This tutorial will be showing you how to set up a local DNS resolver on Ubuntu 22.04/20.04, with the widely-used BIND9 DNS software. A DNS resolver is known by many names, some of which are listed below. They all refer to the same thing. Show
Also, be aware that A DNS server can also be called a name server. Examples of DNS resolver are 8.8.8.8 (Google public DNS server) and 1.1.1.1 (Cloudflare public DNS server). The OS on your computer also has a resolver, although it’s called stub resolver due to its limited capability. A stub resolver is a small DNS client on the end user’s computer that receives DNS requests from applications such as Firefox and forward requests to a recursive resolver. Almost every resolver can cache DNS response to improve performance, so they are also called caching DNS server. Why Run Your Own Local DNS ResolverNormally, your computer or router uses your ISP’s DNS resolver to query DNS names, so why run a local DNS resolver?
If you own a website and want your own DNS server to handle name resolution for your domain name instead of using your domain registrar’s DNS server, then you will need to set up an authoritative DNS server, which is different from a DNS resolver. BIND can act as an authoritative DNS server and a DNS resolver at the same time, but it’s a good practice to separate the two roles on different boxes. This tutorial shows how to set up a local DNS resolver and because it will be used on localhost/local network, no encryption (DNS over TLS or DNS over HTTPS) is needed. Setting up a DoT resolver or DoH resolver will be discussed in a future article. Hint: Local doesn’t mean your home computer. Rather, it means the DNS resolver runs on the same box as the DNS client. You can install BIND DNS resolver on your home computer. It’s local to your home computer. You can install BIND DNS resolver on a cloud server, and it’s local to the cloud server. BIND (Berkeley Internet Name Domain) is an open-source DNS server software widely used on Unix/Linux due to it’s stability and high quality. It’s originally developed by UC Berkeley, and later in 1994 its development was moved to Internet Systems Consortium, Inc (ISC). Run the following command to install BIND 9 on Ubuntu 22.04/20.04, from the default repository. BIND 9 is the current version and BIND 10 is a dead project. sudo apt update sudo apt install bind9 bind9utils bind9-dnsutils bind9-doc bind9-hostCheck version. named -vSample output: BIND 9.16.1-Ubuntu (Stable Release) <id:d497c32>To check the version number and build options, run named -VBy default, BIND automatically starts after installation.You check its status with: systemctl status namedIf it’s not running, then start it with: sudo systemctl start namedAnd enable auto start at boot time: sudo systemctl enable namedThe BIND server will run as the bind user, which is created during installation, and listens on TCP and UDP port 53, as can be seen by running the following command: sudo netstat -lnptu | grep namedUsually DNS queries are sent to the UDP port 53. The TCP port 53 is for responses sizes larger than 512 bytes. The BIND daemon is called named. (A daemon is a piece of software that runs in the background.) The named binary is installed by the bind9 package and there’s another important binary: rndc, the remote name daemon controller, which is installed by the bind9utils package. The rndc binary is used to reload/stop and control other aspects of the BIND daemon. Communication is done over TCP port 953. For example, we can check the status of the BIND name server. sudo rndc statusConfigurations for a Local DNS Resolver/etc/bind/ is the directory that contains configurations for BIND.
The bind9 package on Ubuntu 22.04/20.04 doesn’t ship with a db.root file, it now uses the root hints file at /usr/share/dns/root.hints. The root hints file is used by DNS resolvers to query root DNS servers. There are 13 groups of root DNS servers, from a.root-servers.net to m.root-servers.net. Out of the box, the BIND9 server on Ubuntu provides recursive service for localhost and local network clients only. Outside queries will be denied. So you don’t have to edit the configuration files. To get you familiar with BIND 9 configurations, I will show you how to enable recursion service anyway. The main BIND configuration file /etc/bind/named.conf sources the settings from 3 other files.
