The Penguin's Practical Network Troubleshooting Guide - page 3
Mapping Network Hosts and Services
It is amazing how many different uses nmap has. Just when you think you know it inside out, out pop more interesting and useful features. This command scans a subnet to see what hosts are up:
# nmap -sP 192.168.1.*
Starting nmap 3.81 ( http://www.insecure.org/nmap/ ) at 2006-04-27 14:54 PDT
Host 192.168.1.0 seems to be a subnet broadcast address (returned 2 extra pings).
Host windbag.alrac.net (192.168.1.10) appears to be up.
Host uberpc.alrac.net (192.168.1.11) appears to be up.
MAC Address: 00:10:0A:54:61:DA (Unknown)
Host stinkpad.alrac.net (192.168.1.12) appears to be up.
MAC Address: 00:1A:E2:4A:8B:DD (Wistron)
Host 192.168.1.255 seems to be a subnet broadcast address (returned 2 extra pings).
Nmap finished: 256 IP addresses (3 hosts up) scanned in 7.005 seconds
Want to map your entire network and see what services are running?
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YahooBuzz# nmap -O 192.168.1.*
Starting nmap 3.81 ( http://www.insecure.org/nmap/ ) at 2006-04-27 22:06 PDT
Interesting ports on windbag.alrac.net (192.168.1.10):
(The 1658 ports scanned but not shown below are in state: closed)
PORT STATE SERVICE
22/tcp open ssh
80/tcp open http
139/tcp open netbios-ssn
445/tcp open microsoft-ds
631/tcp open ipp
Device type: general purpose
Running: Linux 2.4.X|2.5.X|2.6.X
OS details: Linux 2.5.25 - 2.6.3 or Gentoo 1.2 Linux 2.4.19 rc1-rc7)
Uptime 1.567 days (since Wed Apr 26 08:30:31 2006)
'output snipped'
Nmap finished: 256 IP addresses (3 hosts up) scanned in 8.341 seconds
There are a whole lot of open services here. The -O tells nmap to try to identity the operating systems.
Related Articles
- see the helpful man pages for all of the commands in this article
- The Linux CLI for Beginners, or, Fear Not the Linux Command Line!
- cURL, the Swiss Army Knife of Download Utilities
- Why Firefox Rocks: Great Firefox Tricks, Part IV
- Understanding Tunneling: Hiding Packets In Plain Sight
Remote Testing
Running tests from outside your LAN, and from different geographical locations, is a great way to pinpoint trouble spots. A good way to do this is to have nice friends in other cities or other countries who give you shell accounts on their servers. Another way is to use Websites that are set up for remote network testing; see Resources for a list. You can do some low-budget remote testing without leaving your network administrator lair by using a dialup Internet account.
Resources
- see the helpful man pages for all of the commands in this article
- Websites with remote testing tools:
- DNSStuff.com
- Traceroute.org
- Sam Spade
Article courtesy of Enterprise Networking Planet
- Skip Ahead
- 1. Three Essential Linux Networking Applications
- 2. Troubleshooting a Non-responsive Server
- 3. Mapping Network Hosts and Services
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