[CentOS] YUM error - are repositories down or something?

Following advice on how to ensure that PHP and MySQL are on my machine and working correctly, I ran the following YUM command, with the subsequent error:

[root@localhost ~]# yum install php php-mysql httpd mysqlclient10 mysql- server Setting up Install Process Setting up Repos http://apt.sw.be/redhat/el4/en/i386/dag/repodata/repomd.xml: [Errno 4] IOError: <urlopen error (113, 'No route to host')> Trying other mirror. Cannot open/read repomd.xml file for repository: dag failure: repodata/repomd.xml from dag: [Errno 256] No more mirrors to try.

Unless I am misunderstanding this error (which is quite likely), it seems to indicate that YUM can not reach the online repositories. Is that the case?

Or does the problem reside on my end?

Dave