I had a wierd situation recently, I could get the ip address, and I could set up apt.conf and proxy correctly, but I just could not connect network, I even could ping a inner desktop, so wierd. Then suddently, I found that it responses twice when ping this ip, so it is probably that the ip is used by other people stactly already, so I need to get a new automatic ip address, here is what I did:


1. release your current dhclient

sudo dhclient -r


sudo dhclient -r eth0

r for release.

2 obtain fresh IP

sudo dhclient


sudo dhclient eth0


3  show the detail information.  

sudo dhclient -v -r eth0


sudo dhclient -v eth0

v for verbose


other option may be useful

ifdown eth0

ifup eth0

/etc/init.d/networking restart