本文以CentOS 6 作为OpenVPN服务器，WIN XP及WIN 7作为客户端操作系统。以下内容大量借鉴了pcman大侠的文章。在此基础上，老熊又根据实际经验改写了一些配置选项。
先说服务器端
1. 安装openvpn
openvpn不在centos默认的yum安装源内。需要先安装Fedora的EPEL源。
rpm -Uvh http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-7.noarch.rpm yum install openvpn -y
其他更多软件包来源，请看EPEL、Remi、RPMForge、RPMFusion安装介绍
2. 初始化
初始化主要是配置openvpn的config文件，并设置openvpn自动启动。
复制配置文件的样本到/etc/openvpn目录下。
[root@esojourn.org ~]# cp /usr/share/doc/openvpn-2.2.2/sample-config-files/server.conf /etc/openvpn/ [root@esojourn.org ~]#
编辑/etc/openvpn/server.conf，修改如下配置，
使用TCP协议来进行访问。打开gateway，推送dns等。
################################################# # Sample OpenVPN 2.0 config file for # # multi-client server. # # # # This file is for the server side # # of a many-clients <-> one-server # # OpenVPN configuration. # # # # OpenVPN also supports # # single-machine <-> single-machine # # configurations (See the Examples page # # on the web site for more info). # # # # This config should work on Windows # # or Linux/BSD systems. Remember on # # Windows to quote pathnames and use # # double backslashes, e.g.: # # "C:\\Program Files\\OpenVPN\\config\\foo.key" # # # # Comments are preceded with '#' or ';' # ################################################# # Which local IP address should OpenVPN # listen on? (optional) ;local a.b.c.d # Which TCP/UDP port should OpenVPN listen on? # If you want to run multiple OpenVPN instances # on the same machine, use a different port # number for each one. You will need to # open up this port on your firewall. port 1194 # TCP or UDP server? proto tcp # proto udp # "dev tun" will create a routed IP tunnel, # "dev tap" will create an ethernet tunnel. # Use "dev tap0" if you are ethernet bridging # and have precreated a tap0 virtual interface # and bridged it with your ethernet interface. # If you want to control access policies # over the VPN, you must create firewall # rules for the the TUN/TAP interface. # On non-Windows systems, you can give # an explicit unit number, such as tun0. # On Windows, use "dev-node" for this. # On most systems, the VPN will not function # unless you partially or fully disable # the firewall for the TUN/TAP interface. ;dev tap dev tun # Windows needs the TAP-Win32 adapter name # from the Network Connections panel if you # have more than one. On XP SP2 or higher, # you may need to selectively disable the # Windows firewall for the TAP adapter. # Non-Windows systems usually don't need this. ;dev-node MyTap # SSL/TLS root certificate (ca), certificate # (cert), and private key (key). Each client # and the server must have their own cert and # key file. The server and all clients will # use the same ca file. # # See the "easy-rsa" directory for a series # of scripts for generating RSA certificates # and private keys. Remember to use # a unique Common Name for the server # and each of the client certificates. # # Any X509 key management system can be used. # OpenVPN can also use a PKCS #12 formatted key file # (see "pkcs12" directive in man page). ca ca.crt cert server.crt key server.key # This file should be kept secret # Diffie hellman parameters. # Generate your own with: # openssl dhparam -out dh1024.pem 1024 # Substitute 2048 for 1024 if you are using # 2048 bit keys. dh dh1024.pem # Configure server mode and supply a VPN subnet # for OpenVPN to draw client addresses from. # The server will take 10.8.0.1 for itself, # the rest will be made available to clients. # Each client will be able to reach the server # on 10.8.0.1. Comment this line out if you are # ethernet bridging. See the man page for more info. server 10.8.0.0 255.255.255.0 # Maintain a record of client <-> virtual IP address # associations in this file. If OpenVPN goes down or # is restarted, reconnecting clients can be assigned # the same virtual IP address from the pool that was # previously assigned. ifconfig-pool-persist ipp.txt # Configure server mode for ethernet bridging. # You must first use your OS's bridging capability # to bridge the TAP interface with the ethernet # NIC interface. Then you must manually set the # IP/netmask on the bridge interface, here we # assume 10.8.0.4/255.255.255.0. Finally we # must set aside an IP range in this subnet # (start=10.8.0.50 end=10.8.0.100) to allocate # to connecting clients. Leave this line commented # out unless