L2TP是一种工业标准的Internet隧道协议，功能大致和PPTP协议类似，比如同样可以对网络数据流进行加密。不过也有不同之处，比如PPTP要求网络为IP网络，L2TP要求面向数据包的点对点连接；PPTP使用单一隧道，L2TP使用多隧道；L2TP提供包头压缩、隧道验证，而PPTP不支持。本文来介绍如何搭建L2TP。
1.先看看你的主机是否支持pptp，返回结果为yes就表示通过
modprobe ppp-compress-18 && echo yes
2.是否开启了TUN
有的虚拟机主机需要开启，返回结果为cat: /dev/net/tun: File descriptor in bad state。就表示通过。
cat /dev/net/tun
3.更新一下再安装
yum install update yum update -y
4.安装EPEL源
yum install -y epel-release
5.安装xl2tpd和libreswan
yum install -y xl2tpd libreswan lsof
6.编辑xl2tpd配置文件
vim /etc/xl2tpd/xl2tpd.conf
修改内容如下：
[global] [lns default] ip range = 172.100.1.100-172.100.1.150 #分配给客户端的地址池 local ip = 172.100.1.1 require chap = yes refuse pap = yes require authentication = yes name = LinuxVPNserver ppp debug = yes pppoptfile = /etc/ppp/options.xl2tpd length bit = yes
7.编辑pppoptfile文件
vim /etc/ppp/options.xl2tpd
修改内容如下：
ipcp-accept-local ipcp-accept-remote ms-dns 8.8.8.8 ms-dns 209.244.0.3 ms-dns 208.67.222.222 name xl2tpd #noccp auth crtscts idle 1800 mtu 1410 #第一次配置不建议设置mtu，mru，否则可能789错误 mru 1410 nodefaultroute debug lock proxyarp connect-delay 5000 refuse-pap refuse-chap refuse-mschap require-mschap-v2 persist logfile /var/log/xl2tpd.log
8.编辑ipsec配置文件
vim /etc/ipsec.confconfig setup protostack=netkey dumpdir=/var/run/pluto/ virtual_private=%v4:10.0.0.0/8,%v4:172.100.0.0/12,%v4:25.0.0.0/8,%v4:100.64.0.0/10,%v6:fd00::/8,%v6:fe80::/10 include /etc/ipsec.d/*.conf
9.编辑include的conn文件
vim /etc/ipsec.d/l2tp-ipsec.conf
修改内容如下：
conn L2TP-PSK-NAT rightsubnet=0.0.0.0/0 dpddelay=10 dpdtimeout=20 dpdaction=clear forceencaps=yes 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=192.168.0.17 #service/VPS的外网地址，某些vps只有eth0一块网卡的， #就填内网地址，内核开启nat转发就可以了， #CentOS7以下的用iptables定义转发规则 leftprotoport=17/1701 right=%any rightprotoport=17/%any
10.设置用户名密码
vim /etc/ppp/chap-secrets
修改内容：
vpnuser * pass * 说明：用户名[空格]service[空格]密码[空格]指定IP
11.设置PSK
vim /etc/ipsec.d/default.secrets: PSK "testvpn"
12.CentOS7防火墙设置
firewall-cmd --permanent --add-service=ipsec firewall-cmd --permanent --add-port=1701/udp firewall-cmd --permanent --add-port=4500/udp firewall-cmd --permanent --add-masquerade firewall-cmd --reload
13.IP_FORWARD 设置
vim /etc/sysctl.d/60-sysctl_ipsec.confnet.ipv4.ip_forward = 1 net.ipv4.conf.all.accept_redirects = 0 net.ipv4.conf.all.rp_filter = 0 net.ipv4.conf.all.send_redirects = 0 net.ipv4.conf.default.accept_redirects = 0 net.ipv4.conf.default.rp_filter = 0 net.ipv4.conf.default.send_redirects = 0 net.ipv4.conf.eth0.accept_redirects = 0 net.ipv4.conf.eth0.rp_filter = 0 net.ipv4.conf.eth0.send_redirects = 0 net.ipv4.conf.eth1.accept_redirects = 0 net.ipv4.conf.eth1.rp_filter = 0 net.ipv4.conf.eth1.send_redirects = 0 net.ipv4.conf.eth2.accept_redirects = 0 net.ipv4.conf.eth2.rp_filter = 0 net.ipv4.conf.eth2.send_redirects = 0 net.ipv4.conf.ip_vti0.accept_redirects = 0 net.ipv4.conf.ip_vti0.rp_filter = 0 net.ipv4.conf.ip_vti0.send_redirects = 0 net.ipv4.conf.lo.accept_redirects = 0 net.ipv4.conf.lo.rp_filter = 0 net.ipv4.conf.lo.send_redirects = 0 net.ipv4.conf.ppp0.accept_redirects = 0 net.ipv4.conf.ppp0.rp_filter = 0 net.ipv4.conf.ppp0.send_redirects = 0
重启生效
systemctl restart network
13.ipsec启动&检查
systemctl enable ipsec systemctl restart ipsec
检查：ipsec verify
正常输出：
Verifying installed system and configuration files Version check and ipsec on-path [OK] Libreswan 3.15 (netkey) on 3.10.0-123.13.2.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] Hardware random device [N/A] 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 FIPSChecking for obsolete ipsec.conf options [OK] Opportunistic Encryption [DISABLED]
14.xl2tpd启动
systemctl enable xl2tpd systemctl restart xl2tpd
15.Windows连接
Windows连接，需要修改注册表键值（据说可以不用修改，但是我的不修改的话，一直789，log无显示）
原文来自：https://www.linuxprobe.com/centos7-install-l2tp.html
Ronny 于 2018-03-03 22:59:35发表:
CentOS7 搭建L2TP