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rfc:bcp:bcp165

[Note that this file is a concatenation of more than one RFC.]

Internet Engineering Task Force (IETF) M. Cotton Request for Comments: 6335 ICANN BCP: 165 L. Eggert Updates: 2780, 2782, 3828, 4340, 4960, 5595 Nokia Category: Best Current Practice J. Touch ISSN: 2070-1721 USC/ISI

                                                         M. Westerlund
                                                              Ericsson
                                                           S. Cheshire
                                                                 Apple
                                                           August 2011

Internet Assigned Numbers Authority (IANA) Procedures for the Management

  of the Service Name and Transport Protocol Port Number Registry

Abstract

 This document defines the procedures that the Internet Assigned
 Numbers Authority (IANA) uses when handling assignment and other
 requests related to the Service Name and Transport Protocol Port
 Number registry.  It also discusses the rationale and principles
 behind these procedures and how they facilitate the long-term
 sustainability of the registry.
 This document updates IANA's procedures by obsoleting the previous
 UDP and TCP port assignment procedures defined in Sections 8 and 9.1
 of the IANA Allocation Guidelines, and it updates the IANA service
 name and port assignment procedures for UDP-Lite, the Datagram
 Congestion Control Protocol (DCCP), and the Stream Control
 Transmission Protocol (SCTP).  It also updates the DNS SRV
 specification to clarify what a service name is and how it is
 registered.

Status of This Memo

 This memo documents an Internet Best Current Practice.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 BCPs is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6335.

Cotton, et al. Best Current Practice [Page 1] RFC 6335 Service Name and Port Number Procedures August 2011

Copyright Notice

 Copyright (c) 2011 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Cotton, et al. Best Current Practice [Page 2] RFC 6335 Service Name and Port Number Procedures August 2011

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
 2.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  5
 3.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  6
 4.  Conventions Used in This Document  . . . . . . . . . . . . . .  8
 5.  Service Names  . . . . . . . . . . . . . . . . . . . . . . . .  8
   5.1.  Service Name Syntax  . . . . . . . . . . . . . . . . . . .  9
   5.2.  Service Name Usage in DNS SRV Records  . . . . . . . . . . 10
 6.  Port Number Ranges . . . . . . . . . . . . . . . . . . . . . . 11
   6.1.  Service Names and Port Numbers for Experimentation . . . . 12
 7.  Principles for Service Name and Transport Protocol Port
     Number Registry Management . . . . . . . . . . . . . . . . . . 12
   7.1.  Past Principles  . . . . . . . . . . . . . . . . . . . . . 13
   7.2.  Updated Principles . . . . . . . . . . . . . . . . . . . . 13
 8.  IANA Procedures for Managing the Service Name and
     Transport Protocol Port Number Registry  . . . . . . . . . . . 16
   8.1.  Service Name and Port Number Assignment  . . . . . . . . . 16
   8.2.  Service Name and Port Number De-Assignment . . . . . . . . 21
   8.3.  Service Name and Port Number Reuse . . . . . . . . . . . . 21
   8.4.  Service Name and Port Number Revocation  . . . . . . . . . 22
   8.5.  Service Name and Port Number Transfers . . . . . . . . . . 22
   8.6.  Maintenance Issues . . . . . . . . . . . . . . . . . . . . 23
   8.7.  Disagreements  . . . . . . . . . . . . . . . . . . . . . . 23
 9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
 10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 24
   10.1. Service Name Consistency . . . . . . . . . . . . . . . . . 24
   10.2. Port Numbers for SCTP and DCCP Experimentation . . . . . . 26
   10.3. Updates to DCCP Registries . . . . . . . . . . . . . . . . 27
 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 28
 12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 28
 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
   13.1. Normative References . . . . . . . . . . . . . . . . . . . 29
   13.2. Informative References . . . . . . . . . . . . . . . . . . 30

Cotton, et al. Best Current Practice [Page 3] RFC 6335 Service Name and Port Number Procedures August 2011

1. Introduction

 For many years, the assignment of new service names and port number
 values for use with the Transmission Control Protocol (TCP) [RFC0793]
 and the User Datagram Protocol (UDP) [RFC0768] has had less than
 clear guidelines.  New transport protocols have been added -- the
 Stream Control Transmission Protocol (SCTP) [RFC4960] and the
 Datagram Congestion Control Protocol (DCCP) [RFC4342] -- and new
 mechanisms like DNS SRV records [RFC2782] have been developed, each
 with separate registries and separate guidelines.  The community also
 recognized the need for additional procedures beyond just assignment;
 notably modification, revocation, and release.
 A key element of the procedural streamlining specified in this
 document is to establish identical assignment procedures for all IETF
 transport protocols.  This document brings the IANA procedures for
 TCP and UDP in line with those for SCTP and DCCP, resulting in a
 single process that requesters and IANA follow for all requests for
 all transport protocols, including future protocols not yet defined.
 In addition to detailing the IANA procedures for the initial
 assignment of service names and port numbers, this document also
 specifies post-assignment procedures that until now have been handled
 in an ad hoc manner.  These include procedures to de-assign a port
 number that is no longer in use, to take a port number assigned for
 one service that is no longer in use and reuse it for another
 service, and the procedure by which IANA can unilaterally revoke a
 prior port number assignment.  Section 8 discusses the specifics of
 these procedures and processes that requesters and IANA follow for
 all requests for all current and future transport protocols.
 IANA is the authority for assigning service names and port numbers.
 The registries that are created to store these assignments are
 maintained by IANA.  For protocols developed by IETF working groups,
 IANA now also offers a method for the "early assignment" [RFC4020] of
 service names and port numbers, as described in Section 8.1.
 This document updates IANA's procedures for UDP and TCP port numbers
 by obsoleting Sections 8 and 9.1 of the IANA Allocation Guidelines
 [RFC2780].  (Note that other sections of the IANA Allocation
 Guidelines, relating to the protocol field values in IPv4 headers,
 were also updated in February 2008 [RFC5237].)  This document also
 updates the IANA assignment procedures for DCCP [RFC4340] [RFC5595]
 and SCTP [RFC4960].

Cotton, et al. Best Current Practice [Page 4] RFC 6335 Service Name and Port Number Procedures August 2011

 The Lightweight User Datagram Protocol (UDP-Lite) shares the port
 space with UDP.  The UDP-Lite specification [RFC3828] says: "UDP-Lite
 uses the same set of port number values assigned by the IANA for use
 by UDP".  An update of the UDP procedures therefore also results in a
 corresponding update of the UDP-Lite procedures.
 This document also clarifies what a service name is and how it is
 assigned.  This will impact the DNS SRV specification [RFC2782],
 because that specification merely makes a brief mention that the
 symbolic names of services are defined in "Assigned Numbers"
 [RFC1700], without stating to which section it refers within that
 230-page document.  The DNS SRV specification may have been referring
 to the list of Port Assignments (known as /etc/services on Unix), or
 to the "Protocol And Service Names" section, or to both, or to some
 other section.  Furthermore, "Assigned Numbers" [RFC1700] has been
 obsoleted [RFC3232] and has been replaced by on-line registries
 [PORTREG] [PROTSERVREG].
 The development of new transport protocols is a major effort that the
 IETF does not undertake very often.  If a new transport protocol is
 standardized in the future, it is expected to follow these guidelines
 and practices around using service names and port numbers as much as
 possible, for consistency.
 At the time of writing of this document, the internal procedures of
 "Expert Review" teams, including that of IANA's port review team, are
 not documented in any RFC and this document doesn't change that.

2. Motivation

 Information about the assignment procedures for the port registry has
 existed in three locations: the forms for requesting port number
 assignments on the IANA web site [SYSFORM] [USRFORM], an introductory
 text section in the file listing the port number assignments
 themselves (known as the port numbers registry) [PORTREG], and two
 brief sections of the IANA Allocation Guidelines [RFC2780].
 Similarly, the procedures surrounding service names have been
 historically unclear.  Service names were originally created as
 mnemonic identifiers for port numbers without a well-defined syntax,
 apart from the 14-character limit mentioned on the IANA website
 [SYSFORM] [USRFORM].  Even that length limit has not been
 consistently applied, and some assigned service names are 15
 characters long.  When service identification via DNS SRV Resource
 Records (RRs) was introduced [RFC2782], it became useful to start
 assigning service names alone, and because IANA had no procedure for
 assigning a service name without an associated port number, this led

Cotton, et al. Best Current Practice [Page 5] RFC 6335 Service Name and Port Number Procedures August 2011

 to the creation of an informal temporary service name registry
 outside of the control of IANA, which now contains roughly 500
 service names [SRVREG].
 This document aggregates all this scattered information into a single
 reference that aligns and clearly defines the management procedures
 for both service names and port numbers.  It gives more detailed
 guidance to prospective requesters of service names and ports than
 the existing documentation, and it streamlines the IANA procedures
 for the management of the registry, so that requests can be completed
 in a timely manner.
 This document defines rules for assignment of service names without
 associated port numbers, for such usages as DNS SRV records
 [RFC2782], which was not possible under the previous IANA procedures.
 The document also merges service name assignments from the non-IANA
 ad hoc registry [SRVREG] and from the IANA Protocol and Service Names
 registry [PROTSERVREG] into the IANA Service Name and Transport
 Protocol Port Number registry [PORTREG], which from here on is the
 single authoritative registry for service names and port numbers.
 An additional purpose of this document is to describe the principles
 that guide the IETF and IANA in their role as the long-term joint
 stewards of the service name and port number registry.  TCP and UDP
 have had remarkable success over the last decades.  Thousands of
 applications and application-level protocols have service names and
 port numbers assigned for their use, and there is every reason to
 believe that this trend will continue into the future.  It is hence
 extremely important that management of the registry follow principles
 that ensure its long-term usefulness as a shared resource.  Section 7
 discusses these principles in detail.

3. Background

 The Transmission Control Protocol (TCP) [RFC0793] and the User
 Datagram Protocol (UDP) [RFC0768] have enjoyed a remarkable success
 over the decades as the two most widely used transport protocols on
 the Internet.  They have relied on the concept of "ports" as logical
 entities for Internet communication.  Ports serve two purposes:
 first, they provide a demultiplexing identifier to differentiate
 transport sessions between the same pair of endpoints, and second,
 they may also identify the application protocol and associated
 service to which processes connect.  Newer transport protocols, such
 as the Stream Control Transmission Protocol (SCTP) [RFC4960] and the
 Datagram Congestion Control Protocol (DCCP) [RFC4342], have also
 adopted the concept of ports for their communication sessions and use
 16-bit port numbers in the same way as TCP and UDP (and UDP-Lite
 [RFC3828], a variant of UDP).

Cotton, et al. Best Current Practice [Page 6] RFC 6335 Service Name and Port Number Procedures August 2011

 Port numbers are the original and most widely used means for
 application and service identification on the Internet.  Ports are
 16-bit numbers, and the combination of source and destination port
 numbers together with the IP addresses of the communicating end
 systems uniquely identifies a session of a given transport protocol.
 Port numbers are also known by their associated service names such as
 "telnet" for port number 23 and "http" (as well as "www" and
 "www-http") for port number 80.
 All involved parties -- hosts running services, hosts accessing
 services on other hosts, and intermediate devices (such as firewalls
 and NATs) that restrict services -- need to agree on which service
 corresponds to a particular destination port.  Although this is
 ultimately a local decision with meaning only between the endpoints
 of a connection, it is common for many services to have a default
 port upon which those servers usually listen, when possible, and
 these ports are recorded by the Internet Assigned Numbers Authority
 (IANA) through the service name and port number registry [PORTREG].
 Over time, the assumption that a particular port number necessarily
 implies a particular service may become less true.  For example,
 multiple instances of the same service on the same host cannot
 generally listen on the same port, and multiple hosts behind the same
 NAT gateway cannot all have a mapping for the same port on the
 external side of the NAT gateway, whether using static port mappings
 configured by hand by the user, or dynamic port mappings configured
 automatically using a port mapping protocol like the NAT Port Mapping
 Protocol [NAT-PMP] or Internet Gateway Device [IGD].
 Applications may use port numbers directly, look up port numbers
 based on service names via system calls such as getservbyname() on
 UNIX, look up port numbers by performing queries for DNS SRV records
 [RFC2782] [DNS-SD], or determine port numbers in a variety of other
 ways like the TCP Port Service Multiplexer (TCPMUX) [RFC1078].
 Designers of applications and application-level protocols may apply
 to IANA for an assigned service name and port number for a specific
 application, and may -- after assignment -- assume that no other
 application will use that service name or port number for its
 communication sessions.  Application designers also have the option
 of requesting only an assigned service name without a corresponding
 fixed port number if their application does not require one, such as
 applications that use DNS SRV records to look up port numbers
 dynamically at run-time.  Because the port number space is finite
 (and therefore conservation is an important goal), the alternative of
 using service names instead of port numbers is RECOMMENDED whenever
 possible.

Cotton, et al. Best Current Practice [Page 7] RFC 6335 Service Name and Port Number Procedures August 2011

4. Conventions Used in This Document

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 "Key words for use in RFCs to Indicate Requirement Levels" [RFC2119].
 This document uses the term "assignment" to refer to the procedure by
 which IANA provides service names and/or port numbers to requesting
 parties; other RFCs refer to this as "allocation" or "registration".
 This document assumes that all these terms have the same meaning, and
 will use terms other than "assignment" only when quoting from or
 referring to text in these other documents.

