OpenVPN 基础

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OpenVPN 基础

This article relies on the following:

Accessing web interface / command-line interface
Managing configs / packages / services / logs

简介

如何在OpenWrt上配置运行OpenVPN服务器.
生成易于在不同的客户端设备间导入导出的OpenVPN客户端配置文件(profiles).
客户端的设置参考OpenVPN client，更多OpenVPN的高级特性的调整参考OpenVPN extras.

目标

使用加密的网络连接模式来增强安全性和私密性
- 避免在客户端发生的数据泄露(Data leak)和流量欺骗(Traffic spoofing)
绕过地区性限制
- 摆脱针对客户端侧的内容审查和过滤
在访问局域网内服务的同时，避免通过端口映射将指定端口提供的服务直接暴露向公共网络

指导

1. 防火墙

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

# Configure firewall
uci set firewall.@zone[0].device="tun0"
uci -q delete firewall.vpn
uci set firewall.vpn="rule"
uci set firewall.vpn.name="Allow-OpenVPN"
uci set firewall.vpn.src="wan"
uci set firewall.vpn.dest_port="1194"
uci set firewall.vpn.proto="udp"
uci set firewall.vpn.target="ACCEPT"
uci commit firewall
service firewall restart

2. PKI（公钥基础设施）

使用EasyRSA来处理PKI相关的事务。如果需要，可以给私钥加上密码保护.

# Install packages
opkg update
opkg install openvpn-easy-rsa
 
# Configuration parameters
export EASYRSA_PKI="/etc/easy-rsa/pki"
export EASYRSA_REQ_CN="vpnca"
 
# Remove and re-initialize the PKI directory
easyrsa --batch init-pki
 
# Generate DH parameters
# May take a while to complete (~25m on WRT3200ACM)
easyrsa --batch gen-dh
 
# Create a new CA
easyrsa --batch build-ca nopass
 
# Generate a key pair and sign locally for vpnserver
easyrsa --batch build-server-full vpnserver nopass
 
# Generate a key pair and sign locally for vpnclient
easyrsa --batch build-client-full vpnclient nopass

3. VPN服务器的配置

安装并配置VPN服务器.

# Install packages
opkg update
opkg install openvpn-openssl
 
# Generate TLS PSK
EASYRSA_PKI="/etc/easy-rsa/pki"
openvpn --genkey --secret "${EASYRSA_PKI}/tc.pem"
 
# Configuration parameters
VPN_DEV="$(uci get firewall.@zone[0].device)"
VPN_POOL="192.168.8.0 255.255.255.0"
VPN_DNS="${VPN_POOL%.* *}.1"
VPN_DOMAIN="$(uci get dhcp.@dnsmasq[0].domain)"
EASYRSA_PKI="/etc/easy-rsa/pki"
DH_KEY="$(cat "${EASYRSA_PKI}/dh.pem")"
TC_KEY="$(sed -e "/^#/d;/^\w/N;s/\n//" "${EASYRSA_PKI}/tc.pem")"
CA_CERT="$(openssl x509 -in "${EASYRSA_PKI}/ca.crt")"
NL=$'\n'
 
# Configure VPN server
grep -l -r -e "TLS Web Server Authentication" "${EASYRSA_PKI}/issued" \
| sed -e "s/^.*\///;s/\.\w*$//" \
| while read VPN_ID
do
VPN_CONF="/etc/openvpn/${VPN_ID}.conf"
VPN_CERT="$(openssl x509 -in "${EASYRSA_PKI}/issued/${VPN_ID}.crt")"
VPN_KEY="$(cat "${EASYRSA_PKI}/private/${VPN_ID}.key")"
cat << EOF > "${VPN_CONF}"
verb 3
user nobody
group nogroup
dev ${VPN_DEV}
port 1194
proto udp
server ${VPN_POOL}
topology subnet
client-to-client
keepalive 10 120
persist-tun
persist-key
push "dhcp-option DNS ${VPN_DNS}"
push "dhcp-option DOMAIN ${VPN_DOMAIN}"
push "redirect-gateway def1"
push "persist-tun"
push "persist-key"
<dh>${NL}${DH_KEY}${NL}</dh>
<tls-crypt>${NL}${TC_KEY}${NL}</tls-crypt>
<ca>${NL}${CA_CERT}${NL}</ca>
<cert>${NL}${VPN_CERT}${NL}</cert>
<key>${NL}${VPN_KEY}${NL}</key>
EOF
chmod "u=rw,g=,o=" "${VPN_CONF}"
done
service openvpn restart

4. 客户端的配置文件(profiles)

为VPN客户端生成配置文件(profiles)。如果需要，也可以设置 DDNS client。

# Fetch WAN IP address
source /lib/functions/network.sh
network_find_wan NET_IF
network_get_ipaddr VPN_SERV "${NET_IF}"
 
# Fetch FQDN from DDNS client
VPN_FQDN="$(uci -q get "$(uci -q show ddns \
| sed -n -e "/\.enabled='1'$/s//.lookup_host/p" \
| sed -n -e "1p")")"
if [ -n "${VPN_FQDN}" ]
then
VPN_SERV="${VPN_FQDN}"
fi
 
# Configuration parameters
VPN_CONF="/etc/openvpn/vpnserver.conf"
VPN_PORT="$(sed -n -e "/^port\s/s///p" "${VPN_CONF}")"
VPN_PROTO="$(sed -n -e "/^proto\s/s///p" "${VPN_CONF}")"
VPN_DEV="$(sed -n -e "/^dev\s/s///p" "${VPN_CONF}")"
EASYRSA_PKI="/etc/easy-rsa/pki"
TC_KEY="$(sed -e "/^#/d;/^\w/N;s/\n//" "${EASYRSA_PKI}/tc.pem")"
CA_CERT="$(openssl x509 -in "${EASYRSA_PKI}/ca.crt")"
NL=$'\n'
 
# Generate VPN client profiles
grep -l -r -e "TLS Web Client Authentication" "${EASYRSA_PKI}/issued" \
| sed -e "s/^.*\///;s/\.\w*$//" \
| while read VPN_ID
do
VPN_CONF="/etc/openvpn/${VPN_ID}.ovpn"
VPN_CERT="$(openssl x509 -in "${EASYRSA_PKI}/issued/${VPN_ID}.crt")"
VPN_KEY="$(cat "${EASYRSA_PKI}/private/${VPN_ID}.key")"
cat << EOF > "${VPN_CONF}"
verb 3
dev ${VPN_DEV%%[0-9]*}
nobind
client
remote ${VPN_SERV} ${VPN_PORT} ${VPN_PROTO}
auth-nocache
remote-cert-tls server
<tls-crypt>${NL}${TC_KEY}${NL}</tls-crypt>
<ca>${NL}${CA_CERT}${NL}</ca>
<cert>${NL}${VPN_CERT}${NL}</cert>
<key>${NL}${VPN_KEY}${NL}</key>
EOF
chmod "u=rw,g=,o=" "${VPN_CONF}"
done
ls /etc/openvpn/*.ovpn

Perform OpenWrt backup. Extract client profiles from the archive and import them to your clients.

测试

建立VPN连接。检查客户端的流量全部经过VPN服务器的网关。

traceroute openwrt.org
traceroute6 openwrt.org

检查客户端的公网IP地址： * ipleak.net

确保在客户端一侧没有DNS leak。 * dnsleaktest.com

Delegate a public IPv6 prefix to the IPv6 VPN network to use IPv6 by default. * ipv6-test.com

Troubleshooting

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 -n -0 /etc/openvpn/*.conf

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