如何解决Docker网络已禁用：警告：IPv4转发已禁用网络将无法正常工作
我查看了http://chrisgilmerproj.github.io/ubuntu/network/docker/2013/09/05/ipv4-forwarding- and- docker.html，它帮助我解决了主机上的问题。
net.ipv4.ip_forward=1
然后，我重新启动了网络服务并验证了设置：
[root@pprdespap322 deploy]# systemctl restart network
[root@pprdespap322 deploy]# sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 1
[root@pprdespap322 deploy]# docker run -ti quay.io/coreos/registry ping ci.docker.company.net
PING pprdespap324.corp.company.net (10.137.55.22) 56(84) bytes of data.
64 bytes from pprdespap324.corp.company.net (10.137.55.22): icmp_seq=1 ttl=63 time=0.329 ms
64 bytes from pprdespap324.corp.company.net (10.137.55.22): icmp_seq=2 ttl=63 time=0.306 ms
^C
--- pprdespap324.corp.company.net ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 0.306/0.317/0.329/0.021 ms
现在，所有容器都可以与外界的容器通信！
解决方法
主机中的容器“突然”失去了与外部容器的连接。但是，有些主机刷新了，突然我们遇到了以下情况：
- 主机可以与其他主机通信。
- 主机中运行的容器无法与其他主机通信。
这是一个例子：
[root@pprdespap322 deploy]# ping ci.docker.company.net
PING pprdespap324.corp.company.net (10.137.55.22) 56(84) bytes of data.
64 bytes from pprdespap324.corp.company.net (10.137.55.22): icmp_seq=1 ttl=64 time=0.282 ms
64 bytes from pprdespap324.corp.company.net (10.137.55.22): icmp_seq=2 ttl=64 time=0.341 ms
^C
--- pprdespap324.corp.company.net ping statistics ---
2 packets transmitted,2 received,0% packet loss,time 1001ms
rtt min/avg/max/mdev = 0.282/0.311/0.341/0.034 ms
现在，从容器本身，我们无法对同一主机执行ping操作：
[root@pprdespap322 deploy]# docker run -ti quay.io/coreos/registry ping ci.docker.company.net
WARNING: IPv4 forwarding is disabled. Networking will not work.
ping: unknown host ci.docker.company.net
我第一次看到此警告是在Docker的初始版本中…有了Docker 1.9.1和1.10.3，如何解决此问题？
