OpenConnect extras
Introduction
- This how-to describes the most common OpenConnect tuning scenarios adapted for OpenWrt.
- Follow OpenConnect server for server setup and OpenConnect client for client setup.
- Follow OpenConnect protocol for client configuration.
- Follow DDNS client to use own server with dynamic IP address.
- Follow Random generator to overcome low entropy issues.
Extras
References
Server certificate
Fetch server certificate from remote VPN server. Beware of possible MITM.
openssl s_client -showcerts -connect ${VPN_SERV}:${VPN_PORT} \ < /dev/null > server-cert.pem
Keep existing gateway
Preserve default route to restore WAN connectivity when VPN is disconnected.
# Preserve default route uci set network.wan.metric="1024" uci commit network service network restart
Gateway redirection
Disable gateway redirection in the client if you don't need to route all traffic through VPN.
uci set network.vpn.defaultroute="0" uci commit network service network restart
Split gateway
If VPN gateway is separate from your LAN gateway. Implement plain routing between LAN and VPN networks assuming that:
192.168.1.0/24- LAN network192.168.1.2/24- VPN gateway192.168.9.0/24- VPN network
Add port forwarding for VPN server on LAN gateway.
uci -q delete firewall.oc uci set firewall.oc="redirect" uci set firewall.oc.name="Redirect-OpenConnect" uci set firewall.oc.src="wan" uci set firewall.oc.src_dport="4443" uci set firewall.oc.dest="lan" uci set firewall.oc.dest_ip="192.168.1.2" uci set firewall.oc.family="ipv4" uci set firewall.oc.proto="tcp udp" uci set firewall.oc.target="DNAT" uci commit firewall service 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="192.168.9.0/24" uci set network.vpn.gateway="192.168.1.2" uci commit network service network restart
IPv6 gateway
Set up IPv6 tunnel broker or use IPv6 NAT or NPT if necessary. Enable IPv6 tunnel on VPN server, offer IPv6 DNS, redirect IPv6 gateway.
VPN_POOL6="fd00:9::/64" VPN_DNS6="${VPN_POOL6%:*}:1" uci set ocserv.config.ip6addr="${VPN_POOL6}" uci -q delete ocserv.dns6 uci set ocserv.dns6="dns" uci set ocserv.dns6.ip="${VPN_DNS6}" uci commit ocserv service ocserv restart
Disable ISP prefix delegation to prevent IPv6 leaks on VPN client.
DNS over VPN
Serve DNS for VPN clients on OpenWrt server when using point-to-point topology.
Route DNS over VPN to prevent DNS leaks on VPN client.
Replace peer DNS with public or VPN-specific DNS provider on OpenWrt client.
Modify the VPN connection using NetworkManager on Linux desktop client.
nmcli connection modify id VPN_CON \ ipv4.dns-search ~. ipv4.dns-priority -50 \ ipv6.dns-search ~. ipv6.dns-priority -50
Kill switch
Prevent traffic leaks on OpenWrt client isolating VPN interface in a separate firewall zone.
uci -q delete firewall.vpn uci set firewall.vpn="zone" uci set firewall.vpn.name="vpn" uci set firewall.vpn.input="REJECT" uci set firewall.vpn.output="ACCEPT" uci set firewall.vpn.forward="REJECT" uci set firewall.vpn.masq="1" uci set firewall.vpn.mtu_fix="1" uci add_list firewall.vpn.network="vpn" uci del_list firewall.wan.network="vpn" uci -q delete firewall.@forwarding[0] uci set firewall.lan_vpn="forwarding" uci set firewall.lan_vpn.src="lan" uci set firewall.lan_vpn.dest="vpn" uci commit firewall service firewall restart
Multi-client
Generate password hash for a new VPN client. Set up multi-client VPN server. Use unique credentials for each client.
# Configure VPN service VPN_USER="USERNAME1" VPN_PASS="PASSWORD1" uci -q delete ocserv.client1 uci set ocserv.client1="ocservusers" uci set ocserv.client1.name="${VPN_USER}" uci set ocserv.client1.password="${VPN_HASH}" uci commit ocserv service ocserv restart
Automated
Automated VPN server installation.
URL="https://openwrt.org/_export/code/docs/guide-user/services/vpn/openconnect/server" cat << EOF > openconnect-server.sh $(wget -U "" -O - "${URL}?codeblock=0") $(wget -U "" -O - "${URL}?codeblock=1") $(wget -U "" -O - "${URL}?codeblock=2") $(wget -U "" -O - "${URL}?codeblock=3") EOF sh openconnect-server.sh