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.


You need a domain name which you can get from any domain name registrar like (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.


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 | 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


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 '' open 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 --webroot -w /etc/dns/dohwww -d

Note: Here, replace '' with your domain name. In this example, we have used '' 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
Using the webroot path /etc/dns/dohwww for all unmatched domains.
Waiting for verification...
Cleaning up challenges

 - Congratulations! Your certificate and chain have been saved at:
   Your key file has been saved at:
   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:
   Donating to EFF:          

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/ which contains the openssl command so that the script can be reused later.

echo "openssl pkcs12 -export -out /etc/letsencrypt/live/ -inkey /etc/letsencrypt/live/ -in /etc/letsencrypt/live/ -certfile /etc/letsencrypt/live/ -passout pass:mypassword" | sudo tee /etc/dns/ > /dev/null

sudo chmod +x /etc/dns/

Here, replace '' 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.


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 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.

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/"

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 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 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;

    return 301 https://$http_host$request_uri;

server {
    listen 443 ssl http2;

    ssl_certificate /etc/letsencrypt/live/;
    ssl_certificate_key /etc/letsencrypt/live/;
    ssl_trusted_certificate /etc/letsencrypt/live/;

    access_log /var/log/nginx/;
    error_log /var/log/nginx/;

    location / {
        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;


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

Sunday, July 19, 2020

How To Disable Firefox DNS-over-HTTPS On Your Network

Firefox includes a quite useful option since more than a year now that enables the web browser to use DNS-over-HTTPS (DoH) protocol to encrypt all the DNS requests on the network. This feature promises enhanced privacy to users such that anyone on your network path, like your ISP, wont be able to monitor or log your DNS traffic. The DoH protocol also protects your DNS requests from Man In The Middle (MITM) attacks which are possible with the default unencrypted UDP based DNS requests.

While, DoH is a really interesting feature to have from privacy perspective, it is Firefox's implementation that is a bit controversial. Firefox has deal with two public DNS providers, Cloudflare and NextDNS, in its Trusted Recursive Resolver (TRR) program which lists these providers directly into the web browser's DoH options. The controversy is Firefox enabling DoH for users automatically with an opt-out policy.

Not just Firefox but, Google Chrome and Microsoft Windows 10 is also implementing DoH support. Google Chrome's approach is a bit different from Firefox. Chrome will upgrade to use DoH protocol if you are already using a public DNS provider that supports DoH protocol. Microsoft is experimenting with a similar DoH upgrade approach with Windows 10 insider builds.

Firefox's opt-out policy bypasses the local network policies by not using the DNS servers provided by the network administrators. This creates headache for network administrators who wish to keep track or filter DNS traffic for security or other reasons. This is an issue even with people who use DNS based filtering software on their home network.

To help network administrators, Firefox has introduced a Canary domain to disable DoH on their networks. Using this canary domain (, a network administrator can signal Firefox on their networks to disable the automatic switch to DoH. However, its important to note that if a user configures DoH manually, then the canary domain signal is ignored by the web browser.
Note: The canary domain only applies to users who have DoH enabled as the default option. It does not apply for users who have made the choice to turn on DoH by themselves.
To disable DoH on your network, you need to either block the canary domain entirely such that the DNS server responds with a NXDOMAIN response code or that the server returns an empty response with no A or AAAA records.

You can do this configuration on your Technitium DNS Server setup by simply adding an empty zone for the canary domain. The zone once added must look like as shown in the screenshot below:

Firefox Canary Domain Zone Configuration
Firefox Canary Domain Zone Configuration
With this configuration, you can ensure that Firefox on your network wont automatically switch to using DoH protocol bypassing your local network DNS servers.

Let me know if you have any queries in the comments below or send an email to

Technitium DNS Server And Mesh Archived In Arctic Code Vault

I just discovered this exciting news that Technitium DNS Server and Technitium Mesh has been archived by the GitHub Archive Program in the Arctic Code Vault!

Arctic Code Vault
GitHub Arctic Code Vault

GitHub Archive Program's mission is to preserve open source software for future generations by storing public open source code repositories in an archive built to last a thousand of years.

