https://libreswan.org/wiki/VPN_server_for_remote_clients_using_IKEv1_XAUTH_with_PSK
https://blog.csdn.net/s2603898260
https://blog.csdn.net/s2603898260/article/details/112975141
https://blog.csdn.net/s2603898260/category_9943778.html
https://blog.csdn.net/s2603898260/article/details/110018251
https://blog.csdn.net/s2603898260/article/details/105831370
https://blog.csdn.net/rtmdk/article/details/77716863
https://blog.csdn.net/u013920085/article/details/50550983
https://juejin.cn/post/7105407021825933349
https://juejin.cn/post/7105407021825933349
https://zhuanlan.zhihu.com/p/100410283
[IPSec 基本原理] (https://blog.csdn.net/qq_38265137/article/details/89423551)
IP 安全与 IPsec 协议,实验A :使用Strongswan 建立两台 PC 间安全通信
Test ikev1/xauth-id-psk-config
VPN server for remote clients using IKEv1 XAUTH with PSK