Scanning Networks in Hindi
1.1Technology Brief
After Footprinting phase, you may have enough information about the target. Now Scanning network phase requires some of this information to proceed further. Network Scanning is a method of getting network information such as identification of hosts, port information, and services by scanning networks and ports. The main Objective of Network Scanning is:
- To identify live hosts on a network
- To identify open & closed ports
- To identify operating system information
- To identify services running on a network
- To identify running processes on a network
- To identify the presence of Security Devices like firewalls
- To identify System architecture
- To identify running services
- To identify vulnerabilities
1.2 Overview of Network Scanning
Scanning Network phase includes probing to the target network for getting information. When a user probes another user, it can reveal much useful information from the reply is received. In-depth identification of a network, ports and running services helps to create a network architecture, and the attacker gets a clearer picture of the target.
What is TCP Communication ?
There are two types of Internet Protocol (IP) traffic. They are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). TCP is connection oriented. Bidirectional communication takes place after successful connection establishment. UDP is a simpler, connectionless Internet protocol. Multiple messages are sent as packets in chunks using UDP. Unlike the TCP, UDP adds no reliability, flow-control, or error-recovery functions to IP packets. Because of UDP’s simplicity, UDP headers contain fewer bytes and consume less network overhead than TCP.
Flag filed in the TCP header is of 9 bits. Which includes the following 6 TCP flags: -
| ID | Flag | Use |
|---|---|---|
| 1 | SYN | Initiates a connection between two hosts to facilitate communication. |
| 2 | ACK | Acknowledge the receipt of a packet. |
| 3 | URG | Indicates that the data contained in the packet is urgent and should process immediately. |
| 4 | PSH | Instructs the sending system to send all buffered data immediately. |
| 5 | FIN | Tells the remote system about the end of the communication. In essence, this gracefully closes a connection. |
| 6 | RST | RST Reset a connection |
There is three-way handshaking while establishing a TCP connection between hosts. This handshaking ensures successful, reliable and connectionoriented session between these hosts. The process of establishment of a TCP connection includes three steps.
Consider Host A wants to communicate with Host B. TCP Connection establishes when host A sends a Sync packet to host B. Host B upon receipt of Sync packet from Host A, reply to Host A with Sync+Ack packet. Host A reply with Ack packet when it receives Sync+Ack packet from host B. After successful handshaking results in the establishment of TCP connection. U.S Dept proposes TCP/IP model. Of Defence by combining OSI Layer Model and DOD. The Transmission Control Protocol (TCP) and the Internet Protocol (IP) are two of the network standards that define the Internet. IP defines how computers can get data to each other over a routed, interconnected set of networks. TCP defines how applications can create reliable channels of communication across such a network. IP defines addressing and routing, while TCP defines how to have a conversation across the link without garbling or losing data. Layers in TCP/IP model perform similar functions with similar specifications like in OSI model. The only difference is they combine top three layers into a single Application Layer.
1.3 Creating Custom Packet Using TCP Flags
Colasoft Packet Builder software enables to create the customized network packets. These Customized Network packets can penetrate the network for attacks. Customization can also use to create fragmented packets. You can download the software from www.colasoft.com.
Colasoft packet builder offers Import and Export options for a set of packets. You can also add a new packet by clicking Add/button. Select the Packet type from the drop-down option. Available options are: -
- ARP Packet
- IP Packet
- TCP Packet
- UDP Packet
After Selecting the Packet Type, now you can customize the packet, Select the Network Adapter and Send it towards the destination.
