Unbound

Jump to navigation Jump to search

Related articles

 Domain name resolution

Unbound is a validating, recursive, and caching DNS resolver. According to Wikipedia:

Unbound has supplanted the Berkeley Internet Name Domain (BIND) as the
default, base-system name server in several open source projects, where it is
perceived as smaller, more modern, and more secure for most applications.

Contents
 1 Installation
 2 Configuration
o 2.1 Local DNS server
o 2.2 Root hints
o 2.3 DNSSEC validation
 2.3.1 Testing validation
o 2.4 Forwarding queries
 2.4.1 Allow local network to use DNS
 2.4.1.1 Using openresolv
 2.4.1.2 Manually specifying DNS servers
 2.4.1.2.1 Include local DNS server
 2.4.2 Forward all remaining requests
 2.4.2.1 Using openresolv
 2.4.2.2 Manually specifying DNS servers
o 2.5 Access control
o 2.6 Forwarding using DNS over TLS
 3 Usage
o 3.1 Starting Unbound
o 3.2 Remotely control Unbound
 3.2.1 Setting up unbound-control
 3.2.2 Using unbound-control
 4 Tips and tricks
o 4.1 Domain blacklisting
o 4.2 Adding an authoritative DNS server
o 4.3 WAN facing DNS
o 4.4 Roothints systemd timer
 5 Troubleshooting
o 5.1 Issues concerning num-threads
 6 See also
Installation
Install the unbound package.

Additionally, the expat package is required for #DNSSEC validation.

Configuration
A default configuration is already included at /etc/unbound/unbound.conf. The
following sections highlight different settings for the configuration file. See
unbound.conf(5) for other settings and more details.

Unless otherwise specified, any options listed in this section are to be placed under the
server section in the configuration like so:

/etc/unbound/unbound.conf

server:
...
setting: value
...

Local DNS server

If you want to use unbound as your local DNS server, set your nameserver to the
loopback addresses ::1 and 127.0.0.1 in /etc/resolv.conf:

/etc/resolv.conf

nameserver ::1
nameserver 127.0.0.1
options trust-ad

Make sure to protect /etc/resolv.conf from modification as described in Domain

name resolution#Overwriting of /etc/resolv.conf.

Tip: A simple way to do this is to install openresolv and configure

/etc/resolvconf.conf:
/etc/resolvconf.conf

name_servers="::1 127.0.0.1"
resolv_conf_options="trust-ad"

Then run resolvconf -u to generate /etc/resolv.conf.

See Domain name resolution#Lookup utilities on how to test your settings.

Check specifically that the server being used is ::1 or 127.0.0.1 after making
permanent changes to resolv.conf.
You can now setup unbound such that it is #Forwarding queries, perhaps all queries, to
the DNS servers of your choice.

Root hints

For recursively querying a host that is not cached as an address, the resolver needs to
start at the top of the server tree and query the root servers, to know where to go for the
top level domain for the address being queried. Unbound comes with default builtin
hints. Therefore, if the package is updated regularly, no manual intervention is required.
Otherwise, it is good practice to use a root-hints file since the builtin hints may become
outdated.

First point unbound to the root.hints file:

root-hints: root.hints

Then, put a root hints file into the unbound configuration directory. The simplest way to
do this is to run the command:

# curl --output /etc/unbound/root.hints

https://www.internic.net/domain/named.cache

When actually using this file, and not the builtin hints, it is a good idea to update
root.hints every six months or so in order to make sure the list of root servers is up to
date. This can be done manually or by using Systemd/Timers. See #Roothints systemd
timer for an example.

DNSSEC validation

To use DNSSEC validation, the following setting for the server trust anchor should be
under server::

/etc/unbound/unbound.conf

trust-anchor-file: trusted-key.key

This setting is done by default[1]. /etc/unbound/trusted-key.key is copied from

/etc/trusted-key.key, which is provided by the dnssec-anchors dependency, whose
PKGBUILD generates the file with unbound-anchor(8).

DNSSEC validation will only be done if the DNS server being queried supports it. If
general #Forwarding queries have been set to DNS servers that do not support
DNSSEC, their answers, whatever they are, should be considered insecure since no
DNSSEC validation could be preformed.

Note: Including DNSSEC checking significantly increases DNS lookup times for initial
lookups before the address is cached.

Testing validation

To test if DNSSEC is working, after starting unbound.service, do:

$ unbound-host -C /etc/unbound/unbound.conf -v
sigok.verteiltesysteme.net

The response should be the ip address with the word (secure) next to it.

$ unbound-host -C /etc/unbound/unbound.conf -v
sigfail.verteiltesysteme.net

Here the response should include (BOGUS (security failure)).

Additionally you can use drill to test the resolver as follows:

$ drill sigfail.verteiltesysteme.net
$ drill sigok.verteiltesysteme.net

The first command should give an rcode of SERVFAIL. The second should give an
rcode of NOERROR.

Forwarding queries

If you only want to forward queries to an external DNS server, skip ahead to #Forward
all remaining requests.