GitHub took a snapshot of all active public open source repositories on 2nd Feb, 2020 to archive in the code vault. The total data of 21 TB was stored using digital photo sensitive archive film designed to last for a thousand years.

Arctic Code Vault Contributor Badge!

To recognize and celebrate the contributions of all the software developers, GitHub now shows a badge on the GitHub profile page. Hovering on the badge shows some of the repositories that were included in the archive.

I hope they do the archive again in coming years since the current archive contains old version with quite a few bugs!

Sunday, July 12, 2020

How To Enforce Google Safe Search And YouTube Restricted Mode On Your Network

With the release of Technitium DNS Server v5, a new feature called ANAME resource record has been introduced. ANAME resource record implementation is similar to the IETF draft with respect to its core functionality that allows adding a CNAME like functionality to the zone root. Essentially, ANAME is similar to CNAME except that the authoritative DNS server resolves the A or AAAA records by itself and returns them.

The new release also adds Conditional Forwarder feature that can be combined with the ANAME feature to enforce Google's Safe Search or YouTube's Restricted Mode.

To configure Google's Safe Search, you need to add a new "" Conditional Forwarder zone with "Use This DNS Server" option enabled. The "Use This DNS Server" option tells the DNS Server to forward all the queries to itself so that you do not need to configure any other DNS server as a forwarder. This option is useful in scenarios like the current one where you just need to override a few records for a particular zone but still wish that the other records in the zone to be resolvable as usual.

Add New Conditional Forwarder Zone

Once you have added the zone, you need to add a CNAME record that points "" to "" and another ANAME record that points "" to "". Check the screenshot below to know how the records should look like.

Enforcing Google Safe Search

You can now test this by clicking on the DNS Client tab and querying for "". Now open "" in your web browser and try doing a search and notice the Safe Search option on the top right corner.

Similarly, to configure YouTube's restricted mode, you need to add a new "" Conditional Forwarder zone with "Use This DNS Server" option enabled. Once the new zone is added, you need to add a CNAME record that points "" to "" and another ANAME record that points "" to "". This will enforce "Strict Restricted Mode".  To enforce "Moderate Restricted Mode" you need to point your ANAME record to "" instead. Once you have configured the records, they should look as shown the screenshot below.

Enforcing YouTube Strict Restricted Mode

You can now test this too with the DNS Client tab by querying "". You can open "" in your web browser and check if the restricted mode is working by searching with any keyword.

The Conditional Forwarder zone is quite useful that not only you can forward queries to one or more DNS providers by adding one or more FWD records, you can override records that you wish and have the zone resolve as usual for other records.

If you have any queries, do let me know in the comments section below. For any feedback or support do send an email to

Sunday, July 5, 2020

Technitium DNS Server v5 Released!

I am really happy to announce the release of Technitium DNS Server v5. This version is a major upgrade with many new core features, a lot of memory and CPU optimizations, and multiple bug fixes done. Download the latest update now!

Technitium DNS Server v5

Technitium DNS Server is a free, open source software that can be used by anyone be it a novice or an expert user. The server aims to have a user friendly approach, providing an easy to use web based GUI, and with defaults that allow the server to run out-of-the-box.

The DNS server can be used to self host domain names, used as a local resolver on a desktop or laptop computer, or used as a DNS server for the entire local network. It supports many useful and powerful features like blocking domain names using block lists, overriding records for any domain, use forwarders or conditional forwarders with DNS-over-TLS or DNS-over-HTTPS, and host your own DNS-over-TLS or DNS-over-HTTPS service.

The DNS Server is cross platform and can run on Windows, Linux and macOS. It has small footprint and thus can run even on a Raspberry Pi.

Once you have used Technitium DNS Server, you will realize how powerful it is and how silly it is to rely on your ISP's DNS servers.

