In order to do networking with linux, having computer networks knowledge is imperative. Linux is widely used for networking due to its flexibility, robustness, and a wide range of built-in tools. Whether you're managing servers, setting up a home network, or troubleshooting connectivity issues, Linux provides powerful networking capabilities. I studied networking (CCNA syllabus) (2015-2016) and did lot of packet tracing with GNS 3 (CISCO IOS).
Linux Networking Command Pallette🌸:
Viewing Network Interfaces : Network interfaces are the connection points between your Linux machine and the network. Each interface is associated with a unique identifier like eth0, wlan0, or lo (loopback interface).
$ ifconfigThis command shows detailed information about all active network interfaces, including IP address, MAC address, MTU, etc.
$ ip addr showThis command provides detailed information about all network interfaces, similar to ifconfig.
Bringing Up/Down Network Interfaces : We can enable or disable a network interface using the ifconfig or ip command.
- Bringing an Interface Up:
$ sudo ifconfig eth0 upor using ip:$ sudo ip link set eth0 up. - Bringing an Interface Down:
$ sudo ifconfig eth0 downor using ip:$ sudo ip link set eth0 down.
Configuring IP Addresses : Assigning a static IP address to a network interface can be done using either ifconfig or ip.
- Using ifconfig:
$ sudo ifconfig eth0 192.168.1.100 netmask 255.255.255.0or using ip:$ 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.
Checking Network Connectivity : You can check whether your system can reach other systems or services on the network using several commands.
$ ping 8.8.8.8: This sends ICMP echo requests to the specified IP address (Google DNS in this case) and shows the response time.- traceroute :
$ traceroute www.example.com: This command traces the path packets take to reach a remote host and shows each hop along the way. - Checking Port Connectivity with nc (Netcat):
$ nc -zv www.example.com 80.
Managing Routing Tables : Routing tables determine the path data takes to reach a network. You can view and modify routing tables using the route or ip command.
- Viewing the Routing Table:
$ route -nor using ip:$ ip route show. - Adding a Route:
$ sudo route add -net 192.168.1.0/24 gw 192.168.1.1or using ip :$ sudo ip route add 192.168.1.0/24 via 192.168.1.1. - Deleting a Route:
$ sudo route del -net 192.168.1.0/24or using ip :$ sudo ip route del 192.168.1.0/24.
Configuring DNS : DNS (Domain Name System) translates domain names into IP addresses. DNS settings are typically configured in /etc/resolv.conf.
- Viewing DNS Settings:
$ cat /etc/resolv.conf. - Adding a DNS Server: Edit the /etc/resolv.conf file and add the following line:
nameserver 8.8.8.8. This adds Google's DNS server.
Network Monitoring : Linux provides several tools to monitor network traffic and performance.
- Using netstat:
$ netstat -tuln, This shows all listening ports and their associated services. - Using ss:
$ ss -tuln, ss is a faster alternative to netstat for displaying detailed socket information. - Using tcpdump:
$ sudo tcpdump -i eth0, This command captures and displays packets transmitted over the network interface eth0.
| command | description |
reference |
|---|---|---|
| ifconfig | Display and manipulate route and network interfaces. |
$ ifconfig |
| ip | It is a replacement of ifconfig command. Use ip link show command to display all network interfaces on the system. |
$ ip link show |
| ip route show | Use the IP route to print or display the routing table. |
$ ip route show |
| ping -c 3 google.com | By default, ping runs in an infinite loop. To send a defined number of packets, use -c flag |
$ ping -c 3 google.com |
| ss -t -a | ss command with -t and -a flags to list all TCP sockets. This displays both listening and non-listening sockets. ss gets details about network sockets. |
$ ss -t -a |
| iftop | Monitors stats related to bandwidth. |
$ iftop |
| dig [domain] | Show DNS information about a domain using the dig command |
$dig [domain] |
| dig -x [ip_address] | Do reverse lookup of an IP address |
$dig -x [ip_address] |
| lastlog | The lastlog command is used to find the details of a recent login of all users or of a given user. |
$lastlog |
| firewalld | CLI tool to configure rules of Firewall. |
$ firewalld |
| tcpdump | Packet sniffing and analyzing utility used to capture, analyze and filter network traffic. |
$ tcpdump |
| ip addr | Show IP addresses and network interfaces (modern replacement for ifconfig). |
$ ip addr |
| ip link | Display and manage network device attributes. |
$ ip link |
| traceroute | Trace the route packets take to reach a destination host. |
$ traceroute <hostname or IP> |
| netstat -nr | Show routing table (deprecated, use ip route instead). |
$ netstat -nr |
| nslookup <hostname> | Query DNS servers for DNS information about a domain. |
$ nslookup <hostname> |
| ss or netstat -tuln | Display information about open network sockets. |
$ ss or netstat -tuln |
| lsof -i | List open files associated with network connections. |
$ lsof -i |
| ifup <interface> | Bring a network interface up. |
$ ifup <interface> |
| ifdown <interface> | Bring a network interface down. |
$ ifdown <interface> |
| vnstat | Monitor network traffic and bandwidth usage. |
$ vnstat |
I have some CISCO IOS here and CCNA labs.
Sockets and the socket API are used to send messages across a network. They provide a form of inter-process communication (IPC). The network can be a logical, local network to the computer, or one that’s physically connected to an external network, with its own connections to other networks. The obvious example is the Internet, which we connect to via your ISP.
import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)Here we made a socket instance and passed it two parameters. The first parameter is AF_INET and the second one is SOCK_STREAM. AF_INET refers to the address-family ipv4. The SOCK_STREAM means connection-oriented TCP protocol. The primary socket API functions and methods in this module are:
socket()
.bind()
.listen()
.accept()
.connect()
.connect_ex()
.send()
.recv()
.close()
| Echo Server | Echo Client |
|---|---|
import socket
# Create a TCP/IP socket
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
# Bind the socket to a specific address and port
server_address = ('localhost', 12345)
server_socket.bind(server_address)
# Listen for incoming connections
server_socket.listen(1)
print("Server is listening on port 12345")
while True:
# Wait for a connection
print("Waiting for a connection...")
client_socket, client_address = server_socket.accept()
try:
print(f"Connection from {client_address}")
data = client_socket.recv(1024)
print(f"Received: {data.decode()}")
# Send the received data back to the client
client_socket.sendall(data)
finally:
# Clean up the connection
client_socket.close()
|
import socket
# Create a TCP/IP socket
client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
# Connect the socket to the server's address and port
server_address = ('localhost', 12345)
client_socket.connect(server_address)
try:
# Send data to the server
message = "Hello, server!"
client_socket.sendall(message.encode())
# Receive the response from the server
data = client_socket.recv(1024)
print(f"Received: {data.decode()}")
finally:
# Clean up the connection
client_socket.close()
|
resources : socket programming, Socket Programming HOWTO