[CentOS] yum update repo problems

[Vahur Jõesalu]

Hi

I noticed today that all my Centos servers are giving same error on "yum 
update". Error is:
----------------------------------
Loading "installonlyn" plugin
Setting up Update Process
Setting up repositories
rpmforge                  100% |=========================| 1.1 kB 
00:00
Could not retrieve mirrorlist 
http://mirrorlist.centos.org/?release=5&arch=i386&repo=os error was
[Errno 4] IOError: <urlopen error (-2, 'Name or service not known')>
Error: Cannot find a valid baseurl for repo: base
----------------------------------

Servers are scattered around in different networks. Yum update has been 
workin OK on all of them. Centos 4.5 servers are giving similar error, 
but with less detail.
Servers are relaying heavily on DNS for everyday work, so that should 
rule out DNS issues (all are running caching-nameservers).

Is there any problem with repos? Anybody else having same erors?

all the best
Vahur