COMPUTER NETWORKS: CHAPTER 5- OSI model cont.

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COMPUTER NETWORKS: CHAPTER 5- OSI model cont.

hello guys ... how is it going ? my gal ditched me :(
anyway i give a damn ...
so we just finished a brief introduction of THE OSI model. today m gonna take a look
at how OSI model works in real life ..here we go baby
(if u are confused a bit about ports and all that dont worry , i will cover it )

ok as you can see in picture , there is a user on left hand side who is using a browser
to connect to internet . say he is typing to www.facebook.com and hits enter or click on go
or watever.Now wat happens when u do that .... ur computer sends a message to a DNS server
which stands for domain name service, and the work of DNS server is to convert ur address
like facebook.com to its ip address.And suppose the IP of ur computer is X.X.X.X and the IP of
the server u r looking for is Y.Y.Y.Y.Now after connecting DNS server , your browser now
knows that it need to go to Y.Y.Y.Y .Now top layer that is application layer asks a webpage coz thats wat ur browser requested, now data passes down to presentation layer which converts or formats it to standard format which is http in this case .Again data is passed to session layer , it says ok this is a separate request so m gonna create a new session so that i dont get confused when reply comes, bcoz at a moment u may b surfing net with multiple tabs.then it passes it down to transport layer, this layer
first decide this is gonna be a reliable transaction or unreliable ... that means it decides that it is
gonna use TCP or UDP (dont panic)..
tcp is for reliable transfer and udp is for unreliable transfer.
now in web browsers TCP works .So server at facebook.com .

DESTINATION PORT

one other very very important thing it does and that is it defines SOURCE and DESTINATION port nos.
suppose a server is both web and email server and u requested a webpage ... how servre gonna
understand that u need a webpage ... for that this layer sets the DESTINATION port to 80 , which is for
http requests .... by this server will understand that ur request is http (web page) not smtp (email).

SOURCE PORT

It is also necessary to assign a source port no. now source port no. is important , suppose in u have 3 browsers and
u have opened google , gmail and facebook..... and u requested something in facebook , requests processed then sent then response comes in ... how ur computer gonna decide that this data is for which browser ??? gmail , google or faebook !!!
so ur source port is assigned randomely and uniqely ... say its 1897

now wat happens ... ur computer requests to server saying my destination port 80, server understands that its a http requests again says my source port is 1897 ... server understands that in response destination port must be 1897. so when response comes in ur computer realises that the data is to be displayed on the browser which
is opening facebook.com

now data goes to network layer which adds SOURCE and DESTINATION IP addresses.which will be original source
and final destination address which will be X.X.X.X and Y.Y.Y.Y
now moving down to data link layer , it adds source and destination MAC addresses, which are physically burned
in ur network card.in next chapter we gonna discuss why MAC address is needed.
physical layer converts data to electric signal
m done ... this chapter is over .... enjoy guys ..and feel free to ask anything...

ABOUT PICS

in first two pics u can see i have established two ftp sessions with two servers 1.>cet.edu.in 2.>cisco.com .. in 3rd pic u can see i have issued netstat command which shows all the connections .. so u can see 2 ftp connections but with different ports (in first coloumn)
thank you :)

STEALTHBASTARD

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COMPUTER NETWORKS :CHAPTER 4

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COMPUTER NETWORKS : CHAPTER 4- The OSI model cont.

hello guys .. how u doin !!! its a little hot in here ... grrrr

anyways enough shit
in last chapter we stopped at session layer...wat is the next layer ??
its transport layer

TRANSPORT LAYER

First of all this is the most important layer in my opinion.this layer describes in which manner
or in which way data will b sent across. When you working with this layer you gotta choose how you sending
your data , there are 2 ways

• RELIABLY
• UNRELAIBLY

now u may b thinking y in hell one should send data unreliably...well for now
just remember that in reliable transfer its gonna take more time than unreliable transfer.
We(not we , applications) use reliable transfer in most of the time like in browsers, in a file transfer
etc.
And unreliable transfer is used more in REAL TIME data transaction like in VoIP , online multiplayer games etc etc.

also one more very important thing ... this layer deals with PORTS ,hackers are very much dependable on ports ....

