nmap lesson 2 (begginer)

Ok so you know how to nmap:
nmap 192.168.1.1
and you know how to nmap –P0 –O
nmap 192.168.1.1 –P0 –O
So now you want to know more. Ok so let’s find out your IP address. If you are in windows do an ipconfig if you are in *nix do a ifconfig. Ok so typically your behind a wireless router or something if you have cable or dsl. Or if your range is in between any of these:
10.0.0.0 to 10.255.255.255
172.16.0.0 to 172.31.255.255
192.168.0.0 to 192.168.255.255
That means you have a private IP address and that your router navigates the internet for you using NAT(PAT technically). So you need to find your publicly routable address. To find this goto ipchicken.com and it will tell you your external IP. So let’s say your IP is 68.52.155.53. Ok take this address and run it through arin.net or ripe.net if you are in Europe or afrinic if you are in Africa, etc..
Ok so my address gives me two, possible selections for Comcast:
Comcast Cable Communications, Inc. JUMPSTART-1 (NET-68-32-0-0-1)
68.32.0.0 - 68.63.255.255
Comcast Cable Communications, Inc. NASHVILLE-3 (NET-68-52-128-0-1)
68.52.128.0 - 68.52.159.255

I am going to choose the Nashville one because that is where I am at and it is a smaller range.
So I want to narrow my range down as much as possible so I have less results to look at. So I want to scan IP’s that are near mine, because most likely those are other Comcast customers and potentially even my neighbors. So I want to scan the range 68.52.155.x . x is going to stand for 0 through 255 and I also want to output this to a text file so that I can review it later, because it is going to take a long time. So here is my command:
nmap 68.52.155.0/24 –P0 –O –oN bob.txt
This well output everything to bob.txt in the current directory.
Next Lesson, interpreting ports.