OpenVPN extras

• This how-to describes the most common OpenVPN tuning scenarios adapted for OpenWrt.
• Follow OpenVPN server for server setup and OpenVPN client for client setup.
• Follow Random generator to overcome low entropy issues.

• OpenVPN for BSD/Linux/Windows
• OpenVPN for Android
• OpenVPN documentation

Install the necessary packages and provide instance management if you want to manage VPN instances using web interface.

# Install packages
opkg update
opkg install luci-app-openvpn
/etc/init.d/rpcd restart

Navigate to LuCI → VPN → OpenVPN to manage OpenVPN instances.

If you need to manage multiple VPN instances or use web interface. Make sure to specify different VPN interface names for each instance.

# Provide VPN instance management
ls /etc/openvpn/*.conf \
| while read -r OVPN_CONF
do
OVPN_ID="$(basename ${OVPN_CONF%.*} | sed -e "s/\W/_/g")"
uci -q delete openvpn.${OVPN_ID}
uci set openvpn.${OVPN_ID}="openvpn"
uci set openvpn.${OVPN_ID}.enabled="1"
uci set openvpn.${OVPN_ID}.config="${OVPN_CONF}"
done
uci commit openvpn
/etc/init.d/openvpn restart

If you use a commercial VPN provider. Set up credentials for username/password authentication and enforce gateway redirection.

# Configuration parameters
OVPN_DIR="/etc/openvpn"
OVPN_ID="client"
OVPN_USER="USERNAME"
OVPN_PASS="PASSWORD"
 
# Save username/password credentials
umask go=
cat << "EOF" > ${OVPN_DIR}/${OVPN_ID}.auth
${OVPN_USER}
${OVPN_PASS}
EOF
 
# Configure VPN service
sed -i -e "
/^auth-user-pass/s/^/#/
\$a auth-user-pass ${OVPN_ID}.auth
/^redirect-gateway/s/^/#/
\$a redirect-gateway def1 ipv6
" ${OVPN_DIR}/${OVPN_ID}.conf
/etc/init.d/openvpn restart

Restart VPN client upon reconnecting WAN interface with hotplug.

# Configure hotplug
cat << "EOF" > /etc/hotplug.d/iface/50-openvpn
if [ "${INTERFACE}" = "wan" -o "${INTERFACE}" = "wan6" ] \
&& [ "${ACTION}" = "ifup" -o "${ACTION}" = "ifupdate" ]
then /etc/init.d/openvpn restart
fi
EOF

If you want to manage VPN interface using web interface. Beware of race condition with netifd service.

uci del_list firewall.wan.device="tun+"
uci add_list firewall.wan.network="vpn"
uci commit firewall
/etc/init.d/firewall restart
uci -q delete network.vpn
uci set network.vpn="interface"
uci set network.vpn.proto="none"
uci set network.vpn.ifname="tun0"
uci commit network
/etc/init.d/network restart

Provide static IP address allocation on VPN server assuming that:

• 192.168.8.0/24 - VPN network
• fdf1:e8a1:8d3f:8::/64 - VPN6 network

umask go=rx
mkdir -p /etc/openvpn/ccd
cat << EOF > /etc/openvpn/ccd/client
ifconfig-push 192.168.8.2 255.255.255.0
ifconfig-ipv6-push fdf1:e8a1:8d3f:8::2/64
EOF
cat << EOF >> /etc/openvpn/server.conf
client-config-dir ccd
EOF
/etc/init.d/openvpn restart

Implement plain routing between server side LAN and client side LAN assuming that:

• 192.168.1.0/24 - server side LAN
• 192.168.2.0/24 - client side LAN

Set up static address allocation on VPN server, add route to client side LAN, push route to server side LAN, selectively disable gateway redirection.

cat << EOF >> /etc/openvpn/ccd/client
iroute 192.168.2.0 255.255.255.0
push-remove redirect-gateway
EOF
cat << EOF >> /etc/openvpn/server.conf
route 192.168.2.0 255.255.255.0 192.168.8.2
push "route 192.168.1.0 255.255.255.0"
EOF
/etc/init.d/openvpn restart

Consider VPN network as private and assign VPN interface to LAN zone on VPN client.

uci del_list firewall.wan.device="tun+"
uci add_list firewall.lan.device="tun+"
uci commit firewall
/etc/init.d/firewall restart

If you do not need to redirect all traffic to VPN. Disable gateway redirection on VPN server.

sed -i -e "
/^push.*redirect-gateway/s/^/#/
" /etc/openvpn/server.conf
/etc/init.d/openvpn restart

