Hack and / - Dynamic Config Files with Nmap
The great thing about tools is that you often can misuse them for a completely different purpose. The end of a screwdriver makes a passable hammer; a butter knife can be a screwdriver, and even a paper clip can substitute for a key in a pinch. Normally, you probably think of nmap as a security tool. After all, it's ideal when you want to test a machine for open, vulnerable ports. The other day though, I realized nmap had another use—a way to scan my network and build a dynamic configuration file based on what machines replied to my scan.
This whole project started when I decided to deploy Munin across my servers so I could graph trending data for each machine on my network. Munin is a great tool for trending, because once you install the agent, it often will discover what services and statistics to monitor and graph automatically. The downside for me though was that I already had a network full of servers. It was bad enough that I had to install an agent on each machine, but I also had to build a giant configuration file on my Munin server by hand that listed each server it should monitor. Plus, any time I added a machine to the network, I had yet another step in my build process as I had to add that new server to my Munin config.
I'm a big fan of automation, and I figured there must be some easier way to add all my machines to this file. When you look at a Munin configuration file, it seems ripe for automation:
dbdir /var/lib/munin htmldir /var/www/munin logdir /var/log/munin rundir /var/run/munin tmpldir /etc/munin/templates [web1.example.net] address web1.example.net [web2.example.net] address web2.example.net [db1.example.net] address db1.example.net [db2.example.net] address db2.example.net
The syntax for a generic munin.conf file is pretty straightforward. First, a few directories are defined, and then each server is defined within a pair of brackets. Inside those brackets, you can assign a name to the server or just use the hostname. After that, the following line lists the hostname or IP address for that server. In the above example, I've defined four servers.
If I wanted to generate this configuration file automatically, I had to figure out some way to detect what servers were running Munin on my network. Munin makes this simple though, because each server has a Munin agent listening on port 4949 by default. All I had to do was use nmap to scan the network and list all the machines that had port 4949 open. I figured I could parse that output and append it to my munin.conf file, and then maybe make a vim macro to go through each line and format it.
The first step was to find the right nmap syntax so that it would scan my network and list all machines that were listening to port 4949. First, I tried the standard command:
$ nmap -p 4949 10.1.1.0/24 Starting Nmap 4.11 ( http://www.insecure.org/nmap/ ) ↪at 2010-03-01 20:18 PST Interesting ports on 10.1.1.1: PORT STATE SERVICE 4949/tcp closed unknown MAC Address: 00:00:0C:01:CD:05 (Cisco Systems) Interesting ports on purple1.example.net (10.1.1.50): PORT STATE SERVICE 4949/tcp closed unknown MAC Address: 08:00:20:CF:9D:D7 (SUN Microsystems) Interesting ports on web1.example.net (10.1.1.53): PORT STATE SERVICE 4949/tcp open unknown MAC Address: 00:50:56:92:34:02 (VMWare) Interesting ports on web2.example.net (10.1.1.67): PORT STATE SERVICE 4949/tcp open unknown MAC Address: 00:30:48:A0:12:98 (Supermicro Computer) . . .
As you can see, for each machine that nmap finds, it lists the IP, whether the port is open, and even tries to identify the type of machine. Even though you could grep out the machines with open ports from this output, it would be quite a pain to parse everything with the multiline output. Instead, I used the -oG argument to nmap, which tells it to output in “grepable format”, along with the - argument, which tells it to send that output to STDOUT. The result was much simpler to parse:
$ nmap -oG - -p 4949 10.1.1.0/24 # Nmap 4.11 scan initiated Mon Mar 1 20:26:45 2010 as: ↪nmap -oG - -p 4949 # 10.1.1.0/24 Host: 10.1.1.1 () Ports: 4949/closed/tcp///// Host: 10.1.1.50 (purple1.example.net) Ports: 4949/closed/tcp///// Host: 10.1.1.53 (web1.example.net) Ports: 4949/open/tcp///// Host: 10.1.1.67 (web2.example.net) Ports: 4949/open/tcp///// . . .
Now I could just grep for “open”, and I'd get a list of all machines running Munin:
$ nmap -oG - -p 4949 10.1.1.0/24 | grep open Host: 10.1.1.53 (web1.example.net) Ports: 4949/open/tcp///// Host: 10.1.1.67 (web2.example.net) Ports: 4949/open/tcp/////
Kyle Rankin is a VP of engineering operations at Final, Inc., the author of a number of books including DevOps Troubleshooting and The Official Ubuntu Server Book, and is a columnist for Linux Journal. Follow him @kylerankin.
|Bitcoin on Amazon! Sort of...||Sep 28, 2016|
|Free Today: September Issue of Linux Journal (Retail value: $5.99)||Sep 27, 2016|
|nginx||Sep 27, 2016|
|Epiq Solutions' Sidekiq M.2||Sep 26, 2016|
|Nativ Disc||Sep 23, 2016|
|Android Browser Security--What You Haven't Been Told||Sep 22, 2016|
- Free Today: September Issue of Linux Journal (Retail value: $5.99)
- Bitcoin on Amazon! Sort of...
- Android Browser Security--What You Haven't Been Told
- Epiq Solutions' Sidekiq M.2
- Nativ Disc
- The Many Paths to a Solution
- Identity: Our Last Stand
- Readers' Choice Awards 2013
- Tech Tip: Really Simple HTTP Server with Python
Pick up any e-commerce web or mobile app today, and you’ll be holding a mashup of interconnected applications and services from a variety of different providers. For instance, when you connect to Amazon’s e-commerce app, cookies, tags and pixels that are monitored by solutions like Exact Target, BazaarVoice, Bing, Shopzilla, Liveramp and Google Tag Manager track every action you take. You’re presented with special offers and coupons based on your viewing and buying patterns. If you find something you want for your birthday, a third party manages your wish list, which you can share through multiple social- media outlets or email to a friend. When you select something to buy, you find yourself presented with similar items as kind suggestions. And when you finally check out, you’re offered the ability to pay with promo codes, gifts cards, PayPal or a variety of credit cards.Get the Guide