OpenVPN server

• This how-to describes the method for setting up OpenVPN server on OpenWrt.
• Follow OpenVPN client for client setup and OpenVPN extras for additional tuning.
• It requires OpenWrt 21.02+ with OpenVPN 2.5+ supporting tls-crypt-v2.
  • OpenWrt 19.07 users with OpenVPN 2.4 should refer to an older revision.

Install the required packages. Specify configuration parameters for VPN server.

# Install packages
opkg update
opkg install openvpn-openssl openvpn-easy-rsa
 
# Configuration parameters
VPN_DIR="/etc/openvpn"
VPN_PKI="/etc/easy-rsa/pki"
VPN_PORT="1194"
VPN_PROTO="udp"
VPN_POOL="192.168.9.0 255.255.255.0"
VPN_DNS="${VPN_POOL%.* *}.1"
VPN_DN="$(uci -q get dhcp.@dnsmasq[0].domain)"
 
# Fetch server address
NET_FQDN="$(uci -q get ddns.@service[0].lookup_host)"
. /lib/functions/network.sh
network_flush_cache
network_find_wan NET_IF
network_get_ipaddr NET_ADDR "${NET_IF}"
if [ -n "${NET_FQDN}" ]
then VPN_SERV="${NET_FQDN}"
else VPN_SERV="${NET_ADDR}"
fi

Use EasyRSA to manage the PKI. Utilize private key password protection if necessary.

# Work around EasyRSA issues
wget -U "" -O /tmp/easyrsa.tar.gz \
https://github.com/OpenVPN/easy-rsa/\
releases/download/v3.1.7/EasyRSA-3.1.7.tgz
tar -z -x -f /tmp/easyrsa.tar.gz
 
# Configuration parameters
cat << EOF > /etc/profile.d/easy-rsa.sh
export EASYRSA_PKI="${VPN_PKI}"
export EASYRSA_TEMP_DIR="/tmp"
export EASYRSA_CERT_EXPIRE="3650"
export EASYRSA_BATCH="1"
alias easyrsa="/root/EasyRSA-3.1.7/easyrsa"
EOF
. /etc/profile.d/easy-rsa.sh
 
# Remove and re-initialize PKI directory
easyrsa init-pki
 
# Generate DH parameters
easyrsa gen-dh
 
# Create a new CA
easyrsa build-ca nopass
 
# Generate server keys and certificate
easyrsa build-server-full server nopass
openvpn --genkey tls-crypt-v2-server ${EASYRSA_PKI}/private/server.pem
 
# Generate client keys and certificate
easyrsa build-client-full client nopass
openvpn --tls-crypt-v2 ${EASYRSA_PKI}/private/server.pem \
--genkey tls-crypt-v2-client ${EASYRSA_PKI}/private/client.pem

Consider VPN network as private. Assign VPN interface to LAN zone to minimize firewall setup. Allow access to VPN server from WAN zone.

# Configure firewall
uci rename firewall.@zone[0]="lan"
uci rename firewall.@zone[1]="wan"
uci del_list firewall.lan.device="tun+"
uci add_list firewall.lan.device="tun+"
uci -q delete firewall.ovpn
uci set firewall.ovpn="rule"
uci set firewall.ovpn.name="Allow-OpenVPN"
uci set firewall.ovpn.src="wan"
uci set firewall.ovpn.dest_port="${VPN_PORT}"
uci set firewall.ovpn.proto="${VPN_PROTO}"
uci set firewall.ovpn.target="ACCEPT"
uci commit firewall
service firewall restart

Configure VPN service and generate client profiles.

# Configure VPN service and generate client profiles
umask go=
VPN_DH="$(cat ${VPN_PKI}/dh.pem)"
VPN_CA="$(openssl x509 -in ${VPN_PKI}/ca.crt)"
ls ${VPN_PKI}/issued \
| sed -e "s/\.\w*$//" \
| while read -r VPN_ID
do
VPN_TC="$(cat ${VPN_PKI}/private/${VPN_ID}.pem)"
VPN_KEY="$(cat ${VPN_PKI}/private/${VPN_ID}.key)"
VPN_CERT="$(openssl x509 -in ${VPN_PKI}/issued/${VPN_ID}.crt)"
VPN_EKU="$(echo "${VPN_CERT}" | openssl x509 -noout -purpose)"
case ${VPN_EKU} in
(*"SSL server : Yes"*)
VPN_CONF="${VPN_DIR}/${VPN_ID}.conf"
cat << EOF > ${VPN_CONF} ;;
user nobody
group nogroup
dev tun
port ${VPN_PORT}
proto ${VPN_PROTO}
server ${VPN_POOL}
topology subnet
client-to-client
keepalive 10 60
persist-tun
persist-key
push "dhcp-option DNS ${VPN_DNS}"
push "dhcp-option DOMAIN ${VPN_DN}"
push "redirect-gateway def1"
push "persist-tun"
push "persist-key"
<dh>
${VPN_DH}
</dh>
EOF
(*"SSL client : Yes"*)
VPN_CONF="${VPN_DIR}/${VPN_ID}.ovpn"
cat << EOF > ${VPN_CONF} ;;
user nobody
group nogroup
dev tun
nobind
client
remote ${VPN_SERV} ${VPN_PORT} ${VPN_PROTO}
auth-nocache
remote-cert-tls server
EOF
esac
cat << EOF >> ${VPN_CONF}
<tls-crypt-v2>
${VPN_TC}
</tls-crypt-v2>
<key>
${VPN_KEY}
</key>
<cert>
${VPN_CERT}
</cert>
<ca>
${VPN_CA}
</ca>
EOF
done
service openvpn restart
ls ${VPN_DIR}/*.ovpn

Basic openvpn server configuration is now complete.

1. Perform OpenWrt backup.
2. Either extract client profile from the archive file, or use SCP to retrieve the /etc/openvpn/client.ovpn file from the router.
3. Review/edit the IP address for the 'remote' line contained within the client.ovpn file.
4. Import the client.ovpn profile into your clients.

For an additional .ovpn after completing the above:

1. Run this multi-client script.
2. Now make a script consisting of the “Configuration parameters” of Part 1 above and all of Part 4 above and run it. Note that the “remote” line may be missing in the new ovpn (use the original as a reference for that).

Collect and analyze the following information.

# Restart services
service log restart; service openvpn restart; sleep 10
 
# Log and status
logread -e openvpn; netstat -l -n -p | grep -e openvpn
 
# Runtime configuration
pgrep -f -a openvpn
ip address show; ip route show table all
ip rule show; ip -6 rule show; nft list ruleset
 
# Persistent configuration
uci show network; uci show firewall; uci show openvpn
head -v -n -0 /etc/openvpn/*.conf

For beginners to OpenVPN server, this PDF guide may be helpful. It is based on above cli instructions with additional note and tips. OpenVPN server setup guide for BT Home Hub 5A