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Technical Tip: Custom DNS servers are not supported with L2TP tunnels

Description

This article describes how custom DNS servers are not supported with L2TP tunnels.

Scope

FortiGate.

Solution

Custom DNS servers are not supported with L2TP tunnels. Users connected via L2TP will always retrieve FortiGate system DNS servers.

To change the configured DNS servers in GUI, Network -> DNS, then set the primary and secondary DNS servers.

With the CLI:

config system dns

set primary x.x.x.x

set secondary y.y.y.y
end

Changing the system DNS is a global change and does not affect only L2TP. The FortiGate will now use the configured DNS servers for DNS queries.

It is possible to configure custom DNS servers on the L2TP adapter in Windows by editing the Internet Protocol Version 4 (TCP/IPv4) settings.

Example:

When the L2TP VPN is connected, use ipconfig /all in Command Prompt or PowerShell to verify the custom DNS servers are configured.

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