17. Why Learn All This Before Kali Linux?
17.2 From Networking to Nmap and Wireshark
Part 1 madhe shiklele ports, TCP/UDP, 3-way handshake aani OSI layers – he Nmap aani Wireshark che "bhasha" aahet.
| You learnt (Part 1) | You will use it for |
|---|---|
| Ports and services (22, 80, 443, 3306...) | Reading Nmap results: which service, which risk |
| TCP 3-way handshake (SYN, SYN-ACK, ACK) | Understanding SYN scan (-sS) vs connect scan (-sT), and why firewalls log half-open connections |
| TCP vs UDP | Why UDP scans (-sU) are slow and need different thinking |
| Private vs public IP, NAT, CIDR | Defining the scope of a test (192.168.56.0/24 lab only) |
| OSI layers | Placing attacks: ARP spoofing (L2), IP spoofing (L3), SYN flood (L4), SQLi/XSS (L7) |
| HTTP vs HTTPS, TLS | Why Wireshark can read HTTP passwords but not HTTPS content |
A small preview – run only against your own machine or your lab network:
nmap -sT -p 22,80,443,3306 127.0.0.1 # which of these ports are open on MY machine?
sudo tcpdump -i any -c 5 port 80 # watch 5 packets of your own HTTP traffic
Each line of the Nmap output (22/tcp open ssh) is something you already understand: a port, a protocol and a service you configured in Part 2 and Part 3.
Why this matters for security
Defenders use the same knowledge the other way: close every port that is not needed, restrict management ports (22, 3306) to specific sources in security groups, and watch for scanning patterns (many SYNs to many ports) in logs. Knowing the handshake is what lets you recognise a scan in Wireshark or a SIEM.
Ravindra Bagale's Tip
Nmap output madhe filtered aani closed madhla farak khup students la kalat nahi. closed mhanje packet server paryant pohochla pan tithe koni aikat nahi; filtered mhanje madhech firewall/security group ne adavla. Part 1 cha handshake aathva – uttar tithech aahe.
Practice task
On your own EC2 instance, list listening ports with sudo ss -tulnp. Predict what Nmap would show from the internet given your security group, and write down which ports should be open and why.