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.
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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
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Contributions published or made publicly available before November
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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.
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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
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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].
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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
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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).
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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.
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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
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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.
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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].
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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.)
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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.
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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.
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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]).
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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
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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.
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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