在百度搜索了很多关于CentOS7搭建VPN的教程，但是有很多走不完全套的，因此浪费了很多时间，在这里我把查到能走通的教程整理了一遍，分享给大家。
更新组件
整个安装过程不用经过编译，组件都是在yum中下载，首先我们更新一下所有组件：
yum update -y
这里有个地方需要注意的是：有些主机的硬件并不支持最新内核，因此在不确定的情况下就不要升级内核了，用以下的命令：
yum –exclude=kernel* update -y
更新需要较长时间，请耐心等待。
非常重要的小插曲
撰写这篇文章并且共享出来，主要是为了能和大家互相学习和交流，但是正在看这篇文章的不乏一些现在就有自己的服务器或VPS，急着马上搭建好一台自己的VPN服务器的同学，如果你是这类同学，请不用心急，因为我制作好了自动运行脚本，脚本的内容和文章内容是一样的，把脚本下载到服务器，运行并配置自己的账号密码、ip和客户端ip即可。
脚本下载地址：https://github.com/BoizZ/PPTP-L2TP-IPSec-VPN-auto-installation-script-for-CentOS-7
运行脚本：sh vpn-script-for-centos7.sh
好，那么希望继续学习的同学请往下看。
安装epel源
为什么要安装epel源呢？是因为必要组件xl2tpd在基础的yum源里面是没有的。
yum install epel-release -y
安装依赖组件
安装完epel源以后就可以直接安装依赖组件了。
yum install -y openswan ppp pptpd xl2tpd wget
修改配置文件
需要等待所有依赖组件安装完成才能执行以下步骤（小标题括号内是文件路径）。
ipsec.conf配置文件（/etc/ipsec.conf）
# /etc/ipsec.conf - Libreswan IPsec configuration file
# This file: /etc/ipsec.conf
#
# Enable when using this configuration file with openswan instead of libreswan
#version 2
#
# Manual: ipsec.conf.5
# basic configuration
config setup
# NAT-TRAVERSAL support,see README.NAT-Traversal
nat_traversal=yes
# exclude networks used on server side by adding %v4:!a.b.c.0/24
virtual_private=%v4:10.0.0.0/8,%v4:192.168.0.0/16,%v4:172.16.0.0/12
# OE is Now off by default. Uncomment and change to on,to enable.
oe=off
# which IPsec stack to use. auto will try netkey,then klips then mast
protostack=netkey
force_keepalive=yes
keep_alive=1800
conn L2TP-PSK-NAT
rightsubnet=vhost:%priv
also=L2TP-PSK-noNAT
conn L2TP-PSK-noNAT
authby=secret
pfs=no
auto=add
keyingtries=3
rekey=no
ikelifetime=8h
keylife=1h
type=transport
left=$serverip
leftid=$serverip
leftprotoport=17/1701
right=%any
rightprotoport=17/%any
dpddelay=40
dpdtimeout=130
dpdaction=clear
# For example connections,see your distribution's documentation directory,# or the documentation which Could be located at
# /usr/share/docs/libreswan-3.*/ or look at https://www.libreswan.org/
#
# There is also a lot of information in the manual page,"man ipsec.conf"
# You may put your configuration (.conf) file in the "/etc/ipsec.d/" directory
# by uncommenting this line
#include /etc/ipsec.d/*.conf
设置预共享密钥配置文件（/etc/ipsec.secrets）
#include /etc/ipsec.d/*.secrets $serverip username PSK password
注解：第二行中username为登录名，password为登录密码
pptpd.conf配置文件(/etc/pptpd.conf)
#ppp /usr/sbin/pppd option /etc/ppp/options.pptpd #debug # stimeout 10 #noipparam logwtmp #vrf test #bcrelay eth1 #delegate #connections 100 localip 10.0.1.2 remoteip 10.0.1.200-254
xl2tpd.conf配置文件(/etc/xl2tpd/xl2tpd.conf)
; ; This is a minimal sample xl2tpd configuration file for use ; with L2TP over IPsec. ; ; The idea is to provide an L2TP daemon to which remote Windows L2TP/IPsec ; clients connect. In this example,the internal (protected) network ; is 192.168.1.0/24. A special IP range within this network is reserved ; for the remote clients: 192.168.1.128/25 ; (i.e. 192.168.1.128 ... 192.168.1.254) ; ; The listen-addr parameter can be used if you want to bind the L2TP daemon ; to a specific IP address instead of to all interfaces. For instance,; you Could bind it to the interface of the internal LAN (e.g. 192.168.1.98 ; in the example below). Yet another IP address (local ip,e.g. 192.168.1.99) ; will be used by xl2tpd as its address on pppx interfaces. [global] ; ipsec saref = yes listen-addr = 104.171.165.91 auth file = /etc/ppp/chap-secrets port = 1701 [lns default] ip range = 10.0.1.100-10.0.1.254 local ip = 10.0.1.1 refuse chap = yes refuse pap = yes require authentication = yes name = L2TPVPN ppp debug = yes pppoptfile = /etc/ppp/options.xl2tpd length bit = yes
options.pptpd配置文件(/etc/ppp/options.pptpd)
