凡高的耳朵

[root@CentOS62 ~]# rpm -qa | grep bind
ypbind-1.20.4-29.el6.i686
bind-libs-9.7.3-8.P3.el6_2.2.i686
samba-winbind-clients-3.5.10-114.el6.i686
bind-utils-9.7.3-8.P3.el6_2.2.i686
PackageKit-device-rebind-0.5.8-19.el6.centos.i686
rpcbind-0.2.0-8.el6.i686
[root@CentOS62 ~]# yum install -y caching-nameserver
Loaded plugins: fastestmirror, refresh-packagekit, security
Loading mirror speeds from cached hostfile
* base: centos.ustc.edu.cn
* extras: centos.ustc.edu.cn
* rpmforge: ftp.riken.jp
* updates: centos.ustc.edu.cn
http://centos.ustc.edu.cn/centos/6.3/os/i386/repodata/repomd.xml: [Errno 14] PYCURL ERROR 6 - "Couldn't resolve host 'centos.ustc.edu.cn'"
Trying other mirror.
出錯了。請問是什么情況啊？