To install yum fastest mirror plugin (yum-plugin-fastestmirror) you can use next command:

yum install yum-plugin-fastestmirror

or

yum install yum-fastestmirror

command result:

[root@server1 ~]# yum install yum-fastestmirror
Loaded plugins: refresh-packagekit
updates/metalink                                         | 4.5 kB     00:00
updates                                                  | 4.4 kB     00:00
updates/primary_db                                       | 3.5 MB     00:04
Setting up Install Process
Resolving Dependencies
–> Running transaction check
—> Package yum-plugin-fastestmirror.noarch 0:1.1.22-1.fc11 set to be updated
–> Finished Dependency Resolution
Dependencies Resolved

================================================================================
Package                      Arch       Version              Repository   Size
================================================================================
Installing:
yum-plugin-fastestmirror noarch     1.1.22-1.fc11        updates      15 k

Transaction Summary
================================================================================
Install      1 Package(s)
Update       0 Package(s)
Remove       0 Package(s)

Total download size: 15 k
Is this ok [y/N]:

Once the installation completed, verify if /etc/yum.conf have the following line :

plugins=1

now, try to perform

yum install

or

yum update