To get information on all the network interfaces on your system

1. ip a

 ip a (or ip addr)

The two interfaces on this system — the loopback (lo) and network (enp0s25) — are displayed along with a lot of stats. The “lo” interface is clearly the loopback. We can see the loopback IPv4 address (127.0.0.1) and the loopback IPv6 (::1) in the listing.
ip a

Why enp0s25 and not eth0?

The new naming scheme is referred to as the “Predictable Network Interface” naming. The “en” simply means “ethernet” just like “eth” does for eth0. The “p” is the bus number of the ethernet card and the “s” is the slot number. So “enp0s25” tells us a lot about the hardware we’re working with.

2. ip route show

ip route show

Displaying a routing table with ip route show. In its simplest form, ip route can be used to display the main routing table output.
ip route show

3. ifconfig

ifconfig

CLi tool for network interface configuration and also used to initialize an interfaces at system boot time.
it can be used to assign an IP Address to an interface and enable or disable the interface on demand.
view the status IP Address, Hardware / MAC address, as well as MTU (Maximum Transmission Unit) size of the currently active interfaces.
ifconfig

ifconfig -a

To list all interfaces which are currently available
ifconfig -a

sudo ifconfig eth0 192.168.0.29 netmask 255.255.255.0

To assign an IP address to an interface (edit IP and netmask accordingly)

sudo ifconfig up eth0

To activate an network interface. (where eth0 is network interface)

sudo ifconfig down eth0

To deactivate or shut down an network interface. (where eth0 is network interface)

4. IP Command

Utility for displaying and manipulating routing, network devices, interfaces. It is a replacement for ifconfig and many other networking commands.

ip addr show

show the IP address and other information about an network interface.
ip addr show

sudo ip addr add 192.168.56.1 dev eth0

To temporarily assign IP Address to a specific network interface (eth0)

sudo ip addr del 192.168.56.15/24 dev eth0

remove an assigned IP address from an network interface (eth0)

ip neigh

To show the current neighbour table in kernel
ip neigh

5. ifup, ifdown, and ifquery command

sudo ifup eth0

actives a network interface, making it available to transfer and receive data

sudo ifdown eth0

disables a network interface, keeping it in a state where it cannot transfer or receive data

sudo ifquery eth0

used to parse the network interface configuration, enabling you to receive answers to query about how it is currently configured.

6. Ethtool Command

Querying and modifying network interface controller parameters and device drivers.

ethtool eth0

to view the parameters for the network interface
ethtool eth0

7. Ping Command

ping 192.168.0.29 (hostname or interface ip)

testing connectivity between two systems on a network (Local Area Network (LAN) or Wide Area Network (WAN)). It use ICMP (Internet Control Message Protocol) to communicate to nodes on a network.

ping -c 4 192.168.0.29

tell ping to exit after a specified number of ECHO_REQUEST packets, using the -c flag as shown.

8. Traceroute Command

utility for tracing the full path from your local system to another network system. It prints number of hops (router IP’s) in that path you travel to reach the end server. It is an easy-to-use network troubleshooting utility after ping command.

traceroute google.com (ip or hostname)

tracing the route packets take from the local system to one of Google’s servers.

9. MTR Network Diagnostic Tool

modern command-line network diagnostic tool that combines the functionality of ping and traceroute into a single diagnostic tool.

mtr google.com OR mtr 216.58.223.78

easiest way of running mtr is to provide it a host name or IP address

mtr -c 4 google.com

limit the number of pings to a specific value and exit mtr after those pings.

10. Route Command

displaying or manipulating the IP routing table of a Linux system. It is mainly used to configure static routes to specific hosts or networks via an interface.

route

view Kernel IP routing table
route

sudo route add default gw

Add a default gateway to the routing table

sudo route add -net gw

Add a network route to the routing table.

sudo route del -net

Delete a specific route entry from the routing table.

11. Nmcli Command

scriptable command-line tool to report network status, manage network connections, and control the NetworkManager.

nmcli dev status

view all your network devices

nmcli con show

To check network connections on your system

nmcli con show -a

o see only the active connections

12. Netstat Command

displays useful information such as network connections, routing tables, interface statistics, and much more, concerning the Linux networking subsystem. It is useful for network troubleshooting and performance analysis. a fundamental network service debugging tool used to check which programs are listening on what ports

sudo netstat -tnlp

Active Internet connections

netstat -r

To view kernel routing table, use the -r flag (which is equivalent to running route command above).

13. ss Command

Although Netstat is a great tool, it is now obsolete (deprecated), its replacement is ss command. utility to investigate sockets. It dumps socket statistics and displays information similar to netstat. In addition, it shows more TCP and state information compared to other similar utilities

ss -ta

to list all TCP ports (sockets) that are open on a server.

ss -to

To display all active TCP connections together with their timers

14. NC (NetCat) Command

used for almost any task related to TCP, UDP, or UNIX-domain sockets. It is used open TCP connections, listen on arbitrary TCP and UDP ports, perform port scanning plus more. you can employ nc together with pv command to transfer files between two computers.

nc -zv server2.network.local 21 22 80 443 3000

will show how to scan a list of ports.

nc -zv server2.network.local 20-90

specify a range of ports as shown

nc -p 3000 -w 10 server2.network.local 5000

shows how to use nc to open a TCP connection to port 5000 on server2.network.local, using port 3000 as the source port, with a timeout of 10 seconds.

15. Nmap Command

gather information about a single host or explore networks an entire network. Nmap is also used to perform security scans, network audit and finding open ports on remote hosts and so much more.

nmap google.com

scan a host using its host name or IP address

16. host Command (DNS Lookup)

host google.com

carrying out DNS lookups, it translates host names to IP addresses and vice versa.

17. dig Command (domain information groper)

Used to query DNS related information such as A Record, CNAME, MX Record.

dig google.com

A Record, CNAME, MX Record for google.com

18. NSLookup Command

To query DNS servers both interactively and non-interactively. It is used to query DNS resource records (RR).

nslookup google.com

find out “A” record (IP address) of a google.com

nslookup 216.58.208.174

ou can also perform a reverse domain lookup

19. (Tcpdump Command) Linux Network Packet Analyzers

Used command-line network sniffer. It is used to capture and analyze TCP/IP packets transmitted or received over a network on a specific interface.

tcpdump -i eth0

To capture packets from a given interface

tcpdump -c 5 -i eth0

To capture a specific number of packets

tcpdump -w captured.pacs -i eth0

You can also capture and save packets to a file for later analysis

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