To enable recursion service, edit the first file. sudo nano /etc/bind/named.conf.optionsIn the options clause, add the following lines. Replace IP addresses in the allow-recursion statement with your own local network addresses. // hide version number from clients for security reasons. version "not currently available"; // optional - BIND default behavior is recursion recursion yes; // provide recursion service to trusted clients only allow-recursion { 127.0.0.1; 192.168.0.0/24; 10.10.10.0/24; }; // enable the query log querylog yes;Save and close the file. Then test the config file syntax. sudo named-checkconfIf the test is successful (indicated by a silent output), then restart BIND9. sudo systemctl restart namedIf you have UFW firewall running on the BIND server, then you need to open port 53 to allow LAN clients to send DNS queries. sudo ufw allow in from 192.168.0.0/24 to any port 53This will open TCP and UDP port 53 to the private network 192.168.0.0/24. Then from another computer in the same LAN, we can run the following command to query the A record of google.com. Replace 192.168.0.102 with the IP address of your BIND resolver. dig A google.com @192.168.0.102Now on the BIND resolver, check the query log with the following command. sudo journalctl -eu namedThis will show the latest log message of the bind9 service unit. I found the following line in the log, which indicates that a DNS query for google.com’s A record has been received from port 57806 of 192.168.0.103. named[1162]: client @0x7f4d2406f0f0 192.168.0.103#57806 (google.com): query: google.com IN A +E(0)K (192.168.0.102)Setting the Default DNS Resolver on Ubuntu 22.04/20.04 ServerSystemd-resolved provides the stub resolver on Ubuntu 22.04/20.04. As mentioned in the beginning of this article, a stub resolver is a small DNS client on the end-user’s computer that receives DNS requests from applications such as Firefox and forward requests to a recursive resolver. The default recursive resolver can be seen with this command. resolvectl statusor on an old version of Ubuntu: systemd-resolve --statusHint: If the above command doesn’t quit immediately, you can make it quit by pressing the Q key. As you can see, BIND isn’t the default. If you run the following command on the BIND server, dig A facebook.comThis DNS query can’t be found in BIND log. Instead, you need to explicitly tell dig to use BIND. dig A facebook.com @127.0.0.1To set BIND as the default resolver, open the systemd-resolved configuration file. sudo nano /etc/systemd/resolved.confIn the [Resolve] section, add the following line. This will set a global DNS server for your server. Save and close the file. Then restart systemd-resolved service. sudo systemctl restart systemd-resolvedNow run the following command to check the default DNS resolver. systemd-resolve --statusNow perform a DNS query without specifying 127.0.0.1. dig A facebook.comYou will see the DNS query in BIND log, which means BIND is now the default recursive resolver. If you don’t see any queries in the BIND log, you might need to configure per-link DNS server. Configure Per-Link DNS Server on Ubuntu 22.04/20.04You can also configure per-link DNS server, which will override the global DNS server. There are two ways to configure per-link DNS servers:
systemd-resolvedList files under /etc/systemd/network/ directory. ls /etc/systemd/network/Sample output: 05-eth0.network 99-default.linkAs you can see, I have two link configuration files. The 05-eth0.network file is for my main network interface, so I edit this file. sudo nano /etc/systemd/network/05-eth0.networkYour filename might be different. If there are no files under this directory, then your per-link DNS configuration is not controlled by systemd-resolved. Comment out the default DNS and Domain entry, and add your own DNS entry. DNS=127.0.0.1Save and close the file. Then restart systemd-resolved and systemd-networkd service. sudo systemctl restart systemd-resolved systemd-networkdnetplanSome Ubuntu servers might be using netplan to configure per-link networking. In this case, you need to configure DNS server in the .yaml file under /etc/netplan/ directory. List files in this directory. ls /etc/netplan/Sample output: 01-netcfg.yamlSo I edit this file. sudo nano /etc/netplan/01-netcfg.yamlSet the DNS server address in the nameservers section. nameservers: search: [ invalid ] addresses: - 127.0.0.1You can specify multiple DNS resolvers like below, which can reduce the chance of DNS failure. nameservers: search: [ invalid ] addresses: - 127.0.0.1 - 8.8.8.8 - 1.1.1.1Save and close the file. Then apply the change. sudo netplan applyNote: If you see the following error message, then netplan can’t process the configuration file. Invalid YAML at /etc/netplan/01-netcfg.yaml inconsistent indentationYou should fix the inconsistent indentation and run sudo netplan apply command again. TroubleshootingCheck the content of /etc/resolv.conf. cat /etc/resolv.confAs you can see, 127.0.0.1 (BIND) is default DNS resolver. If you see a different value, that means BIND is still not your default DNS resolver. You can use the resolveconf utility to set BIND as default resolver. Install the resolvconf package sudo apt install resolvconfThen start the named-resolvconf service. sudo systemctl start named-resolvconf.serviceEnable auto-start at boot time. sudo systemctl enable named-resolvconf.serviceNow check the /etc/resolv.conf file again. BIND should be the default DNS resolver on your Ubuntu server now. cat /etc/resolv.confNote that some hosting providers like Linode may use a network helper to auto-generate the /etc/resolv.conf file. To change the default DNS resolver, you need to disable that network helper in the hosting control panel. If this method still doesn’t work, perhaps it’s due to the fact the /etc/resolv.conf file on your Ubuntu server is not a symbolic link to /run/resolvconf/resolv.conf. You need to delete the /etc/resolv.conf file and create a symbolic link. sudo rm /etc/resolv.conf sudo ln -s /run/resolvconf/resolv.conf /etc/resolv.confYou can also manually create this file and make it read-only to prevent overwritten by other applications on the same server. sudo rm /etc/resolv.conf echo "nameserver 127.0.0.1" | sudo tee /etc/resolv.conf sudo chmod 444 /etc/resolv.confsystemd-resolved isn’t runningIf you see the following error after executing the systemd-resolve --status command, Failed to get global data: Unit dbus-org.freedesktop.resolve1.service not found.It might be systemd-resolved isn’t running. Start it with: sudo systemctl status systemd-resolvedEnable auto-start. sudo systemctl enable systemd-resolvedSetting Default DNS Resolver on Client ComputersOn Ubuntu desktop, you can follow the above instructions to set the default DNS resolver, but remember to replace 127.0.0.1 with the IP address of BIND server. The steps of setting default DNS resolver on MacOS and Windows can be found on the Internet. How to Disable IPv6 in BINDIf you don’t use IPv6 in your network, then it’s a good idea to turn off IPv6 in BIND, otherwise, there will be a lot of errors about IPv6 in BIND log like below. network unreachable resolving 'mirrors.fedoraproject.org/A/IN': 2001:4178:2:1269:dead:beef:cafe:fed5#53 network unreachable resolving 'mirrors.fedoraproject.org/AAAA/IN': 2001:4178:2:1269:dead:beef:cafe:fed5#53 network unreachable resolving 'mirrors.fedoraproject.org/A/IN': 2610:28:3090:3001:dead:beef:cafe:fed5#53 network unreachable resolving 'mirrors.fedoraproject.org/AAAA/IN': 2610:28:3090:3001:dead:beef:cafe:fed5#53To disable IPv6 in BIND on Ubuntu, simply open the /etc/default/named file sudo nano /etc/default/namedAdd -4 to the OPTIONS. OPTIONS="-u bind -4"Save and close the file. Then restart BIND and you are done. sudo systemctl restart namedBIND SERVFAILIf your BIND resolver can’t answer DNS queries (SERVFAIL), and you see the following line in the BIND log. dnssec: warning: managed-keys-zone: Unable to fetch DNSKEY set '.': timed outIt’s probably because your server doesn’t have a working IPv6 connectivity. This happened to one of my servers. I thought IPv6 connectivity is working as usual, but it’s suddenly broken for reasons I didn’t know. Once I disabled IPv6 in BIND, DNS resolution is working again. BIND DNSSEC FailureIf you can find the following errors in the BIND logs, it means BIND has a problem trusting the DNSSEC keys. named[2194196]: managed-keys-zone: DNSKEY set for zone '.' could not be verified with current keys named[2194196]: validating ./NS: no valid signature found named[2194196]: no valid RRSIG resolving './NS/IN': 192.36.148.17#53 named[2194196]: validating ./NS: no valid signature found named[2194196]: no valid RRSIG resolving './NS/IN': 198.97.190.53#53 named[2194196]: validating ./NS: no valid signature found named[2194196]: no valid RRSIG resolving './NS/IN': 199.9.14.201#53 named[2194196]: validating ./NS: no valid signature found named[2194196]: no valid RRSIG resolving './NS/IN': 192.5.5.241#53 named[2194196]: validating ./NS: no valid signature foundTo make it work properly, we can rebuild the managed key database with the following commands. Named Automatic RestartIf for any reason your Named process is killed, you need to run the following command to restart it. sudo systemctl restart namedInstead of manually typing this command, we can make Named automatically restart by editing the named.service systemd service unit. To override the default systemd service configuration, we create a separate directory. sudo mkdir -p /etc/systemd/system/named.service.d/Then create a file under this directory. sudo nano /etc/systemd/system/named.service.d/restart.confAdd the following lines in the file, which will make Named automatically restart 5 seconds after a failure is detected. [Service] Restart=always RestartSec=5sSave and close the file. Then reload systemd. sudo systemctl daemon-reloadTo check if this would work, kill Named with: sudo pkill namedThen check Named status. You will find Named automatically restarted. systemctl status namedBIND max-cache-sizeBIND can cache DNS results on the server to speed up DNS lookup for clients. BIND assumes you are running a dedicated DNS resolver, i.e, no other web services are running on the same host, so the default cache size (defined by max-cache-size) is set to 90% of the total RAM to achieve best performance. You can see a line like below in the BIND log (sudo journalctl -eu named) when BIND starts. none:100: 'max-cache-size 90%' - setting to 7165MB (out of 7961MB)Note that BIND will not use 90% of your RAM immediately. If there are only a few DNS requests, BIND uses only a small amount of RAM, because there’s not many DNS results to cache. If there are lots of DNS requests, then it will use lots of RAM to store the DNS cache. If your RAM is limited, you might not want BIND to use 90% of your RAM for cache. Edit the BIND configuration file /etc/bind/named.conf.options. sudo nano /etc/bind/named.conf.optionsAdd the following directive in the options clause. Change 50% to your preferred value. max-cache-size 50%;Restart BIND for the change to take effect. sudo systemctl restart namedNote: When you restart BIND, its entire cache will be flushed. No servers could be reachedIf you see the following error when using the dig command on client computers ;; connection timed out; no servers could be reachedIt could be that
ConclusionI hope this tutorial helped you set up a local DNS resolver on Ubuntu 22.04/20.04 with BIND9. As always, if you found this post useful, then subscribe to our free newsletter to get more tips and tricks. Take care 🙂 Rate this tutorial |