Change network mask on centos

This post shows how to change the network mask and other ifconfig information on centos. After login to centos run the following command to open and edit the ifcfg-eth0 file:

vi /etc/sysconfig/network-scripts/ifcfg-eth0

Look for the line starting with PREFIX0, change the network mask here (not that this is specified in bits so, "PREFIX0=22" means network mask is 255.255.255.252).

After change is completed, restart the network service by running the following command:

service network restart

Install D-Link DWM-221 Broadband Modem on Ubuntu LTS 14.04 64 Bit

This post shows how to connect to Internet using a D-Link broadband modem dongle (Model DWM-221) on the Ubuntu LTS 14.04 64 Bit OS. Most of the posts i searched online on this topic does not seem to work (most of them on DWM-156 and older versions of Ubuntu), therefore i decides to write something about how to do it after successfully get it to work on my Ubuntu OS.

Firstly, one may need to install the ia32-libs, the following command lines can be followed to install ia32-libs on Ubuntu 14.04:

sudo apt-get install libc6:i386
sudo -i
cd /etc/apt/sources.list.d
echo "deb http://old-releases.ubuntu.com/ubuntu/ raring main restricted universe multiverse" >ia32-libs-raring.list
apt-get update
apt-get install ia32-libs
rm /etc/apt/sources.list.d/ia32-libs-raring.list
apt-get update
exit
sudo apt-get install gcc-multilib

Next plug in your D-link broadband modem to your computer and run the following command lines to mount it

sudo -su
mkdir /media/cdrom
mount /dev/sr1 /media/cdrom

You may try "mount /dev/sr0 /media/cdrom" if "mount /dev/sr0 /media/cdrom" does not work.

Once the D-Link folder has been mounted, you will notice there is a zip file in the folder named "DTLW3_D600B_linux_2.0.0WW_140305.tar.gz". If you try to extract it to a folder on your computer, you may encounter "Cannot create hard links ..." error messages. To get around list, right-click the file and select "Open with Archive Manager", extracts all the files excepts the hard links "device.conf" (which has size 0). Now in the extracted folder, you should have something like the following files and folders:

install.sh
uninstall.sh
linux
  /usr
  /bin
  /etc
    /3g_modem_connection
    /ppp
    /cm.version
    /device.conf

To make it easier, i have share the contents in the extracted folder here:

https://dl.dropboxusercontent.com/u/113201788/Hardware/D-Link%20Modem/DWM-221.tar.gz

In the extracted folder, run the following command:

sudo bash install.sh

Once this is done, go to the networking icons on the upper right corner of the Ubuntu desktop and select "Create new mobile broadband", follow the simple steps (basically a wizard asking several simple questions such as your internet provider and data plan in the form of drop down lists) and you should be able to connect to the internet via your D-Link broadband modem (Can try "sudo 3g_connect.sh ttyUSB0" if still got problem).

Explore Network-Network interface from a client to a host using Traceroute

Traceroute (tracert on Windows OS) is a program that allows user to examine and explore a network by sending packet one hop further at a time (which then returns back and the round trip time to that hop can be computed) until reaching the destination host.

To use it on Windows, open the command line and enter the following example:
tracert www.uw.edu