nmap

Introduction

nmap can be easily found in rpm form and installed on a variety of systems, although it is probably already on your system. It is one of the older port scanners, but still being improved and widely used and appreciated.

The idea with nmap is that you can perform a sophisticated scan of a system looking for open port just like an attacker might. How you differentiate between the types of users is apparently an open problem. With nmap, you can perform scans of ports directly, or you can attempt devious scan methods as might be used by a nefarious, good-for-nothing system cracker. It will allow you to tighten up your defenses and avoid problems. Using nmap can be a complicated process, including a serious investigation of different methods of extracting useful data for further treachery.

The nmap syntax has the following form:

Examples

nmap -v somehost.somenetwork.org
Scans all reserved TCP ports on the target with verbose mode on.

nmap -sS somehost.somenetwork.org/24
Initiates a stealth SYN scan against all hosts on the class C network given.

nmap -sX -p 22,23,53 host1.net.org host2.net.org host3.net.org
Initiates a Christmas Tree scan for ports 22, 23 and 53 on the three hosts shown.