centos7 安装 L2TP服务器
modprobe ppp-compress-18 && echo yes
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
yum install update yum update -y
yum install -y epel-release
yum install -y xl2tpd libreswan lsof
vim /etc/xl2tpd/xl2tpd.conf
修改内容如下：
;
; 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]
listen-addr = 0.0.0.0
;
; requires openswan-2.5.18 or higher - Also does not yet work in combination
; with kernel mode l2tp as present in linux 2.6.23+
ipsec saref = yes
; Use refinfo of 22 if using an SAref kernel patch based on openswan 2.6.35 or
; when using any of the SAref kernel patches for kernels up to 2.6.35.
; saref refinfo = 30
;
; force userspace = yes
;
; debug tunnel = yes
[lns default]
ip range = 172.20.0.20-172.20.0.254
local ip = 172.20.0.1
require chap = yes
refuse pap = yes
require authentication = yes
name = LinuxVPNserver
ppp debug = yes
pppoptfile = /etc/ppp/options.xl2tpd
length bit = yes
vim /etc/ppp/options.xl2tpd
修改内容如下：
ipcp-accept-local
ipcp-accept-remote
ms-dns 223.5.5.5
ms-dns 223.6.6.6
# ms-dns 192.168.1.1
# ms-dns 192.168.1.3
# ms-wins 192.168.1.2
# ms-wins 192.168.1.4
noccp
auth
crtscts
idle 1800
mtu 1410
mru 1410
nodefaultroute
debug
lock
proxyarp
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
8.编辑ipsec配置文件
vim /etc/ipsec.conf
# /etc/ipsec.conf - Libreswan IPsec configuration file
#
# see 'man ipsec.conf' and 'man pluto' for more information
#
# For example configurations and documentation, see https://libreswan.org/wiki/
config setup
# Normally, pluto logs via syslog.
#logfile=/var/log/pluto.log
#
# Do not enable debug options to debug configuration issues!
#
# plutodebug="control parsing"
# plutodebug="all crypt"
plutodebug=none
#
# NAT-TRAVERSAL support
# exclude networks used on server side by adding %v4:!a.b.c.0/24
# It seems that T-Mobile in the US and Rogers/Fido in Canada are
# using 25/8 as "private" address space on their wireless networks.
# This range has never been announced via BGP (at least up to 2015)
nat_traversal=yes
virtual_private=%v4:10.0.0.0/8,%v4:192.168.0.0/16,%v4:172.16.0.0/12,%v4:25.0.0.0/8,%v4:100.64.0.0/10,%v6:fd00::/8,%v6:fe80::/10
# if it exists, include system wide crypto-policy defaults
# include /etc/crypto-policies/back-ends/libreswan.config
# It is best to add your IPsec connections as separate files in /etc/ipsec.d/
include /etc/ipsec.d/*.conf
9.编辑include的conn文件
vim /etc/ipsec.d/l2tp_psk.conf
修改内容如下：
conn L2TP-PSK-NAT
rightsubnet=vhost:%priv
also=L2TP-PSK-noNAT
conn L2TP-PSK-noNAT
authby=secret
pfs=no
auto=add
keyingtries=3
dpddelay=30
dpdtimeout=120
dpdaction=clear
rekey=no
ikelifetime=8h
keylife=1h
type=transport
left=172.31.160.144
leftprotoport=17/1701
right=%any
rightprotoport=17/%any
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
vim /etc/ipsec.d/ipsec.secrets
: PSK "ljp123.cn"
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
vim /etc/sysctl.conf
vm.swappiness = 0
net.ipv4.ip_forward = 1
net.ipv4.neigh.default.gc_stale_time=120
net.ipv4.conf.all.rp_filter=0
net.ipv4.conf.default.rp_filter=0
net.ipv4.conf.default.arp_announce = 2
net.ipv4.conf.all.arp_announce=2
net.ipv4.tcp_max_tw_buckets = 5000
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_max_syn_backlog = 1024
net.ipv4.tcp_synack_retries = 2
net.ipv4.conf.lo.arp_announce=2
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.default.send_redirects = 0
net.ipv4.conf.default.accept_source_route = 0
重启生效
systemctl restart network
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]systemctl enable xl2tpd systemctl restart xl2tpd