Or ignore it on VPN client.

sed -i -e "
/^redirect-gateway/s/^/#/
\$a pull-filter ignore redirect-gateway
" /etc/openvpn/client.conf
/etc/init.d/openvpn restart

If VPN gateway is not your LAN gateway. Implement plain routing between LAN network and VPN network assuming that:

• 192.168.1.0/24 - LAN network
• 192.168.1.2/24 - VPN gateway
• 192.168.8.0/24 - VPN network

Add port forwarding for VPN server on LAN gateway.

uci -q delete firewall.ovpn
uci set firewall.ovpn="redirect"
uci set firewall.ovpn.name="Redirect-OpenVPN"
uci set firewall.ovpn.src="wan"
uci set firewall.ovpn.src_dport="1194"
uci set firewall.ovpn.dest="lan"
uci set firewall.ovpn.dest_ip="192.168.1.2"
uci set firewall.ovpn.family="ipv4"
uci set firewall.ovpn.proto="udp"
uci set firewall.ovpn.target="DNAT"
uci commit firewall
/etc/init.d/firewall restart

Add route to VPN network via VPN gateway on LAN gateway.

uci -q delete network.vpn
uci set network.vpn="route"
uci set network.vpn.interface="lan"
uci set network.vpn.target="192.168.8.0/24"
uci set network.vpn.gateway="192.168.1.2"
uci commit network
/etc/init.d/network restart

Provide IPv6 tunnel connectivity. Set up transitional connectivity or NAT6 with IPv6 masquerading if required.

Enable VPN6 network on VPN server, provide DNS6, redirect GW6. Provide default IPv6 route for VPN clients.

OVPN_POOL6="fdf1:e8a1:8d3f:8::/64"
OVPN_DNS6="${OVPN_POOL6%/*}1"
cat << EOF >> /etc/openvpn/server.conf
proto udp6
server-ipv6 ${OVPN_POOL6}
push "dhcp-option DNS ${OVPN_DNS6}"
push "redirect-gateway ipv6"
EOF
/etc/init.d/openvpn restart
uci set network.wan6.sourcefilter="0"
uci commit network
/etc/init.d/network restart

Use TCP for troubleshooting.

OVPN_PROTO="tcp"
sed -i -e "
/^proto/s/^/#/
\$a proto ${OVPN_PROTO}
" /etc/openvpn/server.conf
/etc/init.d/openvpn restart
uci set firewall.ovpn.proto="${OVPN_PROTO}"
uci commit firewall
/etc/init.d/firewall restart

If you need to utilize bridging. Beware of compatibility issues.

OVPN_ADDR="$(uci get network.lan.ipaddr)"
OVPN_MASK="$(uci get network.lan.netmask)"
OVPN_POOL="${OVPN_ADDR%.*}.128 ${OVPN_ADDR%.*}.254"
OVPN_DNS="${OVPN_ADDR}"
NET_IF="$(uci get network.lan.ifname)"
sed -i -e "
/^dev/s/^/#/
\$a dev tap
/^server/s/^/#/
\$a server-bridge ${OVPN_ADDR} ${OVPN_MASK} ${OVPN_POOL}
/^push.*dhcp-option.*DNS/s/^/#/
\$a push \"dhcp-option DNS ${OVPN_DNS}\"
" /etc/openvpn/server.conf
sed -i -e "
/^dev/s/^/#/
\$a dev tap
" /etc/openvpn/client.ovpn
/etc/init.d/openvpn restart
uci -q delete firewall.lan.device
uci commit firewall
/etc/init.d/firewall restart
uci set network.lan.type="bridge"
uci set network.lan.ifname="${NET_IF%% *} tap0"
uci commit network
/etc/init.d/network restart

Enable lz4 compression. Beware of compatibility and security issues.

cat << EOF >> /etc/openvpn/server.conf
compress lz4
push "compress lz4"
EOF
/etc/init.d/openvpn restart

If using OpenVPN 2.3 or older, replace tls-crypt with tls-auth.

sed -i -e "
/^<.*tls-crypt>/s/crypt/auth/
\$a key-direction 0
" /etc/openvpn/server.conf
/etc/init.d/openvpn restart
 
sed -i -e "
/^<.*tls-crypt>/s/crypt/auth/
\$a key-direction 1
" /etc/openvpn/client.conf
/etc/init.d/openvpn restart

Increase log verbosity for troubleshooting.

sed -i -e "
/^verb/s/^/#/
\$a verb 5
" /etc/openvpn/*.conf
/etc/init.d/openvpn restart

Fix IPv6 routing for Windows desktop client when using dual-stack mode.