# Authentication
name pptpd
#chapms-strip-domain
# Encryption
# BSD licensed ppp-2.4.2 upstream with MPPE only,kernel module ppp_mppe.o
# {{{
refuse-pap
refuse-chap
refuse-mschap
# Require the peer to authenticate itself using MS-CHAPv2 [Microsoft
# Challenge Handshake Authentication Protocol,Version 2] authentication.
require-mschap-v2
# Require MPPE 128-bit encryption
# (note that MPPE requires the use of MSCHAP-V2 during authentication)
require-mppe-128
# }}}
# OpenSSL licensed ppp-2.4.1 fork with MPPE only,kernel module mppe.o
# {{{
#-chap
#-chapms
# Require the peer to authenticate itself using MS-CHAPv2 [Microsoft
# Challenge Handshake Authentication Protocol,Version 2] authentication.
#+chapms-v2
# Require MPPE encryption
# (note that MPPE requires the use of MSCHAP-V2 during authentication)
#mppe-40 # enable either 40-bit or 128-bit,not both
#mppe-128
#mppe-stateless
# }}}
ms-dns 8.8.4.4
ms-dns 8.8.8.8
#ms-wins 10.0.0.3
#ms-wins 10.0.0.4
proxyarp
#10.8.0.100
# Logging
#debug
#dump
lock
nobsdcomp
novj
novjccomp
nologfd
options.xl2tpd配置文件(/etc/ppp/options.xl2tpd)
rm -f /etc/ppp/options.xl2tpd cat >>/etc/ppp/options.xl2tpd<<EOF #require-pap #require-chap #require-mschap ipcp-accept-local ipcp-accept-remote require-mschap-v2 ms-dns 8.8.8.8 ms-dns 8.8.4.4 asyncmap 0 auth crtscts lock hide-password modem debug name l2tpd proxyarp lcp-echo-interval 30 lcp-echo-failure 4 mtu 1400 noccp connect-delay 5000 # To allow authentication against a Windows domain EXAMPLE,and require the # user to be in a group "VPN Users". Requires the samba-winbind package # require-mschap-v2 # plugin winbind.so # ntlm_auth-helper '/usr/bin/ntlm_auth --helper-protocol=ntlm-server-1 --require-membership-of="EXAMPLE\VPN Users"' # You need to join the domain on the server,for example using samba: # http://rootmanager.com/ubuntu-ipsec-l2tp-windows-domain-auth/setting-up-openswan-xl2tpd-with-native-windows-clients-lucid.html
创建chap-secrets配置文件，即用户列表及密码(/etc/ppp/chap-secrets)
# Secrets for authentication using CHAP # client server secret IP addresses username pptpd password * username l2tpd password *
注解：第三第四行中username为登录名，password为登录密码
系统配置
允许IP转发
sysctl -w net.ipv4.ip_forward=1 sysctl -w net.ipv4.conf.all.rp_filter=0 sysctl -w net.ipv4.conf.default.rp_filter=0 sysctl -w net.ipv4.conf.$eth.rp_filter=0 sysctl -w net.ipv4.conf.all.send_redirects=0 sysctl -w net.ipv4.conf.default.send_redirects=0 sysctl -w net.ipv4.conf.all.accept_redirects=0 sysctl -w net.ipv4.conf.default.accept_redirects=0
注解：以上均是命令，复制上去运行即可
也可以修改配置文件(/etc/sysctl.conf)：
net.ipv4.ip_forward = 1 net.ipv4.conf.all.rp_filter = 0 net.ipv4.conf.default.rp_filter = 0 net.ipv4.conf.$eth.rp_filter = 0 net.ipv4.conf.all.send_redirects = 0 net.ipv4.conf.default.send_redirects = 0 net.ipv4.conf.all.accept_redirects = 0 net.ipv4.conf.default.accept_redirects = 0
允许防火墙端口
创建文件/usr/lib/firewalld/services/pptpd.xml并修改：
<?xml version="1.0" encoding="utf-8"?> <service> <short>pptpd</short> <description>PPTP</description> <port protocol="tcp" port="1723"/> </service>
创建文件/usr/lib/firewalld/services/l2tpd.xml并修改：
<?xml version="1.0" encoding="utf-8"?> <service> <short>l2tpd</short> <description>L2TP IPSec</description> <port protocol="udp" port="500"/> <port protocol="udp" port="4500"/> <port protocol="udp" port="1701"/> </service>
初始化并重启防火墙：
firewall-cmd --reload firewall-cmd --permanent --add-service=pptpd firewall-cmd --permanent --add-service=l2tpd firewall-cmd --permanent --add-service=ipsec firewall-cmd --permanent --add-masquerade firewall-cmd --permanent --direct --add-rule ipv4 filter FORWARD 0 -p tcp -i ppp+ -j TCPMSS --syn --set-mss 1356 firewall-cmd --reload
这里是由于CentOS7自带firewall，并且不预装iptables，因此自己也不多此一举去安装了，因为效果都是一样的。
启动并设置开机自启动服务
systemctl enable pptpd ipsec xl2tpd systemctl restart pptpd ipsec xl2tpd
大功告成
最后一步，并且是最重要的一步，当然是连接一下自己刚建好的VPN服务器啦！
现在估计你和我有同样的喜悦，当然如果中间出现什么问题的话，交流区在下方，很乐意大家踊跃参与！