Internet Assigned Numbers Authority (IANA) Procedures for the Management of the Service Name and Transport Protocol Port Number Registry
draft-ietf-tsvwg-iana-ports-08

Abstract

This document defines the procedures that the Internet Assigned Numbers Authority (IANA) uses when handling registration 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 Sections 8 and 9.1 of the IANA allocation guidelines [RFC2780], and it updates the IANA allocation procedures for UDP-Lite [RFC3828], DCCP [RFC4340] and SCTP [RFC4960]. It also updates the DNS SRV specification [RFC2782] to clarify what a service name is and how it is registered.

Status of this Memo

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This Internet-Draft will expire on April 28, 2011.

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Table of Contents

1.  Introduction
2.  Motivation
3.  Background
4.  Conventions Used in this Document
5.  Service Names
    5.1.  Service Name Syntax
    5.2.  Service Name Usage in DNS SRV Records
6.  Port Number Ranges
    6.1.  Service names and Port Numbers for Experimentation
7.  Principles for Service Name and Transport Protocol Port Number Registry Management
    7.1.  Past Principles
    7.2.  Updated Principles
8.  IANA Procedures for Managing the Service Name and Transport Protocol Port Number Registry
    8.1.  Service Name and Port Number Registration
    8.2.  Service Name and Port Number De-Registration
    8.3.  Service Name and Port Number Re-Use
    8.4.  Service Name and Port Number Revocation
    8.5.  Service Name and Port Number Transfers
    8.6.  Maintenance Issues
    8.7.  Disagreements
9.  Security Considerations
10.  IANA Considerations
    10.1.  Service Name Consistency
    10.2.  Port Numbers for SCTP and DCCP Experimentation
    10.3.  Updates to DCCP Registries
11.  Contributors
12.  Acknowledgments
13.  References
    13.1.  Normative References
    13.2.  Informative References
§  Authors' Addresses

1.  Introduction

For many years, the allocation of new service names and port number values for use with the Transmission Control Protocol (TCP) [RFC0793] (Postel, J., “Transmission Control Protocol,” September 1981.) and the User Datagram Protocol (UDP) [RFC0768] (Postel, J., “User Datagram Protocol,” August 1980.) have had less than clear guidelines. New transport protocols have been added - the Stream Control Transmission Protocol (SCTP) [RFC4960] (Stewart, R., “Stream Control Transmission Protocol,” September 2007.) and the Datagram Congestion Control Protocol (DCCP) [RFC4342] (Floyd, S., Kohler, E., and J. Padhye, “Profile for Datagram Congestion Control Protocol (DCCP) Congestion Control ID 3: TCP-Friendly Rate Control (TFRC),” March 2006.) - and new mechanisms like DNS SRV records [RFC2782] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.) 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-register a port number that is no longer in use, to re-use a port number allocated for one application that is no longer in use for another application, and the procedure by which IANA can unilaterally revoke a prior port number assignment. Section 8 (IANA Procedures for Managing the Service Name and Transport Protocol Port Number Registry) 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 registrations are maintained by IANA. For protocols developed by IETF working groups, IANA now also offers a method for the "early assignment" [RFC4020] (Kompella, K. and A. Zinin, “Early IANA Allocation of Standards Track Code Points,” February 2005.) of service names and port numbers, as described in Section 8.1 (Service Name and Port Number Registration).

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] (Bradner, S. and V. Paxson, “IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers,” March 2000.). (Note that other sections of the IANA allocation guidelines, relating to the protocol field values in IPv4 header, were also updated in February 2008 [RFC5237] (Arkko, J. and S. Bradner, “IANA Allocation Guidelines for the Protocol Field,” February 2008.).) This document also updates the IANA allocation procedures for DCCP [RFC4340] (Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006.) and SCTP [RFC4960] (Stewart, R., “Stream Control Transmission Protocol,” September 2007.).

The Lightweight User Datagram Protocol (UDP-Lite) [RFC5237] (Arkko, J. and S. Bradner, “IANA Allocation Guidelines for the Protocol Field,” February 2008.) shares the port space with UDP. The UDP-Lite specification says: "UDP-Lite uses the same set of port number values assigned by the IANA for use by UDP". Thus the update of UDP procedures result in an update also of the UDP-Lite procedures.

