## UDP Scan (-sU)

Although most popular services on the Internet use the TCP protocol, UDP services are widely used. DNS, SNMP, and DHCP (registered ports 53, 161/162, and 67/68) are the three most common UDP services. UDP scanning is usually slower and more difficult than TCP scanning. UDP scanning works by sending a UDP packet to each intended port. In most ports, this packet is empty (without any information), but for a few common ports, protocol-specific data is sent. Based on the response or lack thereof, the port is classified into one of four states (Open, Open/Filtered, closed, filtered).

The most interesting may be the open|filtered state. It is a symptom of the biggest challenges in UDP scanning, as open ports rarely respond to empty queries. Ports for which Nmap has protocol-specific data sections are more likely to receive a response and are marked as open, but for other ports, the target simply redirects the empty packet to a listening application, which usually immediately rejects it as erroneous. Unfortunately, it is also known that firewalls and filtering devices drop packets without responding to them. So when Nmap does not receive a response after several attempts, it cannot determine whether the port is open or filtered.

@exercise d961299845c5


Use the UDP scanning learned in the module and scan port 5000 of the target address. You can use the flag (-p) to specify the port. After a successful scan, you will see the flag on the webpage.

Nmap UDP scan

UDP scan

Nmap is one of the most well-known tools that you can use to perform versatile network scans. Every information security professional should know how to use this tool.

Nmap is one of the most well-known network scanning tools, often used by cybersecurity experts. In this course, we will learn how to use this tool and explore its capabilities. Additionally, we will examine the traffic generated by the tool and analyze the pros and cons of different scanning methods. It is beneficial to have an understanding of how networks operate in this course.

Warning! - Conducting network scans without permission may cause system malfunctions and/or crashes. Please refrain from attempting to scan any address/system without certainty that said system is in your possession or that you have permission to do so.

Computer Networks

What is Nmap?

Nmap installation on your own workstation (optional)

Intro

Defining the destination

Detection of hosts

Host discovery techniques

Finding hosts

Introduction to port scanning

Saving the output and determining the resolution of the output

Configuring ports

Choices related to timing

IPv6 scanning

Port scanning - overview

TCP SYN scan

TCP connect scan

TCP FIN, NULL and Xmas scan

TCP ACK scan

IP Protocol scan

Port scanning techniques

Identification of services (-sV)

Identification of services and operating system

An introduction to Nmap scripts

Nmap scripts

Nmap

UDP scan

Learn to hack — start here