By default, yum client is configured to point to the official Fedora Core Download Server (also known as a Repository or Repo) as following:
[base]
name=Fedora Core $releasever - $basearch - Base
baseurl=http://fedora.redhat.com/releases/fedora-core-$releasever
[updates-released]
name=Fedora Core $releasever - $basearch - Released Updates
baseurl=http://fedora.redhat.com/updates/released/fedora-core-$releasever
If everyone is using the same server at same time, it can be very busy and quite slow to download the base software or updates.
To avoid the overload and increase the speed of yum, try switching to one of many Fedora Core mirror sites.
For example, if you're located in USA West, update your /etc/yum.conf as following and see how much it increased the speed of yum update download speed.
[base]
name=Fedora Core $releasever - $basearch - Base
baseurl=http://mirrors.kernel.org/fedora/core/$releasever/$basearch/os
[updates-released]
name=Fedora Core $releasever - $basearch - Released Updates
baseurl=http://mirrors.kernel.org/fedora/core/updates/$releasever/$basearch
To synchronize with rhn-applet notification and up2date, you should also update your rhn sources at /etc/sysconfig/rhn/sources
from
yum fedora-core-1 http://fedora.redhat.com/releases/fedora-core-1
yum updates-released http://fedora.redhat.com/updates/released/fedora-core-1
to
yum fedora-core-1 http://mirrors.kernel.org/fedora/core/1/i386/os
yum updates-released http://mirrors.kernel.org/fedora/core/updates/1/i386
