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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.
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.
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.
IANA is responsible for the global coordination of the DNS root, IP addressing, and other protocol resources. This includes the registration of commonly used TCP and UDP port numbers for well-known internet services. The port numbers are divided into three ranges: the well-known ports, the registered ports, and the dynamic or private ports.
TCP Transmission Control Protocol: RFC 793: 0x07 7 CBT Core-based trees: RFC 2189: 0x08 8 EGP Exterior Gateway Protocol: RFC 888: 0x09 9 IGP Interior gateway protocol (any private interior gateway, for example Cisco's IGRP) 0x0A 10 BBN-RCC-MON BBN RCC Monitoring 0x0B 11 NVP-II Network Voice Protocol: RFC 741: 0x0C 12 PUP Xerox PUP: 0x0D 13 ...
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.
One concern about the move from TCP to UDP is that TCP is widely adopted and many of the "middleboxes" in the Internet infrastructure are tuned for TCP and rate-limit or even block UDP. Google carried out a number of exploratory experiments to characterize this and found that only a small number of connections were blocked in this manner. [3]