Something about usb driver on beaglebone black

I was using the bone quite well on linux, until recently i have to change back to ubuntu 12.04.
On the new system I plugin the usb cable and run shell script given on the getting start guide, but the usb2ethetnet connection is not established
the terminal given:
prophet@prophet-Inspiron-M4010:~$ ifconfig eth1
eth1 Link encap:Ethernet HWaddr c8:a0:30:ac:82:3a
inet6 addr: fe80::caa0:30ff:feac:823a/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
There is no ip address 192.168.7.1 on the eth1; and i cannot access the bone thru inet6 addr.
The serial interface works great, and on bone i can get:

usb0 Link encap:Ethernet HWaddr FE:13:79:3E:2C:30
inet addr:192.168.7.2 Bcast:192.168.7.3 Mask:255.255.255.252
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:19 errors:0 dropped:0 overruns:0 frame:0
TX packets:15 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:4182 (4.0 KiB) TX bytes:5798 (5.6 KiB)

I think the bone may have correctly loaded the driver, but the module on host machine is not loaded correctly.
So is any of you can give me some suggestion?