Allow local network to use DNS

Using openresolv

If your network manager supports openresolv, you can configure it to provide local
DNS servers and search domains to Unbound:

/etc/resolvconf.conf

...
private_interfaces="*"

# Write out unbound configuration file

unbound_conf=/etc/unbound/resolvconf.conf

Run resolvconf -u to generate the file.

Configure Unbound to read the openresolv's generated file and allow replies with
private IP address ranges[2]:

/etc/unbound/unbound.conf

include: "/etc/unbound/resolvconf.conf"
...
server:
...
private-domain: "intranet"
private-domain: "internal"
private-domain: "private"
private-domain: "corp"
private-domain: "home"
 private-domain: "lan"

unblock-lan-zones: yes
insecure-lan-zones: yes
...

Additionally you may want to disable DNSSEC validation for private DNS
namespaces[3]:

/etc/unbound/unbound.conf

...
server:
...
domain-insecure: "intranet"
domain-insecure: "internal"
domain-insecure: "private"
domain-insecure: "corp"
domain-insecure: "home"
domain-insecure: "lan"
...

Manually specifying DNS servers

If you have a local network which you wish to have DNS queries for and there is a local
DNS server that you would like to forward queries to then you should include this line:

private-address: local_subnet/subnet_mask

For example:

private-address: 10.0.0.0/24
Note: You can use private-address to protect against DNS Rebind attacks. Therefore
you may enable RFC1918 networks (10.0.0.0/8 172.16.0.0/12 192.168.0.0/16
169.254.0.0/16 fd00::/8 fe80::/10). Unbound may enable this feature by default in future
releases.
Include local DNS server

To include a local DNS server for both forward and reverse local addresses a set of lines
similar to these below is necessary with a forward and reverse lookup (choose the IP
address of the server providing DNS for the local network accordingly by changing
10.0.0.1 in the lines below):

local-zone: "10.in-addr.arpa." transparent

This line above is important to get the reverse lookup to work correctly.

forward-zone:
name: "mynetwork.com."
forward-addr: 10.0.0.1
forward-zone:
name: "10.in-addr.arpa."
forward-addr: 10.0.0.1
Note: There is a difference between forward zones and stub zones - stub zones will only
work when connected to an authoritative DNS server directly. This would work for
lookups from a BIND DNS server if it is providing authoritative DNS - but if you are
referring queries to an unbound server in which internal lookups are forwarded on to
another DNS server, then defining the referral as a stub zone in the machine here will
not work. In that case it is necessary to define a forward zone as above, since forward
zones can have daisy chain lookups onward to other DNS servers. i.e. forward zones
can refer queries to recursive DNS servers. This distinction is important as you do not
get any error messages indicating what the problem is if you use a stub zone
inappropriately.

You can set up the localhost forward and reverse lookups with the following lines:

local-zone: "localhost." static

local-data: "localhost. 10800 IN NS localhost."
local-data: "localhost. 10800 IN SOA localhost. nobody.invalid. 1 3600
1200 604800 10800"
local-data: "localhost. 10800 IN A 127.0.0.1"
local-zone: "127.in-addr.arpa." static
local-data: "127.in-addr.arpa. 10800 IN NS localhost."
local-data: "127.in-addr.arpa. 10800 IN SOA localhost. nobody.invalid.
2 3600 1200 604800 10800"
local-data: "1.0.0.127.in-addr.arpa. 10800 IN PTR localhost."

Forward all remaining requests

Using openresolv

If your network manager supports openresolv, you can configure it to provide upstream
DNS servers to Unbound.

/etc/resolvconf.conf

...
# Write out unbound configuration file
unbound_conf=/etc/unbound/resolvconf.conf

Run resolvconf -u to generate the file.

Finally configure Unbound to read the openresolv's generated file[4]:

include: "/etc/unbound/resolvconf.conf"

Manually specifying DNS servers

To use specific servers for default forward zones that are outside of the local machine
and outside of the local network add a forward zone with the name . to the
configuration file. In this example, all requests are forwarded to Google's DNS servers:

forward-zone:
name: "."
forward-addr: 8.8.8.8
forward-addr: 8.8.4.4
Access control

You can specify the interfaces to answer queries from by IP address. The default, is to
listen on localhost.

To listen on all interfaces, use the following:

interface: 0.0.0.0

To control which systems can access the server by IP address, use the access-control
option:

access-control: subnet action

For example:

access-control: 192.168.1.0/24 allow

action can be one of deny (drop message), refuse (polite error reply), allow (recursive
ok), or allow_snoop (recursive and nonrecursive ok). By default everything is refused
except for localhost.

Forwarding using DNS over TLS

To use DNS over TLS, you will need to specify tls-cert-bundle option that points to
the local system's root certificate authority bundle, allow unbound to forward TLS
requests and also specify any number of servers that allow DNS of TLS.

For each server you will need to specify that the connection port using @, and you will
also need to indicate which is its domain name with #. Even though it looks like an
comment the hashtag name allows for the TLS authentication name to be set for stub-
zones and with unbound-control forward control command. There should not be
any spaces between the @ and # markups.

