LWM-Linux/04 - Networking in Linux/Basic Network Configuration.md

# Linux Basic Network Configuration

## 1. Network Interfaces

Linux uses network interfaces to communicate with networks. Common interfaces include:

- eth0, eth1, etc.: Ethernet interfaces
- wlan0, wlan1, etc.: Wireless interfaces
- lo: Loopback interface

To list network interfaces:

`ip link show`

or

`ifconfig -a`

## 2. IP Address Configuration

### Temporary IP configuration:

- To set an IP address temporarily:

`sudo ip addr add 192.168.1.100/24 dev eth0`

- To remove an IP address:

`sudo ip addr del 192.168.1.100/24 dev eth0`

###  Permanent IP configuration:

Edit the network configuration file (location varies by distribution):

- Ubuntu/Debian: /etc/network/interfaces
- CentOS/RHEL: /etc/sysconfig/network-scripts/ifcfg-eth0

Example configuration:

```
auto eth0
iface eth0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1
    dns-nameservers 8.8.8.8 8.8.4.4
```

## 3. DHCP Configuration

For dynamic IP assignment, use DHCP:

```
auto eth0
iface eth0 inet dhcp
```

## 4. Network Manager

Many modern Linux distributions use Network Manager for easier network configuration. You can use the command-line tool 'nmcli' or GUI tools to manage connections.

## 5. Hostname Configuration

Set the hostname:

`sudo hostnamectl set-hostname new-hostname`

Update /etc/hosts file to include the new hostname.

## 6. DNS Configuration

Edit /etc/resolv.conf to set DNS servers:

```
nameserver 8.8.8.8
nameserver 8.8.4.4
```

Note: This file may be overwritten by DHCP. For permanent changes, configure your network manager or DHCP client.

## 7. Routing

View routing table:

`ip route show`

Add a static route:

`sudo ip route add 10.0.0.0/24 via 192.168.1.1 dev eth0`

## 8. Firewall Configuration

Most Linux distributions use iptables or nftables. Ubuntu uses ufw (Uncomplicated Firewall) as a frontend.

Enable UFW:

`sudo ufw enable`

Allow incoming SSH:

`sudo ufw allow ssh`

## 9. Network Diagnostics

- ping: Test connectivity
- traceroute: Trace packet route
- netstat or ss: Display network connections
- tcpdump: Capture and analyze network traffic

## 10. Network Service Management

Start/stop network service:

`sudo systemctl start networking`
`sudo systemctl stop networking`

Enable/disable network service at boot:

`sudo systemctl enable networking`
`sudo systemctl disable networking`

## 11. Wireless Network Configuration

Use 'iwconfig' to configure wireless interfaces:

`sudo iwconfig wlan0 essid "NetworkName" key s:password` #Not advised because it will leave your network password in the bash history!

 For WPA networks, use 'wpa_supplicant'. 
- `wpa_passphrase [ESSID] > /etc/wpa_supplicant/wpa_supplicanmt-[DEVICENAME].conf`. You will then be prompted to enter the password.

## 12. Network Bonding

Combine multiple network interfaces for redundancy or increased throughput. Edit /etc/network/interfaces:

```
auto bond0
iface bond0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1
    bond-slaves eth0 eth1
    bond-mode active-backup
    bond-miimon 100
    bond-primary eth0
```