Conditional Forwarder Zone

Features that you may find interesting in this release:
  • QNAME minimization support in recursive resolver for privacy.
  • ANAME propriety record support to allow using CNAME like feature at zone root.
  • Primary and Secondary zone support with NOTIFY implementation and zone transfer support. 
  • Stub zone support that allows the DNS server to keep track of the name servers of the zone.
  • Conditional Forwarder zone support which allows to configure multiple forwarders for a specific domain name with all protocol support including DNS-over-HTTP or DNS-over-TLS protocols.
  • Ability to override records of a live domain name using conditional forwarder or stub zone. This allows you to easily implements things like forced Google safe search or YouTube's restricted mode.
  • Concurrent querying with more than one forwarder allows to get fastest response from multiple forwarders.
  • Option to change the DNS Server local ports for TCP and UDP protocols. 
Read the change log to know more in details about the latest release.

Conditional Forwarder Zone with Overridden Records For Google Force Safe Search

The DNS Server code has been optimized for CPU, memory and concurrency. The server now notably has a very small memory footprint which allows loading a couple of million blocked domain names easily via the blocks list URLs on a Raspberry Pi with just 1 GB RAM. The time it takes to load the blocked lists too has improved significantly.

The DNS server now internally uses a new ByteTree data structure which is a complete lock less implementation allowing concurrent threads to do read and write operations. This allows the DNS server to handle large amount of concurrent requests easily while also allowing it to update the cache data parallelly.

With the limited hardware that is available with me for testing, the DNS server was load tested on a machine with Intel(R) Core(TM) i7-8700 CPU @ 3.20GHz on a 1 Gbps wired Ethernet network. The server could resolve more than 2 million requests per minute with an average 30% CPU utilization consistently for 3 hours. The client machine that was used to bombard requests however would peak out at 100% CPU preventing from adding any more load on the server for the load test. This update is supposed to fix issues in the previous version that caused the CPU to peak, failing to handle load more that couple of thousand requests per second.

Any comment or feedback is really appreciated and helps a lot in adding new features and fixing bugs. Do send your feedback or support requests to For any feature request or reporting bug, do create an issue on GitHub.

The DNS Server code is available under GNU General Public Licence (GPL) v3 on GitHub.

You can now make your contributions to Technitium by becoming a Patron and help in developing new software, updates and adding more features possible. Become a Patron now!

Sunday, December 8, 2019

Technitium Mesh Released!

Technitium Mesh, a successor to the Bit Chat project, has been released and is available to download directly from the Mesh website.

Technitium Mesh


Mesh is a secure, anonymous, peer-to-peer (p2p), open source instant messenger that provides end-to-end encryption with Perfect Forward Secrecy (PFS). Mesh can be used on the Internet or on offline private LAN networks for private messaging, group messaging and file transfers. Mesh is based on Bit Chat and retains it core concepts but has some major changes.

Unlike Bit Chat, Mesh does away with centralized user profile registration based on email address. Instead, users now can create multiple local profiles that can be used simultaneously and require to use a generated User Id. This major change was decided based on many people unwilling to disclose their email address or accused Technitium of harvesting email addresses. To be clear, Technitium never used the collected email addresses provided during the profile registration process to even inform existing users that the Bit Chat project is closing its operations.

The generated Mesh User Id is required to be exchanged to initiate private chat and can be changed anytime to avoid previously used User Id from being abused by anyone to stalk or harass you. Even when joining a group chat, a new User Id is generated each time so that the User Id disclosed in group chat cannot be used to initiate a private chat invitation. This makes sure that you are in total control over who is allowed to initiate private chat invitations and when.

The User Id is generated using an algorithm that uses RSA public key linked to the user profile and a random number. This algorithm allows each peer to authenticate the other peer during the peer-to-peer connection process to ensure their identity.

Mesh also removes the use of BitTorrent trackers that were being used by Bit Chat. Using torrent trackers created connectivity issues since many ISPs around the globe use deep packet inspection to block BitTorrent traffic. This also affected Bit Chat since ISPs could not differentiate between both the applications and blocked any traffic that was found using torrent trackers. Instead, Mesh now completely relies on Distributed Hash Tables (DHT).

Mesh now allows creating anonymous profiles that use Tor Network. Mesh includes Tor binaries to allow the app to use Tor Network anytime its necessary. Anonymous profiles and peer-to-peer (p2p) profiles are the two type of profiles that are now available. Both the profiles are interoperable such that a p2p profile user can communicate with anonymous profile user using the built in Tor support. This interoperability means that you can have a group where both p2p users and anonymous users can join together. Anonymous profiles use Tor hidden service to accept inbound connection requests but use a new hidden service onion domain name each time the user logs in to the profile to avoid being tracked using the onion domain name.

