running yum w/ sudo not works

I have FC6 and yum-3.0.6-1.fc6
While running `sudo yum update', the yum returns follows message
Loading "fastestmirror" plugin
Loading "installonlyn" plugin
Setting up Update Process
Setting up repositories
Could not retrieve mirrorlist 
http://mirrors.fedoraproject.org/mirrorlist?repo=core-6&arch=i386 error was
[Errno 4] IOError: <urlopen error (110, 'Connection timed out')>
Error: Cannot find a valid baseurl for repo: core

If running yum from `su -c 'yum update''
everything is fine.