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                                 Ephemeral port

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   An ephemeral port is a communications endpoint (port) of a transport layer
   protocol of the Internet protocol suite that is used for only a short
   period of time for the duration of a communication session. Such
   short-lived ports are allocated automatically within a predefined range of
   port numbers by the IP stack software of a computer operating system. The
   Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and
   the Stream Control Transmission Protocol (SCTP) typically use an ephemeral
   port for the client-end of a client–server communication. At the server
   end of the communication session, ephemeral ports may also be used for
   continuation of communications with a client that initially connected to
   one of the services listening with a well-known port. For example, the
   Trivial File Transfer Protocol (TFTP)^[1] and Remote Procedure Call (RPC)
   applications can behave in this manner.

   The allocation of an ephemeral port is temporary and only valid for the
   duration of the communication session. After completion of the session,
   the port is destroyed and the port number becomes available for reuse, but
   many implementations simply increment the last used port number until the
   ephemeral port range is exhausted, when the numbers roll over. Ephemeral
   ports are also called dynamic ports, because they are used on a per
   request basis, and are only known by number once allocated.

Contents

     * 1 Range
     * 2 Configuration characteristics
     * 3 See also
     * 4 Notes
     * 5 References
     * 6 External links

RangeEdit

   The RFC 6056 says that the range for ephemeral ports should be
   1024–65535.^[2]

   The Internet Assigned Numbers Authority (IANA) and RFC 6335 suggests the
   range 49152–65535 (2^15 + 2^14 to 2^16 − 1) for dynamic or private
   ports.^[3]^[4]

   Many Linux kernels use the port range 32768–60999.^[note 1]^[5] FreeBSD
   has used the IANA port range since release 4.6. Previous versions,
   including the Berkeley Software Distribution (BSD), use ports 1024–5000 as
   ephemeral ports.^[6]^[7]

   Microsoft Windows operating systems through Windows XP use the range
   1025–5000 as ephemeral ports by default.^[8] Windows Vista, Windows 7, and
   Server 2008 use the IANA range by default.^[9] Windows Server 2003 uses
   the range 1025–5000 by default, until Microsoft security update MS08-037
   from 2008 is installed, after which it uses the IANA range by
   default.^[10] Windows Server 2008 with Exchange Server 2007 installed has
   a default port range of 1025–60000.^[11] In addition to the default range,
   all versions of Windows since Windows 2000 have the option of specifying a
   custom range anywhere within 1025–65535.^[12]^[13]

   Solaris OS uses 32768–65535 range.

Configuration characteristicsEdit

   If certain server software is used, that uses non-ephemeral custom port
   ranges for initiating some further connections, it needs to be ensured by
   configuration that this custom port range and the ephemeral port range do
   not overlap.^[citation needed]

See alsoEdit

   Look up ephemeral in Wiktionary, the free dictionary. 

     * Registered port
     * List of TCP and UDP port numbers

NotesEdit

    1. ^ The effective range is accessible via procfs at node
       /proc/sys/net/ipv4/ip_local_port_range.

ReferencesEdit

   Link: mw-deduplicated-inline-style
    1. ^ Karen R.Sollins (July 1992). The TFTP Protocol (Revision 2). IETF.
       doi:10.17487/RFC1350. RFC 1350. Retrieved 2020-10-18.
    2. ^
       Link: mw-deduplicated-inline-style
       M. Larsen; F. Gont (January 2011). Recommendations for
       Transport-Protocol Port Randomization. sec. 3.2. Ephemeral Port Number
       Range. RFC 6056. However, ephemeral port selection algorithms should
       use the whole range 1024-65535.
    3. ^ IANA port number assignments
    4. ^
       Link: mw-deduplicated-inline-style
       Cotton, M.; Eggert, L.; Touch, J.; Westerlund, M.; Cheshire, S.
       (August 2011). "Port Number Ranges". Internet Assigned Numbers
       Authority (IANA) Procedures for the Management of the Service Name and
       Transport Protocol Port Number Registry. IETF. sec. 6.
       doi:10.17487/RFC6335. RFC 6335. Retrieved November 14, 2021. the
       Dynamic Ports, also known as the Private or Ephemeral Ports, from
       49152-65535 (never assigned)
    5. ^
       Link: mw-deduplicated-inline-style
       "IP Sysctl". The Linux Kernel documentation. Retrieved 2021-06-27. The
       default values are 32768 and 60999 respectively.
    6. ^
       Link: mw-deduplicated-inline-style
       UNIX Network Programming, Volume 1, Second Edition: Networking APIs:
       Sockets and XTI. Prentice Hall. 1998. pp. 42–43. ISBN 0-13-490012-X.
    7. ^
       Link: mw-deduplicated-inline-style
       Mike Gleason (2001). "The Ephemeral Port Range". Retrieved 2018-01-15.
       note that the Linux 2.4 kernel will default the range of 32768 through
       61000 if adequate kernel memory is available
    8. ^ Microsoft Windows Technet Library
    9. ^ Microsoft KB Article 929851
   10. ^ Microsoft KB Article 956188
   11. ^ Microsoft KB Article 929851
   12. ^ Microsoft KB Article 929851
   13. ^ Microsoft KB Article 196271

External linksEdit

     * RFC 6056 Recommendations for Transport-Protocol Port Randomization
     * The Ephemeral Port Range at NcFTP.com
     * Ephemeral Source Port Selection Strategies at DataPlane.org
   Retrieved from
   "https://en.wikipedia.org/w/index.php?title=Ephemeral_port&oldid=1056616399"
   Last edited on 22 November 2021, at 20:17
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