Introducing Practical Computer Networks: From a Hacker's Prospective Discussion 1

Hello all,

How you been ? Its been a long time since i made any post . :) Missed me ? (kidding ).

So I said i will be making a new series of video discussions titled " Practical Computer Networks: From a Hacker's Prospective", here i am publishing first video of the series.

Well you must be knowing how much important computer networks are if you want to go for hacking or cyber security. So i thought i would help you as much as i can by providing whatever i know. Computer Network is my favorite subject.

I wrote "From a hacker's prospective". What does that mean? actually i am trying to make it more hacking oriented thats why :)

so have fun. Thanks for all your support !

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Block Nmap Scans On Your Server

While browsing the packet storm security, I found a simple Bash script to block the Information disclosing nmap scans. This script is based upon IPTables. so for using this you should have IP tables installed on your server.

Code: 

#!/bin/bash
# To run this file, first give the permission +x and execute this program
# --# chmod +x blocknmap.sh
# --# ./blocknmap.sh


echo "1-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=1"
echo "3                                                                      3"
echo "3     ________   .__          ________                                 3"
echo "7     \______ \  |__|  ______/   __   \     ____    ____    _____      7"
echo "1      |    |  \ |  | /  ___/\____    /   _/ ___\  /  _ \  /     \     1"
echo "3      |        \|  | \___ \    /    /    \  \___ (  <_> )|  Y Y  \    3"
echo "3     /_______  /|__|/____  >  /____/   /\ \___  > \____/ |__|_|  /    3"
echo "7             \/          \/            \/     \/               \/     7"
echo "1                                                                      1"
echo "3              >> The Underground Exploitation Team                    3"
echo "3                                                                      3"
echo "7                                                                      7"
echo "1          [+] Site   : http://www.Dis9.com                            1"
echo "3                                                                      3"
echo "3                                                                      3"
echo "7            ###############################################           7"
echo "1            I'm Liyan Oz Leader of Underground Exploitation           1"
echo "3            ###############################################           3"
echo "3                                                                      3"                                         
echo "7-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-==-=-=-7"
echo "========================================================================"
echo "=                  Block Nmap Scanning using iptables                  ="
echo "=                         C0ded by Liyan Oz                            ="
echo "=                      http://0nto.wordpress.com                       ="
echo "========================================================================" 
echo ""
echo ""
#=====================
# Enable IP Forward
#---------------------


echo 1 > /proc/sys/net/ipv4/ip_forward


#=====================
# Flush semua rules
#---------------------
/sbin/iptables -F
/sbin/iptables -t nat -F


#=====================
# Block
#---------------------


/sbin/iptables -t filter -A INPUT -p TCP -m state --state RELATED,ESTABLISHED -j ACCEPT
/sbin/iptables -t filter -A INPUT -p UDP -m state --state RELATED,ESTABLISHED -j ACCEPT
/sbin/iptables -t filter -A INPUT -p ICMP -m state --state RELATED,ESTABLISHED -j ACCEPT
/sbin/iptables -t filter -A INPUT -m state --state INVALID -j DROP


/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ACK,FIN FIN -j LOG --log-prefix "FIN: "
/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ACK,FIN FIN -j DROP


/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ACK,PSH PSH -j LOG --log-prefix "PSH: "
/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ACK,PSH PSH -j DROP


/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ACK,URG URG -j LOG --log-prefix "URG: "
/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ACK,URG URG -j DROP


/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL ALL -j LOG --log-prefix "XMAS scan: "
/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL ALL -j DROP


/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL NONE -j LOG --log-prefix "NULL scan: "
/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL NONE -j DROP


/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j LOG --log-prefix "pscan: "
/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL SYN,RST,ACK,FIN,URG -j DROP


/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags SYN,FIN SYN,FIN -j LOG --log-prefix "pscan 2: "
/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags SYN,FIN SYN,FIN -j DROP


/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags FIN,RST FIN,RST -j LOG --log-prefix "pscan 2: "
/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags FIN,RST FIN,RST -j DROP


/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL SYN,FIN -j LOG --log-prefix "SYNFIN-SCAN: "
/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL SYN,FIN -j DROP


/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL URG,PSH,FIN -j LOG --log-prefix "NMAP-XMAS-SCAN: "
/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL URG,PSH,FIN -j DROP


/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL FIN -j LOG --log-prefix "FIN-SCAN: "
/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL FIN -j DROP


/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL URG,PSH,SYN,FIN -j LOG --log-prefix "NMAP-ID: "
/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags ALL URG,PSH,SYN,FIN -j DROP
/sbin/iptables -t filter -A INPUT   -p tcp --tcp-flags SYN,RST SYN,RST -j LOG --log-prefix "SYN-RST: "

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NETWORK TOPOLOGY

NETWORK TOPOLOGY

hey awl its smarty ujjwal :)  well  its mah frst post :D. Today i will tell you awl d basics of  NETWORK TOPOLOGY.

                               

What is a Network topology?

A network topology is the geometric arrangement of nodes and cable links in a LAN,


There are two types of topology: physical and logical. The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Logical topology is the method used to pass the information between workstations. Issues involving logical topologies are discussed in the section on
protocols

 The following section discuss the physical topologies used in networks

Main Types of Physical Topologies

    Linear Bus
    Star
    Star-Wired Ring
    Tree

            LINEAR BUS TOPOLOGY


A linear bus topology consists of a main run of cable with a terminator at each end. All nodes (file server, workstations, and peripherals) are connected to the linear cable. Ethernet and LocalTalk networks use a linear bus topology.

Advantages of a Linear Bus Topology

• Easy to connect a computer or peripheral to a linear bus.
• Requires less cable length than a star topology.

Disadvantages of a Linear Bus Topology

• Entire network shuts down if there is a break in the main cable.
• Terminators are required at both ends of the backbone cable.
• Difficult to identify the problem if the entire network shuts down.
• Not meant to be used as a stand-alone solution in a large building.

               STAR

A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub or concentrator.

Data on a star network passes through the hub or concentrator before continuing to its destination. The hub or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow. This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.

The protocols used with star configurations are usually Ethernet or LocalTalk. Token Ring uses a similar topology, called the star-wired ring.

Advantages of a Star Topology

• Easy to install and wire.
• No disruptions to the network when connecting or removing devices.
• Easy to detect faults and to remove parts.

Disadvantages of a Star Topology

• Requires more cable length than a linear topology.
• If the hub or concentrator fails, nodes attached are disabled.
• More expensive than linear bus topologies because of the cost of the concentrators. 

       

 Star-Wired Ring

A star-wired ring topology may appear (externally) to be the same as a star topology. Internally, the MAU (multistation access unit) of a star-wired ring contains wiring that allows information to pass from one device to another in a circle or ring . The Token Ring protocol uses a star-wired ring topology.

  

TREE

A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

 

Advantages of a Tree Topology

• Point-to-point wiring for individual segments.
• Supported by several hardware and software venders.

Disadvantages of a Tree Topology

• Overall length of each segment is limited by the type of cabling used.
• If the backbone line breaks, the entire segment goes down.
• More difficult to configure and wire than other topologies.

                                           

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Computer Networks: Chapter 3

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 !!!

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Computer Networks: chapter 2

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

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Computer Networks : chapter 1

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 .

.

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

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PWNSCAR

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