Scanning your network

One of the basic ways to discover devices is to use a ping sweep with Nmap.  This sends out a ping to a single device or a range of devices. It used to be that hosts that dropped ICMP echo requests (ping) would up show as being down in Nmap. It seems that newer versions of Nmap are able to detect if a host is up if it doesn’t respond to a ping. (Try ping microsoft.com and see what it responds with.)

Pinging a single device

nmap -sP 192.168.0.1

Results

Nmap scan report for 192.168.0.1
Host is up (0.055s latency).

Pinging a range of IP addresses

nmap -sP 192.168.0.1-5

Results

Nmap scan report for 192.168.0.1
Host is up (0.0046s latency).
Nmap scan report for 192.168.0.3
Host is up (0.016s latency).
Nmap scan report for 192.168.0.5
Host is up (0.000098s latency).

Pinging the entire network

nmap -sP 192.168.0.0/24

Results

Nmap scan report for 192.168.0.1
Host is up (0.055s latency).
Nmap scan report for 192.168.0.3
Host is up (0.014s latency).
Nmap scan report for 192.168.0.5
Host is up (0.00029s latency).
Nmap scan report for 192.168.0.100
Host is up (0.0090s latency).

The last command will send a ping out to any device that has their IP address starting with 192.168.0.x.  (The /24 is short-hand for the subnet mask of 255.255.255.0.)

Device Enumeration

Once we have a list of devices on our network we may want to know some information about it.  Simply typing the command nmap along with the IP address or name of the device, will return what ports are open on the device and guess what service is running on the device.  For example, when I run nmap on my own machine I get the following:

nmap 192.168.0.5

PORT     STATE SERVICE
22/tcp   open  ssh
88/tcp   open  kerberos-sec
139/tcp  open  netbios-ssn
445/tcp  open  microsoft-ds
515/tcp  open  printer
631/tcp  open  ipp
3689/tcp open  rendezvous

What if I want some more information like what version of ssh am I running?  Use the -sV flag.

nmap -sV 192.16.0.5

Results

PORT     STATE SERVICE      VERSION
22/tcp   open  ssh          OpenSSH 5.2 (protocol 2.0)
88/tcp   open  kerberos-sec Mac OS X kerberos-sec
139/tcp  open  netbios-ssn  Samba smbd 3.X (workgroup: WORKGROUP)
445/tcp  open  netbios-ssn  Samba smbd 3.X (workgroup: WORKGROUP)
515/tcp  open  printer
631/tcp  open  ipp          CUPS 1.4
3689/tcp open  daap         Apple iTunes DAAP 9.0.3
Service Info: OS: Mac OS X

Also notice we get some extra information such as the OS I’m running and the workgroup my samba shares are on.

Now let’s take what we learned and put them together.  How would I get information on all devices on my network?

nmap -sV 192.168.0.0/24

The output of this is too long for here, but I think you get the idea; it’ll display all the service information (along with service versions) for all hosts on the network.

That’s the basics of using nmap.  With the ideas presented here, you should be able to find out most information about about devices on the network you are currently connected to.

Question #3 asks you to find the largest prime factor of a very large number.  My first instinct was to start at Sqrt(n) and work my way back until I find the first factor.  The problem here is that the first factor you find may not be the first PRIME factor.  Instead, my approach to this problem was to find all factors of the number between 2 and Sqrt(n) and put them in in a list.

Of all the numbers in the list, one of them is the largest prime factor, but which one?  To find out, I made an assumption that turned out to be right:  The composite factors have at least one prime factor that is already in the list.  If I can show that a given number has no factors in the list, then it is a prime factor.  Further, if I have a sorted list and start at the end, I can show that the number is the largest prime factor.

Anyway, here’s the code I used:

n = 600851475143 # Find the largest prime factor of this
div = [x for x in range(2,int(math.sqrt(n))) if n % x == 0] # Get all factors
i, j = 0, len(div) - 1
while j > i: # Determine which one of the factors is the largest prime

# This number is composite, go to the next largest factor
if div[j] % div[i] == 0: i,j = 0,j-1
# See if the next number at the beginning of the list divides the current number
else: i += 1

print div[j] # Print out the largest prime factor

Today I spent some time investing the issue and found out that a lot of people were having the issue, but I didn’t find any fixes.  Long story short the fix was to enable FastCGI PHP5 on Bluehost.  When I did that an error finally appeared on the screen! Apparently I misspelled my database name >_<.

Anyway, if you’re having the same issue, let me know if this fix worked for you.

As an example let’s say I have a drop-down of names.  I want to have the name “Nick” selected as the default value.  Using jQuery and XPATH, we can do this in a clean way:

$('select#name').find("option[@value=" + name + "]").attr("selected","selected");

The first part $('select#name') simply locates the select drop-down that we want (This is done in a fashion similar to CSS selectors).  The next part will find a child that is an option node and has the value of the name specified.  It will then assign the value “selected” to the attribute “selected.”  Simple as that!

•  Learn Python – I feel I should’ve avoided the whole Ruby craze and stuck with Python.  I started the O’Reilly book last summer, but never got around to finishing it.   I hope I have better luck this summer.
• Learn C# – At work I’m pretty much forced to use .NET for some projects.  Since the only .NET language I remember is VB.NET I’ve been using that.  Instead I would prefer something that feels more like Java, thus the desire to want to learn C#.
• Learn iPhone SDK – This is a “if I’m bored enough” idea.  I think it would be cool to write iPhone apps, but this doesn’t have any practical purpose.
• Read – There are a few books I have in mind.  Here are a few that come to mind:
  • GTD – There’s so much information in this book, thus my desire to read it again.
  • The Pragmatic Programmer – Saw it at my school’s library
  • Books on System Theory - Jeff Lindsay started a google group for groksystems.  Of course this got me interested in Systems again.  I plan on finishing Ackoff’s Best and even found a couple books at the school library.
  • Chess books – I admit it: I like chess.
• WeBGoat - This is a neat web security practice app.  It’s essentially a Tomcat server with insecure web pages (written in JSP) that teach you about a certain exploit and how to protect against it.  Sounds neat to me.
• PBWiki QuickEdit – In my last post I had an idea for a notepad-like program that would instead edit wiki pages.  I actually want to make this program this summer.  The first thing I would have to do is make a library that does the communication and then write the application itself.  I’m kind of excited about this one!

So that’s the plan for this summer.  Writing down a list is one thing and doing it is another; we’ll see how it goes.

However, for one of my classes I am writing on various topics of societal issues in computing.  Since most of these papers are based on opinion and research, I figured these would make for great blog posts.  In the future I would like to start posting some of these papers that I write for the sake of sharing with the community.  So get your RSS feeds ready for future posts!