Difference between revisions of "Dnsmasq"

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m (Caching DNS server: typo)
m (DNS addresses file: move Template:Merge below #openresolv, it doesn't apply to it)
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==== DNS addresses file ====
 
==== DNS addresses file ====
 
{{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, 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.
 
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.
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  conf-file=/etc/dnsmasq-openresolv.conf
 
  conf-file=/etc/dnsmasq-openresolv.conf
 
  resolv-file=/etc/dnsmasq-resolv.conf
 
  resolv-file=/etc/dnsmasq-resolv.conf
 +
 +
{{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.}}
  
 
===== resolv.conf =====
 
===== resolv.conf =====

Revision as of 06:55, 21 June 2018

dnsmasq provides a local 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.

Server setup

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:
/etc/dnsmasq.conf
port=0
Tip: To check configuration file(s) syntax, execute:
$ dnsmasq --test

Caching DNS server

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=::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.

listen-address=192.168.1.1    # Example IP

Set the number of cached domain names with cache-size=size (the default is 150) and optionally disable caching of "no such domain" responses with no-negcache:

cache-size=1000
no-negcache

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

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.

openresolv

If your network manager supports openresolv, 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

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#)
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

Tango-edit-cut.pngThis section is being considered for removal.Tango-edit-cut.png

Reason: dhcpcd supports #openresolv. (Discuss in Talk:Dnsmasq#)

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;

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.

DNS server

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

Reason: Add instructions. (Discuss in Talk:Dnsmasq#)

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 /etc/hosts file) as hostname.home.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.

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 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

# Optionally set a domain name
domain=example.com

# Set default gateway
dhcp-option=3,192.168.1.1

# Set DNS servers to announce
dhcp-option=6,8.8.8.8,8.8.4.4

# 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 in dnsmasq.conf:

/etc/dnsmasq.conf
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 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 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