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传输层

传输层的基本概念

Transport layer

The protocols of this layer provide host-to-host communication services for applications.[1] It provides services such as connection-oriented communication, reliability, flow control, and multiplexing.

[1] RFC 1122

套接字

端口

Port (computer networking)

The port numbers are divided into three ranges: the well-known ports, the registered ports, and the dynamic or private ports.

熟知端口

The well-known ports (also known as system ports) are those from 0 through 1023. The requirements for new assignments in this range are stricter than for other registrations,[2] examples include:

  • 20: File Transfer Protocol (FTP) Data Transfer
  • 21: File Transfer Protocol (FTP) Command Control
  • 22: Secure Shell (SSH) Secure Login
  • 23: Telnet remote login service, unencrypted text messages
  • 25: Simple Mail Transfer Protocol (SMTP) E-mail routing
  • 53: Domain Name System (DNS) service
  • 80: Hypertext Transfer Protocol (HTTP) used in the World Wide Web
  • 110: Post Office Protocol (POP3)
  • 119: Network News Transfer Protocol (NNTP)
  • 123: Network Time Protocol (NTP)
  • 143: Internet Message Access Protocol (IMAP) Management of digital mail
  • 161: Simple Network Management Protocol (SNMP)
  • 194: Internet Relay Chat (IRC)
  • 443: HTTP Secure (HTTPS) HTTP over TLS/SSL

The registered ports are those from 1024 through 49151. IANA maintains the official list of well-known and registered ranges.[3] The dynamic or private ports are those from 49152 through 65535. One common use for this range is for ephemeral ports.

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