What are the functions of tcpdump in Linux?

TCPdump is a command-line tool used for analyzing network traffic, capable of capturing and dissecting network packets. It has the following key functionalities:

1. Capture network packets: TCPdump can capture network packets on a specified network interface and display their contents. It can capture packets of various protocols, such as TCP, UDP, ICMP, etc.
2. Packet filtering: TCPdump enables users to specify capturing specific types of packets using BPF filters. Users can filter based on source IP address, destination IP address, port number, and more in order to capture packets of interest.
3. Packet analysis: TCPdump can analyze captured packets and display detailed information, such as source IP address, destination IP address, port number, transmission protocol, packet length, and more.
4. Capturing and saving: TCPdump can store captured packets in a file for later analysis. Users can choose to save all packets or only those that meet specific filtering criteria.
5. Offline analysis: TCPdump can read data packets saved in a file and analyze them offline. Users can use the same filters and parsing functions to analyze offline data packets.
6. Detailed statistics: TCPdump can provide detailed statistical information, such as the number of captured packets, the number of packets for each protocol, and the percentage of traffic for each protocol.

In short, TCPdump is a powerful network analysis tool that helps users capture and analyze network packets, enabling a detailed understanding and debugging of network traffic.