5. Service Names

 Service names are the unique key in the Service Name and Transport
 Protocol Port Number registry.  This unique symbolic name for a
 service may also be used for other purposes, such as in DNS SRV
 records [RFC2782].  Within the registry, this unique key ensures that
 different services can be unambiguously distinguished, thus
 preventing name collisions and avoiding confusion about who is the
 Assignee for a particular entry.
 There may be more than one service name associated with a particular
 transport protocol and port.  There are three ways that such port
 number overloading can occur:
 o  Overloading occurs when one service is an extension of another
    service, and an in-band mechanism exists for determining if the
    extension is present or not.  One example is port 3478, which has
    the service name aliases "stun" and "turn".  Traversal Using
    Relays around NAT (TURN) [RFC5766] is an extension to the Session
    Traversal Utilities for NAT (STUN) [RFC5389] service.  TURN-
    enabled clients wishing to locate TURN servers could attempt to
    discover "stun" services and then check in-band if the server also
    supports TURN, but this would be inefficient.  Enabling them to
    directly query for "turn" servers by name is a better approach.
    (Note that TURN servers in this case should also be locatable via
    a "stun" discovery, because every TURN server is also a STUN
    server.)
 o  By historical accident, the service name "http" has two synonyms
    "www" and "www-http".  When used in SRV records [RFC2782] and
    similar service discovery mechanisms, only the service name "http"
    should be used, not these additional names.  If a server were to
    advertise "www", it would not be discovered by clients browsing
    for "http".  Advertising or browsing for the aliases as well as

Cotton, et al. Best Current Practice [Page 8] RFC 6335 Service Name and Port Number Procedures August 2011

    the primary service name is inefficient, and achieves nothing that
    is not already achieved by using the service name "http"
    exclusively.
 o  As indicated in this document in Section 10.1, overloading has
    been used to create replacement names that are consistent with the
    syntax this document prescribes for legacy names that do not
    conform to this syntax already.  For such cases, only the new name
    should be used in SRV records, to avoid the same issues as with
    historical cases of multiple names, and also because the legacy
    names are incompatible with SRV record use.
 Assignment requests for new names for existing registered services
 will be rejected, as a result.  Implementers are requested to inform
 IANA if they discover other cases where a single service has multiple
 names, so that one name may be recorded as the primary name for
 service discovery purposes.
 Service names are assigned on a "first come, first served" basis, as
 described in Section 8.1.  Names should be brief and informative,
 avoiding words or abbreviations that are redundant in the context of
 the registry (e.g., "port", "service", "protocol", etc.)  Names
 referring to discovery services, e.g., using multicast or broadcast
 to identify endpoints capable of a given service, SHOULD use an
 easily identifiable suffix (e.g., "-disc").

5.1. Service Name Syntax

 Valid service names are hereby normatively defined as follows:
 o  MUST be at least 1 character and no more than 15 characters long
 o  MUST contain only US-ASCII [ANSI.X3.4-1986] letters 'A' - 'Z' and
    'a' - 'z', digits '0' - '9', and hyphens ('-', ASCII 0x2D or
    decimal 45)
 o  MUST contain at least one letter ('A' - 'Z' or 'a' - 'z')
 o  MUST NOT begin or end with a hyphen
 o  hyphens MUST NOT be adjacent to other hyphens
 The reason for requiring at least one letter is to avoid service
 names like "23" (could be confused with a numeric port) or "6000-
 6063" (could be confused with a numeric port range).  Although
 service names may contain both upper-case and lower-case letters,
 case is ignored for comparison purposes, so both "http" and "HTTP"
 denote the same service.

Cotton, et al. Best Current Practice [Page 9] RFC 6335 Service Name and Port Number Procedures August 2011

 Service names are purely opaque identifiers, and no semantics are
 implied by any superficial structure that a given service name may
 appear to have.  For example, a company called "Example" may choose
 to register service names "Example-Foo" and "Example-Bar" for its
 "Foo" and "Bar" products, but the "Example" company cannot claim to
 "own" all service names beginning with "Example-"; they cannot
 prevent someone else from registering "Example-Baz" for a different
 service, and they cannot prevent other developers from using the
 "Example-Foo" and "Example-Bar" service types in order to
 interoperate with the "Foo" and "Bar" products.  Technically
 speaking, in service discovery protocols, service names are merely a
 series of byte values on the wire; for the mnemonic convenience of
 human developers, it can be convenient to interpret those byte values
 as human-readable ASCII characters, but software should treat them as
 purely opaque identifiers and not attempt to parse them for any
 additional embedded meaning.
 As of August 5, 2009, approximately 98% of the so-called "Short
 Names" [SYSFORM] [USRFORM] for existing port number assignments
 [PORTREG] already met the rules for legal service names stated in
 Section 8.1, and hence for these services their service name is
 exactly the same as their historical "Short Name".  In approximately
 2% of cases, the new "service name" is derived based on the old
 "Short Name" as described below in Section 10.1.
 The rules for valid service names, excepting the limit of 15
 characters maximum, are also expressed below (as a non-normative
 convenience) using ABNF [RFC5234].
    SRVNAME = *(1*DIGIT [HYPHEN]) ALPHA *([HYPHEN] ALNUM)
    ALNUM   = ALPHA / DIGIT     ; A-Z, a-z, 0-9
    HYPHEN  = %x2D              ; "-"
    ALPHA   = %x41-5A / %x61-7A ; A-Z / a-z [RFC5234]
    DIGIT   = %x30-39           ; 0-9       [RFC5234]

5.2. Service Name Usage in DNS SRV Records

 The DNS SRV specification [RFC2782] states that the Service Label
 part of the owner name of a DNS SRV record includes a "Service"
 element, described as "the symbolic name of the desired service", but
 as discussed above, it is not clear precisely what this means.
 This document clarifies that the Service Label MUST be a service name
 as defined herein with an underscore prepended.  The service name
 SHOULD be registered with IANA and recorded in the Service Name and
 Transport Protocol Port Number registry [PORTREG].

Cotton, et al. Best Current Practice [Page 10] RFC 6335 Service Name and Port Number Procedures August 2011

 The details of using Service Names in SRV Service Labels are
 specified in the DNS SRV specification [RFC2782].

6. Port Number Ranges

 TCP, UDP, UDP-Lite, SCTP, and DCCP use 16-bit namespaces for their
 port number registries.  The port registries for all of these
 transport protocols are subdivided into three ranges of numbers
 [RFC1340], and Section 8.1.2 describes the IANA procedures for each
 range in detail:
 o  the System Ports, also known as the Well Known Ports, from 0-1023
    (assigned by IANA)
 o  the User Ports, also known as the Registered Ports, from 1024-
    49151 (assigned by IANA)
 o  the Dynamic Ports, also known as the Private or Ephemeral Ports,
    from 49152-65535 (never assigned)
 Of the assignable port ranges (System Ports and User Ports, i.e.,
 port numbers 0-49151), individual port numbers are in one of three
 states at any given time:
 o  Assigned: Assigned port numbers are currently assigned to the
    service indicated in the registry.
 o  Unassigned: Unassigned port numbers are currently available for
    assignment upon request, as per the procedures outlined in this
    document.
 o  Reserved: Reserved port numbers are not available for regular
    assignment; they are "assigned to IANA" for special purposes.
    Reserved port numbers include values at the edges of each range,
    e.g., 0, 1023, 1024, etc., which may be used to extend these
    ranges or the overall port number space in the future.
 In order to keep the size of the registry manageable, IANA typically
 only records the Assigned and Reserved service names and port numbers
 in the registry.  Unassigned values are typically not explicitly
 listed.  (There are very many Unassigned service names and
 enumerating them all would not be practical.)
 As a data point, when this document was written, approximately 76% of
 the TCP and UDP System Ports were assigned, and approximately 9% of
 the User Ports were assigned.  (As noted, Dynamic Ports are never
 assigned.)

Cotton, et al. Best Current Practice [Page 11] RFC 6335 Service Name and Port Number Procedures August 2011

6.1. Service Names and Port Numbers for Experimentation

 Of the System Ports, two TCP and UDP port numbers (1021 and 1022),
 together with their respective service names ("exp1" and "exp2"),
 have been assigned for experimentation with new applications and
 application-layer protocols that require a port number in the
 assigned ports range [RFC4727].
 Please refer to Sections 1 and 1.1 of "Assigning Experimental and
 Testing Numbers Considered Useful" [RFC3692] for how these
 experimental port numbers are to be used.
 This document assigns the same two service names and port numbers for
 experimentation with new application-layer protocols over SCTP and
 DCCP in Section 10.2.
 Unfortunately, it can be difficult to limit access to these ports.
 Users SHOULD take measures to ensure that experimental ports are
 connecting to the intended process.  For example, users of these
 experimental ports might include a 64-bit nonce, once on each segment
 of a message-oriented channel (e.g., UDP), or once at the beginning
 of a byte-stream (e.g., TCP), which is used to confirm that the port
 is being used as intended.  Such confirmation of intended use is
 especially important when these ports are associated with privileged
 (e.g., system or administrator) processes.

7. Principles for Service Name and Transport Protocol Port Number

  Registry Management
 Management procedures for the Service Name and Transport Protocol
 Port Number registry include assignment of service names and port
 numbers upon request, as well as management of information about
 existing assignments.  The latter includes maintaining contact and
 description information about assignments, revoking abandoned
 assignments, and redefining assignments when needed.  Of these
 procedures, careful port number assignment is most critical, in order
 to continue to conserve the remaining port numbers.
 As noted earlier, only about 9% of the User Port space is currently
 assigned.  The current rate of assignment is approximately 400 ports
 per year, and has remained steady for the past 8 years.  At that
 rate, if similar conservation continues, this resource will sustain
 another 85 years of assignment - without the need to resort to
 reassignment of released values or revocation.  The namespace
 available for service names is much larger, which allows for simpler
 management procedures.

Cotton, et al. Best Current Practice [Page 12] RFC 6335 Service Name and Port Number Procedures August 2011

7.1. Past Principles

 The principles for service name and port number management are based
 on the recommendations of the IANA "Expert Review" team.  Until
 recently, that team followed a set of informal guidelines developed
 based on the review experience from previous assignment requests.
 These original guidelines, although informal, had never been publicly
 documented.  They are recorded here for historical purposes only; the
 current guidelines are described in Section 7.2.  These guidelines
 previously were:
 o  TCP and UDP ports were simultaneously assigned when either was
    requested
 o  Port numbers were the primary assignment; service names were
    informative only, and did not have a well-defined syntax
 o  Port numbers were conserved informally, and sometimes
    inconsistently (e.g., some services were assigned ranges of many
    port numbers even where not strictly necessary)
 o  SCTP and DCCP service name and port number registries were managed
    separately from the TCP/UDP registries
 o  Service names could not be assigned in the old ports registry
    without assigning an associated port number at the same time

7.2. Updated Principles

 This section summarizes the current principles by which IANA both
 handles the Service Name and Transport Protocol Port Number registry
 and attempts to conserve the port number space.  This description is
 intended to inform applicants requesting service names and port
 numbers.  IANA has flexibility beyond these principles when handling
 assignment requests; other factors may come into play, and exceptions
 may be made to best serve the needs of the Internet.  Applicants
 should be aware that IANA decisions are not required to be bound to
 these principles.  These principles and general advice to users on
 port use are expected to change over time.
 IANA strives to assign service names that do not request an
 associated port number assignment under a simple "First Come First
 Served" policy [RFC5226].  IANA MAY, at its discretion, refer service
 name requests to "Expert Review" in cases of mass assignment requests
 or other situations where IANA believes "Expert Review" is advisable
 [RFC5226]; use of the "Expert Review" helps advise IANA informally in
 cases where "IETF Review" or "IESG Approval" is used, as with most
 IETF protocols.

Cotton, et al. Best Current Practice [Page 13] RFC 6335 Service Name and Port Number Procedures August 2011

 The basic principle of service name and port number registry
 management is to conserve use of the port space where possible.
 Extensions to support larger port number spaces would require
 changing many core protocols of the current Internet in a way that
 would not be backward compatible and interfere with both current and
 legacy applications.
 Conservation of the port number space is required because this space
 is a limited resource, so applications are expected to participate in
 the traffic demultiplexing process where feasible.  The port numbers
 are expected to encode as little information as possible that will
 still enable an application to perform further demultiplexing by
 itself.  In particular, the principles form a goal that IANA strives
 to achieve for new applications (with exceptions as deemed
 appropriate, especially as for extensions to legacy services) as
 follows:
 o  IANA strives to assign only one assigned port number per service
    or application.
    Note: At the time of writing of this document, there is no IETF
    consensus on when it is appropriate to use a second port for an
    insecure version of a protocol.
 o  IANA strives to assign only one assigned port number for all
    variants of a service (e.g., for updated versions of a service).
 o  IANA strives to encourage the deployment of secure protocols.
 o  IANA strives to assign only one assigned port number for all
    different types of devices using or participating in the same
    service.
 o  IANA strives to assign port numbers only for the transport
    protocol(s) explicitly named in an assignment request.
 o  IANA may recover unused port numbers, via the new procedures of
    de-assignment, revocation, and transfer.
 Where possible, a given service is expected to demultiplex messages
 if necessary.  For example, applications and protocols are expected
 to include in-band version information, so that future versions of
 the application or protocol can share the same assigned port.
 Applications and protocols are also expected to be able to
 efficiently use a single assigned port for multiple sessions, either
 by demultiplexing multiple streams within one port or by using the
 assigned port to coordinate using dynamic ports for subsequent
 exchanges (e.g., in the spirit of FTP [RFC0959]).

