现象
虚拟机配置网卡报错，能连一段时间，然后网卡会宕掉
使用ifup/ifdown/systemctl status/restart network报错
connect: Network is unreachable
Failed to start LSB: Bring up/down networking
Error: Connection activation failed: IP configuration could not be reserved(no available address, timeout, etc.)
尝试使用手动配置试试，网卡正常起来
ifconfig eth0 1.1.1.71 netmask 255.255.255.0 broadcast 1.1.1.255
route add default gw 1.1.1.1