Use ifdown instead of ifconfig down for Ubuntu/Debian

CHANGELOG.md

@@ -6,6 +6,8 @@
   - Log output now goes on `stderr`, since it is utility information.
   - Get rid of case where a `NoMethodError` could be raised while
     determining VirtualBox version. [GH-658]
+  - Debian/Ubuntu uses `ifdown` again, instead of `ifconfig xxx down`, since
+    the behavior seems different/wrong.
 
 ## 0.9.1 (January 18, 2012)
 

lib/vagrant/guest/debian.rb

@@ -38,7 +38,7 @@ module Vagrant
         # each specifically, we avoid reconfiguring eth0 (the NAT interface) so
         # SSH never dies.
         interfaces.each do |interface|
-          vm.channel.sudo("/sbin/ifconfig eth#{interface} down 2> /dev/null")
+          vm.channel.sudo("/sbin/ifdown eth#{interface} 2> /dev/null")
         end
 
         vm.channel.sudo("cat /tmp/vagrant-network-entry >> /etc/network/interfaces")