This document also clarifies what a service name is and how it is registered. This will impact the DNS SRV specification [RFC2782] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.), because that specification merely makes a brief mention that the symbolic names of services are defined in "Assigned Numbers" [RFC1700] (Reynolds, J. and J. Postel, “Assigned Numbers,” October 1994.), 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" is now obsolete [RFC3232] (Reynolds, J., “Assigned Numbers: RFC 1700 is Replaced by an On-line Database,” January 2002.) and has been replaced by on-line registries [PORTREG] (Internet Assigned Numbers Authority (IANA), “Service Name and Transport Protocol Port Number Registry,” .)[PROTSERVREG] (Internet Assigned Numbers Authority (IANA), “Protocol and Service Names Registry,” .).

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, for consistency it is expected to follow as much as possible the guidelines and practices around using service names and port numbers.

2.  Motivation

Information about the registration procedures for the port registry has existed in three locations: the forms for requesting port number registrations on the IANA web site [SYSFORM] (Internet Assigned Numbers Authority (IANA), “Application for System (Well Known) Port Number,” .) [USRFORM] (Internet Assigned Numbers Authority (IANA), “Application for User (Registered) Port Number,” .), an introductory text section in the file listing the port number registrations themselves [PORTREG] (Internet Assigned Numbers Authority (IANA), “Service Name and Transport Protocol Port Number Registry,” .), and two brief sections of the IANA Allocation Guidelines [RFC2780] (Bradner, S. and V. Paxson, “IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers,” March 2000.).

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, beyond the 14-character limit mentioned on the IANA website [SYSFORM] (Internet Assigned Numbers Authority (IANA), “Application for System (Well Known) Port Number,” .) [USRFORM] (Internet Assigned Numbers Authority (IANA), “Application for User (Registered) Port Number,” .). 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, the requirement by IANA to only assign service names and port numbers in combination, led to the creation of an ad hoc service name registry outside of the control of IANA [SRVREG] (, “DNS SRV Service Types Registry,” .).

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 registration of service names without associated port numbers, for such usages as DNS SRV records [RFC2782] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.), which was not possible under the previous IANA procedures. The document also merges service name registrations from the non-IANA ad hoc registry [SRVREG] (, “DNS SRV Service Types Registry,” .) and from the IANA "Protocol and Service Names" registry [PROTSERVREG] (Internet Assigned Numbers Authority (IANA), “Protocol and Service Names Registry,” .) into the IANA "Service Name and Transport Protocol Port Number" registry [PORTREG] (Internet Assigned Numbers Authority (IANA), “Service Name and Transport Protocol Port Number Registry,” .), 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 ports 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 (Principles for Service Name and Transport Protocol Port Number Registry Management) discusses these principles in detail.

3.  Background

The Transmission Control Protocol (TCP) [RFC0793] (Postel, J., “Transmission Control Protocol,” September 1981.) and the User Datagram Protocol (UDP) [RFC0768] (Postel, J., “User Datagram Protocol,” August 1980.) 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 bind. Newer transport protocols, such as the Stream Control Transmission Protocol (SCTP) [RFC4960] (Stewart, R., “Stream Control Transmission Protocol,” September 2007.) and the Datagram Congestion Control Protocol (DCCP) [RFC4342] (Floyd, S., Kohler, E., and J. Padhye, “Profile for Datagram Congestion Control Protocol (DCCP) Congestion Control ID 3: TCP-Friendly Rate Control (TFRC),” March 2006.) 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] (Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., and G. Fairhurst, “The Lightweight User Datagram Protocol (UDP-Lite),” July 2004.), a variant of UDP).

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.

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] (Internet Assigned Numbers Authority (IANA), “Service Name and Transport Protocol Port Number Registry,” .).

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 NAT Port Mapping Protocol (NAT-PMP) (Cheshire, S., “NAT Port Mapping Protocol (NAT-PMP),” April 2008.) [I‑D.cheshire‑nat‑pmp] or Internet Gateway Device (IGD) (UPnP Forum, “Internet Gateway Device (IGD) V 1.0,” November 2001.) [IGD].

Applications may use numeric 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] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.)[I‑D.cheshire‑dnsext‑dns‑sd] (Cheshire, S. and M. Krochmal, “DNS-Based Service Discovery,” March 2010.), or determine port numbers in a variety of other ways like the TCP Port Service Multiplexer (TCPMUX) [RFC1078] (Lottor, M., “TCP port service Multiplexer (TCPMUX),” November 1988.).