Cotton, et al. Best Current Practice [Page 14] RFC 6335 Service Name and Port Number Procedures August 2011

 Ports are used in various ways, notably:
 o  as endpoint process identifiers
 o  as application protocol identifiers
 o  for firewall-filtering purposes
 Both the process-identifier and the protocol-identifier uses suggest
 that anything a single process can demultiplex, or that can be
 encoded into a single protocol, should be.  The firewall-filtering
 use suggests that some uses that could be multiplexed or encoded
 could instead be separated to allow for easier firewall management.
 Note that this latter use is much less sound, because port numbers
 have meaning only for the two endpoints involved in a connection, and
 drawing conclusions about the service that generated a given flow
 based on observed port numbers is not always reliable.
 Effective with the publication of this document, IANA will begin
 assigning port numbers for only those transport protocols explicitly
 included in an assignment request.  This ends the long-standing
 practice of automatically assigning a port number to an application
 for both TCP and UDP, even if the request is for only one of these
 transport protocols.  The new assignment procedure conserves
 resources by assigning a port number to an application for only those
 transport protocols (TCP, UDP, SCTP, and/or DCCP) it actually uses.
 The port number will be marked as Reserved -- instead of Assigned --
 in the port number registries of the other transport protocols.  When
 applications start supporting the use of some of those additional
 transport protocols, the Assignee for the assignment MUST request
 that IANA convert these reserved ports into assignments.  An
 application MUST NOT assume that it can use a port number assigned to
 it for use with one transport protocol with another transport
 protocol without IANA converting the reservation into an assignment.
 When the available pool of unassigned numbers has run out in a port
 range, it will be necessary for IANA to consider the Reserved ports
 for assignment.  This is part of the motivation for not automatically
 assigning ports for transport protocols other than the requested
 one(s).  This will allow more ports to be available for assignment at
 that point.  To help conserve ports, application developers SHOULD
 request assignment of only those transport protocols that their
 application currently uses.
 Conservation of port numbers is improved by procedures that allow
 previously assigned port numbers to become Unassigned, either through
 de-assignment or through revocation, and by a procedure that lets
 application designers transfer an assigned but unused port number to

Cotton, et al. Best Current Practice [Page 15] RFC 6335 Service Name and Port Number Procedures August 2011

 a new application.  Section 8 describes these procedures, which until
 now were undocumented.  Port number conservation is also improved by
 recommending that applications that do not require an assigned port
 should register only a service name without an associated port
 number.

8. IANA Procedures for Managing the Service Name and Transport Protocol

  Port Number Registry
 This section describes the process for handling requests associated
 with IANA's management of the Service Name and Transport Protocol
 Port Number registry.  Such requests include initial assignment, de-
 assignment, reuse, and updates to the contact information or
 description associated with an assignment.  Revocation is an
 additional process, initiated by IANA.

8.1. Service Name and Port Number Assignment

 Assignment refers to the process of providing service names or port
 numbers to applicants.  All such assignments are made from service
 names or port numbers that are Unassigned or Reserved at the time of
 the assignment.
 o  Unassigned names and numbers are assigned according to the rules
    described in Section 8.1.2 below.
 o  Reserved numbers and names are generally only assigned by a
    "Standards Action" or "IESG Approval", and MUST be accompanied by
    a statement explaining the reason a Reserved number or name is
    appropriate for this action.  The only exception to this rule is
    that the current Assignee of a port number MAY request the
    assignment of the corresponding Reserved port number for other
    transport protocols when needed.  IANA will initiate an "Expert
    Review" [RFC5226] for such requests.
 When an assignment for one or more transport protocols is approved,
 the port number for any non-requested transport protocol(s) will be
 marked as Reserved.  IANA SHOULD NOT assign that port number to any
 other application or service until no other port numbers remain
 Unassigned in the requested range.  It is anticipated that at such
 time a new document will be published specifying IANA procedures for
 assignment of such ports.

Cotton, et al. Best Current Practice [Page 16] RFC 6335 Service Name and Port Number Procedures August 2011

8.1.1. General Assignment Procedure

 A service name or port number assignment request contains the
 following information.  The service name is the unique identifier of
 a given service:
    Service Name (REQUIRED)
    Transport Protocol(s) (REQUIRED)
    Assignee (REQUIRED)
    Contact (REQUIRED)
    Description (REQUIRED)
    Reference (REQUIRED)
    Port Number (OPTIONAL)
    Service Code (REQUIRED for DCCP only)
    Known Unauthorized Uses (OPTIONAL)
    Assignment Notes (OPTIONAL)
 o  Service Name: A desired unique service name for the service
    associated with the assignment request MUST be provided.  This
    name may be used with various service selection and discovery
    mechanisms (including, but not limited to, DNS SRV records
    [RFC2782]).  The name MUST be compliant with the syntax defined in
    Section 5.1.  In order to be unique, they MUST NOT be identical to
    any currently assigned service name in the IANA registry
    [PORTREG].  Service names are case-insensitive; they may be
    provided and entered into the registry with mixed case for
    clarity, but case is ignored otherwise.
 o  Transport Protocol(s): The transport protocol(s) for which an
    assignment is requested MUST be provided.  This field is currently
    limited to one or more of TCP, UDP, SCTP, and DCCP.  Requests
    without any port assignment and only a service name are still
    required to indicate which protocol the service uses.
 o  Assignee: Name and email address of the party to whom the
    assignment is made.  This is REQUIRED.  The Assignee is the
    organization, company or individual person responsible for the
    initial assignment.  For assignments done through RFCs published
    via the "IETF Document Stream" [RFC4844], the Assignee will be the
    IESG <iesg@ietf.org>.
 o  Contact: Name and email address of the Contact person for the
    assignment.  This is REQUIRED.  The Contact person is the
    responsible person for the Internet community to send questions
    to.  This person is also authorized to submit changes on behalf of
    the Assignee; in cases of conflict between the Assignee and the
    Contact, the Assignee decisions take precedence.  Additional

Cotton, et al. Best Current Practice [Page 17] RFC 6335 Service Name and Port Number Procedures August 2011

    address information MAY be provided.  For assignments done through
    RFCs published via the "IETF Document Stream" [RFC4844], the
    Contact will be the IETF Chair <chair@ietf.org>.
 o  Description: A short description of the service associated with
    the assignment request is REQUIRED.  It should avoid all but the
    most well-known acronyms.
 o  Reference: A description of (or a reference to a document
    describing) the protocol or application using this port.  This is
    REQUIRED.  The description must state whether the protocol uses
    IP-layer broadcast, multicast, or anycast communication.
    For assignments requesting only a Service Name, or a Service Name
    and User Port, a statement that the protocol is proprietary and
    not publicly documented is also acceptable, provided that the
    required information regarding the use of IP broadcast, multicast,
    or anycast is given.
    For any assignment request that includes a User Port, the
    assignment request MUST explain why a port number in the Dynamic
    Ports range (discovered by clients dynamically at run-time) is
    unsuitable for the given application.
    For any assignment request that includes a System Port, the
    assignment request MUST explain why a port number in the User
    Ports or Dynamic Ports ranges is unsuitable, and a reference to a
    stable protocol specification document MUST be provided.
    IANA MAY accept early assignment [RFC4020] requests (known as
    "early allocation" therein) from IETF working groups that
    reference a sufficiently stable Internet-Draft instead of a
    published Standards-Track RFC.
 o  Port Number: If assignment of a port number is desired, either the
    port number the requester suggests for assignment or indication of
    port range (user or system) MUST be provided.  If only a service
    name is to be assigned, this field is left empty.  If a specific
    port number is requested, IANA is encouraged to assign the
    requested number.  If a range is specified, IANA will choose a
    suitable number from the User or System Ports ranges.  Note that
    the applicant MUST NOT use the requested port in implementations
    deployed for use on the public Internet prior to the completion of
    the assignment, because there is no guarantee that IANA will
    assign the requested port.

Cotton, et al. Best Current Practice [Page 18] RFC 6335 Service Name and Port Number Procedures August 2011

 o  Service Code: If the assignment request includes DCCP as a
    transport protocol, then the request MUST include a desired unique
    DCCP service code [RFC5595], and MUST NOT include a requested DCCP
    service code otherwise.  Section 19.8 of the DCCP specification
    [RFC4340] defines requirements and rules for assignment, updated
    by this document.  Note that, as per the DCCP Service Codes
    document [RFC5595], some service codes are not assigned; zero
    (absence of a meaningful service code) and 4294967295 (0xFFFFFFFF;
    invalid service code) are permanently reserved, and the Private
    service codes 1056964608-1073741823 (0x3F000000-0x3FFFFFFF; i.e.,
    32-bit values with the high-order byte equal to a value of 63
    (0x3F), corresponding to the ASCII character '?') are not
    centrally assigned.
 o  Known Unauthorized Uses: A list of uses by applications or
    organizations who are not the Assignee.  This is OPTIONAL.  This
    list may be augmented by IANA after assignment when unauthorized
    uses are reported.
 o  Assignment Notes: Indications of owner/name change, or any other
    assignment process issue.  This is OPTIONAL.  This list may be
    updated by IANA after assignment to help track changes to an
    assignment, e.g., de-assignment, owner/name changes, etc.
 If the assignment request is for the addition of a new transport
 protocol to a previously assigned service name and the requester is
 not the Assignee or Contact for the previously assigned service name,
 IANA needs to confirm with the Assignee for the existing assignment
 whether this addition is appropriate.
 If the assignment request is for a new service name sharing the same
 port as a previously assigned service name (see port number
 overloading in Section 5), IANA needs to confirm with the Assignee
 for the existing service name and other appropriate experts whether
 the overloading is appropriate.
 When IANA receives an assignment request -- containing the above
 information -- that is requesting a port number, IANA SHALL initiate
 an "Expert Review" [RFC5226] in order to determine whether an
 assignment should be made.  For requests that are not seeking a port
 number, IANA SHOULD assign the service name under a simple "First
 Come First Served" policy [RFC5226].

Cotton, et al. Best Current Practice [Page 19] RFC 6335 Service Name and Port Number Procedures August 2011

8.1.2. Variances for Specific Port Number Ranges

 Section 6 describes the different port number ranges.  It is
 important to note that IANA applies slightly different procedures
 when managing the different port ranges of the service name and port
 number registry:
 o  Ports in the Dynamic Ports range (49152-65535) have been
    specifically set aside for local and dynamic use and cannot be
    assigned through IANA.  Application software may simply use any
    dynamic port that is available on the local host, without any sort
    of assignment.  On the other hand, application software MUST NOT
    assume that a specific port number in the Dynamic Ports range will
    always be available for communication at all times, and a port
    number in that range hence MUST NOT be used as a service
    identifier.
 o  Ports in the User Ports range (1024-49151) are available for
    assignment through IANA, and MAY be used as service identifiers
    upon successful assignment.  Because assigning a port number for a
    specific application consumes a fraction of the shared resource
    that is the port number registry, IANA will require the requester
    to document the intended use of the port number.  For most IETF
    protocols, ports in the User Ports range will be assigned under
    the "IETF Review" or "IESG Approval" procedures [RFC5226] and no
    further documentation is required.  Where these procedures do not
    apply, then the requester must input the documentation to the
    "Expert Review" procedure [RFC5226], by which IANA will have a
    technical expert review the request to determine whether to grant
    the assignment.  Regardless of the path ("IETF Review", "IESG
    Approval", or "Expert Review"), the submitted documentation is
    expected to be the same, as described in this section, and MUST
    explain why using a port number in the Dynamic Ports range is
    unsuitable for the given application.  Further, IANA MAY utilize
    the "Expert Review" process informally to inform their position in
    participating in "IETF Review" and "IESG Approval".
 o  Ports in the System Ports range (0-1023) are also available for
    assignment through IANA.  Because the System Ports range is both
    the smallest and the most densely assigned, the requirements for
    new assignments are more strict than those for the User Ports
    range, and will only be granted under the "IETF Review" or "IESG
    Approval" procedures [RFC5226].  A request for a System Port
    number MUST document *both* why using a port number from the
    Dynamic Ports range is unsuitable *and* why using a port number
    from the User Ports range is unsuitable for that application.

Cotton, et al. Best Current Practice [Page 20] RFC 6335 Service Name and Port Number Procedures August 2011

8.2. Service Name and Port Number De-Assignment

 The Assignee of a granted port number assignment can return the port
 number to IANA at any time if they no longer have a need for it.  The
 port number will be de-assigned and will be marked as Reserved.  IANA
 should not reassign port numbers that have been de-assigned until all
 unassigned port numbers in the specific range have been assigned.
 Before proceeding with a port number de-assignment, IANA needs to
 reasonably establish that the value is actually no longer in use.
 Because there is much less danger of exhausting the service name
 space compared to the port number space, it is RECOMMENDED that a
 given service name remain assigned even after all associated port
 number assignments have become de-assigned.  Under this policy, it
 will appear in the registry as if it had been created through a
 service name assignment request that did not include any port
 numbers.
 On rare occasions, it may still be useful to de-assign a service
 name.  In such cases, IANA will mark the service name as Reserved.
 IANA will involve their IESG-appointed expert in such cases.
 IANA will include a comment in the registry when de-assignment
 happens to indicate its historic usage.

