title: Linux vanilla kernel on QEMU and networking with eth0
body: <p>I have downloaded and compiled vanilla linux kernel (3.7.1)
  I used busybox for ramdisk then I booted it using QEMU. 
  This is my QEMU command line</p>
  
  <pre><code>qemu-system-i386 -kernel bzImage -initrd ramdisk.img -append "root=/dev/ram rw console=ttyS0 rdinit=/bin/ash" -nographic -net nic -net user
  </code></pre>
  
  <p>everything goes well.
  However, I can't use networking on vanilla kernel with busybox.</p>
  
  <p>'ifup eth0' tells me </p>
  
  <pre><code>/ # ifup eth0
  ip: SIOCGIFFLAGS: No such device
  </code></pre>
  
  <p>I googled the Internet but can' get any clue...
  some advice would be nice
  thank you in advance.</p>