Nmap – A Penetration Testing Tool To Perform Information Gathering (Guide)

Nmap is an open-source network monitoring and port scanning tool to find the hosts and services in the computer by sending the packets to the target host for network discovery and security auditing.

Numerous frameworks and system admins additionally think that it’s helpful for assignments, for example, network inventory, overseeing administration overhaul timetables, and observing host or administration uptime.

Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics.

It was designed to rapidly scan large networks but works fine against single hosts. it runs on all major computer operating systems, and official binary packages are available for Linux, Windows, and Mac OS X.

In addition to the classic command-line Nmap executable, the Nmap suite includes an advanced GUI and results in the viewer (Zenmap), a flexible data transfer, redirection, and debugging tool (Ncat), a utility for comparing scan results (Ndiff), and a packet generation and response analysis tool (Nping).

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Nmap is …

• Flexible: Supports dozens of advanced techniques for mapping out networks filled with IP filters, firewalls, routers, and other obstacles. This includes many port scanning mechanisms (both TCP & UDP), OS detection, version detection, ping sweeps, and more. See the documentation page.
• Powerful: Nmap has been used to scan huge networks of literally hundreds of thousands of machines.
• Portable: Most operating systems are supported, including Linux, Microsoft Windows, FreeBSD, OpenBSD, Solaris, IRIX, Mac OS X, HP-UX, NetBSD, Sun OS, Amiga, and more.
• Easy: While NMAP offers a rich set of advanced features for power users, you can start out as simply as “nmap -v -A targethost“. Both traditional command line and graphical (GUI) versions are available to suit your preference.
• Free: The primary goals of this  NMAP Project is to help make the Internet a little more secure and to provide administrators/auditors/hackers with an advanced tool for exploring their networks. it is available for free download and also comes with full source code that you may modify and redistribute under the terms of the license.
• Well Documented: Significant effort has been put into comprehensive and up-to-date man pages, whitepapers, tutorials, and even a whole book! Find them in multiple languages here.
• Supported: While it comes with no warranty, it is well supported by a vibrant community of developers and users. Most of this interaction occurs on the Nmap mailing lists. Most bug reports and questions should be sent to the Nmap-dev list, but only after you read the guidelines.
• Acclaimed: Nmap has won various honors, including “Information Security Product of the Year” by Linux Journal, Info World, and Codetalker Digest. It has been included in many magazine articles, a few motion pictures, many books, and one comic book arrangement. Visit the press page for further subtleties.
• Popular: Thousands of people download every day, and it is included with many operating systems (Redhat Linux, Debian Linux, Gentoo, FreeBSD, OpenBSD, etc). It is among the top ten (out of 30,000) programs at the Freshmeat.Net repository. This is important because it lends Nmap its vibrant development and user support communities.

 TOP NMAP COMMEANDS:

1: To find out nmap version, run:

 # nmap --version

Sample outputs:

Nmap version 5.51 ( http://nmap.org )

2: To scan an IP address or a host name (FQDN), run:


 # nmap 1.2.3.4
 # nmap localhost
 # nmap 192.168.1.1

3:  Information out of the remote system:


 # nmap -v -A scanme.nmap.org
 # nmap -v -A 192.168.1.1

Sample outputs:

 Starting Nmap 5.00 ( http://nmap.org ) at 2012-11-19 16:38 IST
 NSE: Loaded 30 scripts for scanning.
 Initiating ARP Ping Scan at 16:38
 Scanning 192.168.1.1 [1 port]
 Completed ARP Ping Scan at 16:38, 0.04s elapsed (1 total hosts)
 Initiating Parallel DNS resolution of 1 host. at 16:38
 Completed Parallel DNS resolution of 1 host. at 16:38, 0.00s elapsed
 Initiating SYN Stealth Scan at 16:38
 Scanning 192.168.1.1 [1000 ports]
 Discovered open port 80/tcp on 192.168.1.1
 Discovered open port 22/tcp on 192.168.1.1
 Completed SYN Stealth Scan at 16:38, 0.27s elapsed (1000 total ports)

4:  Scan multiple IP address or subnet (IPv4):


 nmap 192.168.1.1 192.168.1.2 192.168.1.3
 ## works with same subnet i.e. 192.168.1.0/24
 nmap 192.168.1.1,2,3

