Linux/Networking

networking

ping

Okay, you have managed to run ping. You have even figured out how to use the -c flag. In this case, ping will attempt four times, stop, and then report some basic statistics to you.

Knowing how to check whether or not you're connected is one thing, but what do you do when you're not? Or what if your network connection is active, but reports invalid information and you need to reconfigure it?

First, let's explore how to check our current configuration. In Debian, the file that controls the network devices by default is the following:

/etc/network/interfaces

Depending on several variables, which include how you configured your Debian installation, this file may be created differently. First, you may see several interfaces listed, such as your loopback adapter, wired Ethernet, and wireless. If you have more than one wired interface, you'll see any additional adapters here as well. This file is, simply put, a configuration file. It's a text file that contains information that the underlying Linux system understands, and causes a device to be configured as designated in the file.

To edit files such as these, there are many Linux text editors available, both GUI and terminal based. My personal favorite is vim, though many administrators typically start off with nano. The nano text editor is fairly easy to use, though very light on features. Alternatively, vim has many more features than nano but is a bit harder to get used to. Take your pick. To open a file in nano, all you need to do is type nano along with the name of a text file you would like to edit. If the file doesn't exist, the command will create it if you save the file. In the case of our /etc/network/interfaces file, the command will be similar to this:

# vim /etc/network/interfaces

continuing

/etc/network/interfaces

file is not required for network hardware to work - it is optional. if nothing is set in the above file, network is probably being managed by network manager. system level daemon that makes things "just work".

desktops/laptops usually want network manager, servers/embedded computers/etc want stuff configured in /etc/network/interfaces

barebones interfaces file:

$ cat /etc/network/interfaces

# The loopback network interface
auto lo
iface lo inet loopback

check for network manager

$ ps ax | grep NetworkManager

kill it! kill it!!!

446 ?        Ssl    0:00 /usr/sbin/NetworkManager --no-daemon

die die die - ok back to what we were doing.

to add ethernet hardware, and let it autoconfigure using a dhcp server (i.e., you'll be plugging it into a router or other device running a dhcp server that will hand out ip addresses)

# The loopback network interface
auto lo
iface lo inet loopback

# Wired connection eth0
auto eth0
iface eth0 inet dhcp

manual static

# The loopback network interface
auto lo
iface lo inet loopback

# Wired connection eth0
auto eth0
iface eth0 inet static
    address 10.10.10.12
    netmask 255.255.248.0
    network 10.10.10.0
    broadcast 10.10.10.255
    gateway 10.10.10.1

the following line changed:

iface eth0 inet static

static, not dhcp

if you declare dhcp, all other configuration details ignored

next declare ip address, 10.10.10.12

declare subnet mask to 255.255.248.0

declare the network we're joining to 10.10.10.0

declare the broadcast ID as 10.10.10.255

decalre the gateway as 10.10.10.1

now restart networking service

$ systemctl restart networking.service

or 

$ service networking restart

figure out what networking interfaces are available

$ ifconfig 

or 

$ ip addr show