Analyzing Telnet services is a crucial part of network management and security. NMAP is one of the valuable tools widely used for this purpose. Telnet is a protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communication facility using a virtual terminal connection (source: RFC 854).
First, to understand NMAP, it is an open-source tool used for network exploration and security auditing, as described by its official documentation (source: Nmap.org). Nmap distributes with a feature of port scanning, version detection, DNS resolution, scriptable interactions with the target, such as various specific checks, or exploiting potential vulnerabilities.
To analyze telnet services with Nmap, the first command you might want use is the basic Telnet service detection command:
```
nmap -p 23
```
This command instructs Nmap to perform a scan (-p) on port 23, which is the default port for Telnet services, of the target IP (source: Nmap.org).
For a more detailed view, you might want to ask Nmap to determine the service/version information with -sV:
```
nmap -p 23 -sV
```
While -sV option is used to determine the version of the service running on port, -p option followed by the port number 23 helps to specify the scanning of telnet services running on that port.
Nmap also comes with a host of scripts under its Nmap Scripting Engine (NSE). These scripts assist in more targeted service detection, potential vulnerability detection, brute-force attacks among other things (source: Nmap.org). To use NSE scripts for Telnet, you might use the following command:
```
nmap —script telnet* -p 23
```
Nmap also has a neat feature called “version intensity” which sets the intensity of the version scanning (source: Nmap.org). With this setting, Nmap will make a guess about the service running on the open ports even with less information. For instance:
```
nmap -sV —version-intensity 5
```
The —version-intensity 5 here instructs Nmap to use normal intensity when fingerprinting.
While using NMAP and Telnet service, be aware that Telnet itself is not encrypted and the data flows in plain text which could lead to serious security issues (source: RFC 854).
Lastly, it is a good practice to use these tools ethically and responsibly. Never scan or exploit machines on a network without explicit permission.
Sources:
- RFC 854: Telnet Protocol Specification
(https://tools.ietf.org/html/rfc854)
- Nmap Documentation
(https://nmap.org/book/man.html)
- Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and Security Scanning
(https://nmap.org/book/nmap-overview.html)