You can scan a range of IP address too:

nmap 192.168.1.1-20

You can scan a range of IP address using a wildcard:

nmap 192.168.1.*

Finally, you scan an entire subnet:

nmap 192.168.1.0/24

5: Find out if a host/network is protected by a firewall:

 nmap -sA 192.168.1.254
 nmap -sA server1.gbhackers.com

6: Turn on OS and version detection scanning script (IPv4):

 nmap -A 192.168.1.254
 nmap -v -A 192.168.1.1
 nmap -A -iL /tmp/scanlist.txt 

7:  Scan a host when protected by the firewall:

 nmap -PN 192.168.1.1
 nmap -PN server1.gbhackers.com

8: Scan an IPv6 host/address:


 The -6 option enable IPv6 scanning. The syntax is:

 nmap -6 IPv6-Address-Here
 nmap -6 server1.gbhackers.com
 nmap -6 2607:f0d0:1002:51::4
 nmap -v A -6 2607:f0d0:1002:51::4

9:  How do I perform a fast scan:

 nmap -F 192.168.1.1

10: Display the reason a port is in a particular state:


 nmap --reason 192.168.1.1
 nmap --reason server1.gbhackers.com

11: Only show open (or possibly open) ports:

 nmap --open 192.168.1.1
 nmap --open server1.gbhackers.com

12: Show all packets sent and received:

 nmap --packet-trace 192.168.1.1
 nmap --packet-trace server1.gbhackers.com

13: Show host interfaces and routes:

This is useful for debugging (ip command or route command or netstat command like
 output using nmap)

 nmap --iflist

Sample outputs:

Starting Nmap 5.00 ( http://nmap.org ) at 2012-11-27 02:01 IST
 ************************INTERFACES************************
 DEV (SHORT) IP/MASK TYPE UP MAC
 lo (lo) 127.0.0.1/8 loopback up
 eth0 (eth0) 192.168.1.5/24 ethernet up B8:AC:6F:65:31:E5
 vmnet1 (vmnet1) 192.168.121.1/24 ethernet up 00:50:56:C0:00:01
 vmnet8 (vmnet8) 192.168.179.1/24 ethernet up 00:50:56:C0:00:08
 ppp0 (ppp0) 10.1.19.69/32 point2point up

**************************ROUTES**************************
 DST/MASK DEV GATEWAY
 10.0.31.178/32 ppp0
 209.133.67.35/32 eth0 192.168.1.2
 192.168.1.0/0 eth0
 192.168.121.0/0 vmnet1
 192.168.179.0/0 vmnet8
 169.254.0.0/0 eth0
 10.0.0.0/0 ppp0
 0.0.0.0/0 eth0 192.168.1.2


14: How do I scan specific ports:

 nmap -p [port] hostName
 ## Scan port 80
  nmap -p 80 192.168.1.1

## Scan TCP port 80
 nmap -p T:80 192.168.1.1

## Scan UDP port 53
 nmap -p U:53 192.168.1.1

## Scan two ports ##
 nmap -p 80,443 192.168.1.1

## Scan port ranges ##
 nmap -p 80-200 192.168.1.1

## Combine all options ##
 nmap -p U:53,111,137,T:21-25,80,139,8080 192.168.1.1
 nmap -p U:53,111,137,T:21-25,80,139,8080 server1.cyberciti.biz
 nmap -v -sU -sT -p U:53,111,137,T:21-25,80,139,8080 192.168.1.254

## Scan all ports with * wildcard ##
 nmap -p "*" 192.168.1.1

## Scan top ports i.e. scan $number most common ports ##
 nmap --top-ports 5 192.168.1.1
 nmap --top-ports 10 192.168.1.1

Sample outputs:

Starting Nmap 5.00 ( http://nmap.org ) at 2012-11-27 01:23 IST
 Interesting ports on 192.168.1.1:
 PORT STATE SERVICE
 21/tcp closed ftp
 22/tcp open ssh
 23/tcp closed telnet
 25/tcp closed smtp
 80/tcp open http
 110/tcp closed pop3
 139/tcp closed netbios-ssn
 443/tcp closed https
 445/tcp closed microsoft-ds
 3389/tcp closed ms-term-serv
 MAC Address: BC:AE:C5:C3:16:93 (Unknown)

nmap done: 1 IP address (1 host up) scanned in 0.51 seconds

Conclusion

Nmap can perform various scanning operations and it has been the leading scanning tool in the security industry since its release in 1997, also the world’s leading port scanner to find out open ports and firewalls.

still, Nmap is used by various organizations and penetration testers to find out loops and secure the network.

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Also Read:

SPARTA – Network Penetration Testing GUI Toolkit

SN1PER – A Detailed Explanation of Most Advanced Automated Information Gathering & Penetration Testing Tool

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theHarvester-Advanced Information Gathering Tool for Pentesters & Ethical Hackers