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 successful registration - assume that no other application will use that service name or port number for its communication sessions. Alternatively, application designers may also ask for only an assigned service name, if their application does not require a fixed port number. The latter alternative is encouraged when possible, in order to conserve the more limited port number space. This is applicable, for example, to applications that use DNS SRV records to look up port numbers at runtime.

4.  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 "Key words for use in RFCs to Indicate Requirement Levels" [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

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 (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.) [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 Registrant 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 service name overloading can occur:

• 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". TURN [RFC5766] (Mahy, R., Matthews, P., and J. Rosenberg, “Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN),” April 2010.) is an extension to the STUN [RFC5389] (Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, “Session Traversal Utilities for NAT (STUN),” October 2008.) service. TURN-enabled clients wishing to locate TURN servers could attempt to discover "stun" services and then check in-band if the server 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.)
• By historical accident the service name "http" corresponds to the same port number as "www" and "www-http". When used in SRV records [RFC2782] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.), and similar service discovery mechanisms only the service name "http" should be used, not these additional names. If a server were to advertise "www" then it would not be discovered by clients browsing for "http". Advertising or browsing for the aliases as well as the primary service name would be inefficient, and achieves nothing that it not already achieved by using the service name "http" exclusively.
• As indicated in this document, in Section 10.1 (Service Name Consistency), to enable legacy names to be replaced with names consistent with the syntax this document prescribes. In this case, only the new name should be used in SRV records, both to avoid the same issues as with historical cases of multiple names, as well as because the legacy names are incompatible with SRV record use.

For future assignments, applications will not be permitted that merely request a new name exactly duplicating an existing service. Having multiple names for the same service serves no purpose. 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 (Service Name and Port Number Registration). 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:

• MUST be at least 1 character and no more than 15 characters long
• MUST contain only US-ASCII [ANSI.X3‑4.1986] (American National Standards Institute, “Coded Character Set - 7-bit American Standard Code for Information Interchange,” 1986.) letters 'A' - 'Z' and 'a' - 'z', digits '0' - '9', and hyphens ('-', ASCII 0x2D or decimal 45)
• MUST contain at least one letter ('A' - 'Z' or 'a' - 'z')
• MUST NOT begin or end with a hyphen
• 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 number) or "6000-6063" (could be confused with a numeric port number 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.

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 can't claim to "own" all service names beginning with "Example-", they can't prevent someone else registering "Example-Baz" for a different service, and they can't 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.

In approximately 98% of cases, the new "service name" is exactly the same as the old historic "short name" from the IANA web forms [SYSFORM] (Internet Assigned Numbers Authority (IANA), “Application for System (Well Known) Port Number,” .) [USRFORM] (Internet Assigned Numbers Authority (IANA), “Application for User (Registered) Port Number,” .). In approximately 2% of cases, the new "service name" is derived from the old historic "short name" as described below in Section 10.1 (Service Name Consistency).

The rules for valid service names, excepting the limit of 15 characters maximum, are also expressed below (as a non-normative convenience) using ABNF (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” January 2008.) [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] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.) 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. The service name SHOULD be registered with IANA and recorded in the Service Name and Transport Protocol Port Number Registry [PORTREG] (Internet Assigned Numbers Authority (IANA), “Service Name and Transport Protocol Port Number Registry,” .).

The details of using Service Names in SRV Service Labels are specified in the DNS SRV specification [RFC2782] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.). This document does not change that specification.

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 these transport protocols are subdivided into three ranges of numbers, and Section 8.1.1 (Variances for Specific Port Number Ranges) describes the IANA procedures for each range in detail:

• the System Ports, also known as the Well Known Ports, from 0-1023 (assigned by IANA)
• the User Ports, also known as the Registered Ports, from 1024-49151 (assigned by IANA)
• the Dynamic Ports, also known as the Private 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:

• Assigned: Assigned port numbers are currently allocated to the service indicated in the registry.
• Unassigned: Unassigned port numbers are currently available for assignment upon request, as per the procedures outlined in this document.
• 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 an near-infinite number of 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.)

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 ranges [RFC4727] (Fenner, B., “Experimental Values In IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers,” November 2006.).