Read more technical details on the Frequently Asked Questions (FAQ) page.


  • Completely decentralized, peer-to-peer architecture that works even on offline private LAN networks. No centralized profile registration is needed.
  • End-to-end encryption with Perfect Forward Secrecy (PFS).
  • Allows you to create anonymous profiles that use Tor Network.
  • Multiple profile support allows you to create many profiles and use all of them simultaneously.
  • Allows creating private chat and group chat with file transfer support.
  • User profiles are stored locally using strong encryption protected by passphrase. 
  • Works peer-to-peer with IPv4 as well as IPv6 networks.
  • Automatic port forwarding using your router's UPnP feature.

Open Source

Mesh is open source and source code is available under GNU General Public License v3 on GitHub. The software code is made open source to increase confidence in the security that we intend to provide.

Alpha Version

Technitium Mesh current release is in alpha version. This means the software is not fully complete and will undergo major changes in its protocol or user interface design. There may be noticeable bugs which will be addressed with an automatic update. You are welcome to report any issues by sending an email to For any issues, feedback, or feature request you may create an issue on GitHub.

Further, you may like to read the original concept in this old blog post.

Saturday, September 28, 2019

Analyzing DNS-over-HTTPS And DNS-over-TLS Privacy and Security Claims

DNS-over-HTTPS (DoH) and DNS-over-TLS (DoT) are two new protocol options available for secure DNS transport. Of which DoH has been pretty controversial with strong opposition from notable people in the DNS community. There have been questions raised for even the existence of IETF DoH standard when DoT standard was already an option.

Firefox has builtin DoH support with Cloudflare DNS configured that is being rolled out as a default for all users in the USA. This has consequences of subverting local network policies of organizations or private networks. Firefox has announced a canary domain name that can be blocked locally to prevent Firefox to use DoH by default making the entire effort vulnerable to downgrade attacks.

There have been serious concerns raised about DoH as a means for centralization of the DNS infrastructure. There are only a few public DoH and DoT service providers and thus it attempts to centralize the DNS infrastructure. Sending a handful of DNS providers all your DNS traffic does not really improve your overall privacy. It is a trade-off that each user needs to decide on his/her own.

DNS is one important control planes in a network. It essentially allows network administrators to block content based on domain names making it quite useful tool in the arsenal. It is being widely used to provide content filtering services, parental controls, and to block known malware command and control. Its so popular that a lot of people install a locally running DNS server on their home networks to block Internet Ads using block lists.

Applications or devices using DoH by default will bypass all the local control measures configured by the network administrator. The argument for applications to use DoH is that it allows users to bypass censorship, and provide security and privacy. However, this might not be what the user expects without a consent.

But, are users of DoT or DoH really being protected? Lets first understand the default DNS-over-UDP/TCP (Do53), DoH and DoT protocols in technical terms.

Do53 is the core protocol that is used by the entire DNS infrastructure. By default all DNS queries use UDP protocol since it is more efficient for simple request/response queries. TCP is usually used only when the response is expected to be large enough to not be suitable for UDP. Do53 does not provide any security or privacy as anyone on network path can see all DNS requests and even manipulate responses essentially doing a man-in-the-middle attack. This has been exploited in many malware attacks that compromise routers and change DNS settings to use attacker's DNS server to spread further or to compromise users further. Many ISPs have also tried to hijack DNS to show advertisements when user enters a non-existent domain name in the web browser.

DoT protocol is really just DNS-over-TCP tunneled inside TLS. Thus it provides all the features from the core protocol with addition of on path security and privacy. DoT uses default TCP 853 port and thus is easy to block with any network firewall.

DoH uses HTTPS protocol to send and receive DNS data in wire format. This means that DoH server is really a standard web server with a back end web application reading the DNS requests and proxying them to a configured DNS server. DoH can also be directly supported by a DNS server using a built in web server. DoH, just like DoT, also provides on path security and privacy. Since DoH uses the same TCP 443 port that HTTPS uses, it becomes almost impossible to block it with a network firewall since firewall cannot distinguish between normal HTTPS traffic and DoH.

