Updates basics_of_linux.md

Network cards \(NIC\) are identified by their mac address, hosts by theirip address andapplications by their port number.

### In a nutshell what you need to know

Things you really need to know are:

```

# Configuration files

/etc/network/interfaces

/etc/resolve.config

# Tools

ip

ip route

dhclient

wpa_supplicant

iptables

netstat

dnsmasq

```

### Configure Network Interface Cards \(NIC\)

On debian NIC:s are defined and configured in `/etc/network/interfaces`.

```

# automatically start eth0 on boot

auto eth0

# give the eth0 an ip through dhcp

iface eth0 inet dhcp

# start up the loopback interface

auto lo 

iface lo inet loopback

# A bridge called br1 - can be called  whatever.

# This bridge has a static ip

auto br1

iface br1 inet static

    address 192.168.55.1

    netmask 255.255.255.0

    broadcast 192.168.55.255

    bridge_ports none

```

**Take a interface up and down / start and stop**

It is recommended to take a interface down before configuring it.

sudo ip link set dev eth0 down 

sudo ip link set dev eth0 down

# You can also use ifconfig to bring an interface up and down. The difference is that ifconfig 

# will use the current configuration, and not take into account changes from /etc/network/interfaces.

# So use ifup and ifdown!

Remember that these routes will only be temporary

### Wireless

### Wireless - wpa\_supplicant

So if you manage to disable networkManager you can connect to a wireless network using wpa\_supplicant instead. I think that is what NetworkManager actually uses underneith.

sudo iwlist wlan0 scan

```

Then we need to create a config-file for our specific access-point.

Then we need to create a config-file for our specific access-point. We can do that with wpa\_passphrase, after running the command we are asked to write the password, which also gets stored in the config file. In plaintext.

```

wpa_passphrase NameOfWIfi > wpa.conf

```

Now we just connect to the AP:

```

wpa_supplicant -Dwext -iwlan0 -c/etc/wpa_supplicant/wpa.conf

```

After this you do not have an IP-address, or you might not have a updated dhcp lease. So first you need to release the current lease. 

```

.conf

sudo dhclient wlan0 -r

# Then get a new dhcp lease

sudo dhclient wlan0

```

This page explains it quite well:

Now you should be able to surf the internetz.

[http://linux.icydog.net/wpa.php](http://linux.icydog.net/wpa.php)

### Netstat - Find outgoing and incoming connections