/etc/unbound/unbound.conf

...
server:
...
tls-cert-bundle: /etc/ssl/certs/ca-certificates.crt
...
forward-zone:
name: "."
forward-tls-upstream: yes
forward-addr: 1.1.1.1@853#cloudflare-dns.com

Usage
Starting Unbound

Start/enable the unbound.service systemd service.

Remotely control Unbound

unbound ships with the unbound-control utility which enables us to remotely

administer the unbound server. It is similar to the pdnsd-ctl command of pdnsd.

Setting up unbound-control

Before you can start using it, the following steps need to be performed:

1) Firstly, you need to run the following command

# unbound-control-setup

which will generate a self-signed certificate and private key for the server, as well as the
client. These files will be created in the /etc/unbound directory.

2) After that, edit /etc/unbound/unbound.conf and put the following contents in that.
The control-enable: yes option is necessary, the rest can be adjusted as required.

remote-control:
# Enable remote control with unbound-control(8) here.
# set up the keys and certificates with unbound-control-setup.
control-enable: yes

# what interfaces are listened to for remote control.

# give 0.0.0.0 and ::0 to listen to all interfaces.
control-interface: 127.0.0.1

# port number for remote control operations.

control-port: 8953

# unbound server key file.

server-key-file: "/etc/unbound/unbound_server.key"

# unbound server certificate file.

server-cert-file: "/etc/unbound/unbound_server.pem"

# unbound-control key file.

control-key-file: "/etc/unbound/unbound_control.key"

# unbound-control certificate file.

control-cert-file: "/etc/unbound/unbound_control.pem"

Using unbound-control

Some of the commands that can be used with unbound-control are:

 print statistics without resetting them

# unbound-control stats_noreset

 dump cache to stdout

 # unbound-control dump_cache

 flush cache and reload configuration

# unbound-control reload

Please refer to unbound-control(8) for a detailed look at the operations it supports.

Tips and tricks

Domain blacklisting

To blacklist a domain, use local-zone: "domainname" always_refuse.

Save the blacklist as a separate file (e.g. /etc/unbound/blacklist.conf) for ease of

management and include it from /etc/unbound/unbound.conf. For example:

/etc/unbound/blacklist.conf

local-zone: "blacklisted.example" always_refuse

local-zone: "anotherblacklisted.example" always_refuse
/etc/unbound/unbound.conf

server:
...
include: /etc/unbound/blacklist.conf
Tip:

 In order to return some OK statuses on those hosts, you can change the 127.0.0.1
redirection to a server you control and have that server respond with empty 204
replies, see this page
 To convert a hosts file from another source to the unbound format do:

$ grep '^0\.0\.0\.0' hostsfile | awk '{print "local-

zone: \""$2"\" always_refuse"}' > /etc/unbound/blacklist.conf

 A list of potential sources for the blacklist can be found in OpenWrt's adblock
package's README.

Adding an authoritative DNS server

The factual accuracy of this article or section is disputed.

Reason: Running two DNS servers is not inherently more secure than running one
providing all features. (Discuss in Talk:Unbound#Two DNS servers are not inherently
more secure than one)

For users who wish to run both a validating, recursive, caching DNS server as well as
an authoritative DNS server on a single machine then it may be useful to refer to the
wiki page NSD which gives an example of a configuration for such a system. Having
one server for authoritative DNS queries and a separate DNS server for the validating,
recursive, caching DNS functions gives increased security over a single DNS server
providing all of these functions. Many users have used Bind as a single DNS server, and
some help on migration from Bind to the combination of running NSD and Bind is
provided in the NSD wiki page.

WAN facing DNS

It is also possible to change the configuration files and interfaces on which the server is
listening so that DNS queries from machines outside of the local network can access
specific machines within the LAN. This is useful for web and mail servers which are
accessible from anywhere, and the same techniques can be employed as has been
achieved using bind for many years, in combination with suitable port forwarding on
firewall machines to forward incoming requests to the right machine.

Roothints systemd timer

Here is an example systemd service and timer that update root.hints monthly using
the method in #Root hints:

/etc/systemd/system/roothints.service

[Unit]
Description=Update root hints for unbound
After=network.target

[Service]
ExecStart=/usr/bin/curl -o /etc/unbound/root.hints
https://www.internic.net/domain/named.cache
/etc/systemd/system/roothints.timer

[Unit]
Description=Run root.hints monthly

[Timer]
OnCalendar=monthly
Persistent=true

[Install]
WantedBy=timers.target

Start/enable the roothints.timer systemd timer.

Troubleshooting
Issues concerning num-threads

The man page for unbound.conf mentions:

outgoing-range: <number>
Number of ports to open. This number of file descriptors
can be opened per thread.
and some sources suggest that the num-threads parameter should be set to the number
of cpu cores. The sample unbound.conf.example file merely has:

# number of threads to create. 1 disables threading.

# num-threads: 1