8.3. Service Name and Port Number Reuse

 If the Assignee of a granted port number assignment no longer has a
 need for the assigned number, but would like to reuse it for a
 different application, they can submit a request to IANA to do so.
 Logically, port number reuse is to be thought of as a de-assignment
 (Section 8.2) followed by an immediate (re-)assignment (Section 8.1)
 of the same port number for a new application.  Consequently, the
 information that needs to be provided about the proposed new use of
 the port number is identical to what would need to be provided for a
 new port number assignment for the specific ports range.
 Because there is much less danger of exhausting the service name
 space compared to the port number space, it is RECOMMENDED that the
 original service name associated with the prior use of the port
 number remains assigned, and a new service name be created and
 associated with the port number.  This is again consistent with
 viewing a reuse request as a de-assignment followed by an immediate
 (re-)assignment.  Reusing an assigned service name for a different
 application is NOT RECOMMENDED.

Cotton, et al. Best Current Practice [Page 21] RFC 6335 Service Name and Port Number Procedures August 2011

 IANA needs to carefully review such requests before approving them.
 In some instances, the Expert Reviewer will determine that the
 application the port number was assigned to has found usage beyond
 the original Assignee, or that there is a concern that it may have
 such users.  This determination MUST be made quickly.  A community
 call concerning revocation of a port number (see below) MAY be
 considered, if a broader use of the port number is suspected.

8.4. Service Name and Port Number Revocation

 A port number revocation can be thought of as an IANA-initiated de-
 assignment (Section 8.2), and has exactly the same effect on the
 registry.
 Sometimes, it will be clear that a specific port number is no longer
 in use and that IANA can revoke it and mark it as Reserved.  At other
 times, it may be unclear whether a given assigned port number is
 still in use somewhere in the Internet.  In those cases, IANA must
 carefully consider the consequences of revoking the port number, and
 SHOULD only do so if there is an overwhelming need.
 With the help of their IESG-appointed Expert Reviewer, IANA SHALL
 formulate a request to the IESG to issue a four-week community call
 concerning the pending port number revocation.  The IESG and IANA,
 with the Expert Reviewer's support, SHALL determine promptly after
 the end of the community call whether revocation should proceed, and
 then communicate their decision to the community.  This procedure
 typically involves similar steps to de-assignment except that it is
 initiated by IANA.
 Because there is much less danger of exhausting the service name
 space compared to the port number space, revoking service names is
 NOT RECOMMENDED.

8.5. Service Name and Port Number Transfers

 The value of service names and port numbers is defined by their
 careful management as a shared Internet resource, whereas enabling
 transfer allows the potential for associated monetary exchanges.  As
 a result, the IETF does not permit service name or port number
 assignments to be transferred between parties, even when they are
 mutually consenting.
 The appropriate alternate procedure is a coordinated de-assignment
 and assignment: The new party requests the service name or port
 number via an assignment and the previous party releases its
 assignment via the de-assignment procedure outlined above.

Cotton, et al. Best Current Practice [Page 22] RFC 6335 Service Name and Port Number Procedures August 2011

 With the help of their IESG-appointed Expert Reviewer, IANA SHALL
 carefully determine if there is a valid technical, operational, or
 managerial reason to grant the requested new assignment.

8.6. Maintenance Issues

 In addition to the formal procedures described above, updates to the
 Description and Contact information are coordinated by IANA in an
 informal manner, and may be initiated by either the Assignee or by
 IANA, e.g., by the latter requesting an update to current Contact
 information.  (Note that the Assignee cannot be changed as a separate
 procedure; see instead Section 8.5 above.)

8.7. Disagreements

 In the case of disagreements around any request, there is the
 possibility of appeal following the normal appeals process for IANA
 assignments as defined by Section 7 of "Guidelines for Writing an
 IANA Considerations Section in RFCs" [RFC5226].

9. Security Considerations

 The IANA guidelines described in this document do not change the
 security properties of UDP, TCP, SCTP, or DCCP.
 Assignment of a service name or port number does not in any way imply
 an endorsement of an application or product, and the fact that
 network traffic is flowing to or from an assigned port number does
 not mean that it is "good" traffic, or even that it is used by the
 assigned service.  Firewall and system administrators should choose
 how to configure their systems based on their knowledge of the
 traffic in question, not based on whether or not there is an assigned
 service name or port number.
 Services are expected to include support for security, either as
 default or dynamically negotiated in-band.  The use of separate
 service name or port number assignments for secure and insecure
 variants of the same service is to be avoided in order to discourage
 the deployment of insecure services.

Cotton, et al. Best Current Practice [Page 23] RFC 6335 Service Name and Port Number Procedures August 2011

10. IANA Considerations

 This document obsoletes Sections 8 and 9.1 of the March 2000 IANA
 Allocation Guidelines [RFC2780].
 Upon approval of this document for publication as an RFC, IANA worked
 with Stuart Cheshire, maintainer of the independent service name
 registry [SRVREG], to merge the contents of that private registry
 into the official IANA registry.  The independent registry web page
 has been updated with pointers to the IANA registry and to this RFC.
 IANA created a new service name entry in the service name and port
 number registry [PORTREG] for all entries in the Protocol and Service
 Names registry [PROTSERVREG] that did not already have one assigned.
 IANA also indicates in the Assignment Notes for "www" and "www-http"
 that they are duplicate terms that refer to the "http" service, and
 should not be used for discovery purposes.  For this conceptual
 service (human-readable web pages served over HTTP), the correct
 service name to use for service discovery purposes is "http" (see
 Section 5).

10.1. Service Name Consistency

 Section 8.1 defines which character strings are well-formed service
 names, which until now had not been clearly defined.  The definition
 in Section 8.1 was chosen to allow maximum compatibility of service
 names with current and future service discovery mechanisms.
 As of August 5, 2009, approximately 98% of the so-called "Short
 Names" from existing port number assignments [PORTREG] met the rules
 for legal service names stated in Section 8.1, and hence for these
 services their service name is exactly the same as their "Short
 Name".
 The remaining approximately 2% of the existing "Short Names" are not
 suitable to be used directly as well-formed service names because
 they contain illegal characters such as asterisks, dots, pluses,
 slashes, or underscores.  All existing "Short Names" conform to the
 length requirement of 15 characters or fewer.  For these 96
 unsuitable "Short Names", listed in the table below, the service name
 is the Short Name with any illegal characters replaced by hyphens.
 IANA added an entry to the registry that uses the new well-formed
 primary service name for the existing service and that otherwise
 duplicates the original assignment information.  In the description
 field of this new entry giving the primary service name, IANA
 recorded that it has assigned a well-formed service name for the
 previous service and references the original assignment.  In the

Cotton, et al. Best Current Practice [Page 24] RFC 6335 Service Name and Port Number Procedures August 2011

 Assignment Notes field of the original assignment, IANA added a note
 that this entry is an alias to the new well-formed service name, and
 that the old service name is historic, not usable for use with many
 common service discovery mechanisms.
 96 names containing illegal characters to be replaced by hyphens:
        +----------------+-----------------+-----------------+
        | 914c/g         | acmaint_dbd     | acmaint_transd  |
        | atex_elmd      | avanti_cdp      | badm_priv       |
        | badm_pub       | bdir_priv       | bdir_pub        |
        | bmc_ctd_ldap   | bmc_patroldb    | boks_clntd      |
        | boks_servc     | boks_servm      | broker_service  |
        | bues_service   | canit_store     | cedros_fds      |
        | cl/1           | contamac_icm    | corel_vncadmin  |
        | csc_proxy      | cvc_hostd       | dbcontrol_agent |
        | dec_dlm        | dl_agent        | documentum_s    |
        | dsmeter_iatc   | dsx_monitor     | elpro_tunnel    |
        | elvin_client   | elvin_server    | encrypted_admin |
        | erunbook_agent | erunbook_server | esri_sde        |
        | EtherNet/IP-1  | EtherNet/IP-2   | event_listener  |
        | flr_agent      | gds_db          | ibm_wrless_lan  |
        | iceedcp_rx     | iceedcp_tx      | iclcnet_svinfo  |
        | idig_mux       | ife_icorp       | instl_bootc     |
        | instl_boots    | intel_rci       | interhdl_elmd   |
        | lan900_remote  | LiebDevMgmt_A   | LiebDevMgmt_C   |
        | LiebDevMgmt_DM | mapper-ws_ethd  | matrix_vnet     |
        | mdbs_daemon    | menandmice_noh  | msl_lmd         |
        | nburn_id       | ncr_ccl         | nds_sso         |
        | netmap_lm      | nms_topo_serv   | notify_srvr     |
        | novell-lu6.2   | nuts_bootp      | nuts_dem        |
        | ocs_amu        | ocs_cmu         | pipe_server     |
        | pra_elmd       | printer_agent   | redstorm_diag   |
        | redstorm_find  | redstorm_info   | redstorm_join   |
        | resource_mgr   | rmonitor_secure | rsvp_tunnel     |
        | sai_sentlm     | sge_execd       | sge_qmaster     |
        | shiva_confsrvr | sql*net         | srvc_registry   |
        | stm_pproc      | subntbcst_tftp  | udt_os          |
        | universe_suite | veritas_pbx     | vision_elmd     |
        | vision_server  | wrs_registry    | z39.50          |
        +----------------+-----------------+-----------------+
 In addition to the 96 names listed above, the service name for
 "whois++" is "whoispp", following the example set by the
 "application/whoispp-query" MIME Content-Type [RFC2957].

Cotton, et al. Best Current Practice [Page 25] RFC 6335 Service Name and Port Number Procedures August 2011

 There were four names recorded in IANA's Port Number Registry
 [PORTREG] that conflicted with names previously recorded in the ad
 hoc SRV name registry [SRVREG]: esp, hydra, recipe, and xmp.
 The name conflicts were resolved amicably:
 The IANA Port Number Registry Short Name "esp" had been registered by
 Andrew Chernow, and he informed the authors that the port was no
 longer in use and the registration was no longer required.  The SRV
 registry entry for "esp" remains in effect.
 The SRV name "hydra" for SubEthaEdit had already been retired in
 favor of the new SRV name "see".  The IANA Port Number Registry entry
 for "hydra" remains in effect.
 The SRV name "recipe" was in use in an open source project that had
 not yet been packaged for distribution, and the registrant Daniel
 Taylor was willing to change to a different service name.  Thanks to
 Daniel Taylor for accommodating this change.  The IANA Port Number
 Registry entry for "recipe" remains in effect.
 The IANA Port Number Registry Short Name "xmp" had been registered by
 Bobby Krupczak, but since his registration included an assigned port
 number (which is still in use and remains unaffected by this change),
 he was willing to switch to a different service name.  Thanks to
 Bobby Krupczak for accommodating this change.  The SRV registry entry
 for "xmp" remains in effect.

10.2. Port Numbers for SCTP and DCCP Experimentation

 Two System UDP and TCP ports, 1021 and 1022, have been reserved for
 experimental use [RFC4727].  This document assigns the same port
 numbers for SCTP and DCCP, updates the TCP and UDP assignments, and
 also instructs IANA to automatically assign these two port numbers
 for any future transport protocol with a similar 16-bit port number
 namespace.
 Note that these port numbers are meant for temporary experimentation
 and development in controlled environments.  Before using these port
 numbers, carefully consider the advice in Section 6.1 in this
 document, as well as in Sections 1 and 1.1 of "Assigning Experimental
 and Testing Numbers Considered Useful" [RFC3692].  Most importantly,
 application developers must request a permanent port number
 assignment from IANA as described in Section 8.1 before any kind of
 non-experimental deployment.

Cotton, et al. Best Current Practice [Page 26] RFC 6335 Service Name and Port Number Procedures August 2011

         +--------------------+-----------------------------+
         | Service Name       | exp1                        |
         | Transport Protocol | DCCP, SCTP, TCP, UDP        |
         | Assignee           | IESG <iesg@ietf.org>        |
         | Contact            | IETF Chair <chair@ietf.org> |
         | Description        | RFC3692-style Experiment 1  |
         | Reference          | [RFC4727] [RFC6335]         |
         | Port Number        | 1021                        |
         +--------------------+-----------------------------+
         +--------------------+-----------------------------+
         | Service Name       | exp2                        |
         | Transport Protocol | DCCP, SCTP, TCP, UDP        |
         | Assignee           | IESG <iesg@ietf.org>        |
         | Contact            | IETF Chair <chair@ietf.org> |
         | Description        | RFC3692-style Experiment 2  |
         | Reference          | [RFC4727] [RFC6335]         |
         | Port Number        | 1022                        |
         +--------------------+-----------------------------+

10.3. Updates to DCCP Registries

 This document updates the IANA assignment procedures for the DCCP
 Port Number and DCCP Service Codes Registries [RFC4340].

10.3.1. DCCP Service Code Registry

 Service codes are assigned on a "first come, first served" basis
 according to Section 19.8 of the DCCP specification [RFC4340].  This
 document updates that section by extending the guidelines given there
 in the following ways:
 o  IANA MAY assign new service codes without seeking "Expert Review"
    using their discretion, but SHOULD seek "Expert Review" if a
    request asks for more than five service codes.
 o  IANA should feel free to contact the DCCP Expert Reviewer with any
    questions related to requests for DCCP-related codepoints.