you are ethernet bridging. ;server-bridge 10.8.0.4 255.255.255.0 10.8.0.50 10.8.0.100 # Configure server mode for ethernet bridging # using a DHCP-proxy, where clients talk # to the OpenVPN server-side DHCP server # to receive their IP address allocation # and DNS server addresses. You must first use # your OS's bridging capability to bridge the TAP # interface with the ethernet NIC interface. # Note: this mode only works on clients (such as # Windows), where the client-side TAP adapter is # bound to a DHCP client. ;server-bridge # Push routes to the client to allow it # to reach other private subnets behind # the server. Remember that these # private subnets will also need # to know to route the OpenVPN client # address pool (10.8.0.0/255.255.255.0) # back to the OpenVPN server. push "route 10.8.0.0 255.255.255.0" push "route 192.168.5.0 255.255.255.0" ;push "route 192.168.20.0 255.255.255.0" # To assign specific IP addresses to specific # clients or if a connecting client has a private # subnet behind it that should also have VPN access, # use the subdirectory "ccd" for client-specific # configuration files (see man page for more info). # EXAMPLE: Suppose the client # having the certificate common name "Thelonious" # also has a small subnet behind his connecting # machine, such as 192.168.40.128/255.255.255.248. # First, uncomment out these lines: ;client-config-dir ccd ;route 192.168.40.128 255.255.255.248 # Then create a file ccd/Thelonious with this line: # iroute 192.168.40.128 255.255.255.248 # This will allow Thelonious' private subnet to # access the VPN. This example will only work # if you are routing, not bridging, i.e. you are # using "dev tun" and "server" directives. # EXAMPLE: Suppose you want to give # Thelonious a fixed VPN IP address of 10.9.0.1. # First uncomment out these lines: ;client-config-dir ccd ;route 10.9.0.0 255.255.255.252 # Then add this line to ccd/Thelonious: # ifconfig-push 10.9.0.1 10.9.0.2 # Suppose that you want to enable different # firewall access policies for different groups # of clients. There are two methods: # (1) Run multiple OpenVPN daemons, one for each # group, and firewall the TUN/TAP interface # for each group/daemon appropriately. # (2) (Advanced) Create a script to dynamically # modify the firewall in response to access # from different clients. See man # page for more info on learn-address script. ;learn-address ./script # If enabled, this directive will configure # all clients to redirect their default # network gateway through the VPN, causing # all IP traffic such as web browsing and # and DNS lookups to go through the VPN # (The OpenVPN server machine may need to NAT # or bridge the TUN/TAP interface to the internet # in order for this to work properly). ;push "redirect-gateway def1 bypass-dhcp" push "redirect-gateway" # Certain Windows-specific network settings # can be pushed to clients, such as DNS # or WINS server addresses. CAVEAT: # http://openvpn.net/faq.html#dhcpcaveats # The addresses below refer to the public # DNS servers provided by opendns.com. push "dhcp-option DNS 60.195.250.225" push "dhcp-option DNS 8.8.8.8" # Uncomment this directive to allow different # clients to be able to "see" each other. # By default, clients will only see the server. # To force clients to only see the server, you # will also need to appropriately firewall the # server's TUN/TAP interface. ;client-to-client # Uncomment this directive if multiple clients # might connect with the same certificate/key # files or common names. This is recommended # only for testing purposes. For production use, # each client should have its own certificate/key # pair. # # IF YOU HAVE NOT GENERATED INDIVIDUAL # CERTIFICATE/KEY PAIRS FOR EACH CLIENT, # EACH HAVING ITS OWN UNIQUE "COMMON NAME", # UNCOMMENT THIS LINE OUT. ;duplicate-cn # The keepalive directive causes ping-like # messages to be sent back and forth over # the link so that each side knows when # the other side has gone down. # Ping every 10 seconds, assume that remote # peer is down if no ping received during # a 120 second time period. keepalive 10 120 # For extra security beyond that provided # by SSL/TLS, create an "HMAC firewall" # to help block DoS attacks and UDP port flooding. # # Generate with: # openvpn --genkey --secret ta.key # # The server and