在对一台centos5.3 yum list的时候开始报错，yum clean all 都试过，但是没效果，最后发现是dns的问题：

原先dns：
#nameserver 211.155.235.201
#nameserver 211.155.235.188
报错：
[root@sunnes ~]# yum list
Loaded plugins: fastestmirror
Determining fastest mirrors
YumRepo Error: All mirror URLs are not using ftp, http[s] or file.
 Eg. </html>/
removing mirrorlist with no valid mirrors: //var/cache/yum/base/mirrorlist.txt
Error: Cannot find a valid baseurl for repo: base
[root@sunnes ~]#

谷歌dns，使用8.8.8.8报错：
[root@sunnes ~]# yum list
Loaded plugins: fastestmirror
Determining fastest mirrors
Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=5&arch=i386&repo=os error was
[Errno 4] IOError: <urlopen error (104, ‘Connection reset by peer’)>
Error: Cannot find a valid baseurl for repo: base
[root@sunnes ~]#

最后换成谷歌8.8.4.4没问题了,并且找到最快的yum源为163的。
再yum list 没问题了。