首先，推荐跑下面的脚本：
https://github.com/BoizZ/PPTP-L2TP-IPSec-VPN-auto-installation-script-for-CentOS-7
这个脚本将pptp l2tp ipsec都按照，并且配置好，当然很多配置不准确
跑脚本的时候配置好ip规划，PPsk共享秘钥（这个后面客户端连接需要用到） 用户名 ，密码 （后面连接都需要用到）
PSK共享秘钥在/etc/ipsec.secrets可以找到和配置
用户名密码在/etc/ppp/chap-secrets 可以找到配置
下面的简单修改流程：
vim /etc/ipsec.conf
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=47.52.219.118 #这里要写外网ip
leftid=47.52.219.118 #id随便填
leftprotoport=17/1701 #端口
right=%any
rightprotoport=17/%any
dpddelay=40
dpdtimeout=130
dpdaction=clear
leftnexthop=%defaultroute
rightnexthop=%defaultroute
ike=3des-sha1,aes-sha1,aes256-sha1,aes256-sha2_256
phase2alg=3des-sha1,aes-sha1,aes256-sha1,aes256-sha2_256
sha2-truncbug=yes
vim /etc/xl2tpd/xl2tpd.conf
[global] ; ipsec saref = yes listen-addr = 外网ip auth file = /etc/ppp/chap-secrets (用户名密码文件） port = 1701 [lns default] ip range = 10.81.24.100-10.81.24.199 （这个根据自己的内网网段和需要的ip数配置) local ip = 10.81.24.1 (分配给自己的ip) refuse chap = yes refuse pap = yes require authentication = yes name = L2TPVPN ppp debug = yes pppoptfile = /etc/ppp/options.xl2tpd 这里有xl2tpd的一些配置 length bit = yes
vim /etc/ppp/options.xl2tpd
#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 #这几个注释的是新的配置里面没有，原来有的，注释掉就正常了 #lock hide-password #modem debug name l2tpd proxyarp lcp-echo-interval 30 lcp-echo-failure 4 mtu 1400 noccp connect-delay 5000
vim /etc/pptpd.conf
#ppp /usr/sbin/pppd option /etc/ppp/options.pptpd pptpd的一些配置 #debug # stimeout 10 #noipparam logwtmp #vrf test #bcrelay eth1 #delegate #connections 100 localip 10.81.24.2 remoteip 10.81.24.200-254
系统配置/etc/sysctl.conf文件：
net.ipv4.ip_forward = 1 net.ipv4.conf.all.rp_filter = 0 net.ipv4.conf.default.rp_filter = 0 net.ipv4.conf.eth1.rp_filter = 0 这个允许转发的接口要配置好 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
防火墙配置
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>
执行命令：
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
开机启动设置：
systemctl enable pptpd ipsec xl2tpd systemctl restart pptpd ipsec xl2tpd
ipsec检查：全部ok ，碰到不是ok的，就看报错来解决，很多配置以及去掉了 会报错
Verifying installed system and configuration files
Version check and ipsec on-path [OK]
Libreswan 3.25 (netkey) on 3.10.0-514.26.2.el7.x86_64
Checking for IPsec support in kernel [OK]
NETKEY: Testing XFRM related proc values
ICMP default/send_redirects [OK]
ICMP default/accept_redirects [OK]
XFRM larval drop [OK]
Pluto ipsec.conf syntax [OK]
Two or more interfaces found, checking IP forwarding [OK]
Checking rp_filter [OK]
Checking that pluto is running [OK]
Pluto listening for IKE on udp 500 [OK]
Pluto listening for IKE/NAT-T on udp 4500 [OK]
Pluto ipsec.secret syntax [OK]
Checking 'ip' command [OK]
Checking 'iptables' command [OK]
Checking 'prelink' command does not interfere with FIPS [OK]
Checking for obsolete ipsec.conf options [OK]