ABOUT PORTS

Now ports basically classifies type of service u are availing, like suppose you are trying to open Google on ur browser
and the server ur pc is requesting data is a web server and also an e-mail server, so how wud the server know wat service
you are trying to access...this is where port come in role.

MUCH MORE ON THIS LAYER IS ABOUT TO COME !!!

NETWORK LAYER

OOOO this is a hell of a layer.... later on this series m gonna camp on this layer.
this layer deals with logical addressing , suppose you are assigning a new IP to ur pc or router or watever,
you are dealing with network layer.
It also take u to ur destination over internet the best way possible . that means suppose u r trying to open a site
and there are many many routers and servers between ur pc and the destination so this layer finds best way possible

DATA LINK LAYER

this layer assigns physical address like MAC address , and ensures data is error free.

PHYSICAL LAYER

it simply converts all digital data to electric signals and deals with cables ...

so briefing of all the layer is over !!!
in next chapter we gonna c some real life example .. enjoy,take care

STEALTHBASTARD

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COMPUTER NETWORKS :CHAPTER 3- Understanding the OSI model

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COMPUTER NETWORKS :CHAPTER 3- Understanding the OSI model

Hello guys, here we are on chapter 3 0f computer networks.Sorry i was
out of town so i coudnt post , anyways in this post i will be
discussing about THE OSI MODEL.
some of you might have heard OSI model.Or you may have heard "this
is a layer 4 function or this layer deals with data packets etc etc".
Anyway its a model and it has layers , each of the layer do things.

m gonna walk you through what OSI model is and wats the concept behind
this and how it is usefull to us in this chapter and next few chapter .

LAYERS

Ok here is the mythical OSI model :

1. Application
2. Presentation
3. Session
4. Transport
5. Network
6. Data link
7. Physical

(I RECOMMEND YOU TO MEMORIZE THESE LAYERS)

FUNCTION :
suppose you building a house, you just dont get everything and try messing with it.
You have to do it in a ordered way or in phases, and you have specialized people , specialized
equipment to complete it,
in same way OSI model helps us to break down network functions , it helps to understand how network
works.
creates standard for equipment manufacturing.Like in physical layer we deal with hardwares,hubs,
switches,routers,cables.. so manufacturer have to concentrate on physical layer and works according to
standard, dont worry u will understand :)

LAYERS INDIVIDUALLY

• Application layer

ok this is the top layer of the OSI model, now this layer is the most familiar layer becoz this is wat you see.
Any application you use which communicate through ur network like browser , e-mail client or COUNTER STRIKE ..these
all application deals with application layer .
AS SOON AS it starts sending data it passes through presentation layer

• Presentation layer

Accd. to cbt "presentation layer generi-fies the data", this means it formats ur data such that any server you are communicating
with understands your request.
Also this layer has encryption services, more precisely generic encryption services.
then data get passed to session layer

• Session layer

As name suggests , it starts and ends sessions and it keeps sessions separate like you using more than one application which is using your network then which data sud go to which app. this will b decided by session layer

thats all for today, will post tomorrow... and yeah stay tuned some really interesting (practicals) things to come and u gonna enjoy !!!

STEALTHBASTARD

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COMPUTER NETWORKS : CHAPTER 2 - some more basics

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COMPUTER NETWORKS : CHAPTER 2 -basic communication

I hope you read first chapter , well if you already know that than no problem .
we will start chapter 2 and i will be writing about how devices communicate in a LAN and how they communicate to cloud.

BRIEF INFRA OF LAN

Ok now u are in a LAN , then you must see a cable connected to your laptop or PC or watever device is there in your network.Those cables are called Ethernet Cable , and that cable is connected to NIC (network interface card ). NIC is installed in your computer , the port to which cable is connected is a part of NIC .
The cable is then connected to a SWITCH . A switch connect all the devices within your network and then in most cases switch is connected to a ROUTER .A ROUTER connects your network to outside world, which may be INTERNET or to another network.
So this was a brief infra of your LAN.

CLOUD

i have used the term CLOUD. U must have heard this word (not sky clouds LOL).Cloud is a common word by which we refer a very large
network or a very large collection of networks, which is internet.
In cloud there are a hell lot of networks which are interconnected , which are distributed all over the globe.
You can find all the servers in cloud like FTP servers, HTTP servers, SMTP servers, DHCP servers etc.