Please refer to Sections 1 and 1.1 of "Assigning Experimental and Testing Numbers Considered Useful" [RFC3692] (Narten, T., “Assigning Experimental and Testing Numbers Considered Useful,” January 2004.) for how these experimental port numbers are to be used.

This document registers the same two service names and port numbers for experimentation with new application-layer protocols over SCTP and DCCP in Section 10.2 (Port Numbers for SCTP and DCCP Experimentation).

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 allocation of service names and port numbers upon request, as well as management of information about existing allocations. The latter includes maintaining contact and description information about assignments, revoking abandoned assignments, and redefining assignments when needed. Of these procedures, careful port number allocation 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.

7.1.  Past Principles

Before the publication of this document, the principles of service name and port number management followed a few mostly-undocumented guidelines. They are recorded here for historical purposes, and this document updates them in Section 7.2 (Updated Principles). These principles were:

• TCP and UDP ports were simultaneously allocated when either was requested
• Port numbers were the primary allocation; service names were informative only, and did not have a well-defined syntax
• Port numbers were conserved informally, and sometimes inconsistently (e.g., some services were allocated ranges of many port numbers even where not strictly necessary)
• SCTP and DCCP service name and port number registries were managed separately from the TCP/UDP registries
• Service names could not be assigned in the old ports registry without assigning an associated port number at the same time

This document clarifies and aligns these guidelines in order to more conservatively manage the limited remaining port number space and to enable and promote the use of service names for service identification without associated port numbers, where possible.

7.2.  Updated Principles

This section summarizes the basic principles by which IANA 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 are not required to be bound by these principles when handling requests; other factors may come into play, and exceptions may occur where deemed in the best interest of the Internet.

IANA will begin assigning service names that do not request an associated port number allocation under a simple "First Come, First Served" policy [RFC5226] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.). IANA MAY, at its discretion, refer service name requests to "Expert Review" in cases of mass registrations or other situations where IANA believes expert review is advisable.

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. To help ensure this conservation the policy for any registration request for port number allocations uses the "Expert Review" policy [RFC5226] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.).

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:

• IANA will allocate only one assigned port number per service or application
• IANA will allocate only one assigned port number for all versions of a service (e.g., running the service with or without a security mechanism, or for updated variants of a service)
• IANA will allocate only one assigned port number for all different types of device using or participating in the same service
• IANA will allocate port numbers only for the transport protocol(s) explicitly named in a registration request
• IANA may recover unused port numbers, via the new procedures of de-registration, 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 allocated port. Applications and protocols are also expected to be able to efficiently use a single allocated port for multiple sessions, either by demultiplexing multiple streams within one port, or using the allocated port to coordinate using dynamic ports for subsequent exchanges (e.g., in the spirit of FTP [RFC0959] (Postel, J. and J. Reynolds, “File Transfer Protocol,” October 1985.)).

Ports are used in various ways, notably:

• as endpoint process identifiers
• as application protocol identifiers
• 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. Further, previous separation of protocol variants based on security capabilities (e.g., HTTP on TCP port 80 vs. HTTPS on TCP port 443) is not recommended for new protocols, because all new protocols should be security-capable and capable of negotiating the use of security in-band.

IANA will begin assigning port numbers for only those transport protocols explicitly included in a registration request. This ends the long-standing practice of automatically assigning a port number to an application for both TCP and a UDP, even if the request is for only one of these transport protocols. The new allocation procedure conserves resources by allocating 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 Registrant for the registration MUST request IANA to convert the reservation into a proper assignment. 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 asking IANA to convert the reservation into an assignment.

When the available pool of unassigned numbers has run out in a ports 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 when that time comes. To help conserve ports, application developers should register only the transport protocols that their application currently uses.

Conservation of port numbers is improved by procedures that allow previously allocated port numbers to become Unassigned, either through de-registration or through revocation, and by a procedure that lets application designers transfer an allocated but unused port number to a new application. Section 8 (IANA Procedures for Managing the Service Name and Transport Protocol Port Number Registry) describes these procedures, which until now were undocumented. Port number conservation is also improved by recommending that applications that do not require an allocated 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 registration, de-registration, re-use, changes to the service name, and updates to the contact information or description associated with an assignment. Revocation is as additional process, initiated by IANA.