NETSH_IPV6="C:\\\\Windows\\\\System32\\\\cmd.exe /c netsh interface ipv6"
cat << EOF >> /etc/openvpn/client.ovpn
script-security 2
up '${NETSH_IPV6} set privacy state=disabled store=active & echo'
ipchange '${NETSH_IPV6} set global randomizeidentifiers=disabled store=active & echo'
route-up '${NETSH_IPV6} delete route prefix=%ifconfig_ipv6_local%/%ifconfig_ipv6_netbits% interface=%dev_idx% store=active'
EOF

Modify the VPN client profile for Windows desktop client.

cat << EOF >> /etc/openvpn/client.ovpn
block-outside-dns
EOF

Use DNS and domain provided by VPN server on OpenWrt client.

cat << "EOF" > /etc/openvpn/client.sh
#!/bin/sh
env | sed -n -e "
/^foreign_option_.*=dhcp-option.*DNS/s//nameserver/p
/^foreign_option_.*=dhcp-option.*DOMAIN/s//search/p
" | sort -u > /tmp/resolv.conf.vpn
case ${script_type} in
(up) uci set dhcp.@dnsmasq[0].resolvfile="/tmp/resolv.conf.vpn" ;;
(down) uci set dhcp.@dnsmasq[0].resolvfile="/tmp/resolv.conf.auto" ;;
esac
/etc/init.d/dnsmasq restart &
EOF
chmod +x /etc/openvpn/client.sh
 
sed -i -e "
/^script-security/s/^/#/
\$a script-security 2
/^up/s/^/#/
\$a up /etc/openvpn/client.sh
/^down/s/^/#/
\$a down /etc/openvpn/client.sh
" /etc/openvpn/client.conf
/etc/init.d/openvpn restart

Prevent traffic leak on OpenWrt client isolating VPN interface in a separate firewall zone.

uci rename firewall.@forwarding[0]="lan_wan"
uci set firewall.lan_wan.enabled="0"
uci -q delete firewall.vpn
uci set firewall.vpn="zone"
uci set firewall.vpn.name="vpn"
uci set firewall.vpn.input="REJECT"
uci set firewall.vpn.output="ACCEPT"
uci set firewall.vpn.forward="REJECT"
uci set firewall.vpn.masq="1"
uci set firewall.vpn.mtu_fix="1"
uci add_list firewall.vpn.device="tun+"
uci del_list firewall.wan.device="tun+"
uci -q delete firewall.lan_vpn
uci set firewall.lan_vpn="forwarding"
uci set firewall.lan_vpn.src="lan"
uci set firewall.lan_vpn.dest="vpn"
uci commit firewall
/etc/init.d/firewall restart
 
cat << "EOF" > /etc/openvpn/killswitch.sh
#!/bin/sh
if pgrep openvpn
then
uci set firewall.lan_wan.enabled="1"
/etc/init.d/openvpn stop &
else
uci set firewall.lan_wan.enabled="0"
/etc/init.d/openvpn start &
fi
/etc/init.d/firewall restart &
EOF
chmod +x /etc/openvpn/killswitch.sh

Set up multi-client VPN server. Use EasyRSA to add clients or revoke their certificates via CRL.

# Configuration parameters
OVPN_PKI="/etc/easy-rsa/pki"
export EASYRSA_PKI="${OVPN_PKI}"
export EASYRSA_BATCH="1"
 
# Add one more client
easyrsa build-client-full client1 nopass
 
# Add another client encrypting its private key
easyrsa build-client-full client2
 
# Revoke client certificate
easyrsa revoke client
 
# Generate a CRL
easyrsa gen-crl
 
# Enable CRL verification
OVPN_CRL="$(cat ${OVPN_PKI}/crl.pem)"
sed -i -e "
/^<crl-verify>/,/^<\/crl-verify>/s/^/#/
\$a <crl-verify>\n${OVPN_CRL//$'\n'/\\n}\n</crl-verify>
" /etc/openvpn/server.conf
/etc/init.d/openvpn restart

Automated VPN server installation and client profiles generation.

opkg update
opkg install curl
URL="https://openwrt.org/_export/code/docs/guide-user/services/vpn/openvpn"
cat << EOF > openvpn-server.sh
$(curl "${URL}/server?codeblock=0")
$(curl "${URL}/server?codeblock=1")
$(curl "${URL}/server?codeblock=2")
$(curl "${URL}/server?codeblock=3")
EOF
sh openvpn-server.sh