Local DNS#

New VPN server installations, performed using deploy_${DIST}.sh, will use the the public DNS service offered by Quad9 by default.

It is possible to run your own local DNS resolver for the VPN clients. This has a number of benefits:

• Ability to apply filters to e.g. block known malware domains;
• The upstream DNS is unreliable, sells your query data or is slow;
• You do not want to use the “public DNS” services as offered by Quad9, Cloudflare or Google.

Running your own DNS resolver can also be a good idea if no upstream DNS server is provided by your ISP.

NOTE: if your organization has a (trusted) DNS service you SHOULD probably use that one! See Profile Config, look for the dnsServerList option.

Configuration#

Setting a local recursive DNS server takes a few steps:

1. Install a recursive DNS server, we’ll use Unbound here;
2. Configure the DNS server to allow the VPN clients to use it for recursive queries;
3. Configure the VPN firewall to allow VPN clients to access the local DNS server;
4. Make the VPN profiles use the “local DNS”.

Install Unbound#

Fedora#

$ sudo dnf -y install unbound

You MUST disable the systemd-resolved “stub” resolver if you want to have unbound listen on all interfaces on port 53. Create the directory, and then the file /etc/systemd/resolved.conf.d/stub-listener.conf with the following content:

[Resolve]
DNSStubListener=no

Restart systemd-resolved:

$ sudo systemctl daemon-reload
$ sudo systemctl restart systemd-resolved

Debian#

$ sudo apt -y install unbound

Configure Unbound#

You need to change the Unbound configuration. You can add the following file to /etc/unbound/conf.d/VPN.conf on CentOS/Fedora, and in /etc/unbound/unbound.conf.d/VPN.conf on Debian:

server:
    interface: 0.0.0.0
    interface: ::0
    access-control: 10.0.0.0/8 allow
    access-control: 172.16.0.0/12 allow
    access-control: 192.168.0.0/16 allow
    access-control: fc00::/7 allow

    # disable DoH
    # See: https://use-application-dns.net/
    # See: https://support.mozilla.org/en-US/kb/configuring-networks-disable-dns-over-https
    local-zone: use-application-dns.net refuse

    # disable iCloud Private Relay
    # See: https://developer.apple.com/support/prepare-your-network-for-icloud-private-relay
    local-zone: mask.icloud.com. refuse
    local-zone: mask-h2.icloud.com. refuse

With these options Unbound listens on all interfaces and the RFC 1981 and 4193 ranges are allowed. These ranges are the defaults for deploys done by the deploy_${DIST}.sh scripts.

Enable Unbound during boot, and (re)start it:

$ sudo systemctl enable unbound
$ sudo systemctl restart unbound

Profile Configuration#

Modify /etc/vpn-user-portal/config.php for each of the VPN profiles where you want to use “local DNS”, point the dnsServerList entry to the IPv4 (and IPv6) address(es) of your DNS server or the template variables @GW4@ and/or @GW6@:

'dnsServerList' => ['@GW4@', '@GW6@'],

The @GW4@ and @GW6@ template variables are replaced by the gateway IP addresses of the VPN server. You can of course also specify real IP addresses here, but make sure the DNS servers are reachable by the VPN clients and that traffic to the DNS server(s) is routed over the VPN if you are not using a “default gateway” configuration.

NOTE: the template variables @GW4@ and @GW6@ are available in vpn-user-portal >= 3.1.6.

Firewall#

In order to allow the VPN clients to reach the DNS server, the firewall needs to be relaxed to allow traffic to udp/53 and tcp/53 coming from the VPN clients.

Apply#

To apply the configuration changes:

$ sudo vpn-maint-apply-changes