Finally, I figured out the problem that I had with network connection. The problem was with Realtek (RTL8111/RTL8168) NIC, which somehow detected differently by ubuntu 11.10 and uses r8169 kernel module driver.
To be sure, do check your NIC using:
$ sudo lscpi
You should see something like ...Realtek (RTL8111/RTL8168)...
Next step is to remove the r8169 module using:
$ rmmod r8169
If necessary install build-essential, etc:
$ sudo apt-get install build-essential linux-headers-$(uname -r) linux-source
Then, download the proper driver for that particular NIC from here. The file name should be something like r8168-8.027.00.tar.bz2.
Uncompress the file, and run the shell script file, as root:
Check the newly compiled driver:
$ sudo lsmod | grep r8168
$ ifconfig -a
Blacklist the r8169 module driver, by editing /etc/modprobe.d/blacklist.conf, add:
#blacklist r8169 driver
Reboot your system if necessary.