Cotton, et al. Best Current Practice [Page 27] RFC 6335 Service Name and Port Number Procedures August 2011

10.3.2. DCCP Port Numbers Registry

 The DCCP ports registry is defined by Section 19.9 of the DCCP
 specification [RFC4340].  Assignments in this registry require prior
 assignment of a service code.  Not all service codes require IANA-
 assigned ports.  This document updates that section by extending the
 guidelines given there in the following way:
 o  IANA should normally assign a value in the range 1024-49151 to a
    DCCP server port.  IANA requests to assign port numbers in the
    System Ports range (0 through 1023) require an "IETF Review"
    [RFC5226] prior to assignment by IANA [RFC4340].
 o  IANA MUST NOT assign more than one DCCP server port to a single
    service code value.
 o  The assignment of multiple service codes to the same DCCP port is
    allowed, but subject to "Expert Review".
 o  The set of service code values associated with a DCCP server port
    should be recorded in the service name and port number registry.
 o  A request for additional service codes to be associated with an
    already assigned port number requires "Expert Review".  These
    requests will normally be accepted when they originate from the
    contact associated with the port assignment.  In other cases,
    these applications will be expected to use an unassigned port,
    when this is available.
 The DCCP specification [RFC4340] notes that a short port name MUST be
 associated with each DCCP server port that has been assigned.  This
 document clarifies that this short port name is the service name as
 defined here, and this name MUST be unique.

11. Contributors

 Alfred Hoenes (ah@tr-sys.de) and Allison Mankin (mankin@psg.com) have
 contributed text and ideas to this document.

12. Acknowledgments

 The text in Section 10.3 is based on a suggestion originally proposed
 as a part of the DCCP Service Codes document [RFC5595] by Gorry
 Fairhurst.
 Lars Eggert is partly funded by the Trilogy Project [TRILOGY], a
 research project supported by the European Commission under its
 Seventh Framework Program.

Cotton, et al. Best Current Practice [Page 28] RFC 6335 Service Name and Port Number Procedures August 2011

13. References

13.1. Normative References

 [ANSI.X3.4-1986]  American National Standards Institute, "Coded
                   Character Set - 7-bit American Standard Code for
                   Information Interchange", ANSI X3.4, 1986.
 [RFC0768]         Postel, J., "User Datagram Protocol", STD 6,
                   RFC 768, August 1980.
 [RFC0793]         Postel, J., "Transmission Control Protocol", STD 7,
                   RFC 793, September 1981.
 [RFC2119]         Bradner, S., "Key words for use in RFCs to Indicate
                   Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2780]         Bradner, S. and V. Paxson, "IANA Allocation
                   Guidelines For Values In the Internet Protocol and
                   Related Headers", BCP 37, RFC 2780, March 2000.
 [RFC2782]         Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS
                   RR for specifying the location of services (DNS
                   SRV)", RFC 2782, February 2000.
 [RFC3828]         Larzon, L-A., Degermark, M., Pink, S., Jonsson,
                   L-E., and G. Fairhurst, "The Lightweight User
                   Datagram Protocol (UDP-Lite)", RFC 3828, July 2004.
 [RFC4020]         Kompella, K. and A. Zinin, "Early IANA Allocation
                   of Standards Track Code Points", BCP 100, RFC 4020,
                   February 2005.
 [RFC4340]         Kohler, E., Handley, M., and S. Floyd, "Datagram
                   Congestion Control Protocol (DCCP)", RFC 4340,
                   March 2006.
 [RFC4727]         Fenner, B., "Experimental Values In IPv4, IPv6,
                   ICMPv4, ICMPv6, UDP, and TCP Headers", RFC 4727,
                   November 2006.
 [RFC4960]         Stewart, R., "Stream Control Transmission
                   Protocol", RFC 4960, September 2007.
 [RFC5226]         Narten, T. and H. Alvestrand, "Guidelines for
                   Writing an IANA Considerations Section in RFCs",
                   BCP 26, RFC 5226, May 2008.

Cotton, et al. Best Current Practice [Page 29] RFC 6335 Service Name and Port Number Procedures August 2011

 [RFC5234]         Crocker, D. and P. Overell, "Augmented BNF for
                   Syntax Specifications: ABNF", STD 68, RFC 5234,
                   January 2008.
 [RFC5595]         Fairhurst, G., "The Datagram Congestion Control
                   Protocol (DCCP) Service Codes", RFC 5595,
                   September 2009.

13.2. Informative References

 [DNS-SD]          Cheshire, S. and M. Krochmal, "DNS-Based Service
                   Discovery", Work in Progress, February 2011.
 [IGD]             UPnP Forum, "Internet Gateway Device (IGD) V 1.0",
                   November 2001.
 [NAT-PMP]         Cheshire, S., "NAT Port Mapping Protocol (NAT-
                   PMP)", Work in Progress, April 2008.
 [PORTREG]         Internet Assigned Numbers Authority (IANA),
                   "Service Name and Transport Protocol Port Number
                   Registry",
                   <http://www.iana.org/assignments/port-numbers>.
 [PROTSERVREG]     Internet Assigned Numbers Authority (IANA),
                   "Protocol and Service Names Registry",
                   <http://www.iana.org/assignments/service-names>.
 [RFC0959]         Postel, J. and J. Reynolds, "File Transfer
                   Protocol", STD 9, RFC 959, October 1985.
 [RFC1078]         Lottor, M., "TCP port service Multiplexer
                   (TCPMUX)", RFC 1078, November 1988.
 [RFC1340]         Reynolds, J. and J. Postel, "Assigned Numbers",
                   RFC 1340, July 1992.
 [RFC1700]         Reynolds, J. and J. Postel, "Assigned Numbers",
                   RFC 1700, October 1994.
 [RFC2957]         Daigle, L. and P. Faltstrom, "The application/
                   whoispp-query Content-Type", RFC 2957,
                   October 2000.
 [RFC3232]         Reynolds, J., "Assigned Numbers: RFC 1700 is
                   Replaced by an On-line Database", RFC 3232,
                   January 2002.

Cotton, et al. Best Current Practice [Page 30] RFC 6335 Service Name and Port Number Procedures August 2011

 [RFC3692]         Narten, T., "Assigning Experimental and Testing
                   Numbers Considered Useful", BCP 82, RFC 3692,
                   January 2004.
 [RFC4342]         Floyd, S., Kohler, E., and J. Padhye, "Profile for
                   Datagram Congestion Control Protocol (DCCP)
                   Congestion Control ID 3: TCP-Friendly Rate Control
                   (TFRC)", RFC 4342, March 2006.
 [RFC4844]         Daigle, L. and Internet Architecture Board, "The
                   RFC Series and RFC Editor", RFC 4844, July 2007.
 [RFC5237]         Arkko, J. and S. Bradner, "IANA Allocation
                   Guidelines for the Protocol Field", BCP 37,
                   RFC 5237, February 2008.
 [RFC5389]         Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
                   "Session Traversal Utilities for NAT (STUN)",
                   RFC 5389, October 2008.
 [RFC5766]         Mahy, R., Matthews, P., and J. Rosenberg,
                   "Traversal Using Relays around NAT (TURN): Relay
                   Extensions to Session Traversal Utilities for NAT
                   (STUN)", RFC 5766, April 2010.
 [SRVREG]          "DNS SRV Service Types Registry",
                   <http://www.dns-sd.org/ServiceTypes.html>.
 [SYSFORM]         Internet Assigned Numbers Authority (IANA),
                   "Application for System (Well Known) Port Number",
                   <http://www.iana.org/>.
 [TRILOGY]         "Trilogy Project",
                   <http://www.trilogy-project.org/>.
 [USRFORM]         Internet Assigned Numbers Authority (IANA),
                   "Application for User (Registered) Port Number",
                   <http://www.iana.org/>.

Cotton, et al. Best Current Practice [Page 31] RFC 6335 Service Name and Port Number Procedures August 2011

Authors' Addresses

 Michelle Cotton
 Internet Corporation for Assigned Names and Numbers
 4676 Admiralty Way, Suite 330
 Marina del Rey, CA  90292
 USA
 Phone: +1 310 823 9358
 EMail: michelle.cotton@icann.org
 URI:   http://www.iana.org/
 Lars Eggert
 Nokia Research Center
 P.O. Box 407
 Nokia Group  00045
 Finland
 Phone: +358 50 48 24461
 EMail: lars.eggert@nokia.com
 URI:   http://research.nokia.com/people/lars_eggert/
 Joe Touch
 USC/ISI
 4676 Admiralty Way
 Marina del Rey, CA  90292
 USA
 Phone: +1 310 448 9151
 EMail: touch@isi.edu
 URI:   http://www.isi.edu/touch
 Magnus Westerlund
 Ericsson
 Farogatan 6
 Stockholm  164 80
 Sweden
 Phone: +46 8 719 0000
 EMail: magnus.westerlund@ericsson.com

Cotton, et al. Best Current Practice [Page 32] RFC 6335 Service Name and Port Number Procedures August 2011

 Stuart Cheshire
 Apple Inc.
 1 Infinite Loop
 Cupertino, CA  95014
 USA
 Phone: +1 408 974 3207
 EMail: cheshire@apple.com
 URI:   http://stuartcheshire.org/

Cotton, et al. Best Current Practice [Page 33]

Internet Engineering Task Force (IETF) J. Touch Request for Comments: 7605 USC/ISI BCP: 165 August 2015 Category: Best Current Practice ISSN: 2070-1721

      Recommendations on Using Assigned Transport Port Numbers

Abstract

 This document provides recommendations to designers of application
 and service protocols on how to use the transport protocol port
 number space and when to request a port assignment from IANA.  It
 provides designer guidance to requesters or users of port numbers on
 how to interact with IANA using the processes defined in RFC 6335;
 thus, this document complements (but does not update) that document.
 It provides guidelines for designers regarding how to interact with
 the IANA processes defined in RFC 6335, thus serving to complement
 (but not update) that document.

Status of This Memo

 This memo documents an Internet Best Current Practice.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 BCPs is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7605.

Touch Best Current Practice [Page 1] RFC 7605 Recommendations for Transport Port Use August 2015

Copyright Notice

 Copyright (c) 2015 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1. Introduction ....................................................3
 2. Conventions Used in This Document ...............................3
 3. History .........................................................3
 4. Current Port Number Use .........................................5
 5. What is a Port Number? ..........................................5
 6. Conservation ....................................................7
    6.1. Guiding Principles .........................................7
    6.2. Firewall and NAT Considerations ............................8
 7. Considerations for Requesting Port Number Assignments ...........9
    7.1. Is a port number assignment necessary? .....................9
    7.2. How many assigned port numbers are necessary? .............11
    7.3. Picking an Assigned Port Number ...........................12
    7.4. Support for Security ......................................13
    7.5. Support for Future Versions ...............................14
    7.6. Transport Protocols .......................................14
    7.7. When to Request an Assignment .............................16
    7.8. Squatting .................................................17
    7.9. Other Considerations ......................................18
 8. Security Considerations ........................................18
 9. IANA Considerations ............................................19
 10. References ....................................................19
    10.1. Normative References .....................................19
    10.2. Informative References ...................................20
 Acknowledgments ...................................................24
 Author's Address ..................................................24

Touch Best Current Practice [Page 2] RFC 7605 Recommendations for Transport Port Use August 2015

1. Introduction

 This document provides information and advice to application and
 service designers on the use of assigned transport port numbers.  It
 provides a detailed historical background of the evolution of
 transport port numbers and their multiple meanings.  It also provides
 specific recommendations to designers on how to use assigned port
 numbers.  Note that this document provides information to potential
 port number applicants that complements the IANA process described in
 [RFC6335] (the sole document of BCP 165 before this document), but it
 does not change any of the port number assignment procedures
 described therein.  Because they are thus so closely related, this
 document and RFC 6335 are now known together as BCP 165.  This
 document is intended to address concerns typically raised during
 Expert Review (see [RFC5226]) of assigned port number applications,
 but it is not intended to bind those reviews.  RFC 6335 also
 describes the interaction between port experts and port requests in
 IETF consensus documents.  Authors of IETF consensus documents should
 nevertheless follow the advice in this document and can expect
 comment on their port requests from the port experts during IETF Last
 Call or at other times when review is explicitly sought.

2. Conventions Used in This Document

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [RFC2119].
 In this document, these words will appear with that interpretation
 only when in ALL CAPS.  Lowercase uses of these words are not to be
 interpreted as carrying significance described in RFC 2119.
 In this document, the characters ">>" preceding an indented line(s)
 indicates a statement using the key words listed above.  This
 convention aids reviewers in quickly identifying or finding
 requirements for registration and recommendations for use of port
 numbers in this RFC.

