DNS inspection with DoT and DoH

DNS over TLS (DoT) and DNS over HTTPS (DoH) are supported in DNS inspection. Prior to 7.6.0, DoT and DoH inspection can only be processed in proxy mode. Starting in 7.6.0, both proxy and flow inspection modes are able to handle DoT and DoH.

In the following examples, the FortiGate inspects DNS queries made over DoT and DoH to a Cloudflare DNS server. The DNS filter profile blocks the education category.

To configure DNS inspection of DoT and DoH queries in the GUI:

1. Configure the SSL-SSH profile:
   1. Go to Security Profiles > SSL/SSH Inspection and click Create New.
   2. Set Inspection method to Full SSL Inspection. DoT and DoH can only be inspected using doing deep inspection.
   3. In the Protocol Port Mapping section, enable DNS over TLS.

      

   4. Configure the other settings as needed.
   5. Click OK.
2. Configure the DNS filter profile:
   1. Go to Security Profiles > DNS Filter and click Create New.
   2. Enable Redirect botnet C&C requests to Block Portal.
   3. Enable FortiGuard Category Based Filter and set the Action for the Education category to Redirect to Block Portal.
   4. Configure the other settings as needed.
   5. Click OK.
3. Configure the firewall policy:
   1. Go to Policy & Objects > Firewall Policy and click Create New.
   2. Enable DNS Filter and select the profile you created.
   3. For SSL Inspection, select the profile you created.
   4. Configure the other settings as needed.
   5. Click OK.

To configure DNS inspection of DoT and DoH queries in the CLI:

1. Configure the SSL-SSH profile:

   config firewall ssl-ssh-profile
       edit "ssl"
           config dot
               set status deep-inspection
               set client-certificate bypass
               set unsupported-ssl-cipher allow
               set unsupported-ssl-negotiation allow
               set expired-server-cert block
               set revoked-server-cert block
               set untrusted-server-cert allow
               set cert-validation-timeout allow
               set cert-validation-failure block
           end
       next
   end
   

2. Configure the DNS filter profile:

   config dnsfilter profile
       edit "dnsfilter"
           config ftgd-dns
               config filters
                   edit 1
                       set category 30
                       set action block
                   next
               end
           end
           set block-botnet enable
       next
   end

3. Configure the firewall policy:

   config firewall policy
       edit 1
           set srcintf "port1"
           set dstintf "port3"
           set srcaddr "all"
           set dstaddr "all"
           set action accept
           set schedule "always"
           set service "ALL"
           set utm-status enable
           set inspection-mode proxy
           set profile-protocol-options "protocol"
           set ssl-ssh-profile "ssl"
           set webfilter-profile "webfilter"
           set dnsfilter-profile "dnsfilter"
           set nat enable
       next
   end

Testing the connection

To query DNS over TLS:

1. Send a DNS query over TLS to the Cloudflare server 1.1.1.1 (this example uses kdig on an Ubuntu client). The www.ubc.ca domain belongs to the education category:

   ~$ kdig -d @1.1.1.1 +tls-ca +tls-host=cloudflare-dns.com www.ubc.ca
   ;; DEBUG: Querying for owner(www.ubc.ca.), class(1), type(1), server(1.1.1.1), port(853), protocol(TCP)
   ;; DEBUG: TLS, imported 128 system certificates
   ;; DEBUG: TLS, received certificate hierarchy:
   ;; DEBUG:  #1, C=US,ST=California,L=San Francisco,O=Cloudflare\, Inc.,CN=cloudflare-dns.com
   ;; DEBUG:      SHA-256 PIN: elpYCnCs9ZtkQBI4+cb2QtZcyOl5UI9jMkSvbTsTad0=
   ;; DEBUG:  #2, C=US,ST=California,L=Sunnyvale,O=Fortinet,OU=Certificate Authority,CN=FG3H1E5818903681,EMAIL=support@fortinet.com
   ;; DEBUG:      SHA-256 PIN: s48VtdODlNZfAG2g/92hMLhitU51qsP9pkHAUtTJ+f4=
   ;; DEBUG: TLS, skipping certificate PIN check
   ;; DEBUG: TLS, The certificate is trusted.
   ;; TLS session (TLS1.3)-(ECDHE-SECP256R1)-(ECDSA-SECP256R1-SHA256)-(AES-256-GCM)
   ;; ->>HEADER<<- opcode: QUERY; status: NOERROR; id: 56850
   ;; Flags: qr rd; QUERY: 1; ANSWER: 1; AUTHORITY: 0; ADDITIONAL: 0
   
   ;; QUESTION SECTION:
   ;; www.ubc.ca.                  IN      A
   
   ;; ANSWER SECTION:
   www.ubc.ca.             60      IN      A       208.91.112.55
   
   ;; Received 44 B
   ;; Time 2021-03-12 06:53:37 UTC
   ;; From 1.1.1.1@853(TCP) in 6.0 ms

   In this query, the FortiGate inspects the DNS query to the Cloudflare DNS server. It replaces the result with the IP of the FortiGuard block page, which successfully blocks the query.

To query DNS over HTTPS:

1. In your browser, enable DNS over HTTPS.
2. Go to www.ubc.ca. The website is redirected to the block page.