each client must have # a copy of this key. # The second parameter should be '0' # on the server and '1' on the clients. ;tls-auth ta.key 0 # This file is secret # Select a cryptographic cipher. # This config item must be copied to # the client config file as well. ;cipher BF-CBC # Blowfish (default) ;cipher AES-128-CBC # AES ;cipher DES-EDE3-CBC # Triple-DES # Enable compression on the VPN link. # If you enable it here, you must also # enable it in the client config file. comp-lzo # The maximum number of concurrently connected # clients we want to allow. ;max-clients 100 # It's a good idea to reduce the OpenVPN # daemon's privileges after initialization. # # You can uncomment this out on # non-Windows systems. ;user nobody ;group nobody # The persist options will try to avoid # accessing certain resources on restart # that may no longer be accessible because # of the privilege downgrade. persist-key persist-tun # Output a short status file showing # current connections, truncated # and rewritten every minute. status openvpn-status.log # By default, log messages will go to the syslog (or # on Windows, if running as a service, they will go to # the "\Program Files\OpenVPN\log" directory). # Use log or log-append to override this default. # "log" will truncate the log file on OpenVPN startup, # while "log-append" will append to it. Use one # or the other (but not both). ;log openvpn.log ;log-append openvpn.log # Set the appropriate level of log # file verbosity. # # 0 is silent, except for fatal errors # 4 is reasonable for general usage # 5 and 6 can help to debug connection problems # 9 is extremely verbose verb 3 # Silence repeating messages. At most 20 # sequential messages of the same message # category will be output to the log. ;mute 20
vi /etc/sysctl.conf。在最下面加入如下内容。
如果是RHEL5，建议把以#屏蔽的选项全打开。是照某公司久经考验的文档写的。
据神秘的老熊分享，在RHEL6下应该把那一堆参数屏蔽。我在centos 6下，已经照此配置测试通过了。
# Added for openvpn. esojourn.org net.ipv6.conf.eth0.forwarding = 1 net.ipv6.conf.default.forwarding = 1 net.ipv6.conf.all.forwarding = 1 net.ipv6.conf.lo.forwarding = 1 # net.ipv4.conf.tun0.mc_forwarding = 1 # net.ipv4.conf.tun0.forwarding = 1 # net.ipv4.conf.eth0.mc_forwarding = 1 net.ipv4.conf.eth0.forwarding = 1 # net.ipv4.conf.lo.mc_forwarding = 1 net.ipv4.conf.lo.forwarding = 1 # net.ipv4.conf.default.mc_forwarding = 1 net.ipv4.conf.default.forwarding = 1 # net.ipv4.conf.all.mc_forwarding = 1 net.ipv4.conf.all.forwarding = 1 # net.ipv4.ip_forward = 1
sysctl -p使规则生效
vi /etc/sysconfig/iptables 在最上面加下nat表
诸位新手、准新手们，千万别用天杀的setup或者system-config-firewall来配防火墙了。
血泪史啊，不多解释了。好好学基本功吧。我也在学习中。
*nat :PREROUTING ACCEPT [0:0] :POSTROUTING ACCEPT [0:0] :OUTPUT ACCEPT [0:0] -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE COMMIT
然后在下面*filter表里，最后一条拒绝规则前面，加上
-A FORWARD -d 10.8.0.0/24 -j ACCEPT -A FORWARD -s 10.8.0.0/24 -j ACCEPT
service iptables restart
3. 生成服务器端证书
生成服务器端证书主要有如下几个步骤：
1． 设置环境变量
2． 生成ca文件
3． 生成cert/key文件
4． 生成dh文件
进入openvpn的对应安装目录。将所有脚本设置为可执行属性
cd /usr/share/doc/openvpn-2.2.2/easy-rsa chmod 700 build*
vi /etc/bashrc，在最下面加上环境变量
# Add for openvpn export KEY_CONFIG=/usr/share/doc/openvpn-2.2.2/easy-rsa/openssl.cnf export KEY_DIR=/usr/share/doc/openvpn-2.2.2/easy-rsa/keys export KEY_SIZE=1024 export KEY_COUNTRY=CN export KEY_PROVINCE=BJ export KEY_CITY=BJ export KEY_ORG="www.esojourn.org" export KEY_EMAIL="[email]abc@esojourn.org[/email]"
建立存放key的目录 mkdir cd /usr/share/doc/openvpn-2.2.2/easy-rsa/keys
通过clean-all生成serial和index.txt
chmod 700 clean-all ./clean-all
开始生成ca文件。需要注意的是，ca一旦生成就不能更换了，否则所有key都会失效，要重新签署。
[root@esojourn.org /usr/share/doc/openvpn-2.2.2/easy-rsa]# ./build-ca Generating a 1024 bit RSA private key ..............................................................................................++++++ ..........++++++ writing new private key to 'ca.key' ----- You are about to be asked to enter information that will be incorporated into your certificate request. What you are about to enter is what is called a Distinguished Name or a DN. There are quite a few fields but you can leave some blank For some fields there will be a default value, If you enter '.', the field will be left blank. ----- Country Name (2 letter code) [CN]: State or Province Name (full name) [BJ]: Locality Name (eg, city) [BJ]: Organization Name (eg, company) [esojourn.org]: Organizational Unit Name (eg, section) []: Common Name (eg, your name or your server's hostname) []: Email Address [[email]pcman@esojourn.org[/email]]: [root@esojourn.org /usr/share/doc/openvpn-2.2.2/easy-rsa]#
