OpenWRT - How to set up an OpenVPN Tun Route between two routers

Complete guide how to set up an OpenVPN Tun Route between two OpenWRT routers.
Copy + Paste Instructions listed below. Click Show More in description.
opkg update
opkg install luci-app-openvpn openvpn-easy-rsa openvpn-openssl nano tcpdump

easyrsa init-pki
easyrsa build-ca nopass
easyrsa build-server-full Server_SiteA nopass
easyrsa build-client-full Client_SiteB_SiteA nopass
easyrsa gen-dh

OpenVPN Server Config

config openvpn 'VPN_Tun_Server'
option cipher 'AES-256-GCM'
option client_config_dir '/etc/openvpn/ccd'
option client_to_client '1'
option comp_lzo 'no'
option dev 'tun0'
option ifconfig_pool_persist '/etc/openvpn/ipp.txt'
option keepalive '10 60'
option mssfix '1420'
option mode 'server'
option persist_key '1'
option persist_tun '1'
option port '7500'
option proto 'udp'
option remote_cert_tls 'client'
option reneg_sec '0'
option route '192.168.3.0 255.255.255.0'
option server '10.20.0.0 255.255.255.0'
option topology 'subnet'
option verb '3'
option ca '/etc/openvpn/ca_tuntest.crt'
option dh '/etc/openvpn/dh_tuntest.pem'
option cert '/etc/openvpn/tuntest_Server.crt'
option key '/etc/openvpn/tuntest_Server.key'
option enabled '1'

OpenVPN Client Config

config openvpn 'VPN_Tun_Client'
list remote 'server.dyndns.org'
option auth_nocache '1'
option cipher 'AES-256-GCM'
option client '1'
option comp_lzo 'no'
option connect_retry '5 60'
option dev 'tun0'
option nobind '1'
option persist_key '1'
option persist_tun '1'
option port '7500'
option proto 'udp'
option remote_cert_tls 'server'
option reneg_sec '0'
option verb '3'
option ca '/etc/openvpn/ca_tuntest.crt'
option cert '/etc/openvpn/tuntest_Client.crt'
option key '/etc/openvpn/tuntest_Client.key'
option enabled '1'

Problems?
* Restart both routers and clients.
* Test temporarily disabling Windows Firewall to ensure this is not blocking ping.
* Ensure the file in CCD directory matches OpenVPN Client common name e.g Client_SiteB_SiteA
* Ensure OpenVPN config has the correct remote server address / IP.routers.

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