3. History

 The term 'port' was first used in [RFC33] to indicate a simplex
 communication path from an individual process and originally applied
 to only the Network Control Program (NCP) connection-oriented
 protocol.  At a meeting described in [RFC37], an idea was presented
 to decouple connections between processes and links that they use as
 paths and, thus, to include numeric source and destination socket

Touch Best Current Practice [Page 3] RFC 7605 Recommendations for Transport Port Use August 2015

 identifiers in packets.  [RFC38] provides further detail, describing
 how processes might have more than one of these paths and that more
 than one path may be active at a time.  As a result, there was the
 need to add a process identifier to the header of each message so
 that incoming messages could be demultiplexed to the appropriate
 process.  [RFC38] further suggests that 32-bit numbers be used for
 these identifiers.  [RFC48] discusses the current notion of listening
 on a specific port number, but does not discuss the issue of port
 number determination.  [RFC61] notes that the challenge of knowing
 the appropriate port numbers is "left to the processes" in general,
 but introduces the concept of a "well-known" port number for common
 services.
 [RFC76] proposes a "telephone book" by which an index will allow port
 numbers to be used by name, but still assumes that both source and
 destination port numbers are fixed by such a system.  [RFC333]
 proposes that a port number pair, rather than an individual port
 number, be used on both sides of the connection for demultiplexing
 messages.  This is the final view in [RFC793] (and its predecessors,
 including [IEN112]), and brings us to their current meaning.
 [RFC739] introduces the notion of generic reserved port numbers for
 groups of protocols, such as "any private RJE server" [RFC739].
 Although the overall range of such port numbers was (and remains) 16
 bits, only the first 256 (high 8 bits cleared) in the range were
 considered assigned.
 [RFC758] is the first to describe port numbers as being used for TCP
 (previous RFCs all refer to only NCP).  It includes a list of such
 well-known port numbers, as well as describes ranges used for
 different purposes:
    Decimal   Octal     Description
    -----------------------------------------------------------
    0-63      0-77      Network Wide Standard Function
    64-127    100-177   Hosts Specific Functions
    128-223   200-337   Reserved for Future Use
    224-255   340-377   Any Experimental Function
 In [RFC820], those range meanings disappear, and a single list of
 number assignments is presented.  This is also the first time that
 port numbers are described as applying to a connectionless transport
 (e.g., UDP) rather than only connection-oriented transports.
 By [RFC900], the ranges appear as decimal numbers rather than the
 octal ranges used previously.  [RFC1340] increases this range from
 0-255 to 0-1023 and begins to list TCP and UDP port number
 assignments individually (although the assumption was that once
 assigned a port number applies to all transport protocols, including

Touch Best Current Practice [Page 4] RFC 7605 Recommendations for Transport Port Use August 2015

 TCP, UDP, recently Stream Control Transmission Protocol (SCTP) and
 Datagram Congestion Control Protocol (DCCP), as well as ISO-TP4 for a
 brief period in the early 1990s).  [RFC1340] also establishes the
 Registered range of 1024-59151, though it notes that it is not
 controlled by the IANA (at that point).  The list provided by
 [RFC1700] in 1994 remained the standard until it was declared
 replaced by an online version, as of [RFC3232] in 2002.

4. Current Port Number Use

 RFC 6335 indicates three ranges of port number assignments:
    Binary         Hex
    -----------------------------------------------------------
    0-1023         0x0000-0x03FF  System (also Well-Known)
    1024-49151     0x0400-0xBFFF  User (also Registered)
    49152-65535    0xC000-0xFFFF  Dynamic (also Private)
 System (also Well-Known) encompasses the range 0-1023.  On some
 systems, use of these port numbers requires privileged access, e.g.,
 that the process run as 'root' (i.e., as a privileged user), which is
 why these are referred to as System port numbers.  The port numbers
 from 1024-49151 denotes non-privileged services, known as User (also
 Registered), because these port numbers do not run with special
 privileges.  Dynamic (also Private) port numbers are not assigned.
 Both System and User port numbers are assigned through IANA, so both
 are sometimes called 'registered port numbers'.  As a result, the
 term 'registered' is ambiguous, referring either to the entire range
 0-49151 or to the User port numbers.  Complicating matters further,
 System port numbers do not always require special (i.e., 'root')
 privilege.  For clarity, the remainder of this document refers to the
 port number ranges as System, User, and Dynamic, to be consistent
 with IANA process [RFC6335].

5. What is a Port Number?

 A port number is a 16-bit number used for two distinct purposes:
 o  Demultiplexing transport endpoint associations within an end host
 o  Identifying a service
 The first purpose requires that each transport endpoint association
 (e.g., TCP connection or UDP pairwise association) using a given
 transport between a given pair of IP addresses use a different pair
 of port numbers, but it does not require either coordination or

Touch Best Current Practice [Page 5] RFC 7605 Recommendations for Transport Port Use August 2015

 registration of port number use.  It is the second purpose that
 drives the need for a common registry.
 Consider a user wanting to run a web server.  That service could run
 on any port number, provided that all clients knew what port number
 to use to access that service at that host.  Such information can be
 explicitly distributed -- for example, by putting it in the URI:
    http://www.example.com:51509/
 Ultimately, the correlation of a service with a port number is an
 agreement between just the two endpoints of the association.  A web
 server can run on port number 53, which might appear as DNS traffic
 to others but will connect to browsers that know to use port number
 53 rather than 80.
 As a concept, a service is the combination of ISO Layers 5-7 that
 represents an application-protocol capability.  For example, www
 (port number 80) is a service that uses HTTP as an application
 protocol and provides access to a web server [RFC7230].  However, it
 is possible to use HTTP for other purposes, such as command and
 control.  This is why some current services (HTTP, e.g.) are a bit
 overloaded -- they describe not only the application protocol, but a
 particular service.
 IANA assigns port numbers so that Internet endpoints do not need
 pairwise, explicit coordination of the meaning of their port numbers.
 This is the primary reason for requesting port number assignment by
 IANA -- to have a common agreement between all endpoints on the
 Internet as to the default meaning of a port number, which provides
 the endpoints with a default port number for a particular protocol or
 service.
 Port numbers are sometimes used by intermediate devices on a network
 path, either to monitor available services, to monitor traffic (e.g.,
 to indicate the data contents), or to intercept traffic (to block,
 proxy, relay, aggregate, or otherwise process it).  In each case, the
 intermediate device interprets traffic based on the port number.  It
 is important to recognize that any interpretation of port numbers --
 except at the endpoints -- may be incorrect, because port numbers are
 meaningful only at the endpoints.  Further, port numbers may not be
 visible to these intermediate devices, such as when the transport
 protocol is encrypted (as in network- or link-layer tunnels) or when
 a packet is fragmented (in which case only the first fragment has the
 port number information).  Such port number invisibility may
 interfere with these capabilities, which are implemented inside the
 network and based on a port number.

Touch Best Current Practice [Page 6] RFC 7605 Recommendations for Transport Port Use August 2015

 Port numbers can also be used for other purposes.  Assigned port
 numbers can simplify end-system configuration, so that individual
 installations do not need to coordinate their use of arbitrary port
 numbers.  Such assignments may also have the effect of simplifying
 firewall management, so that a single, fixed firewall configuration
 can either permit or deny a service that uses the assigned ports.
 It is useful to differentiate a port number from a service name.  The
 former is a numeric value that is used directly in transport protocol
 headers as a demultiplexing and service identifier.  The latter is
 primarily a user convenience, where the default map between the two
 is considered static and resolved using a cached index.  This
 document focuses on the former because it is the fundamental network
 resource.  Dynamic maps between the two, i.e., using DNS SRV records,
 are discussed further in Section 7.1.

6. Conservation

 Assigned port numbers are a limited resource that is globally shared
 by the entire Internet community.  As of 2014, approximately 5850 TCP
 and 5570 UDP port numbers had been assigned out of a total range of
 49151.  As a result of past conservation, current assigned port use
 is small and the current rate of assignment avoids the need for
 transition to larger number spaces.  This conservation also helps
 avoid the need for IANA to rely on assigned port number reclamation,
 which is practically impossible even though procedurally permitted
 [RFC6335].
 IANA aims to assign only one port number per service, including
 variants [RFC6335], but there are other benefits to using fewer port
 numbers for a given service.  Use of multiple assigned port numbers
 can make applications more fragile, especially when firewalls block a
 subset of those port numbers or use ports numbers to route or
 prioritize traffic differently.  As a result:
 >> Each assigned port requested MUST be justified by the applicant as
 an independently useful service.

6.1. Guiding Principles

 This document provides recommendations for users that also help
 conserve assigned port number space.  Again, this document does not
 update [RFC6335] (originally the sole document of BCP 165), which
 describes the IANA procedures for managing assigned transport port
 numbers and services, but rather augments it by now becoming part of
 BCP 165 (i.e., BCP 165 now refers to both documents together).
 Assigned port number conservation is based on a number of basic
 principles:

Touch Best Current Practice [Page 7] RFC 7605 Recommendations for Transport Port Use August 2015

 o  A single assigned port number can support different functions over
    separate endpoint associations, determined using in-band
    information.  An FTP data connection can transfer binary or text
    files, the latter translating line-terminators, as indicated in-
    band over the control port number [RFC959].
 o  A single assigned port number can indicate the Dynamic port
    number(s) on which different capabilities are supported, as with
    passive-mode FTP [RFC959].
 o  Several existing services can indicate the Dynamic port number(s)
    on which other services are supported, such as with Multicast DNS
    (mDNS) and portmapper [RFC1833] [RFC6762] [RFC6763].
 o  Copies of some existing services can be differentiated using in-
    band information (e.g., URIs in the HTTP Host field and TLS Server
    Name Indication extension) [RFC7230] [RFC6066].
 o  Services requiring varying performance properties can already be
    supported using separate endpoint associations (connections or
    other associations), each configured to support the desired
    properties.  For example, a high-speed and low-speed variant can
    be determined within the service using the same assigned port.
 Assigned port numbers are intended to differentiate services, not
 variations of performance, replicas, pairwise endpoint associations,
 or payload types.  Assigned port numbers are also a small space
 compared to other Internet number spaces; it is never appropriate to
 consume assigned port numbers to conserve larger spaces such as IP
 addresses, especially where copies of a service represent different
 endpoints.

6.2. Firewall and NAT Considerations

 Ultimately, port numbers indicate services only to the endpoints, and
 any intermediate device that assigns meaning to a value can be
 incorrect.  End systems might agree to run web services (HTTP) over
 port number 53 (typically used for DNS) rather than port number 80,
 at which point a firewall that blocks port number 80 but permits port
 number 53 would not have the desired effect.  Nonetheless, assigned
 port numbers are often used to help configure firewalls and other
 port-based systems for access control.
 Using Dynamic port numbers, or explicitly indicated port numbers
 indicated in-band over another service (such as with FTP) often
 complicates firewall and NAT interactions [RFC959].  FTP over
 firewalls often requires direct support for deep-packet inspection
 (to snoop for the Dynamic port number for the NAT to correctly map)

Touch Best Current Practice [Page 8] RFC 7605 Recommendations for Transport Port Use August 2015

 or passive-mode FTP (in which both connections are opened from the
 client side).

7. Considerations for Requesting Port Number Assignments

 Port numbers are assigned by IANA by a set of documented procedures
 [RFC6335].  The following section describes the steps users can take
 to help assist with responsible use of assigned port numbers and with
 preparing an application for a port number assignment.

7.1. Is a port number assignment necessary?

 First, it is useful to consider whether a port number assignment is
 required.  In many cases, a new number assignment may not be needed.
 The following questions may aid in making this determination:
 o  Is this really a new service or could an existing service suffice?
 o  Is this an experimental service [RFC3692]?  If so, consider using
    the current experimental ports [RFC2780].
 o  Is this service independently useful?  Some systems are composed
    from collections of different service capabilities, but not all
    component functions are useful as independent services.  Port
    numbers are typically shared among the smallest independently
    useful set of functions.  Different service uses or properties can
    be supported in separate pairwise endpoint associations after an
    initial negotiation, e.g., to support software decomposition.
 o  Can this service use a Dynamic port number that is coordinated
    out-of-band?  For example:
    o  By explicit configuration of both endpoints.
    o  By internal mechanisms within the same host (e.g., a
       configuration file, indicated within a URI or using
       interprocess communication).
    o  Using information exchanged on a related service: FTP [RFC959],
       SIP [RFC3261], etc.
    o  Using an existing port discovery service: portmapper [RFC1833],
       mDNS [RFC6762] [RFC6763], etc.

Touch Best Current Practice [Page 9] RFC 7605 Recommendations for Transport Port Use August 2015

 There are a few good examples of reasons that more directly suggest
 that not only is a port number assignment not necessary, but it is
 directly counter-indicated:
 o  Assigned port numbers are not intended to differentiate
    performance variations within the same service, e.g., high-speed
    versus ordinary speed.  Performance variations can be supported
    within a single assigned port number in context of separate
    pairwise endpoint associations.
 o  Additional assigned port numbers are not intended to replicate an
    existing service.  For example, if a device is configured to use a
    typical web browser, then the port number used for that service is
    a copy of the http service that is already assigned to port number
    80 and does not warrant a new assignment.  However, an automated
    system that happens to use HTTP framing -- but is not primarily
    accessed by a browser -- might be a new service.  A good way to
    tell is to ask, "Can an unmodified client of the existing service
    interact with the proposed service?".  If so, that service would
    be a copy of an existing service and would not merit a new
    assignment.
 o  Assigned port numbers not intended for intra-machine
    communication.  Such communication can already be supported by
    internal mechanisms (interprocess communication, shared memory,
    shared files, etc.).  When Internet communication within a host is
    desired, the server can bind to a Dynamic port that is indicated
    to the client using these internal mechanisms.
 o  Separate assigned port numbers are not intended for insecure
    versions of existing (or new) secure services.  A service that
    already requires security would be made more vulnerable by having
    the same capability accessible without security.
    Note that the converse is different, i.e., it can be useful to
    create a new, secure service that replicates an existing insecure
    service on a new port number assignment.  This can be necessary
    when the existing service is not backward-compatible with security
    enhancements, such as the use of TLS [RFC5246] or DTLS [RFC6347].
 o  Assigned port numbers are not intended for indicating different
    service versions.  Version differentiation should be handled in-
    band, e.g., using a version number at the beginning of an
    association (e.g., connection or other transaction).  This may not
    be possible with legacy assignments, but all new services should
    incorporate support for version indication.

