Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=6&arch=x86_64&repo=os&infra=stock error was
14: PYCURL ERROR 7 - "Failed to connect to 2001:4178:5:200::10: Network is unreachable"
后来发现是防火墙的原因，执行如下命令，关闭 iptables 后恢复正常。
service iptables stop
原文：http://blog.51cto.com/zengwj1949/2350632