8.1.  Service Name and Port Number Registration

Registration refers to the allocation of service names or port numbers to applicants. All such registrations are made from service names or port numbers that are Unassigned or Reserved at the time of the allocation. Unassigned names and numbers are allocated according to the rules described in Section 8.1.1 (Variances for Specific Port Number Ranges) below. Reserved numbers and names are assigned only by Standards Action or IESG Approval, and MUST accompanied by a statement explaining the reason a Reserved number or name is appropriate for this action.

When a registration 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. The current Registrant for a port number MAY register these Reserved port numbers for other transport protocols when needed.

A service name or port number registration request contains the following information. The service name is the unique identifier of a given service:

Service Name (REQUIRED)
Transport Protocol(s) (REQUIRED)
Registrant (REQUIRED)
Contact (REQUIRED)
Description (REQUIRED)
Reference (REQUIRED)
Port Number (OPTIONAL)
Service Code (REQUIRED for DCCP only)
Known Unauthorized Uses (OPTIONAL)
Assignment Notes (OPTIONAL)

• Service Name: A desired unique service name for the service associated with the registration request MUST be provided, for use in various service selection and discovery mechanisms (including, but not limited to, DNS SRV records [RFC2782] (Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000.)). The name MUST be compliant with the syntax defined in Section 5.1 (Service Name Syntax). In order to be unique, they MUST NOT be identical to any currently assigned service name in the IANA registry [PORTREG] (Internet Assigned Numbers Authority (IANA), “Service Name and Transport Protocol Port Number Registry,” .). Service names are case-insensitive; they may be provided and entered into the registry with mixed case for clarity, but for the comparison purposes the case is ignored.
• Transport Protocol(s): The transport protocol(s) for which a allocation is requested MUST be provided. This field is currently limited to one or more of TCP, UDP, SCTP, and DCCP. Requests without any port allocation and only a service name are still required to indicate which protocol the service uses.
• Registrant: Name and email address of the Registrant. This is REQUIRED. The Registrant is the Organization or Company responsible for the initial registration. For registrations done through IETF-published RFCs, the Registrant will be the IESG.
• Contact: Name and email address of the Contact person for the registration. This is REQUIRED. The Contact person is the responsible person for the Internet community to send questions to. This person would also be authorized to submit changes on behalf of the Registrant; in cases of conflict between the Registrant and the Contact, the Registrant decisions take precedence. Additional address information MAY be provided. For registrations done through IETF-published RFCs, the Contact will be the IESG.
• Description: A short description of the service associated with the registration request is REQUIRED. It should avoid all but the most well-known acronyms.
• Reference: A description of (or a reference to a document describing) the protocol or application using this port. The description must state whether the protocol uses broadcast, multicast, or anycast communication.
  
  For registrations 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 use of broadcast, multicast, or anycast is given.
  
  For registration requests for a User Port, the registration request MUST explain why a port number in the Dynamic Ports range is unsuitable for the given application.
  
  For registration requests for a System Port, the registration 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. For requests from IETF Working Groups, IANA MAY accept "early registration" [RFC4020] (Kompella, K. and A. Zinin, “Early IANA Allocation of Standards Track Code Points,” February 2005.) requests referencing a sufficiently stable Internet Draft instead of a published Standards-Track RFC.
• Port Number: If assignment of a port number is desired, either the currently Unassigned or Reserved port number the requester suggests for allocation, or indication of which port range, user or system, that the requester requires, 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 allocate 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 prior to the completion of the registration.
• Service Code: If the registration request includes DCCP as a transport protocol then the request MUST include a desired unique DCCP service code [RFC5595] (Fairhurst, G., “The Datagram Congestion Control Protocol (DCCP) Service Codes,” September 2009.), and MUST NOT include a requested DCCP service code otherwise. Section 19.8 of the DCCP specification [RFC4340] (Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006.) defines requirements and rules for allocation, updated by this document.
• Known Unauthorized Uses: A list of uses by applications or organizations who are not the Registrant. This list may be augmented by IANA after assignment when unauthorized uses are reported.
• Assignment Notes: Indications of owner/name change, or any other assignment process issue. This list may be updated by IANA after assignment to help track changes to an assignment, e.g., de-registration, owner/name changes, etc.

If the registration request is for the addition of a new transport protocol to an already assigned service name, IANA needs to confirm with the Registrant for the existing assignment whether this addition is appropriate.

