yum problem

sudo yum update
Loading "installonlyn" plugin
Setting up Update Process
Could not retrieve mirrorlist http://mirrors.fedoraproject.org/mirrorlist?repo=fedora-7&arch=i386 error was
[Errno 4] IOError: <urlopen error (111, 'Conexi\xc3\xb3n rehusada')>
Error: Cannot open/read repomd.xml file for repository: fedora

I am under proxy  and not like forming it, in the page it leaves:

http_proxy=ip_proxy:port
export http_proxy

but when adding these lines give the following error me

sudo yum update
CRITICAL:yum.cli:Config Error: Parsing file failed: File contains parsing errors: file:///etc/yum.conf
        [line 17]: 'export http_proxy'

as I can solve this problem

greetings