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DNS Privacy

Eric Sauvageau edited this page May 8, 2019 · 3 revisions

DNS Privacy

Introduced in 384.11, DNS Privacy allows you to better secure your DNS queries through the use of a secured/encrypted connection. At this time, only DNS-over-TLS (or DoT for short) is supported.

Configuration

The feature can be configured on the WAN -> Internet Connection page. When enabling it, you must also enter at least one server in the DoT server list. You can pick them from the Presets drop-down menu by selecting an entry, and then clicking on the Add button in the list below to add it to the table. You can also manually enter the server parameters in the list to add a server not available from the existing presets. Note that the server must explicitly support the DoT protocol, you cannot use a regular DNS server there such as the ones provided by your ISP. DoH and DNSCrypt servers are not currently supported either.

Description of the server entry fields:

  • Address: The IP address of the DNS server.
  • TLS Port (optional): Port to use (defaults to 853 if left empty).
  • TLS Hostname: the TLS Hostname used by the security certificate.
  • SPKI Fingerprint (optional): a SHA256 hash of the certificate (check if your server provider requires this, or leave empty)

To ensure enhanced security, it's recommended to also enable DNSSEC, and set it to also validate unsigned replies (make sure the DoT servers you use do support DNSSEC first, otherwise name resolution will fail).

IMPORTANT: make sure you didn't enter a custom DNS server on the LAN -> DHCP page. For DNS Privacy to work, the DHCP server must point your client at the router's IP to use as their DNS server. Likewise, your client must not be configured with a static DNS other than the router's IP.

You can monitor that DoT is properly being used by installing tcpdump through Entware, and monitoring trafic on ports 53 and 853 of the WAN interface (usually eth0):

tcpdump -i eth0 -p port 853 or 53 -n

Ideally, there should no longer be any trafic on port 53, and everything being sent to port 853.

NOTE: There is currently an issue with the popular DoT/DoH test site provided by Cloudflare where it will fail to use properly signed DNSSEC hostnames during the test, causing the test to fail to correctly detect that you are using DoT. This does not indicate that your setup doesn't work, and is something that will hopefully eventually be fixed by Cloudflare. You can avoid this by temporarily disabling validation of unsigned records, however it is recommended to re-enable that option afterward.

How this works

When enabled, all DNS requests you send to your router will be redirected to the servers you have configured for DNS Privacy, encrypting the connection between your router and those servers. Local name resolutions will be unaffected, and dnsmasq will still be able to provide full DNSSEC and rebind protection services.

Note that TLS requires a properly configured clock. DNS Privacy won't use encryption until after your router's clock has been properly set through NTP.

DNSFilter

DNSFilter still works as before, as an override for the DNS configuration used on your router's WAN page, or on the clients themselves. If a client is configured to use a specific DNS server (for example, OpenDNS), then that client will still use OpenDNS, bypassing the DNS Privacy settings. This also means you can force your clients to use DNS Privacy by configuring DNSFilter for "Router" mode. This way, any DNS queries done on your LAN (even with hardcoded DNS servers, like the Netflix Android application which is hardcoded to use 8.8.8.8) will use DNS Privacy.

OpenVPN Clients

This will mostly work as before. OpenVPN clients with "Accept DNS configuration" set to "Exclusive" will still use the DNS servers provided by the VPN server, bypassing DNS Privacy. Setting DNS configuration to "Disabled" on the OpenVPN client configuration will allow it to use DNS Privacy, however note that some VPN providers will block the use of DNS servers other than their own, to protect you against leaking information by sending DNS queries outside of the tunnel. If you trust the OpenVPN server you connect to, it's usually best to leave the setting to Exclusive mode - your DNS queries are already encrypted by the VPN tunnel anyway (for all clients configured to use the tunnel).

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