MEMORY ESSENTIALS

I know all of you know this but just for a quick revision m going through how we memories are defined in computers:
smallest unit is a BIT.
byte=8*bit
kilobyte = 1024*byte
megabyte = 1024*kilobyte
gigabyte = 1024*megabyte
terabyte = 1024*gigabyte

IMP NOTE - Whenever you say your connection speed is some Kbps or some Mbps , means your connection speed is some kilobit per second or some megabit per second
not kilobyte or megabyte .

BANDWIDTH

a rate of data transfer, bit rate or throughput, measured in bits per second (bps)
or u can say this how wide the road is

DELAY

the delay of an IP packet within an IP network
or u can say how fast cars are moving.

So thats all for this chapter . Feel free to ask. Stay connected

P.S- the symbols for router and switch shown are standard symbol . keep them in mind

©STEALTHBASTARD

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COMPUTER NETWORKS : CHAPTER 1

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COMPUTER NETWORKS

Hello guys , This is kumar sourav. I m writing my first post and i will be concentrating on computer networks as you gonna need it in long run. I will write these in different chapters , and i will focus mainly on CISCO routers , switches and hubs .

Anyway thanks a lot to HACK WITH STYLE and XEO HACKER .

Now we start.There is mainly two types of hacking :

• System hacking
• Network hacking

For network hacking you gonna need sound knowledge of computer networks.According to wiki A computer network, often simply referred to as a network, is a collection of computers and devices interconnected by communications channels that facilitate communications and allows sharing of resources and information among interconnected devices.

Or as i say this is a collection of devices which can communicate with each other

There are 4 types of networks

1. Local area network
2. Metropolitan area network
3. Wide area network
4. Wireless networks (both LANs & WANs)

• LOCAL AREA NETWORKS : these networks are relatively small networks and is generally implemented in a building .
• METROPOLITAN AREA NETWORKS : these are larger networks than LAN . these are generally implemented in a city or in a town.
• WIDE AREA NETWORKS : these networks cover a big area , you can say internet is also a WAN.
• WIRELESS NETWORKS : these are wireless networks which consists of both LAN & WAN.

M gonna focus on LAN for some days.

as this is my first post , m not gonna make it long so i stop here. But in next chapters onwards m gonna discuss a lot !!!

THANK YOU

by stealthbastard

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AthTek NetWalk – Network Monitoring, Packet Sniffing & Analysis

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AthTek NetWalk Personal Edition is a robust application to help in the administration of all kinds of networks. It is particularly useful for new network administrators who wish to gain in depth knowledge about network infrastructure and management. AthTek NetWalk contains graphical representations of the network with the use of advanced packet sniffing, to help project the network state in statistical and graphical format.

After installation, you will be prompted to select a network adapter to view stats from. You can also enable capturing packets in promiscuous mode by checking the relevant checkbox. Chose an adapter and hit Ok.

This will represent the overview of the network stats in a graphical user interface. This includes a monitoring dashboard, top MAC hosts pie chart, top IP hosts chart, and layered summary of application, net/transport and physical layers.

You can either click on any of the categories of the layered summary of application, net/transport and physical layers or select the Layered View option from the top left corner of the main interface (below the Overview tab below Monitoring). The layered view can be utilized to view information regarding DNS name resolution, HTTP – World Wide Web, QQ – Technet IM, ICMP Analysis, MAC hosts, VLAN, SMTP, Telnet and much more.

You can also chose the Events option below layered View to analyze network integrity and see a map of the network via the Matrix Map option (below Events).

To see a graphical representation of the network state click on the Graphs tab (below Matrix Map). From here, you can view current utilization, application layer protocol packets, ping requests and replies, TCP vs UDP, ARP requests and replies, broadcast vs multicast total, DNS (successful and failed queries), packet size distribution and TCP SYNs, Fins and RSTs.
AthTek NetWalk is a comprehensive network infrastructure analysis tool which helps in managing, maintaining and troubleshooting all kinds of networks. It works on Windows XP, Windows Vista, Windows 7 and Windows Server 2008.
Download AthTek NetWalk Personal Edition (Free Edition)

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