title: Network calls fail during image build on corporate network
body: <p>I'm having a problem building Docker images on my corporate network. I'm just getting started with Docker, so I have the following Dockerfile for a hello-world type app: </p>
  
  <pre><code># DOCKER-VERSION 0.3.4
  FROM    centos:6.4
  # Enable EPEL for Node.js
  RUN     rpm -Uvh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
  # Install Node.js and npm
  RUN     yum install -y npm
  # Bundle app source
  ADD . /src
  # Install app dependencies
  RUN cd /src; npm install
  EXPOSE  8080
  CMD ["node", "/src/index.js"]
  </code></pre>
  
  <p>This works fine when I build it on my laptop at home, on my own wireless network. It pulls down the requisite dependencies and builds the image correctly.</p>
  
  <p>However, when I'm on my corporate network at work, this same docker build fails when trying to pull down the RPM from download.fedoraproject.org, with this error message:</p>
  
  <blockquote>
    <p>Step 2 : RUN     rpm -Uvh <a href="http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm" rel="noreferrer">http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm</a>
     ---> Running in e0c26afe9ed5
    curl: (5) Couldn't resolve proxy 'some.proxy.address'
    error: skipping <a href="http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm" rel="noreferrer">http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm</a> - transfer failed</p>
  </blockquote>
  
  <p>On my corporate network, I can access that URL just fine from my laptop. But once Docker is trying to build the container, all of a sudden it can't resolve at all. This behavior is the same for a variety of external resources (apt-get, etc.): They all can resolve just fine on my laptop on the corporate network, but Docker can't resolve them.</p>
  
  <p>I don't have the network know-how to figure out what's going on here. Does anyone know why this strange behaviour would be occurring when building Docker containers?</p>