"http_proxy"
PPM uses LWP to access remote repositories. If you need HTTP traffic pass via a proxy server to reach the repository, you must set the "http_proxy" environment variable. Some examples:

Using bash:
export http_proxy=http://proxy.mycompany.com

Using cmd.exe:
set http_proxy=http://username:password@proxy.mycompany.com:8008

See "env_proxy" in LWP::UserAgent for more.