I had a machine that started hanging when running yum update on it. And the only way to actually stop yum then was to kill the process from another shell, pretty strange.
I noticed that it was trying to look up and old proxy server which was not in use anymore, the machine itself got online without issues on other services but then i realised that the file “/etc/sysconfig/rhn/up2date” had a entry for yum proxy settings.
It is also worth checking all files in your “/etc/yum” folder and make sure that none of your repo files have dedicated proxy settings defined since that will override anything from up2date.
When commenting out that proxy setting, yum started behaving again.