If the registration request is for a service name overloading a port number (see Section 5), IANA needs to confirm with the Registrant for the existing service name whether the registration of the overloading is appropriate.

When IANA receives a registration request - containing the above information - that is requesting a port number, IANA SHALL initiate an "Expert Review" [RFC5226] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) in order to determine whether an assignment should be made. For requests that are not requesting a port number, IANA SHOULD assign the service name under a simple "First Come First Served" policy [RFC5226] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.).

8.1.1.  Variances for Specific Port Number Ranges

Section 6 (Port Number Ranges) 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:

• 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 them for communication without any sort of registration. 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.
• Ports in the User Ports range (1024-49151) are available for registration through IANA, and MAY be used as service identifiers upon successful registration. Because registering 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. This documentation will be input to the "Expert Review" allocation procedure [RFC5226] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.), by which IANA will have a technical expert review the request to determine whether to grant the registration. The submitted documentation MUST explain why using a port number in the Dynamic Ports range is unsuitable for the given application. Ports in the User Ports range may also be assigned under the "IETF Review" or "IESG Approval" allocation procedures [RFC5226] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.), which is how most assignments for IETF protocols are handled.
• Ports in the System Ports range (0-1023) are also available for registration through IANA. Because the System Ports range is both the smallest and the most densely allocated, the requirements for new allocations are more strict than those for the User Ports range, and will only be granted under the "IETF Review" or "IESG Approval" allocation procedures [RFC5226] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.). A request for a System Port number MUST document *both* why using a port number from the User Ports is unsuitable *and* why using a port number from the Dynamic Ports ranges is unsuitable for that application.

8.2.  Service Name and Port Number De-Registration

The Registrant 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-registered and will be marked as Reserved. IANA should not re-assign port numbers that have been de-registered until all unassigned port numbers in the specific range have been assigned.

Before proceeding with a port number de-registration, 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-registered. Under this policy, it will appear in the registry as if it had been created through a service name registration request that did not include any port numbers.

On rare occasions, it may still be useful to de-register 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-registration happens to indicate its historic usage.

8.3.  Service Name and Port Number Re-Use

If the Registrant of a granted port number assignment no longer have a need for the assigned number, but would like to re-use it for a different application, they can submit a request to IANA to do so.

Logically, port number re-use is to be thought of as a de-registration (Section 8.2 (Service Name and Port Number De-Registration)) followed by an immediate re-registration (Section 8.1 (Service Name and Port Number Registration)) 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 allocation 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 be created and associated with the port number. This is again consistent with viewing a re-use request as a de-registration followed by an immediate re-registration. Re-using an assigned service name for a different application is NOT RECOMMENDED.

IANA needs to carefully review such requests before approving them. In some instances, the Expert Reviewer will determine that the application that the port number was assigned to has found usage beyond the original requester, 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-registration (Section 8.2 (Service Name and Port Number De-Registration)), 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-registration 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-registration and registration: The new party requests the service name or port number via a registration and the previous party releases its assignment via the de-registration procedure outlined above.

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 registrant or by IANA, e.g., by the latter requesting an update to current contact information. (Note that Registrant cannot be changed; see Section 8.5 (Service Name and Port Number Transfers) above.)

8.7.  Disagreements

In the case of disagreements around any request there is the possibility of appeal following the normal appelas process for IANA registrations as defined by Section 7 of "Guidelines for Writing an IANA Considerations Section in RFCs" (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) [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.

10.  IANA Considerations

This document obsoletes Sections 8 and 9.1 of the March 2000 IANA Allocation Guidelines [RFC2780] (Bradner, S. and V. Paxson, “IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers,” March 2000.).

Upon approval of this document, IANA is requested to contact Stuart Cheshire, maintainer of the independent service name registry [SRVREG] (, “DNS SRV Service Types Registry,” .), in order to merge the contents of that private registry into the official IANA registry. It is expected that the independent registry web page will be updated with pointers to the IANA registry and to this RFC.

IANA is instructed to create a new service name entry in the service name and port number registry [PORTREG] (Internet Assigned Numbers Authority (IANA), “Service Name and Transport Protocol Port Number Registry,” .) for any entry in the "Protocol and Service Names" registry [PROTSERVREG] (Internet Assigned Numbers Authority (IANA), “Protocol and Service Names Registry,” .) that does not already have one assigned.