Since both DoT and DoH use TLS for security, they essentially look similar over network. In fact, if DoT is configured on port 443 instead of its default port 853, it too would become difficult to block with a network firewall. Thus the only benefit of DoH seems to be that it allows the service to be hosted using a standard web server where the same IP address and port is shared with multiple other HTTPS websites.

Even though both DoT and DoH claim to provide security and privacy there are multiple catches. Both DoT and DoH provide security only from client to the recursive DNS server thus they do not provide any end-to-end security. Client is essentially trusting a configured recursive DNS server.

Even when DNS requests are encrypted, you are still leaking domain names of website you visit due to TLS Server Name Indication (SNI) extension. SNI essentially allows a web server running on a single IP address to host multiple HTTPS websites. SNI extension includes the domain name of the website you visit so that the web server can use correct SSL/TLS certificate that is configured for that domain name. SNI thus can reliably be used as an option to block websites combined with DNS based filtering.

SNI extension is being upgraded to Encrypted SNI (ESNI) that will encrypt the entire SNI extension in the TLS request. But practically speaking, even when ESNI becomes generally available on all web servers and web browsers, it will take many many years before significant amount of HTTPS websites configure ESNI for their domain name. Its been more than 3 year now that free SSL/TLS certificates are available to be used by any website but still there are a lot of websites that do not have HTTPS deployed (link requires login).

Even when DNS request are encrypted and TLS ESNI extension is used, most websites can still be identified by the IP address they are hosted on. Thus privacy provided by all these measures is still inadequate.

What about DNSSEC? DNSSEC is designed to provide security such that a recursive DNS server can validate responses before responding to client requests. It does not provide end-to-end security as clients never really perform validations and rely totally on the configured recursive DNS server. Another issue with DNSSEC is that its not widely deployed with only a small percentage of domain names have it configured. Most popular websites on the internet still do not have DNSSEC deployed making DNSSEC not really useful for most end users.

With all these technical issues in mind, its clear that both DoT and DoH are not really safe to be used by people to bypass censorship. Anyone with serious concerns with privacy is better off using Tor Browser or use a decent VPN service.

DoT and DoH are still useful as they protect users from man-in-the-middle attacks by on path network attackers. DoH however is really designed with an aim to bypass local network policies. Both are capable from hiding your DNS traffic on private network or from ISP.

A better way for many people is to run their own local DNS server that does recursive resolution. Locally running recursive DNS server will cache most common name servers records which usually have long TTL values configured in days and only query them when records are required or expired. This prevents DNS queries from going to centralized networks and avoid getting logged on ISP DNS server. Having authoritative DNS servers support DoT by default will add much value to running recursive DNS servers as it will dramatically improve security and privacy over the network.

All major ISPs deploying DoT and major Operating Systems (OS) supporting DoT will significantly help improve privacy and security as well as maintain the decentralization. Newer Android mobile devices have already started supporting DoT. Once the entire ecosystem supports and deploys DoT, it will improve the current state that DNS is in.

Tuesday, January 1, 2019

Turn Raspberry Pi Into Network Wide DNS Server

Turn your Raspberry Pi into a network wide DNS server for security, privacy and blocking Internet Ads on your private network!

Raspberry Pi 3 Model B+

With Technitium DNS Server version 2.2 release, it is now possible to run it on Raspberry Pi (Raspbian Stretch) using .NET Core and we have a single line automatic installer ready to make it easy to get it running.

Install DNS Server

Just connect to your Raspberry Pi using SSH and run the command below to install the DNS server:

curl -sSL | sudo bash

You can install the software manually too if you do not wish to directly run the install script. You will need to first manually install .NET Core on your Raspberry Pi and then use these steps to install the DNS Server.

Once the installation is complete, open the DNS Server web console to view the dashboard and customize the settings.

Technitium DNS Server web console on Raspberry Pi 3 Model B+

Configure Your Router

To use it as a network wide DNS server, you need to configure your network router's DHCP settings and add your Raspberry Pi's IP address as a custom DNS server. You may also need to configure the WAN settings to override the default ISP provided DNS servers with your Raspberry Pi one. Check your router's manual for the configuration details.

