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