Saturday, October 10, 2020

How To Host Your Own DNS-over-HTTPS And DNS-over-TLS Services

With Technitium DNS Server, you can not just consume DNS-over-HTTPS (DoH) or DNS-over-TLS (DoT) services using forwarders but you can also host these services yourself. There can be several reasons to host your own DoH or DoT service. You may wish to have better privacy by not sharing your data with public DNS providers. Or your network or ISP blocks popular DoT and DoH services and also interferes with unencrypted DNS traffic.

In this post, we will setup DoT and DoH services on a cloud server and configure a locally running Technitium DNS Server to use the DoH service as a forwarder bypassing any network restrictions that may be in place. 

Home Network

In the about home network diagram, the locally running Technitium DNS Server is installed on a desktop PC or a Raspberry Pi that is connected to your WiFi router. The Cloud Linux server will host the DoH service which will be configured as a forwarder in the locally running DNS server on your network.

Once the configuration is complete, all DNS traffic will be encrypted between your locally running DNS server and the DoH server running on the cloud server. This effectively means that all your local DNS traffic will exit from the cloud server and thus wont be visible to your network provider or your ISP.

Requirements

You need a domain name which you can get from any domain name registrar like Name.com (referral link). If you already own a domain name then you can use a sub domain on it for hosting these services. A domain name is required since both these services run over TLS protocol which uses SSL/TLS certificate to work. A domain name will usually cost around $13/yr which depends on the extension. You can check for the pricing here.

You need a Linux server which you can get from any cloud hosting provider like Digital Ocean (referral link). You can get a server for as low as $5/mo with 1GB RAM. I would recommend to create a server with Ubuntu Server as the OS since this blog post will be using the same.

Installation

We will be using Ubuntu server in this blog post but you can choose any distro of your choice and follow similar instructions.

You can install Technitium DNS Server using the single line installation command as shown:

curl -sSL https://download.technitium.com/dns/install.sh | sudo bash

If the above command fails since you do not have curl installed, install it as shown below and try the above command again:

sudo apt update
sudo apt install curl

You can also manually install the DNS server by following the install instructions.

We will be using Let's Encrypt TLS certificate and will be using certbot which does automatic certificate renewal for Let's Encrypt. Run the commands below to install certbot:

sudo apt update
sudo apt install certbot

Configuration

To proceed with the DNS configuration, login to the DNS server web console using the server's IP address and port 5380. For example, if your server's IP address is '1.2.3.4' open http://1.2.3.4:5380/ in your web browser. Chrome, Firefox and Edge web browsers are supported well.

The first configuration to be done is to enable Optional DNS Server Protocols i.e. DNS-over-HTTPS and DNS-over-TLS in the DNS server Settings as shown below:

Optional DNS Server Protocols
Optional DNS Server Protocols

Note: If you wish to only run DoH service, enable only the DNS-over-HTTPS protocol in the settings.

Save the settings by clicking Save Settings button at the bottom and restart the DNS server using this command:

sudo systemctl restart dns

Note: It is important to restart the DNS server after enabling DNS-over-HTTPS optional protocol to allow the server to start a web server on port 80 which is required when generating the TLS certificate using certbot.

We also need to create a root directory for the DoH web server:

sudo mkdir /etc/dns/dohwww

Now, we can run certbot command with the webroot plugin to issue the TLS certificate as shown below:

sudo certbot certonly --agree-tos --email admin@example.com --webroot -w /etc/dns/dohwww -d dns.example.com

Note: Here, replace 'example.com' with your domain name. In this example, we have used 'dns.example.com' in which the sub domain 'dns' gives a good idea that you may be running a DoH service. You may wish to avoid this by not using sub domain names like dns, doh or dot and instead use something which is very common like "mail", or "blog", etc. This will make it difficult for someone on your network to identify if you are using a DoH service by looking at the domain name.

