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Unbound
Unbound is a validating, recursive, and caching DNS server. It is quite useful for enforcing DNSSEC and caching DNS queries. Best used in conjunction with DNSCrypt.
Contents
Installation
Unix-like
Install it from your distro's repository, or download it from here.
Windows
Windows children may download it from the official page.
What to expect
There are numerous advantages to having a DNS server like Unbound, most of which can be summed up in a few short sentences:
- Enforces DNSSEC;
- Reduces privacy exposure by caching DNS queries;
- Consequentially, decreases DNS look up latency if the DNS query has already been cached;
- Hardens DNS queries.
Configuration
This is how a proper unbound.conf file ought to look like: unbound.conf (do not copy paste this unless your CPU has 4 threads, you're using Linux, and you have libevent).
General
server:
interface: 127.0.0.1
# using zero means to listen on _all_ interfaces, but unsupported on some systems
# interface 0.0.0.0
# interface ::0 #IPv6
access-control: <YOUR ROUTER'S IP Range, for example 192.168.1.1>/16 allow
access-control: ::1 allow #IPv6 localhost
# only use access-control if you want to stray away from the default, in which only the localhost is allowed, and the rest is refused
verbosity: 1
port: 53
do-ip4: yes
do-ip6: <yes, if your ISP/router supports it>
do-udp: yes
do-tcp: yes
do-daemonize: yes
logfile: "<where you want your log files to be, for example /var/log/unbound>"
Performance
# use all threads
num-threads: <number of threads>
# 2^{number_of_threads}
msg-cache-slabs: <same>
rrset-cache-slabs: <same>
infra-cache-slabs: <same>
key-cache-slabs: <same>
# more cache memory
rrset-cache-size: 100m
msg-cache-size: <rrset-cache-size/2>
# more outgoing connections
# depends on number of threads
outgoing-range: <(1024/threads)-50>
num-queries-per-thread: <(1024/threads)/2>
# Larger socket buffer
so-rcvbuf: 4m
so-sndbuf: 4m
# Faster UDP with multithreading (only on Linux).
so-reuseport: yes
Note: If you have libevent, the outgoing-range can be increased to 4096 or 8192, for a slight performance gain. In which case, num-queries-threads should be <(outgoing-range/2)+50> to guarantee that every query can get a socket, and some to spare for queries-for-nameservers.
Security
hide-identity: yes
hide-version: yes
harden-short-bufsize: yes
harden-large-queries: yes
harden-glue: yes
harden-dnssec-stripped: yes
harden-below-nxdomain: yes
harden-referral-path: yes
use-caps-for-id: yes
# enables support for DNSSEC(!)
auto-trust-anchor-file: "<path to your root.key file, whose location should ideally be inside the unbound folder. Generate it using `unbound-anchor -a '/desired/path/to/root.key' as root>"
Security consideration: it is best to use an extra user to run it (new group as well), with no privileges, and no home folder.
with DNSCrypt
# this is necessary for the local host, in this case DNSCrypt, to be used to send queries
do-not-query-localhost: no
forward-zone:
name: "."
# 127.0.0.1 is DNSCrypt's --local-address; 40 is the port DNSCrypt is using, which is probably either 40 or 53
forward-addr: 127.0.0.1@40
Additional considerations
It is possible to sandbox Unbound and even recommended, amongst the considerations already highlighted in this article (separate user with no home directory).
To do this, simply edit your systemd/openrc scripts by installing firejail and adding the prefix 'firejail' before unbound. Firejail comes bundled with a profile for Unbound and many more, which you can analyse, and even edit, by issuing vim /etc/firejail
Troubleshooting
The log file will most definitely wield the answer to your woes. In most cases, the problem will lie in either not setting the path to the root.key file right, setting the forward-address to the wrong port, or a port that's already being used.
Example of a log file, where the path to the root-anchors file was deliberately wrong (or, in my case, didn't belong to the right user): unbound.log
