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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.
When the length of the answer exceeds 512 bytes and both client and server support Extension Mechanisms for DNS (EDNS), larger UDP packets may be used. [41] Use of DNS over UDP is limited by, among other things, its lack of transport-layer encryption, authentication, reliable delivery, and message length.
DNS over TLS (DoT) is a network security protocol for encrypting and wrapping Domain Name System (DNS) queries and answers via the Transport Layer Security (TLS) protocol. The goal of the method is to increase user privacy and security by preventing eavesdropping and manipulation of DNS data via man-in-the-middle attacks.
The actual data transfer process begins by the client sending a query (opcode 0) with the special query type AXFR (value 252) over the TCP connection to the server. Although DNS technically supports AXFR over User Datagram Protocol (UDP), it is considered not acceptable due to the risk of lost, or spoofed packets.
UDP User Datagram Protocol: RFC 768: 0x12 18 MUX Multiplexing: IEN 90 [3] 0x13 19 DCN-MEAS DCN Measurement Subsystems 0x14 20 HMP Host Monitoring Protocol: RFC 869: 0x15 21 PRM Packet Radio Measurement 0x16 22 XNS-IDP XEROX NS IDP 0x17 23 TRUNK-1 Trunk-1 0x18 24 TRUNK-2 Trunk-2 0x19 25 LEAF-1 Leaf-1 0x1A 26 LEAF-2 Leaf-2 0x1B 27 RDP Reliable ...
For TCP, port number 0 is reserved and cannot be used, while for UDP, the source port is optional and a value of zero means no port. A process associates its input or output channels via an internet socket , which is a type of file descriptor , associated with a transport protocol , a network address such as an IP address , and a port number.
IN: standard DNS class field (this is always IN). SRV: Type of Record (this is always SRV). priority: the priority of the target host, lower value means more preferred. weight: A relative weight for records with the same priority, higher value means higher chance of getting picked. port: the TCP or UDP port on which the service is to be found.
This value is set by the originator of a query and copied into the response. This specification defines the behavior of standard queries and responses (opcode value of zero). Future specifications may define the use of other opcodes with LLMNR. C - Conflict. TC - TrunCation. T - Tentative. Z - Reserved for future use. RCODE - Response code.