[root@localhost ~]# docker build -t test1 .
...省略...
WARNING: IPv4 forwarding is disabled. Networking will not work.
error:xxxxxxx
...
解決辦法：
在宿主機上面執行：
# net.ipv4.ip_forward=1 >> /usr/lib/sysctl.d/00-system.conf
重啓network和docker服務
# systemctl restart network && systemctl restart docker
成功解決！！