Setup your VPN service to your DD-WRT enabled router

Router: Netgear X6 R8000
Firmware: DD-WRT firmware for Netgear R8000 Based on revision 27261 KONG
By: SeNsUi

I had tested Kong & Tagatha firmwares from 2015/2016 and found 27261 to be the most stable with good WiFi signal and OpenVPN working correctly.
By default, DD-WRT may use your ISP's DNS servers using DHCP. For privacy reasons, we'll instead configure DD-WRT to explicitly use alternate DNS servers. The below servers are provided as an example, you can use any Public DNS service you would prefer, such as Google DNS (8.8.8.8 and 8.8.4.4), OpenDNS (208.67.222.222 and 208.67.220.220), Level 3 (4.2.2.1, 4.2.2.2, 4.2.2.3), or you can use a combination to fill in the 3 Static DNS fields.

• In the DD-WRT Administrative Interface, navigate to Setup > Basic Setup.
• Under Network Address Server Settings (DHCP), set: Static DNS 1 = 8.8.8.8 Static DNS 2 = 8.8.4.4 Static DNS 3 = 4.2.2.2 Use DNSMasq for DHCP = Checked Use DNSMasq for DNS = Checked DHCP-Authoritative = Checked
• Apply Settings.

• To Disable IPv6, Navigate to Setup > IPV6
• Set IPv6 to Disable, then Save & Apply Settings.
• Disable IPv6

• To Enable Local DNS, Navigate to Services > Services
• If there is a DNS Suffix, Remove that
• Under DHCP Server, Set Used Domain to LAN & WLAN
• Under DNSMasq Ensure that DNSMasq, Local DNS, and No DNS Rebind are all enabled
• Save & Apply Settings

• Navigate to Service > VPN
• Under OpenVPN Client, set Start OpenVPN Client = Enable. Other options will appear.
• Set Advanced Options to Enable, More options will appear.
• Set the following:

Server IP/Name = fra1.seedboxes.cc (Choose a server from all available regions)
Port = 1194
Tunnel Device = TUN
Tunnel Protocol = UDP
Encryption Cipher = Blowfish CBC
Hash Algorithm = SHA1
User Pass Authentication = Enable
Username, Password = Your VPN username & password
TLS Cipher = None
LZO Compression = Disabled
NAT = Enable
Firewall = Enable (Enable and Disable worked for me)

• In Additional Config, Type:

persist-key
persist-tun
tls-client
remote-cert-tls server

• Download the OpenVPN config of your choice from seedboxes.cc client area under vpn section.
• Open file with Notepad ex. Frankfurt-fra1.ovpn

• In DD-WRT, Copy - Paste the contents in the CA Cert field. Be sure that the entire text gets pasted in, including "-----BEGINCERTIFICATE-----" and "-----END CERTIFICATE-----".

• Save and Apply Settings
• To Verify the VPN is Working, Navigate to Status > OpenVPN Under State, you should see the message "Client: CONNECTED SUCCESS"