装完Ubuntu 12.04 之后， 发现自己得机子网络连接有问题， 无法上网。
搜索发现这个问题很常见：
http://askubuntu.com/questions/46942/how-do-i-stop-my-ethernet-network-connection-from-dropping
该文提供了一个解决方案， 那就是再装一下驱动, 你一定要看清硬件配置啊。
此处复制粘贴一下原文：
Wake-on-lan after shutdown - this didn't work
BUT!!! i know how to fix it!!! it's not provider's fault it's broken r8169 driver!!!
here's the instruction:
Download the official realtek driver
then remove the r8169 module from the linux kernel.
# rmmod r8169
<Quick install with proper kernel settings>
Unpack the tarball :
# tar vjxf r8168-8.aaa.bb.tar.bz2
Change to the directory:
# cd r8168-8.aaa.bb
If you are running the target kernel, then you should be able to do :
# ./autorun.sh (as root or with sudo)
You can check whether the driver is loaded by using following commands.
# lsmod | grep r8168
# ifconfig -a
If there is a device name, ethX, shown on the monitor, the linux
driver is loaded. Then, you can use the following command to activate
the ethX.
# ifconfig ethX up
Finally, blacklist the r8169 driver add the following to /etc/modprobe.d/blacklist.conf:
#blacklist r8169 driver
blacklist r8169
i found it here
and it works!!! now it's all good with net speed