Touch Best Current Practice [Page 10] RFC 7605 Recommendations for Transport Port Use August 2015

 Some services may not need assigned port numbers at all, e.g., SIP
 allows voice calls to use Dynamic ports [RFC3261].  Some systems can
 register services in the DNS, using SRV entries.  These services can
 be discovered by a variety of means, including mDNS, or via direct
 query [RFC6762] [RFC6763].  In such cases, users can more easily
 request an SRV name, which are assigned first-come, first-served from
 a much larger namespace.
 IANA assigns port numbers, but this assignment is typically used only
 for servers, i.e., the host that listens for incoming connections or
 other associations.  Clients, i.e., hosts that initiate connections
 or other associations, typically refer to those assigned port numbers
 but do not need port number assignments for their endpoint.
 Finally, an assigned port number is not a guarantee of exclusive use.
 Traffic for any service might appear on any port number, due to
 misconfiguration or deliberate misuse.  Application and service
 designers are encouraged to validate traffic based on its content.

7.2. How many assigned port numbers are necessary?

 As noted earlier, systems might require a single port number
 assignment, but rarely require multiple port numbers.  There are a
 variety of known ways to reduce assigned port number consumption.
 Although some may be cumbersome or inefficient, they are nearly
 always preferable to consuming additional port number assignments.
 Such techniques include:
 o  Use of a discovery service, either a shared service (mDNS) or a
    discovery service for a given system [RFC6762] [RFC6763].
 o  Multiplex packet types using in-band information, either on a per-
    message or per-connection basis.  Such demultiplexing can even
    hand off different messages and connections among different
    processes, such as is done with FTP [RFC959].
 There are some cases where NAT and firewall traversal are
 significantly improved by having an assigned port number.  Although
 NAT traversal protocols supporting automatic configuration have been
 proposed and developed (e.g., Session Traversal Utilities for NAT
 (STUN) [RFC5389], Traversal Using Relays around NAT (TURN) [RFC5766],
 and Interactive Connectivity Establishment (ICE) [RFC5245]), not all
 application and service designers can rely on their presence as of
 yet.

Touch Best Current Practice [Page 11] RFC 7605 Recommendations for Transport Port Use August 2015

 In the past, some services were assigned multiple port numbers or
 sometimes fairly large port ranges (e.g., X11).  This occurred for a
 variety of reasons: port number conservation was not as widely
 appreciated, assignments were not as ardently reviewed, etc.  This no
 longer reflects current practice and such assignments are not
 considered to constitute a precedent for future assignments.

7.3. Picking an Assigned Port Number

 Given a demonstrated need for a port number assignment, the next
 question is how to pick the desired port number.  An application for
 a port number assignment does not need to include a desired port
 number; in that case, IANA will select from those currently
 available.
 Users should consider whether the requested port number is important.
 For example, would an assignment be acceptable if IANA picked the
 port number value?  Would a TCP (or other transport protocol) port
 number assignment be useful by itself?  If so, a port number can be
 assigned to a service for one transport protocol where it is already
 (or can be subsequently) assigned to a different service for other
 transport protocols.
 The most critical issue in picking a number is selecting the desired
 range, i.e., System versus User port numbers.  The distinction was
 intended to indicate a difference in privilege; originally, System
 port numbers required privileged ('root') access, while User port
 numbers did not.  That distinction has since blurred because some
 current systems do not limit access control to System port numbers
 and because some System services have been replicated on User numbers
 (e.g., IRC).  Even so, System port number assignments have continued
 at an average rate of 3-4 per year over the past 7 years (2007-2013),
 indicating that the desire to keep this distinction continues.
 As a result, the difference between System and User port numbers
 needs to be treated with caution.  Developers are advised to treat
 services as if they are always run without privilege.
 Even when developers seek a System port number assignment, it may be
 very difficult to obtain.  System port number assignment requires
 IETF Review or IESG Approval and justification that both User and
 Dynamic port number ranges are insufficient [RFC6335].  Thus, this
 document recommends both:
 >> Developers SHOULD NOT apply for System port number assignments
 because the increased privilege they are intended to provide is not
 always enforced.

Touch Best Current Practice [Page 12] RFC 7605 Recommendations for Transport Port Use August 2015

 >> System implementers SHOULD enforce the need for privilege for
 processes to listen on System port numbers.
 At some future date, it might be useful to deprecate the distinction
 between System and User port numbers altogether.  Services typically
 require elevated ('root') privileges to bind to a System port number,
 but many such services go to great lengths to immediately drop those
 privileges just after connection or other association establishment
 to reduce the impact of an attack using their capabilities.  Such
 services might be more securely operated on User port numbers than on
 System port numbers.  Further, if System port numbers were no longer
 assigned, as of 2014 it would cost only 180 of the 1024 System values
 (17%), or 180 of the overall 49152 assigned (System and User) values
 (<0.04%).

7.4. Support for Security

 Just as a service is a way to obtain information or processing from a
 host over a network, a service can also be the opening through which
 to compromise that host.  Protecting a service involves security,
 which includes integrity protection, source authentication, privacy,
 or any combination of these capabilities.  Security can be provided
 in a number of ways, and thus:
 >> New services SHOULD support security capabilities, either directly
 or via a content protection such as TLS [RFC5246] or Datagram TLS
 (DTLS) [RFC6347], or transport protection such as the TCP-AO
 [RFC5925].  Insecure versions of new or existing secure services
 SHOULD be avoided because of the new vulnerability they create.
 Secure versions of legacy services that are not already security-
 capable via in-band negotiations can be very useful.  However, there
 is no IETF consensus on when separate ports should be used for secure
 and insecure variants of the same service [RFC2595] [RFC2817]
 [RFC6335].  The overall preference is for use of a single port, as
 noted in Section 6 of this document and Section 7.2 of [RFC6335], but
 the appropriate approach depends on the specific characteristics of
 the service.  As a result:
 >> When requesting both secure and insecure port assignments for the
 same service, justification is expected for the utility and safety of
 each port as an independent service (Section 6).  Precedent (e.g.,
 citing other protocols that use a separate insecure port) is
 inadequate justification by itself.

Touch Best Current Practice [Page 13] RFC 7605 Recommendations for Transport Port Use August 2015

 It's also important to recognize that port number assignment is not
 itself a guarantee that traffic using that number provides the
 corresponding service or that a given service is always offered only
 on its assigned port number.  Port numbers are ultimately meaningful
 only between endpoints and any service can be run on any port.  Thus:
 >> Security SHOULD NOT rely on assigned port number distinctions
 alone; every service, whether secure or not, is likely to be
 attacked.
 Applications for a new service that requires both a secure and
 insecure port may be found, on Expert Review, to be unacceptable, and
 may not be approved for allocation.  Similarly, an application for a
 new port to support an insecure variant of an existing secure
 protocol may be found unacceptable.  In both cases, the resulting
 security of the service in practice will be a significant
 consideration in the decision as to whether to assign an insecure
 port.

7.5. Support for Future Versions

 Requests for assigned port numbers are expected to support multiple
 versions on the same assigned port number [RFC6335].  Versions are
 typically indicated in-band, either at the beginning of a connection
 or other association or in each protocol message.
 >> Version support SHOULD be included in new services rather than
 relying on different port number assignments for different versions.
 >> Version numbers SHOULD NOT be included in either the service name
 or service description, to avoid the need to make additional port
 number assignments for future variants of a service.
 Again, the assigned port number space is far too limited to be used
 as an indicator of protocol version or message type.  Although this
 has happened in the past (e.g., for NFS), it should be avoided in new
 requests.

7.6. Transport Protocols

 IANA assigns port numbers specific to one or more transport
 protocols, typically UDP [RFC768] and TCP [RFC793], but also SCTP
 [RFC4960], DCCP [RFC4340], and any other standard transport protocol.
 Originally, IANA port number assignments were concurrent for both UDP
 and TCP, and other transports were not indicated.  However, to
 conserve the assigned port number space and to reflect increasing use
 of other transports, assignments are now specific only to the
 transport being used.

Touch Best Current Practice [Page 14] RFC 7605 Recommendations for Transport Port Use August 2015

 In general, a service should request assignments for multiple
 transports using the same service name and description on the same
 port number only when they all reflect essentially the same service.
 Good examples of such use are DNS and NFS, where the difference
 between the UDP and TCP services are specific to supporting each
 transport.  For example, the UDP variant of a service might add
 sequence numbers and the TCP variant of the same service might add
 in-band message delimiters.  This document does not describe the
 appropriate selection of a transport protocol for a service.
 >> Service names and descriptions for multiple transport port number
 assignments SHOULD match only when they describe the same service,
 excepting only enhancements for each supported transport.
 When the services differ, it may be acceptable or preferable to use
 the same port number, but the service names and descriptions should
 be different for each transport/service pair, reflecting the
 differences in the services.  For example, if TCP is used for the
 basic control protocol and UDP for an alarm protocol, then the
 services might be "name-ctl" and "name-alarm".  A common example is
 when TCP is used for a service and UDP is used to determine whether
 that service is active (e.g., via a unicast, broadcast, or multicast
 test message) [RFC1122].  IANA has, for several years, used the
 suffix "-disc" in service names to distinguish discovery services,
 such as are used to identify endpoints capable of a given service.
 >> Names of discovery services SHOULD use an identifiable suffix; the
 suggestion is "-disc".
 Some services are used for discovery, either in conjunction with a
 TCP service or as a stand-alone capability.  Such services will be
 more reliable when using multicast rather than broadcast (over IPv4)
 because IP routers do not forward "all nodes" broadcasts (all 1's,
 i.e., 255.255.255.255 for IPv4) and have not been required to support
 subnet-directed broadcasts since 1999 [RFC1812] [RFC2644].
 This issue is relevant only for IPv4 because IPv6 does not support
 broadcast.
 >> UDP over IPv4 multi-host services SHOULD use multicast rather than
 broadcast.
 Designers should be very careful in creating services over transports
 that do not support congestion control or error recovery, notably
 UDP.  There are several issues that should be considered in such
 cases, as summarized in Table 1 in [RFC5405].  In addition, the
 following recommendations apply to service design:

Touch Best Current Practice [Page 15] RFC 7605 Recommendations for Transport Port Use August 2015

 >> Services that use multipoint communication SHOULD be scalable and
 SHOULD NOT rely solely on the efficiency of multicast transmission
 for scalability.
 >> Services SHOULD NOT use UDP as a performance enhancement over TCP,
 e.g., to circumnavigate TCP's congestion control.

7.7. When to Request an Assignment

 Assignments are typically requested when a user has enough
 information to reasonably answer the questions in the IANA
 application.  IANA applications typically take up to a few weeks to
 process, with some complex cases taking up to a month.  The process
 typically involves a few exchanges between the IANA Ports Expert
 Review team and the applicant.
 An application needs to include a description of the service, as well
 as to address key questions designed to help IANA determine whether
 the assignment is justified.  The application should be complete and
 not refer solely to an Internet-Draft, RFC, website, or any other
 external documentation.
 Services that are independently developed can be requested at any
 time, but are typically best requested in the last stages of design
 and initial experimentation, before any deployment has occurred that
 cannot easily be updated.
 >> Users MUST NOT deploy implementations that use assigned port
 numbers prior their assignment by IANA.
 >> Users MUST NOT deploy implementations that default to using the
 experimental System port numbers (1021 and 1022 [RFC4727]) outside a
 controlled environment where they can be updated with a subsequent
 assigned port [RFC3692].
 Deployments that use unassigned port numbers before assignment
 complicate IANA management of the port number space.  Keep in mind
 that this recommendation protects existing assignees, users of
 current services, and applicants for new assignments; it helps ensure
 that a desired number and service name are available when assigned.
 The list of currently unassigned numbers is just that -- *currently*
 unassigned.  It does not reflect pending applications.  Waiting for
 an official IANA assignment reduces the chance that an assignment
 request will conflict with another deployed service.
 Applications made through Internet-Draft posting or RFC publication
 (in any stream) typically use a placeholder ("PORTNUM") in the text,
 and implementations use an experimental port number until a final

Touch Best Current Practice [Page 16] RFC 7605 Recommendations for Transport Port Use August 2015

 assignment has been made [RFC6335].  That assignment is initially
 indicated in the IANA Considerations section of the document, which
 is tracked by the RFC Editor.  When a document has been approved for
 publication, that request is forwarded to IANA for handling.  IANA
 will make the new assignment accordingly.  At that time, IANA may
 also request that the applicant fill out the application form on
 their website, e.g., when the RFC does not directly address the
 information expected as per [RFC6335].  "Early" assignments can be
 made when justified, e.g., for early interoperability testing,
 according to existing process [RFC7120] [RFC6335].
 >> Users writing specifications SHOULD use symbolic names for port
 numbers and service names until an IANA assignment has been
 completed.  Implementations SHOULD use experimental port numbers
 during this time, but those numbers MUST NOT be cited in
 documentation except as interim.

