I write this to try and save people such as myslef the hours of trying to get yum to work behind a proxy. This is the exact format of my /etc/yum.conf file that got the yum to connect behind the uni proxy server.

[main]
http_proxy=http://username:password@proxyaddress:port/
proxy_username=username
proxy_password=password
cachedir=/var/cache/yum
keepcache=0
debuglevel=2
logfile=/var/log/yum.log
pkgpolicy=newest
distroverpkg=redhat-release
tolerant=1
exactarch=1
obsoletes=1
gpgcheck=1
plugins=1
metadata_expire=1800

# PUT YOUR REPOS HERE OR IN separate files named file.repo
# in /etc/yum.repos.d

The / at the end of the http_proxy is very important as i found out after 30 mins of mucking about. This might not be the most elegant solution, but it works.

You must also as root type: http_proxy=proxyaddress:port
export http_proxy

Note the lack of / when exporting the proxy, very important