [[DNSSEC#Testing]].
 
=== DNS server ===
 
 
{{Expansion|Add instructions.}}
 
 
==== 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 {{ic|/etc/hosts}} file) as {{ic|''hostname''.home.lan}}.
 
 
Uncomment {{ic|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 {{ic|/etc/hosts}}.
 
  
 
=== DHCP server ===
 
=== DHCP server ===
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{{Expansion|Add instructions for IPv6 and router advertisement.}}
 
{{Expansion|Add instructions for IPv6 and router advertisement.}}
  
By default dnsmasq has the DHCP functionality turned off, if you want to use it you must turn it on in ({{ic|/etc/dnsmasq.conf}}).  Here are the important settings:
+
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:
  
 
{{bc|<nowiki>
 
{{bc|<nowiki>
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# Set default gateway
 
# Set default gateway
dhcp-option=3,192.168.1.1
+
dhcp-option=3,0.0.0.0
  
 
# Set DNS servers to announce
 
# Set DNS servers to announce
dhcp-option=6,8.8.8.8,8.8.4.4
+
dhcp-option=6,0.0.0.0
  
 
# Dynamic range of IPs to make available to LAN PC and the lease time.  
 
# Dynamic range of IPs to make available to LAN PC and the lease time.  
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For increased security it is advised to use dnsmasq's TFTP secure mode. In secure mode only files owned by the {{ic|dnsmasq}} user will be served over TFTP. You will need to [[chown]] TFTP root and all files in it to {{ic|dnsmasq}} user to use this feature.
 
For increased security it is advised to use dnsmasq's TFTP secure mode. In secure mode only files owned by the {{ic|dnsmasq}} user will be served over TFTP. You will need to [[chown]] TFTP root and all files in it to {{ic|dnsmasq}} user to use this feature.
  
Enable TFTP in {{ic|dnsmasq.conf}}:
+
Enable TFTP:
  
{{hc|/etc/dnsmasq.conf|2=
+
enable-tftp
enable-tftp
+
tftp-root=/srv/tftp
tftp-root=/srv/tftp
+
tftp-secure
tftp-secure
 
}}
 
  
 
See {{man|8|dnsmasq}} for more options.
 
See {{man|8|dnsmasq}} for more options.
Line 256: Line 218:
 
PXE requires DHCP and TFTP servers, both functions can be provided by dnsmasq.
 
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:
+
{{Tip|dnsmasq can run in "proxy-DHCP" mode and add PXE booting options to a network with an already running DHCP server:
  
{{hc|/etc/dnsmasq.conf|2=
+
{{bc|1=
 
interface=''enp0s0''
 
interface=''enp0s0''
 
bind-dynamic
 
bind-dynamic
Line 330: Line 292:
 
  bind-dynamic
 
  bind-dynamic
  
{{Note|This is default in libvirt.}}
+
{{Note|This is default in [[libvirt]].}}
  
 
== See also ==
 
== See also ==
  
 
* [http://www.g-loaded.eu/2010/09/18/caching-nameserver-using-dnsmasq/ Caching Nameserver using dnsmasq, and a few other tips and tricks.]
 
* [http://www.g-loaded.eu/2010/09/18/caching-nameserver-using-dnsmasq/ Caching Nameserver using dnsmasq, and a few other tips and tricks.]

Latest revision as of 17:21, 9 September 2018

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

Install the dnsmasq package.

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, you need to edit /etc/dnsmasq.conf. The file contains extensive comments explaining its options. For all available options see dnsmasq(8).

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:
port=0
Tip: To check configuration file(s) syntax, execute:
$ 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
dnssec-check-unsigned

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 not a recursive DNS server 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-openresolv.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-openresolv.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

See Domain name resolution#Overwriting of /etc/resolv.conf on how to protect /etc/resolv.conf from modification.

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

Tango-view-fullscreen.pngThis article or section needs expansion.Tango-view-fullscreen.png

Reason: Add instructions for IPv6 and router advertisement. (Discuss in Talk:Dnsmasq#)

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

# 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

# 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.

Tip: dnsmasq can run in "proxy-DHCP" mode and add PXE booting options to a network with an already running DHCP server:
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 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
Note: This is default in libvirt.

See also