Basics of network

network

In general, the term network can refer to any interconnected group or system. More specifically, a network is any method of sharing information between two systems (human, electrical or mechanical).


classification of network

1. According to the size of the Network:
LAN 
MAN 
WAN 
PAN 
CAN
2. According to type of connection used:
Wired Network
Wireless Network
lan(local area network)


Characteristics:
1) A Local Area Network is a group of computers and network 
2) Communication devices within a limited geographic area, such as an office building. For example, a library will have a wired or wireless LAN for users to interconnect local devices(e.g., printers, and servers).
3) Local area networking uses switches, bridges and/or repeaters, and hubs to interconnect LANs and increase overall size. Routers are used to connect a LAN to a WAN or MAN.
4) LAN are characterized by the following:
5) High data transfer speeds.
6) Generally less expensive technologies 
7) Limited geographic area
8) Security 
9) Scalability 
10) Reliability
man(metropolitan area network)

A Metropolitan Area Network is a network that connects two or more Local Area Networks or Campus Area Networks together but does not extend beyond the boundaries of the immediate town, city, or metropolitan area. A MAN can range anywhere from 5 to 50km in diameter.
wan(wide area network)

A WAN is a data communications network that covers a relatively broad geographic area (i.e. one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies. They are generally connected with each other using routers.
WAN are characterized by the following:
1) Multiple interconnected LANs. 
2) Generally more expensive technology.
3) More sophisticated to implement than LANs.
4) Exist in an unlimited geographic area.

pan(personal area network)

A personal area network (PAN) is a computer network used for Communication among computer devices close to one person. 
Some examples of devices that may be used in a PAN are printers, fax machines, telephones, scanners. The reach of a PAN is typically within about 20-30 feet (approximately 6-9 Meters).
san(storage area network)

We have a lot of data in the form of audio and video. We need to store data for quick access and transfer on special storage devices.
SAN may be referred to as a sub network or special purpose network. Its special purpose is to allow users on a larger network to connect various data storage devices with clusters of data servers.
vpn(virtual private network)

VPN is a private network that lets you access public networks remotely. 
VPN uses encryption and security protocols to retain privacy while it accesses outside resources by creating a virtual network.
according to the type of connection used

1) Wired Network: A network that connects devices using cables (wires) like Coaxial Cable, Twisted pair Cable, Optical Fiber Cable etc.
2) Wireless Network: A network that connects devices using wireless technologies like Bluetooth, infrared, radio frequency etc.
according to the type of functional group


peer to peer network(workgroup)


A workgroup is a collection of computers on a LAN that share common resources and responsibilities. 
Workgroups provide easy sharing of files, printers and other network resources.
client-server network(domain)


1) A Domain is a "Network Architecture" in which each computer or process on the network is either a client or a server.
2) servers are powerful computers or processes dedicated to managing disk drives (file servers), printers (print servers) etc. 
3) Clients are PCs or workstations on which users run applications.
4) Clients rely on servers for resources, such as files, devices, and even processing power.

Network attacks

NETWORK ATTACKS

attacks on network

Men in middle attack
Attackers position themselves between two systems and actively participate
in the connection to gather data. The attacker may also run program which
spoofs dns reply, configured to send false DNS information so that a DNS query
for a given website will resolve to the attacker's IP address. Then the attacker will
activate a program such that it will transparently proxy all HTTP and HTTPS traffic it receives. The DNS spoof program detects DNS request for www.abc.com and redirects the client to
attacker's machine. The ARP table convinces the victim's machine that it is indeed talking
to the intended web server. The victim's browser starts to establish a secure connection.

All messages for establishing SSL connection are sent to MITM running on the attacker's machine.
Hacker's system acts as a SSL proxy, establishing two SSL connections-one from victim to the attacker's
machine and the other from attacker's machine to the actual web server. When establishing the SSL session
between the victim machine and the attacker machine, MITM program will send the attacker's own certificate. The victim's browser will notice that the certificate is not signed by a trusted Certificate Authority and show
a message to the user asking the user whether to accept this un-trusted certificate or not. The normal tendency is to accept
it, thinking it is some error message.
denial of service(DOS)
A denial of service attack (DOS) is an attack through which a person can render
a system unusable or significantly slow down the system for legitimate users by overloading
the resources, so that no one can access it. If an attacker is unable to gain access to a machine, the attacker most probably will
just crash the machine to accomplish a denial of service attack.

Network Attacks

NETWORK ATTACKS
Attacks on network

Attacking a network means either defacing it to ground or accessing a data which
you should not. In a network there are mainly two types of attacks are possible.
1). Denial of Service (DOS) attack.
2). Data Stealing.
network-infrastructure attacks
Hacker attacks against network infrastructures can be easy, because many
networks can be reached from anywhere in the world via the Internet. Here are some examples of network-infrastructure attacks: Connecting into a network through a rogue modem attached to a computer behind
a firewall Exploiting weaknesses in network transport mechanisms, such as TCP/IP and NetBIOS Flooding a network with too many requests, creating a denial of service (DoS)
for legitimate requests installing a network analyzer on a network and capturing every packet that travels across it, revealing confidential information in clear text.
common network attacks

1) Sniffing Attack.
2) Man in middle attack.
3) DOS attacks.
sniffing attacks

Sniffers monitor network data. A sniffer can be a self-contained software program or a hardware device with
the appropriate software or firmware programming.
Sniffers usually act as network probes or "snoops" examining network traffic but
not intercepting or altering it. Some sniffers work only with TCP/IP packets, but the more sophisticated tools can work with many other protocols and at lower levels such as the Ethernet frame.
concept

A sniffer is a piece of software that captures the traffic on a network. They are available for
several platforms in both commercial and open-source variations. Some of simplest packages use a command line interface and dump captured data to the screen, while sophisticated ones use GUI, graph traffic statistics, track multiple sessions and offer several configuration options.
Sniffers are also the engines for other programs. Network Intrusion Detection Systems (NIDS)
use sniffers to match packets against a rule-set designed to flag anything malicious or strange. Network utilization and monitoring programs often use sniffers to gather data necessary for metrics and analysis. It is to be noted that sniffers do not intercept or alter the data it captures.
The most common way of networking computers is through Ethernet. The Ethernet protocol works by broadcasting packets to all
hosts on the network, with the packet header containing the MAC address of the machine that is meant to receive the packet. All others are supposed to ignore it. A NIC (Network Interface Card, also known as Ethernet card) that is accepting all packets, regardless of the intended machine is said to be in promiscuous mode. A sniffer is a program that sets the desired NIC into promiscuous mode.
note
A packet sniffer is known for its ability to "sniff" plain text passwords. On a normal LAN there are thousands
of packets being conversed by numerous machines every minute. Therefore, anything transmitted in plaintext, such as passwords, web pages, database queries and messaging over the network will be vulnerable to sniffing. man in the middle