openvpn compile & install

[TOC]

为了方便团队成员从异地访问开发环境，考虑使用OpenVPN搭建虚拟局域网。部署的环境和版本信息如下:

CentOS 7
OpenVPN

1.easy-rsa生成证书

从这里下载easy-rsa。

$ unzip easy-rsa-old-master.zip
$ cd easy-rsa-old-master/easy-rsa/2.0
 
$ ls
build-ca        build-key-pkcs12  inherit-inter      pkitool
build-dh        build-key-server  list-crl           revoke-full
build-inter     build-req         openssl-0.9.6.cnf  sign-req
build-key       build-req-pass    openssl-0.9.8.cnf  vars
build-key-pass  clean-all         openssl-1.0.0.cnf  whichopensslcnf

$ln -s openssl-1.0.0.cnf openssl.cnf

可修改vars文件中定义的变量用于生成证书的基本信息。下面生成CA证书：

$source vars
$./clean-all
$./build-ca

因为已经在var中填写了证书的基本信息，所以一路回车即可。生成证书如下：

$ ls keys/
ca.crt  ca.key  index.txt  serial

生成服务器端秘钥：

$ ./build-key-server server
......
Common Name (eg, your name or your server's hostname) [server]:
A challenge password []:1234
......

$ ls keys
01.pem  ca.crt  ca.key  index.txt  index.txt.attr  index.txt.old  serial  serial.old  server.crt  server.csr  server.key

生成客户端证书：

$ ./build-key client
......
Common Name (eg, your name or your server's hostname) [client]:
A challenge password []:1234
......

Common Name用于区分客户端，不同的客户端应该有不同的名称。

Generating DH parameters：

$ ./build-dh

$ ls keys/
01.pem  02.pem  ca.crt  ca.key  client.crt  client.csr  client.key  dh2048.pem  index.txt  index.txt.attr  index.txt.attr.old  index.txt.old  serial  serial.old  server.crt  server.csr  server.key

2.编译OpenVPN

2.1 安装依赖

pam-devel 和 lzo：

$ yum install -y pam-devel ;lzo-devel

2.2 编译安装OpenVPN

下载OpenVPN源码：

$ wget https://swupdate.openvpn.org/community/releases/openvpn-2.4.4.tar.gz

编译安装OpenVPN：

$ tar -zxvf openvpn-2.4.4.tar.gz
$ cd openvpn-2.4.4
$ ./configure --prefix=/usr/local/openvpn
$ make 
$ make install

3.配置OpenVPN

$ mkdir -p /etc/openvpn
$ mkdir -p /etc/openvpn/pki

生成tls-auth key并将其拷贝到证书目录中：

$ /usr/local/openvpn/sbin/openvpn --genkey --secret ta.key
$ mv ta.key /etc/openvpn/pki

将签名生成的CA证书秘钥和服务端证书秘钥拷贝到证书目录中：

$ cp ca.key ca.crt server.crt server.key dh2048.pem /etc/openvpn/pki/

$ ls /etc/openvpn/pki/
ca.crt  ca.key  dh2048.pem  server.crt  server.key

将OpenVPN源码下的配置文件sample/sample-config-files/server.conf拷贝到/etc/openvpn目录。

编辑服务端配置文件/etc/openvpn/server.conf：

$ vim /etc/openvpn/server.conf
local 192.168.1.2 # 服务端IP
port 1194

proto tcp
dev tun

ca /etc/openvpn/pki/ca.crt
cert /etc/openvpn/pki/server.crt
key /etc/openvpn/pki/server.key
dh /etc/openvpn/pki/dh2048.pem

server 10.8.0.0 255.255.255.0 # 分配给客户端的虚拟局域网段
ifconfig-pool-persist ipp.txt

# 推送路由和DNS到客户端
push "route 192.168.1.0 255.255.255.0"
push "redirect-gateway def1 bypass-dhcp"
push "dhcp-option DNS 192.168.1.1"
push "dhcp-option DNS 8.8.8.8"

client-to-client

keepalive 10 120

tls-auth /etc/openvpn/pki/ta.key 0

cipher AES-256-CBC

comp-lzo

max-clients 10

user nobody
group nobody

persist-key
persist-tun

status /var/log/openvpn-status.log
log  /var/log/openvpn.log
log-append  /var/log/openvpn.log

verb 3

确认内核已经开启路由转发功能:

$ sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 1

确认iptables filter表的FOWARD链是ACCEPT状态：

$ iptables -nvL

$ iptables -P FORWARD ACCEPT

添加iptables转发规则，对所有源地址（openvpn为客户端分配的地址）为10.8.0.0/24的数据包转发后进行源地址转换，伪装成openvpn服务器内网地址192.168.1.2，这样VPN客户端就可以访问服务器内网的其他机器了。

$ iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o em1 -j SNAT --to-source 192.168.1.2

贴一下我的iptables表：

# Generated by iptables-save v1.4.7 on Wed Jan 30 10:50:41 2019
*nat
:PREROUTING ACCEPT [511307:27018662]
:POSTROUTING ACCEPT [0:0]
:OUTPUT ACCEPT [8863045:542441750]
-A POSTROUTING -j MASQUERADE 
-A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE 
COMMIT
# Completed on Wed Jan 30 10:50:41 2019
# Generated by iptables-save v1.4.7 on Wed Jan 30 10:50:41 2019
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [8105799:4491852599]
:OUTPUT ACCEPT [579627360:226177092815]
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT 
-A INPUT -p icmp -j ACCEPT 
-A INPUT -i lo -j ACCEPT 
-A INPUT -p udp -m state --state NEW -m udp --dport 1194 -j ACCEPT 
-A INPUT -p tcp -m tcp --dport 1194 -j ACCEPT 
-A INPUT -p udp -m udp --dport 1194 -j ACCEPT 
-A INPUT -j REJECT --reject-with icmp-host-prohibited 
COMMIT
# Completed on Wed Jan 30 10:50:41 2019

创建openvpn的systemd unit文件：

cat > /etc/systemd/system/openvpn.service <<EOF
[Unit]
Description=openvpn
After=network.target

[Service]
EnvironmentFile=-/etc/openvpn/openvpn
ExecStart=/usr/local/openvpn/sbin/openvpn \
       --config /etc/openvpn/server.conf
Restart=on-failure
Type=simple
LimitNOFILE=65536

[Install]
WantedBy=multi-user.target
EOF

启动并设置为开机启动：

$ systemctl start openvpn
$ systemctl enable openvpn

查看端口监听：

$ netstat -nltp | grep 1194
tcp        0      0 192.168.1.2:1194        0.0.0.0:*                           88462/openvpn

4.客户端连接测试

从这里下载OPENVPN的windows客户端，安装完成后。将以下证书和秘钥文件拷贝到安装目录中C:\Program Files\OpenVPN\config：

ca.crt
client.crt
client.key
ta.key

在这个目录下创建客户端的配置文件client.ovpn：

client
dev tun
proto tcp
remote xxx.xxx.xxx.xxx 11194
resolv-retry infinite
nobind
persist-key
persist-tun

ca ca.crt
cert client.crt
key client.key
remote-cert-tls server
tls-auth ta.key 1
cipher AES-256-CBC

comp-lzo
verb 3

其中 xxx.xxx.xxx.xxx 11194是外网IP和端口映射到了内网服务器的192.168.1.2 1194上。

接下来连接测试即可。