7.8. Squatting

 "Squatting" describes the use of a number from the assignable range
 in deployed software without IANA assignment for that use, regardless
 of whether the number has been assigned or remains available for
 assignment.  It is hazardous because IANA cannot track such usage and
 thus cannot avoid making legitimate assignments that conflict with
 such unauthorized usage.
 Such "squatted" port numbers remain unassigned, and IANA retains the
 right to assign them when requested by other applicants.  Application
 and service designers are reminded that is never appropriate to use
 port numbers that have not been directly assigned [RFC6335].  In
 particular, any unassigned code from the assigned ranges will be
 assigned by IANA, and any conflict will be easily resolved as the
 protocol designer's fault once that happens (because they would not
 be the assignee).  This may reflect in the public's judgment on the
 quality of their expertise and cooperation with the Internet
 community.
 Regardless, there are numerous services that have squatted on such
 numbers that are in widespread use.  Designers who are using such
 port numbers are encouraged to apply for an assignment.  Note that
 even widespread de facto use may not justify a later IANA assignment
 of that value, especially if either the value has already been
 assigned to a legitimate applicant or if the service would not
 qualify for an assignment of its own accord.

Touch Best Current Practice [Page 17] RFC 7605 Recommendations for Transport Port Use August 2015

7.9. Other Considerations

 As noted earlier, System port numbers should be used sparingly, and
 it is better to avoid them altogether.  This avoids the potentially
 incorrect assumption that the service on such port numbers run in a
 privileged mode.
 Assigned port numbers are not intended to be changed; this includes
 the corresponding service name.  Once deployed, it can be very
 difficult to recall every implementation, so the assignment should be
 retained.  However, in cases where the current assignee of a name or
 number has reasonable knowledge of the impact on such uses, and is
 willing to accept that impact, the name or number of an assignment
 can be changed [RFC6335]
 Aliases, or multiple service names for the same assigned port number,
 are no longer considered appropriate [RFC6335].

8. Security Considerations

 This document focuses on the issues arising when designing services
 that require new port assignments.  Section 7.4 addresses the
 security and security-related issues of that interaction.
 When designing a secure service, the use of TLS [RFC5246], DTLS
 [RFC6347], or TCP-AO [RFC5925] mechanisms that protect transport
 protocols or their contents is encouraged.  It may not be possible to
 use IPsec [RFC4301] in similar ways because of the different
 relationship between IPsec and port numbers and because applications
 may not be aware of IPsec protections.
 This document reminds application and service designers that port
 numbers do not protect against denial-of-service attack or guarantee
 that traffic should be trusted.  Using assigned numbers for port
 filtering isn't a substitute for authentication, encryption, and
 integrity protection.  The port number alone should not be used to
 avoid denial-of-service attacks or to manage firewall traffic because
 the use of port numbers is not regulated or validated.
 The use of assigned port numbers is the antithesis of privacy because
 they are intended to explicitly indicate the desired application or
 service.  Strictly, port numbers are meaningful only at the
 endpoints, so any interpretation elsewhere in the network can be
 arbitrarily incorrect.  However, those numbers can also expose
 information about available services on a given host.  This
 information can be used by intermediate devices to monitor and

Touch Best Current Practice [Page 18] RFC 7605 Recommendations for Transport Port Use August 2015

 intercept traffic as well as to potentially identify key endpoint
 software properties ("fingerprinting"), which can be used to direct
 other attacks.

9. IANA Considerations

 The entirety of this document focuses on suggestions that help ensure
 the conservation of port numbers and provide useful hints for issuing
 informative requests thereof.

10. References

10.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2780]  Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
            Values In the Internet Protocol and Related Headers", BCP
            37, RFC 2780, DOI 10.17487/RFC2780, March 2000,
            <http://www.rfc-editor.org/info/rfc2780>.
 [RFC3692]  Narten, T., "Assigning Experimental and Testing Numbers
            Considered Useful", BCP 82, RFC 3692,
            DOI 10.17487/RFC3692, January 2004,
            <http://www.rfc-editor.org/info/rfc3692>.
 [RFC4727]  Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4,
            ICMPv6, UDP, and TCP Headers", RFC 4727,
            DOI 10.17487/RFC4727, November 2006,
            <http://www.rfc-editor.org/info/rfc4727>.
 [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246,
            DOI 10.17487/RFC5246, August 2008,
            <http://www.rfc-editor.org/info/rfc5246>.
 [RFC5405]  Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
            for Application Designers", BCP 145, RFC 5405,
            DOI 10.17487/RFC5405, November 2008,
            <http://www.rfc-editor.org/info/rfc5405>.
 [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
            Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
            June 2010, <http://www.rfc-editor.org/info/rfc5925>.

Touch Best Current Practice [Page 19] RFC 7605 Recommendations for Transport Port Use August 2015

 [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
            Cheshire, "Internet Assigned Numbers Authority (IANA)
            Procedures for the Management of the Service Name and
            Transport Protocol Port Number Registry", BCP 165, RFC
            6335, DOI 10.17487/RFC6335, August 2011,
            <http://www.rfc-editor.org/info/rfc6335>.
 [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
            Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
            January 2012, <http://www.rfc-editor.org/info/rfc6347>.

10.2. Informative References

 [IEN112]   Postel, J., "Transmission Control Protocol", IEN 112,
            August 1979.
 [RFC33]    Crocker, S., "New Host-Host Protocol", RFC 33,
            DOI 10.17487/RFC0033, February 1970,
            <http://www.rfc-editor.org/info/rfc33>.
 [RFC37]    Crocker, S., "Network Meeting Epilogue, etc", RFC 37,
            DOI 10.17487/RFC0037, March 1970,
            <http://www.rfc-editor.org/info/rfc37>.
 [RFC38]    Wolfe, S., "Comments on Network Protocol from NWG/RFC
            #36", RFC 38, DOI 10.17487/RFC0038, March 1970,
            <http://www.rfc-editor.org/info/rfc38>.
 [RFC48]    Postel, J. and S. Crocker, "Possible protocol plateau",
            RFC 48, DOI 10.17487/RFC0048, April 1970,
            <http://www.rfc-editor.org/info/rfc48>.
 [RFC61]    Walden, D., "Note on Interprocess Communication in a
            Resource Sharing Computer Network", RFC 61,
            DOI 10.17487/RFC0061, July 1970,
            <http://www.rfc-editor.org/info/rfc61>.
 [RFC76]    Bouknight, J., Madden, J., and G. Grossman, "Connection by
            name: User oriented protocol", RFC 76,
            DOI 10.17487/RFC0076, October 1970,
            <http://www.rfc-editor.org/info/rfc76>.

Touch Best Current Practice [Page 20] RFC 7605 Recommendations for Transport Port Use August 2015

 [RFC333]   Bressler, R., Murphy, D., and D. Walden, "Proposed
            experiment with a Message Switching Protocol", RFC 333,
            DOI 10.17487/RFC0333, May 1972,
            <http://www.rfc-editor.org/info/rfc333>.
 [RFC739]   Postel, J., "Assigned numbers", RFC 739,
            DOI 10.17487/RFC0739, November 1977,
            <http://www.rfc-editor.org/info/rfc739>.
 [RFC758]   Postel, J., "Assigned numbers", RFC 758,
            DOI 10.17487/RFC0758, August 1979,
            <http://www.rfc-editor.org/info/rfc758>.
 [RFC768]   Postel, J., "User Datagram Protocol", STD 6, RFC 768,
            DOI 10.17487/RFC0768, August 1980,
            <http://www.rfc-editor.org/info/rfc768>.
 [RFC793]   Postel, J., "Transmission Control Protocol", STD 7, RFC
            793, DOI 10.17487/RFC0793, September 1981,
            <http://www.rfc-editor.org/info/rfc793>.
 [RFC820]   Postel, J., "Assigned numbers", RFC 820,
            DOI 10.17487/RFC0820, August 1982,
            <http://www.rfc-editor.org/info/rfc820>.
 [RFC900]   Reynolds, J. and J. Postel, "Assigned Numbers", RFC 900,
            DOI 10.17487/RFC0900, June 1984,
            <http://www.rfc-editor.org/info/rfc900>.
 [RFC959]   Postel, J. and J. Reynolds, "File Transfer Protocol", STD
            9, RFC 959, DOI 10.17487/RFC0959, October 1985,
            <http://www.rfc-editor.org/info/rfc959>.
 [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
            Communication Layers", STD 3, RFC 1122,
            DOI 10.17487/RFC1122, October 1989,
            <http://www.rfc-editor.org/info/rfc1122>.
 [RFC1340]  Reynolds, J. and J. Postel, "Assigned Numbers", RFC 1340,
            DOI 10.17487/RFC1340, July 1992,
            <http://www.rfc-editor.org/info/rfc1340>.
 [RFC1700]  Reynolds, J. and J. Postel, "Assigned Numbers", RFC 1700,
            DOI 10.17487/RFC1700, October 1994,
            <http://www.rfc-editor.org/info/rfc1700>.

Touch Best Current Practice [Page 21] RFC 7605 Recommendations for Transport Port Use August 2015

 [RFC1812]  Baker, F., Ed., "Requirements for IP Version 4 Routers",
            RFC 1812, DOI 10.17487/RFC1812, June 1995,
            <http://www.rfc-editor.org/info/rfc1812>.
 [RFC1833]  Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
            RFC 1833, DOI 10.17487/RFC1833, August 1995,
            <http://www.rfc-editor.org/info/rfc1833>.
 [RFC2595]  Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC
            2595, DOI 10.17487/RFC2595, June 1999,
            <http://www.rfc-editor.org/info/rfc2595>.
 [RFC2644]  Senie, D., "Changing the Default for Directed Broadcasts
            in Routers", BCP 34, RFC 2644, DOI 10.17487/RFC2644,
            August 1999, <http://www.rfc-editor.org/info/rfc2644>.
 [RFC2817]  Khare, R. and S. Lawrence, "Upgrading to TLS Within
            HTTP/1.1", RFC 2817, DOI 10.17487/RFC2817, May 2000,
            <http://www.rfc-editor.org/info/rfc2817>.
 [RFC3232]  Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced
            by an On-line Database", RFC 3232, DOI 10.17487/RFC3232,
            January 2002, <http://www.rfc-editor.org/info/rfc3232>.
 [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
            A., Peterson, J., Sparks, R., Handley, M., and E.
            Schooler, "SIP: Session Initiation Protocol", RFC 3261,
            DOI 10.17487/RFC3261, June 2002,
            <http://www.rfc-editor.org/info/rfc3261>.
 [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
            Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
            December 2005, <http://www.rfc-editor.org/info/rfc4301>.
 [RFC4340]  Kohler, E., Handley, M., and S. Floyd, "Datagram
            Congestion Control Protocol (DCCP)", RFC 4340,
            DOI 10.17487/RFC4340, March 2006,
            <http://www.rfc-editor.org/info/rfc4340>.
 [RFC4960]  Stewart, R., Ed., "Stream Control Transmission Protocol",
            RFC 4960, DOI 10.17487/RFC4960, September 2007,
            <http://www.rfc-editor.org/info/rfc4960>.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            DOI 10.17487/RFC5226, May 2008,
            <http://www.rfc-editor.org/info/rfc5226>.

Touch Best Current Practice [Page 22] RFC 7605 Recommendations for Transport Port Use August 2015

 [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
            (ICE): A Protocol for Network Address Translator (NAT)
            Traversal for Offer/Answer Protocols", RFC 5245,
            DOI 10.17487/RFC5245, April 2010,
            <http://www.rfc-editor.org/info/rfc5245>.
 [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
            "Session Traversal Utilities for NAT (STUN)", RFC 5389,
            DOI 10.17487/RFC5389, October 2008,
            <http://www.rfc-editor.org/info/rfc5389>.
 [RFC5766]  Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
            Relays around NAT (TURN): Relay Extensions to Session
            Traversal Utilities for NAT (STUN)", RFC 5766,
            DOI 10.17487/RFC5766, April 2010,
            <http://www.rfc-editor.org/info/rfc5766>.
 [RFC6066]  Eastlake 3rd, D., "Transport Layer Security (TLS)
            Extensions: Extension Definitions", RFC 6066,
            DOI 10.17487/RFC6066, January 2011,
            <http://www.rfc-editor.org/info/rfc6066>.
 [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
            DOI 10.17487/RFC6762, February 2013,
            <http://www.rfc-editor.org/info/rfc6762>.
 [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
            Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
            <http://www.rfc-editor.org/info/rfc6763>.
 [RFC7120]  Cotton, M., "Early IANA Allocation of Standards Track Code
            Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
            2014, <http://www.rfc-editor.org/info/rfc7120>.
 [RFC7230]  Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
            Transfer Protocol (HTTP/1.1): Message Syntax and Routing",
            RFC 7230, DOI 10.17487/RFC7230, June 2014,
            <http://www.rfc-editor.org/info/rfc7230>.

Touch Best Current Practice [Page 23] RFC 7605 Recommendations for Transport Port Use August 2015

Acknowledgments

 This work benefited from the feedback from David Black, Lars Eggert,
 Gorry Fairhurst, and Eliot Lear, as well as discussions of the IETF
 TSVWG WG.
 This document was initially prepared using 2-Word-v2.0.template.dot.

Author's Address

 Joe Touch
 USC/ISI
 4676 Admiralty Way
 Marina del Rey, CA 90292-6695
 United States
 Phone: +1 (310) 448-9151
 Email: touch@isi.edu

Touch Best Current Practice [Page 24]

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