Port scanner, TCP/IP, Firewall & the Bouncer

Thought writing little something about what port scanners, TCP/IP and Firewall in general.

Read this. Don't skip!

When we talk about port it's necessary we also know what packet is. A pack it a little portion of a file that's transferred from one computer to another, and when this pack is transferred it's given destination and source IP address along with a port number. When a computer on receiving end receives this packet their firewall checks for rules set for that port or the IP. Firewall basically is like an entry point on your computer, everything that goes in or out goes through it.

See every app runs on different port. Must've heard of HTTP and FTP? no? Joined internet today or what?


FTP (File Transfer Protocol) - Port 21
SMTP (Simple Mail Transfer Protocol) - Port 25
Login (Login Host Protocol) - Port 49
HTTP (Hypertext Transfer Protocol) - Port 80 But I still don't understand??!
Right that's expected. Lets get a little more practical now. Your friend's computer wont open any webpage. He brings the computer to you and asks if you can fix. You check if it has internet. You do some other check but still cant figure out the problem.
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What about checking whether firewall has port 80 opened? as you see, port 80 is used to make HTTP connections. It's possible that firewall is blocking it. Did you guys notice how workplace restricts your access to pornographic websites? Yes, firewalls list of rules are blocking those IP addresses.

So what's firewall again?
It's just a dude with list check-list in hand making sure who can come in, and how can go out. Understood? right! get a snicker!


TCP/IP(that's on scary acronym.. gonna drive me sane!) Don't worry.
Transmission control Protocol(TCP) is a language/protocol that ensures your packets are sent from one computer to another securely. You know when data is broken into packets it's a mess! thanks to TCP it's pasted back together into same order it when it goes to receiving end.

Okay..

This almighty TCP seem to know it all.. how does it know where to send data to? Well its friend Internet Protocol does! It contains the destination and source address and knows where the packet goes.

Alright? what's my IP address then? Click here to find out your IP address http://ipchicken.com/

Hmm.. What about TCP, can I see it too? Nop. But you can make sure it's running. If you send a packet using ping command followed by loopback address(this is virtual address for testing) it should return responses. Meaning TCP/IP is working properly. But you really shouldn't worry much about it because computers already comes with this stack installed.

What's port scanner?
As you seen above, different programs run on different protocol. If someone creates a program that checks for open ports on your computer and finds a vulnerability for that port then you're screwed isn't it. That's why people tell to keep un-used ports closed all the time. Check this PDF to find out common vulnerabilities on ports. http://www.tenable.com/sites/drupal...s/Vulnerability Reporting by Common Ports.pdf



Didn't understand anything? Well atleast you put some effort I guess? It's time you learn "basics of how Internet works".

Goodluck! any questions feel free to ask!