Do make sure that your Raspberry Pi has a static IP address so that it does not change later causing issues with failed domain resolutions on the entire network. Also make sure to install heat sinks for your Raspberry Pi to prevent overheating issues since you will be running it round the clock.

If you have any queries or feedback, do comment below to let me know. You can also email your queries to

Quick And Easy Guide To Install .NET Core On Raspberry Pi

.NET Core is a cross-platform runtime available for x64 and ARM processors that can be used to run ASP.NET Core web applications and standalone .NET Core console applications on Windows, Linux and macOS.

Installing .NET Core is straight forward for most Desktop platforms with clear instructions available on the download website. However, many would find it trickier to install it on something like Raspberry Pi which uses ARM based processor. So, here is a quick and easy guide to install .NET Core 2.2 on Raspberry Pi 3 Model B+ with the latest Raspbian that is based on Debian 9 (Stretch).

Connect to your Raspberry Pi using SSH and get started!

Raspberry Pi 3 Model B+

Installing Dependencies

First you need to install a few dependencies required by the .NET Core runtime:

sudo apt-get -y update
sudo apt-get -y install curl libunwind8 gettext apt-transport-https

Installing .NET Core

Go to the .NET Core download page and download the Linux ARM32 runtime. Or you could just copy the download URL from there to use with wget like I did and follow these steps:

sudo mkdir -p /opt/dotnet
sudo tar -zxf aspnetcore-runtime-2.2.0-linux-arm.tar.gz -C /opt/dotnet
sudo ln -s /opt/dotnet/dotnet /usr/bin

Now just enter dotnet on the command line to confirm.

Its Done!

Now you are ready to run ASP.NET Core or .NET Core console apps on your Raspberry Pi!

Tuesday, December 25, 2018

Configuring DNS-over-TLS and DNS-over-HTTPS with any DNS Server

The new DNS-over-TLS (DoT) and DNS-over-HTTPS (DoH) protocols are available for enabling end user's privacy and security given the fact that most DNS clients use UDP or TCP protocols which are prone to eavesdropping, vulnerable to Man-in-the-Middle (MitM) attacks and, are frequently abused by ISPs in many countries with Internet censorship.

Public DNS providers like Cloudflare & Quad9, have already deployed these protocols and web browsers like Mozilla Firefox has built in DoH support. However, most operating systems and applications do not support them but, end users can still use these protocols on their computer by installing Technitium DNS Server locally and configuring any DoT or DoH provider as a forwarder to bypass ISP's control over DNS.

Both these protocols are IETF standards and are equally secure considering the fact that HTTPS itself runs over TLS. However, both protocols have slightly different ideas and there are a lot of arguments between engineers over the reason why DoH protocol exists in first place when a superior DoT protocol exists that implements RFC 7766 guidelines. The argument of having DoH is more political since DNS requests over DoH look just like normal HTTPS traffic over port 443 and thus hard to stop unlike DoT running on port 853. This makes DoH protocol desirable to users in countries with Internet censorship.

In this post we will explore configuring both these protocols for any DNS server that you already have running on your network. Both these services require SSL certificates which can be obtained for free using Let's Encrypt certificate authority which is trusted by all major web browsers. You can configure Certbot for automatic Let's Encrypt certificate renewal or manually generate one using Get HTTPS For Free utility.

DNS-over-TLS (DoT)

DNS-over-TLS standard is specified in RFC 7858 which is very straight forward to implement. Essentially, the standard specifies to use the existing DNS-over-TCP protocol support, that most DNS servers already have and, add TLS to it. DoT support can be available as a addon feature in your DNS server software or you can use Nginx web server to enable it.

Nginx supports SSL termination for TCP upstream which I will be using to enable DoT to use with Technitium DNS Server. I am using Ubuntu Server 18.04 LTS for this setup but, you should be able to do similar config on any Linux distro.