IANA is also instructed to indicate 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 (Service Names)).

10.1.  Service Name Consistency

Section 8.1 (Service Name and Port Number Registration) defines which character strings are well-formed service names, which until now had not been clearly defined. The definition in Section 8.1 (Service Name and Port Number Registration) 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 registrations [PORTREG] (Internet Assigned Numbers Authority (IANA), “Service Name and Transport Protocol Port Number Registry,” .) meet the rules for legal service names stated in Section 8.1 (Service Name and Port Number Registration), and hence for these services their service name will be exactly the same as their "Short Name".

The remaining approximately 2% of the exiting "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 unsuitable "Short Names", listed in the table below, the service name will be the Short Name with any illegal characters replaced by hyphens. IANA SHALL add an entry to the registry giving the new well-formed primary service name for the existing service, that otherwise duplicates the original assignment information. In the description field of this new entry giving the primary service name, IANA SHALL record that it assigns a well-formed service name for the previous service and reference the original assignment. In the Assignment Notes field of the original assignment, IANA SHALL add 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.

Names containing illegal characters to be replaced by hyphens:

Following the example set by the "application/whoispp-query" MIME Content-Type [RFC2957] (Daigle, L. and P. Faltstrom, “The application/whoispp-query Content-Type,” October 2000.), the service name for "whois++" will be "whoispp".

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] (Fenner, B., “Experimental Values In IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers,” November 2006.). This document assigns the same port numbers for SCTP and DCCP, updates the TCP and UDP registrations, 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 (Service names and Port Numbers for Experimentation) in this document, as well as in Sections 1 and 1.1 of "Assigning Experimental and Testing Numbers Considered Useful" [RFC3692] (Narten, T., “Assigning Experimental and Testing Numbers Considered Useful,” January 2004.). Most importantly, application developers must request a permanent port number assignment from IANA as described in Section 8.1 (Service Name and Port Number Registration) before any kind of non-experimental deployment.

[RFC Editor Note: Please change "yyyy" to the RFC number allocated to this document before publication.]

10.3.  Updates to DCCP Registries

This document updates the IANA allocation procedures for the DCCP Port Number and DCCP Service Codes Registries [RFC4340] (Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006.).

10.3.1.  DCCP Service Code Registry

Service Codes are allocated first-come-first-served according to Section 19.8 of the DCCP specification [RFC4340] (Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006.). This document updates that section by extending the guidelines given there in the following ways:

• IANA MAY assign new Service Codes without seeking Expert Review using their discretion, but SHOULD seek expert review if a request seeks more than five Service Codes.
• IANA should feel free to contact the DCCP Expert Reviewer with questions on any registry, regardless of the registry policy, for clarification or if there is a problem with a request [RFC4340] (Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006.).

10.3.2.  DCCP Port Numbers Registry

The DCCP ports registry is defined by Section 19.9 of the DCCP specification [RFC4340] (Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006.). Allocations in this registry require prior allocation 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:

• IANA should normally assign a value in the range 1024-49151 to a DCCP server port. IANA allocation requests to allocate port numbers in the System Ports range (0 through 1023), require an "IETF Review" [RFC5226] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008.) prior to allocation by IANA [RFC4340] (Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006.).
• IANA MUST NOT allocate more than one DCCP server port to a single service code value.
• The allocation of multiple service codes to the same DCCP port is allowed, but subject to expert review.
• The set of Service Code values associated with a DCCP server port should be recorded in the service name and port number registry.
• A request for additional Service Codes to be associated with an already allocated Port Number requires Expert Review. These requests will normally be accepted when they originate from the contact associated with the port registration. In other cases, these applications will be expected to use an unallocated port, when this is available.

The DCCP specification [RFC4340] (Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006.) 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 (Updates to DCCP Registries) is based on a suggestion originally proposed as a part of the DCCP Service Codes document[RFC5595] (Fairhurst, G., “The Datagram Congestion Control Protocol (DCCP) Service Codes,” September 2009.) by Gorry Fairhurst.

Lars Eggert is partly funded by the Trilogy Project [TRILOGY] (, “Trilogy Project,” .), a research project supported by the European Commission under its Seventh Framework Program.

13.  References

13.1. Normative References

13.2. Informative References

Authors' Addresses