YUM error - are repositories down or something?

[dave at tokyocomedy.com (Dave Gutteridge)]

> It seems your network is not working, and yum can't reach it's
> repositories.
> Make shore you can ping google.com or similar !

So far as I can tell, I can use the internet, send email (as evidenced
by this response), and ping google.com:

--- google.com ping statistics ---
10 packets transmitted, 10 received, 0% packet loss, time 9009ms
rtt min/avg/max/mdev = 182.396/182.734/183.188/0.551 ms, pipe 2

It would seem to me that my network is working... so is there some
specific configuration that needs to be checked?

Also, I should mention that YUM has worked fine up until this error, and
I have not made any changes to my network configuration since installing
CentOS.

Dave