Once the certbot command succeeds, you will see the path of the certificate that was generated in the output which should be in the /etc/letsencrypt/live/<your-domain>/ directory.

Below is the output that you should see if the certbot command succeeds.

Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator webroot, Installer None

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Would you be willing to share your email address with the Electronic Frontier
Foundation, a founding partner of the Let's Encrypt project and the non-profit
organization that develops Certbot? We'd like to send you email about our work
encrypting the web, EFF news, campaigns, and ways to support digital freedom.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
(Y)es/(N)o: N
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for dns.example.com
Using the webroot path /etc/dns/dohwww for all unmatched domains.
Waiting for verification...
Cleaning up challenges

IMPORTANT NOTES:
 - Congratulations! Your certificate and chain have been saved at:
   /etc/letsencrypt/live/dns.example.com/fullchain.pem
   Your key file has been saved at:
   /etc/letsencrypt/live/dns.example.com/privkey.pem
   Your cert will expire on 2021-01-08. To obtain a new or tweaked
   version of this certificate in the future, simply run certbot
   again. To non-interactively renew *all* of your certificates, run
   "certbot renew"
 - Your account credentials have been saved in your Certbot
   configuration directory at /etc/letsencrypt. You should make a
   secure backup of this folder now. This configuration directory will
   also contain certificates and private keys obtained by Certbot so
   making regular backups of this folder is ideal.
 - If you like Certbot, please consider supporting our work by:

   Donating to ISRG / Let's Encrypt:   https://letsencrypt.org/donate
   Donating to EFF:                    https://eff.org/donate-le

Since, the DNS server requires the certificate in PKCS #12 (.pfx) format, we need to convert the issued certificate using the openssl command. We will create a small script file at /etc/dns/pkcs12convert.sh which contains the openssl command so that the script can be reused later.

echo "openssl pkcs12 -export -out /etc/letsencrypt/live/example.com/example.com.pfx -inkey /etc/letsencrypt/live/example.com/privkey.pem -in /etc/letsencrypt/live/example.com/cert.pem -certfile /etc/letsencrypt/live/example.com/chain.pem -passout pass:mypassword" | sudo tee /etc/dns/pkcs12convert.sh > /dev/null

sudo chmod +x /etc/dns/pkcs12convert.sh

Here, replace 'example.com' with your domain name and 'mypassword' with a password of your choice or keep it blank to generate the pfx file with no password.

Lets run the script that we just created so that it generates the pfx certificate file.

/etc/dns/pkcs12convert.sh

Now, we can configure the DNS server with the pfx certificate file path in the settings as shown below:

Optional DNS Server Protocols With TLS Certificate
Optional DNS Server Protocols With TLS Certificate

Type in the same password that you had used while generating the pkcs12 certificate for the TLS Certificate Password option.

Save the settings by clicking the Save Settings button at the bottom and restart the DNS server again using the command below so that the DNS server can start the DoT and DoH services using the newly configured TLS certificate.

sudo systemctl restart dns

Once the DNS server starts, your DoT and DoH services are ready to be used. You may want to check the DNS Server logs from the web console to find out if there were any errors while starting these services.

Testing The Service

For DoT service, you need to use the domain name that was used to generate the certificate with port 853. Thus your DoT configuration for clients will be tls-certificate-domain:853.

For DoH service, you need to use the domain name that was used to generate the certificate in a URL format. Thus you DoH configuration for clients will be https://tls-certificate-domain/dns-query.

You can test both the DoH and DoT services using the DNS Client tool. Put in the DoT tls-certificate-domain:853 or the DoH url https://tls-certificate-domain/dns-query as the Server in the DNS Client, type in a domain name, select an appropriate protocol either TLS or HTTPS and click Resolve to test both the services.

Note: By default, the "Allow Recursion Only For Private Networks" recursive resolver option (as shown below) in the DNS server settings is enabled and thus the DNS server will refuse to respond with an answer (RCODE=Refused) when you test it with the DNS Client. You will need to disable this option to be able to use these services from the public Internet.