生成server端key和crt文件。注意，其中Common Name项目必须填写，其余项目可直接按回车使用环境变量预先设置的默认值。
[root@esojourn.org /usr/share/doc/openvpn-2.2.2/easy-rsa]# ./build-key-server server Generating a 1024 bit RSA private key ............++++++ ..........++++++ writing new private key to 'server.key' ----- You are about to be asked to enter information that will be incorporated into your certificate request. What you are about to enter is what is called a Distinguished Name or a DN. There are quite a few fields but you can leave some blank For some fields there will be a default value, If you enter '.', the field will be left blank. ----- Country Name (2 letter code) [CN]: State or Province Name (full name) [BJ]: Locality Name (eg, city) [BJ]: Organization Name (eg, company) [esojourn.org]: Organizational Unit Name (eg, section) []: Common Name (eg, your name or your server's hostname) []:openvpn.esojourn.org Email Address [[email]pcman@esojourn.org[/email]]: Please enter the following 'extra' attributes to be sent with your certificate request A challenge password []: An optional company name []: Using configuration from /usr/share/doc/openvpn-2.2.2/easy-rsa/openssl.cnf Check that the request matches the signature Signature ok The Subject's Distinguished Name is as follows countryName :PRINTABLE:'CN' stateOrProvinceName :PRINTABLE:'BJ' localityName :PRINTABLE:'BJ' organizationName :PRINTABLE:'esojourn.org' commonName :PRINTABLE:'openvpn.esojourn.org' emailAddress :IA5STRING:'[email]pcman@esojourn.org[/email]' Certificate is to be certified until Jul 13 16:17:39 2017 GMT (3650 days) Sign the certificate? [y/n]:y 1 out of 1 certificate requests certified, commit? [y/n]y Write out database with 1 new entries Data Base Updated [root@esojourn.org /usr/share/doc/openvpn-2.2.2/easy-rsa]#
证书生成完毕。生成dh文件。
[root@esojourn.org /usr/share/doc/openvpn-2.2.2/easy-rsa]# ./build-dh Generating DH parameters, 1024 bit long safe prime, generator 2 This is going to take a long time ..............................+........................................................................................................+.......................................................+.........................................................
现在将刚才生成的证书和配置文件复制到相应目录下。
[root@esojourn.org /usr/share/doc/openvpn-2.2.2/easy-rsa]# cp keys/ca.crt /etc/openvpn/ [root@esojourn.org /usr/share/doc/openvpn-2.2.2/easy-rsa]# cp keys/server.crt /etc/openvpn/ [root@esojourn.org /usr/share/doc/openvpn-2.2.2/easy-rsa]# cp keys/server.key /etc/openvpn/ [root@esojourn.org /usr/share/doc/openvpn-2.2.2/easy-rsa]# cp keys/dh1024.pem /etc/openvpn/ sysctl -p
4. 创建新的客户端
openvpn服务器配置好之后，新的客户端还不能立刻连接进来，需要为客户端分别创建属于自己的ssl证书方可。创建的方式如下：
进入openvpn的对应安装目录。生成证书文件。注意，在提示输入CommonName的时候，必须输入唯一一个用户名名字或者域名，以和其他的用户证书相区别。
cd /usr/share/doc/openvpn-2.2.2/easy-rsa[root@esojourn.org /usr/share/doc/openvpn-2.2.2/easy-rsa]# ./build-key client Generating a 1024 bit RSA private key ....++++++ .......++++++ writing new private key to 'client.key' ----- You are about to be asked to enter information that will be incorporated into your certificate request. What you are about to enter is what is called a Distinguished Name or a DN. There are quite a few fields but you can leave some blank For some fields there will be a default value, If you enter '.', the field will be left blank. ----- Country Name (2 letter code) [CN]: State or Province Name (full name) [BJ]: Locality Name (eg, city) [BJ]: Organization Name (eg, company) [esojourn.org]: Organizational Unit Name (eg, section) []: Common Name (eg, your name or your server's hostname) []:pcman Email Address [[email]pcman@esojourn.org[/email]]: Please enter the following 'extra' attributes to be sent with your certificate request A challenge password []: An optional company name []: Using configuration from /usr/share/doc/openvpn-2.2.2/easy-rsa/openssl.cnf Check that the request matches the signature Signature ok The Subject's Distinguished Name is as follows countryName :PRINTABLE:'CN' stateOrProvinceName :PRINTABLE:'BJ' localityName :PRINTABLE:'BJ' organizationName :PRINTABLE:'esojourn.org' commonName :PRINTABLE:'pcman' emailAddress :IA5STRING:'[email]pcman@esojourn.org[/email]' Certificate is to be certified until Jul 13 17:08:27 2017 GMT (3650 days) Sign the certificate? [y/n]:y 1 out of 1 certificate requests certified, commit? [y/n]y Write out database with 1 new entries Data Base Updated [root@esojourn.org /usr/share/doc/openvpn-2.2.2/easy-rsa]#
