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netcat (often abbreviated to nc) is a computer networking utility for reading from and writing to network connections using TCP or UDP. The command is designed to be a dependable back-end that can be used directly or easily driven by other programs and scripts.
UDP is a simple message-oriented transport layer protocol that is documented in RFC 768.Although UDP provides integrity verification (via checksum) of the header and payload, [4] it provides no guarantees to the upper layer protocol for message delivery and the UDP layer retains no state of UDP messages once sent.
This is a list of TCP and UDP port numbers used by protocols for operation of network applications. The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) only need one port for bidirectional traffic. TCP usually uses port numbers that match the services of the corresponding UDP implementations, if they exist, and vice versa.
Troubleshooting network devices that use network clients (devices that "phone home" via UDP, TCP, or SSL—Packet Sender can capture these requests) Testing and development of new network protocols (send a packet, see if device behaves appropriately) Reverse-engineering network protocols for security analysis (such as malware)
A packet-switched network transmits data that is divided into units called packets.A packet comprises a header (which describes the packet) and a payload (the data). The Internet is a packet-switched network, and most of the protocols in this list are designed for its protocol stack, the IP protocol suite.
Tools commonly used to perform banner grabbing are Telnet, Nmap and Netcat. For example, one could establish a connection to a target web server using Netcat , then send an HTTP request. The response will typically contain information about the service running on the host:
Another message send service is defined as a datagram-based application on UDP. A service listens for UDP datagrams on port 18. When a datagram is received by the receiver, an answering datagram is sent back to the sender containing exactly the same data.
UDP hole punching is a method for establishing bidirectional UDP connections between Internet hosts in private networks using network address translators. The technique is not applicable in all scenarios or with all types of NATs, as NAT operating characteristics are not standardized.