DNS and domains

When a client connects to a location, Defguard can push DNS settings to it so that name resolution happens through the VPN tunnel. This lets clients resolve internal hostnames (for example server.internal) and, when a search domain is configured, use short names instead of fully qualified domain names.

Two settings control this behaviour:

• DNS – one or more DNS server IP addresses the client should use while the tunnel is up. Separate multiple addresses with commas (,). These are typically your internal resolvers, so private zones resolve correctly.

• Search domain – a domain that is automatically appended to unqualified hostnames. For example, with a search domain of internal, resolving server is treated as server.internal.

Changing DNS settings

To add or change DNS settings or a DNS search domain:

• Go to Locations.

• From the action menu select Edit.

• In the Internal VPN section you can modify the DNS field. Enter the IP addresses of DNS servers (separated by commas ,) and a search domain.

• Save the changes.

The new settings are applied to clients the next time they connect (or reconnect) to the location.

For example:

The DNS server's IP address must be reachable through the tunnel.

For DNS queries to actually travel over the VPN, the DNS server's IP address has to fall within the location's Allowed IPs. Allowed IPs define which destinations are routed into the tunnel, so if the DNS server is not covered by them, one of two things happens:

• DNS leak – if the client has another route to reach that IP (for example over the local network), queries are sent outside the tunnel. Your lookups are then visible to whoever controls that path, and internal-only zones may fail to resolve.

• Broken resolution – if there is no alternate path to the DNS server, name resolution stops working entirely while the tunnel is up, which can make the connection appear "dead" even though the tunnel itself is healthy.

To avoid both, make sure the subnet containing your DNS server is included in Allowed IPs. If you route all traffic through the tunnel (Allowed IPs set to 0.0.0.0/0, ::/0) this is already covered.