生成完毕。在keys目录下即可找到client.key和client.crt。
下面再来看看客户端
5. 客户端的下载安装
官网下载 http://openvpn.net/index.php/download.html
Windows Installer v2.2.2：http://swupdate.openvpn.org/community/releases/openvpn-2.2.2-install.exe
安装时所有组件全装。安装时会装上一个虚拟网卡，系统可能会提示不兼容，不安全什么的。不用管，继续确定安装即可。
6. 初始化
OpenVPN的数据传输过程是基于OpenSSL安全加密的，通信的双方：VPN服务器端、VPN客户端都需要IP安全证书，否则无法建立连接。IP证书也是建立连接的必须条件，基于OpenVPN的VPN建立是没有传统密码验证的。下边配置证书。
首先获得证书。把刚才升成的客户端证书拷过来。3个文件! ca.crt, client.crt, client.key。
另外新建一个esojourn.org.ovpn的文件，用于客户端配置。包含证书文件名、地址等相应参数。ca.crt是全局的CA证书，而client.crt和client.key则是颁发给每个人的个人证书。每个人的个人证书文件不一样，而另外两个文件则一样。
ovpn文件如下，其他ca ca.crt，cert client.crt，key client.key，根据自己的文件名改。
############################################## # Sample client-side OpenVPN 2.0 config file # # for connecting to multi-client server. # # # # This configuration can be used by multiple # # clients, however each client should have # # its own cert and key files. # # # # On Windows, you might want to rename this # # file so it has a .ovpn extension # ############################################## # Specify that we are a client and that we # will be pulling certain config file directives # from the server. client # Use the same setting as you are using on # the server. # On most systems, the VPN will not function # unless you partially or fully disable # the firewall for the TUN/TAP interface. ;dev tap dev tun # Windows needs the TAP-Win32 adapter name # from the Network Connections panel # if you have more than one. On XP SP2, # you may need to disable the firewall # for the TAP adapter. ;dev-node MyTap # Are we connecting to a TCP or # UDP server? Use the same setting as # on the server. proto tcp # proto udp # The hostname/IP and port of the server. # You can have multiple remote entries # to load balance between the servers. remote www.esojourn.org 1194 ;remote my-server-2 1194 # Choose a random host from the remote # list for load-balancing. Otherwise # try hosts in the order specified. ;remote-random # Keep trying indefinitely to resolve the # host name of the OpenVPN server. Very useful # on machines which are not permanently connected # to the internet such as laptops. resolv-retry infinite # Most clients don't need to bind to # a specific local port number. nobind # Downgrade privileges after initialization (non-Windows only) ;user nobody ;group nobody # Try to preserve some state across restarts. persist-key persist-tun # If you are connecting through an # HTTP proxy to reach the actual OpenVPN # server, put the proxy server/IP and # port number here. See the man page # if your proxy server requires # authentication. ;http-proxy-retry # retry on connection failures ;http-proxy [proxy server] [proxy port #] # Wireless networks often produce a lot # of duplicate packets. Set this flag # to silence duplicate packet warnings. ;mute-replay-warnings # SSL/TLS parms. # See the server config file for more # description. It's best to use # a separate .crt/.key file pair # for each client. A single ca # file can be used for all clients. ca ca.crt cert client.crt key client.key # Verify server certificate by checking # that the certicate has the nsCertType # field set to "server". This is an # important precaution to protect against # a potential attack discussed here: # http://openvpn.net/howto.html#mitm # # To use this feature, you will need to generate # your server certificates with the nsCertType # field set to "server". The build-key-server # script in the easy-rsa folder will do this. ns-cert-type server # If a tls-auth key is used on the server # then every client must also have the key. ;tls-auth ta.key 1 # Select a cryptographic cipher. # If the cipher option is used on the server # then you must also specify it here. ;cipher x # Enable compression on the VPN link. # Don't enable this unless it is also # enabled in the server config file. comp-lzo # Set log file verbosity. verb 3 # Silence repeating messages ;mute 20
将这几个文件全部复制到OpenVPN的安装目录下的“config”目录中。如：C:\Program Files\OpenVPN\config
配置完成。