====== Создание туннеля IPIP ======

  * https://wiki.linuxfoundation.org/networking/tunneling#ipip-tunnels
  * http://blog.rts-mirea.msk.ru/туннель-ipip-между-двумя-linux/
  * https://adminbook.click/centos7-nastrojka-ipip-tunnelya-za-5-minut/
  * https://blog.sbolshakov.ru/5-1-tunnel-basic/
  * https://sites.google.com/site/suminknowledgebase/linux-knowledge-base/howtoestablishipiptunnelonlinux
  * http://netwild.ru/linuxipip/
  * https://wiki.linuxfoundation.org/networking/tunneling#manual-configuration-example