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The ICMP header starts after the IPv4 header and is identified by its protocol number, 1. [6] All ICMP packets have an eight-byte header and variable-sized data section. The first four bytes of the header have fixed format, while the last four bytes depend on the type and code of the ICMP packet. [3]
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 duplex, bidirectional traffic. They usually use port numbers that match the services of the corresponding TCP or UDP implementation, if they exist.
This is a list of the IP protocol numbers found in the field Protocol of the IPv4 header and the Next Header field of the IPv6 header. It is an identifier for the encapsulated protocol and determines the layout of the data that immediately follows the header. Both fields are eight bits wide.
Protocols that do not use port numbers (for example, Resource Reservation Protocol (RSVP), Encapsulating Security Payload (ESP), ICMP or ICMPv6) are supported for IPv4 firewall, IPv6 firewall and NPTv6 (IPv6 prefix translation) functions, but cannot be supported by more than one client per external IP address in the case of NAT. [3]
Sequence Number Reset 139 ICMP Node Information Query 0 The Data field contains an IPv6 address which is the Subject of this Query. 1 The Data field contains a name which is the Subject of this Query, or is empty, as in the case of a NOOP. 2 The Data field contains an IPv4 address which is the Subject of this Query. 140 ICMP Node Information ...
The most common transport protocols that use port numbers are the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP); those port numbers are 16-bit unsigned numbers. A port number is always associated with a network address of a host, such as an IP address, and the type of transport protocol used for communication. It ...
For example, the HyperText Transfer Protocol uses server port 80 and Telnet uses server port 23. Clients connecting to a service usually use ephemeral ports, i.e., port numbers assigned only for the duration of the transaction at random or from a specific range configured in the application.
Port numbers are categorized into three basic categories: well-known, registered, and dynamic or private. The well-known ports are assigned by the Internet Assigned Numbers Authority (IANA) and are typically used by system-level processes. Well-known applications running as servers and passively listening for connections typically use these ports.