Recursive Resolver Options
Recursive Resolver Options

Once the tests are successful, you can configure your locally running Technitium DNS Server to use these services as a forwarder. Once you have configured the service as a forwarder your local DNS traffic will bypassing all your network or ISP restrictions.

Technitium DNS Server Forwarder Configuration
Technitium DNS Server Forwarder Configuration

Auto Renewing TLS Certificate

Since, the certificate obtained from Let's Encrypt expires in 90 days, we need to configure auto renewal mechanism so that we do not have to manually renew the certificate ever again. The certbot utility will automatically configure a cron job so that the TLS certificates are renewed. But since the DNS server requires a PKCS #12 certificate, we need to add the --renew-hook option and provide the openssl command that we used earlier to convert to PKCS #12 certificate.

The cron job file is located at /etc/cron.d/certbot. We need to edit the file to add the --renew-hook option as shown below. Here we will be using the pkcs12convert.sh script that we created earlier.

# /etc/cron.d/certbot: crontab entries for the certbot package
#
# Upstream recommends attempting renewal twice a day
#
# Eventually, this will be an opportunity to validate certificates
# haven't been revoked, etc.  Renewal will only occur if expiration
# is within 30 days.
#
# Important Note!  This cronjob will NOT be executed if you are
# running systemd as your init system.  If you are running systemd,
# the cronjob.timer function takes precedence over this cronjob.  For
# more details, see the systemd.timer manpage, or use systemctl show
# certbot.timer.
SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

0 */12 * * * root test -x /usr/bin/certbot -a \! -d /run/systemd/system && perl -e 'sleep int(rand(43200))' && certbot -q renew --renew-hook "/etc/dns/pkcs12convert.sh"

To test the certbot renewal process, we can run the dry run command. If there are no errors reported then it means the renewal was successful.

sudo certbot renew --dry-run

Running DoH With Another Web Server

You may have a requirement to run both the DNS server with DoH service and another web server for hosting websites. In such cases since both the DoH service and the web server would require to use ports 80 and 443, it would create a conflict.

A solution in such a scenario is to use the web server as a reverse proxy to the DoH service. You will need to configure the web server with TLS certificate and virtual hosting to reverse proxy to http://127.0.0.1:8053/dns-query and enable only the DNS-over-HTTP optional DNS server protocol as shown below.

Optional DNS Server Protocols With TLS Certificate
Optional DNS Server Protocols With TLS Certificate

With this setup, your web server will terminate TLS and do reverse proxy allowing the DoH service through it. If your web server supports TLS termination for TCP streams then you can point it to 127.0.0.1:53 and also provide DoT service through it.

If you are using nginx as your web server, you can use the snippet below to configure a reverse proxy for the DoH service. For more details, you can refer to the blog post on using nginx as a DoT or DoH gateway.

server {
    listen 80;
    server_name dns.example.com;

    return 301 https://$http_host$request_uri;
}

server {
    listen 443 ssl http2;
    server_name dns.example.com;

    ssl_certificate /etc/letsencrypt/live/dns.example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/dns.example.com/privkey.pem;
    ssl_trusted_certificate /etc/letsencrypt/live/dns.example.com/chain.pem;

    access_log /var/log/nginx/dns.example.com-access.log;
    error_log /var/log/nginx/dns.example.com-error.log;

    location / {
        proxy_pass http://127.0.0.1:8053/;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Host $http_host;

        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header X-Nginx-Proxy true;

        proxy_redirect off;
    }
}

Conclusion

Using Technitium DNS Server combined with certbot, you can setup DoH and DoT services with automatic TLS certificate renewal. If you already have a web server like nginx running, you can use it for TLS termination and provide both DoH and DoT services on the same server.

If you have any queries do let me know in the comments below or send an email to support@technitium.com.