Split Tunnel#

Configuring “split tunnel”, i.e. only routing certain traffic over the VPN can be configured. It consists of three parts, although some may not be required for your particular setup:

1. Configuring the “routes” to the client to inform them which IP ranges need to be routed over the VPN and make sure the VPN is not used as a “default gateway”;
2. Configure and (internal) DNS server to be used by the clients that possibly resolves “local” names only;
3. Restrict other traffic from being sent over the VPN to other locations than the pushed routes, the clients should not be able to override the “route” configuration, e.g. by forcing “default gateway”.

NOTE: if there are no internal-only DNS entries to resolve, you SHOULD NOT push DNS servers to the client. If there are, then make sure to also specify dnsDomain and/or dnsDomainSearch. In addition, make sure they are also included in the routes.

Example#

We have an organization example.local that has two IP ranges, 10.42.42.0/24 and 10.43.43.0/24 that clients need access to from home. The internal DNS server, on 10.1.1.1/32 is responsible for resolving the example.local domain for internal servers. Only traffic to these IP ranges and the DNS server should be allowed from the VPN server.

Profile Configuration#

Configure an office profile in /etc/vpn-server-api/config.php, e.g.:

'vpnProfiles' => [
    'office' => [
        'profileNumber' => 1,
        'displayName' => 'Office',
       // issued to VPN clients
        'range' => '10.0.0.0/24',
        'range6' => 'fd00::/64',
        // hostname VPN clients will connect to
        'hostName' => 'office.example.org',

        ...
        ...

        // push the routes to the client, *including* the DNS IP
        'routes' => ['10.42.42.0/24', '10.43.43.0/24', '10.1.1.1/32'],

        // push the local DNS to the clients as well
        'dns' => ['10.1.1.1'],

        // Connection-specific DNS Suffix
        'dnsDomain' => 'example.local',

        // Connection-specific DNS Suffix Search List
        'dnsDomainSearch' => ['example.local', 'foo.example.local', 'bar.example.local'],
    ],
],

Take special note of the routes, dns, dnsDomain and dnsDomainSearch options. See PROFILE_CONFIG for other configuration options that may be relevant for your situation.

To apply the configuration changes:

$ sudo vpn-maint-apply-changes

If the command is not available, install the vpn-maint-scripts package first.

Firewall Configuration#

Restricting network access for VPN clients is already documented in firewall.md, but just to be complete, the (FORWARD) configuration of the firewall would be like this, assuming eth0 is the interface connecting to your local network from your VPN server:

-A FORWARD -i tun+ -o eth0 -d 10.42.42.0/24 -j ACCEPT
-A FORWARD -i tun+ -o eth0 -d 10.43.43.0/24 -j ACCEPT
-A FORWARD -i tun+ -o eth0 -d 10.1.1.1/32 -j ACCEPT
-A FORWARD -i eth0 -o tun+ -j ACCEPT
-A FORWARD -j REJECT --reject-with icmp-host-prohibited

NOTE: restart the firewall after making modifications!

NOTE: for IPv6 routes it works exactly the same.