[nmap/en] Add tool: nmap

nmap.html.markdown

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+---
+category: tool
+tool: Nmap
+contributors:
+  - [ "Sebastian Oberdorfer" , "https://github.com/SOberdorfer" ]
+filename: LearnNmap.txt
+---
+
+### Learn Nmap in Y Minutes
+
+So, you’re connected to a network and want to know what else is connected to it.
+Maybe you’re trying to find that mystery device eating up bandwidth or check
+if there are services running you didn’t know about, or you just want to verify
+what ports are exposed on your machine?
+
+Meet your swiss-army network knife named **Nmap**!
+
+---
+
+### Introduction
+
+**Nmap 101**  
+Nmap is an open-source network scanning tool built by Gordon Lyon. Designed to
+help you find devices, open ports and services across your network.
+It’s a swiss-army knife for network admins, security folks, dev's and anyone
+curious about what’s living on their network.
+
+**When to Use It**
+
+- **Finding Devices**: What’s connected, and what’s running?
+- **Network Troubleshooting**: Resolve DNS or connection issues.
+- **Vulnerability Detection**: Spotting potentially risky services.
+- **Network Security**: Evaluate exposed ports.
+
+**When *Not* to Use It**
+
+- **Public Networks**: Scanning Starbucks WiFi might land you in hot tea.
+- **Corporate Networks**: Scanning your corporate network without permission, is
+  potentially not allowed.
+- **Global Web**: In some cases scanning across the web can be illegal.
+
+Certain scans are intrusive and can trigger security alarms, so stick to **only
+**
+scanning networks or systems where you have permission. Unauthorized scanning
+can be considered illegal under cybersecurity laws in many regions, and
+companies
+might view it as a hacking attempt.
+
+Use Nmap extensively and wisely.
+
+---
+
+### Installation
+
+Installation is straightforward, thoroughly explained on [nmap.org - install](https://nmap.org/book/install.html)
+
+---
+
+### The Basics
+
+These are low-key scans that safe to use since they don’t do deep probing.
+
+- **Ping Scan**:  
+  A low-impact scan just to check if devices are online. Typically fine on
+  trusted networks.
+    - Scan a single device
+      ```bash
+       nmap -sn 192.168.1.1
+      ```
+    - Scan a range of devices
+      ```bash
+      nmap -sn 192.168.1.1-100
+      ```
+    - Scan a CIDR range of devices
+      ```bash
+      nmap -sn 192.168.1.0/24   # Range 192.168.1.0 to 192.168.1.255
+      nmap -sn 192.168.0.0/16   # Range 192.168.0.0 to 192.168.255.255
+      nmap -sn 192.0.0.0/8      # Range 192.0.0.0 to 192.255.255.255
+      ```
+
+- **Fast Scan**:  
+  Quickly checks the 100 most common ports. Great for a quick peek without
+  probing all 65,535 ports.
+  ```bash
+  nmap -F 192.168.1.1
+  ```
+
+- **Operating System Detection**:  
+  OS detection requires some extra probing, which might be detectable by
+  Intrusion Detection Systems (IDS).
+  ```bash
+  nmap -O 192.168.1.1
+  ```
+
+- **Output to File**  
+  Specific scanning and saving the output to a file, enables you to scan more
+  thorough without overloading your network.
+    - Plain text
+      ```bash
+      nmap -oN output.txt 192.168.1.1 
+      ```
+    - XML, handy for using elsewhere
+      ```bash
+      nmap -oX output.xml 192.168.1.1
+      ```
+
+---
+
+### Moving Up: More Insightful Scans
+
+These scans dig a bit deeper, so they may trigger alarms on security systems.
+Use these only on networks where you have explicit permission to scan.
+
+- **Service Version Detection**:  
+  Tries to identify versions of services on open ports. Useful but more
+  invasive.
+  ```bash
+  nmap -sV 192.168.1.1
+  ```
+
+- **Aggressive Scan**:  
+  The aggressive scan mode (`-A`) combines multiple checks, like OS detection,
+  version detection and traceroute. This is likely to be flagged on
+  any network and can be considered illegal on networks you don’t own.
+  ```bash
+  nmap -A 192.168.1.1
+  ```
+
+- **Scanning Specific Ports**:  
+  Narrowing scans to specific ports is generally fine.
+    - Scan a specific port
+      ```bash
+      nmap -p 80 192.168.1.1
+      ```
+    - Scan a range of ports
+      ```bash
+      nmap -p 1-100 192.168.1.1
+      ```
+
+---
+
+### Advanced Scans: When You’re the Power User
+
+So, you’re getting into the advanced stuff—maybe testing your own firewall or
+finding rogue services.
+The following scans are loud and intrusive that definitely trigger security
+defenses.
+
+- **Scripted Scans (NSE)**  
+  Nmap’s script engine is like a toolbox of plugins. Need to check for a
+  specific vulnerability? There’s likely an NSE script for it.
+  ```bash
+  nmap --script=http-vuln-cve2021-12345 192.168.1.1
+  ```
+
+- **Aggressive and fastest Scans**:
+  `-T5` turns up to knob to 11. `-A` scans all ports.
+  Use it sparse and only if you really need full visibility.
+  ```bash
+  nmap -T5 -A 192.168.1.1
+  ```
+
+- **TCP and UDP Combined Scans**:  
+  Combining TCP and UDP scans (`-sS` for SYN scans and `-sU` for UDP) gives
+  complete coverage but increases the scan’s footprint, making it detectable.
+  ```bash
+  nmap -sS -sU 192.168.1.1
+  ```
+
+- **Spoofing and Decoy Scans**:  
+  Using decoys (`-D`) or spoofed IP addresses to hide your real IP can be seen
+  as deceptive. These scans are easily flagged by IDS and could lead to legal
+  repercussions if you’re not authorized.
+  ```bash
+  # 10 random IP decoys
+  nmap -D RND:10 192.168.1.1 
+  ```
+
+---
+
+### Practical Tips and Tricks
+
+**Timing Templates**  
+Nmap has timing options from `-T0` (paranoid) to `-T5` (insane). Stick with
+`-T2` or `-T3` for a good balance between speed and not making too much noise.
+More
+on [nmap - timing-templates](https://nmap.org/book/performance-timing-templates.html)
+
+**Check Out Nmap’s Scripts**  
+NSE scripts make Nmap super versatile. From DNS enumeration to vulnerability
+checks, there’s probably a script for whatever you need.
+More on [nmap - Nmap Scripting Engine](https://nmap.org/book/man-nse.html)
+
+**Use aggressive scans and decoys only on networks you own** or with formal
+authorization, such as during a penetration test with client permission. If
+you’re running scans at work, talk to the network admins first.
+
+**Know When to Stop**  
+Once you’ve got the info you need, wrap it up. It’s easy to get scan-happy.
+
+---
+
+Happy scanning!