Yum shows a 'timed out' error message and does not work.

Issue

• Yum-related commands are not working properly.
• We can see a "timed out" message in its output:

# yum check-update
Not loading "rhnplugin" plugin, as it is disabled
Loading "product-id" plugin
Loading "subscription-manager" plugin
Running "config" handler for "subscription-manager" plugin
Updating Subscription Management repositories.
timed out

• We are accessing the Internet via a proxy that has already been configured.