First install the nginx web server:

sudo apt-get -y install nginx

Now all you need to configure DoT is to copy the following stream config block in your /etc/nginx/nginx.conf file and save the certificate and key files to path given as in the config. Don't forget to update the upstream DNS server IP addresses to your existing DNS servers.

stream {
    upstream dns-servers {

    server {
        listen 853 ssl;
        proxy_pass dns-servers;

        ssl_certificate            /etc/nginx/ssl/dot-server.crt;
        ssl_certificate_key        /etc/nginx/ssl/dot-server.key;

        ssl_protocols        TLSv1.2;
        ssl_ciphers          HIGH:!aNULL:!MD5;
        ssl_handshake_timeout    10s;
        ssl_session_cache        shared:SSL:20m;
        ssl_session_timeout      4h;

Once done, reload nginx web server to finish the configuration:

sudo service nginx reload

DNS-over-HTTPS (DoH)

DNS-over-HTTPS standard is specified in RFC 8484 and is a bit different to implement since it uses HTTP protocol. The DNS queries are send in wire format as a HTTP POST method or as a base64 encoded HTTP GET parameter. Using GET method allows caching of the response which may be undesirable considering that the DNS protocol controls expiry using TTL values which may get overridden by a HTTP based cache server.

Technitium has released DNS-over-HTTPS (DoH) open source web application that can be used with any DNS server. The web application can be deployed on Windows IIS Web Server or the cross-platform .NET Core version can be deployed on any supported platforms (Windows/macOS/Linux).

Installation on Windows IIS Web Server is as simple as deploying any other website. Just create the website from the IIS console, download the DNS-over-HTTPS ASP.NET web application zip file and extract it to the website root folder. Configure SSL certificate for IIS just like you would do for any website. Finally, you will need to configure the Web.config file's application settings, shown in the snippet below, to point the web app to your DNS server. You can use any of the supported protocols (Udp, Tcp, Tls or Https) to connect to the specified DNS server.

      <setting name="DnsServerProtocol" serializeAs="String">
      <setting name="DnsTimeout" serializeAs="String">
      <setting name="DnsServer" serializeAs="String">

The DoH cross-platform web app runs using ASP.NET Core and can be deployed on Windows, Linux or macOS. I am using Ubuntu Server 18.04 LTS to deploy this web app but, you can follow similar steps on any other Linux distro. ASP.NET Core Web Applications run as a separate process with its own built in web server. We would need to combine nginx for SSL termination for this web app to support HTTPS protocol.

To deploy the DoH ASP.NET Core app, you would first need to install the latest .NET Core Runtime. Once this is done, follow these steps below to install the DoH web app.

sudo mkdir -p /var/aspnetcore/doh
cd /var/aspnetcore/doh
sudo wget
sudo apt-get -y install unzip
sudo unzip

Edit the appsettings.json app settings config file to specify your DNS server and supported protocol. You can use any of the supported protocols (Udp, Tcp, Tls or Https) to connect to the specified DNS server.

sudo nano appsettings.json

Install the DoH web app as a systemd service:

sudo cp systemd.service /etc/systemd/system/doh.service
sudo systemctl enable doh.service
sudo systemctl start doh.service

Or, if your distro does not support systemd then you can use supervisor instead:

sudo apt-get -y install supervisor
sudo cp supervisor.conf /etc/supervisor/conf.d/doh.conf
sudo service supervisor restart

You can now confirm if the DoH web app is running on port 8053:

sudo netstat -nlpt | grep ":8053"

If the DoH web app is not running with systemd, run the following command to get details:

journalctl --unit doh --follow

The final step is to configure nginx web server for SSL termination. First install the nginx web server:

sudo apt-get -y install nginx

Create a config file for your domain name at /etc/nginx/sites-enabled/ with the config shown below. Save the certificate and key files to path given as in the config.

server {
    listen 443 ssl;

    ssl_certificate /etc/nginx/ssl/doh-server.crt;
    ssl_certificate_key /etc/nginx/ssl/doh-server.key;

    location / {

Reload nginx web server to finish the configuration:

sudo service nginx reload

And Its Ready!

You can now use the DoT service ( or DoH service ( with any supported DNS client or as a forwarder with Technitium DNS Server.

If you have any queries or feedback, do comment below to let me know. You can also email your queries to