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Versions: (draft-touch-tsvwg-port-use)  00 01 02   Best Current Practice
          03 04 05 06 07 08 09 10 11 rfc7605                            
TSVWG                                                          J. Touch
Internet Draft                                                 USC/ISI
Intended status: Best Current Practice                    July 15, 2013
Expires: January 2014

                  Recommendations for Transport Port Uses

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 15, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
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   document must include Simplified BSD License text as described in
   Section 4.e of the Trust Legal Provisions and are provided without

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   warranty as described in the Simplified BSD License.


   This document provides recommendations to application and service
   designers on how to use the transport protocol port number space to
   help in its preservation.

Table of Contents

   1. Introduction...................................................2
   2. Conventions used in this document..............................3
   3. History........................................................3
   4. Current Port Use...............................................4
   5. What is a Port?................................................5
   6. Conservation...................................................6
      6.1. Firewall and NAT Considerations...........................7
   7. How to Use Assigned Ports......................................7
      7.1. Do You Need a Port?.......................................7
      7.2. How Many Ports?...........................................9
      7.3. Picking a Port Number.....................................9
      7.4. Support for Security.....................................10
      7.5. Support for Future Versions..............................11
      7.6. Transport Protocols......................................11
      7.7. When to Request an Assignment............................13
      7.8. Squatting................................................14
      7.9. Other Considerations.....................................14
   8. Security Considerations.......................................15
   9. IANA Considerations...........................................15
   10. References...................................................15
      10.1. Normative References....................................15
      10.2. Informative References..................................15
   11. Acknowledgments..............................................17

1. Introduction

   This document provides information and advice to system designers on
   the use of transport port numbers and services. It provides a
   detailed historical background of the evolution of transport port
   numbers and their multiple meanings. It also provides specific
   recommendations on how to use assigned ports.

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2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.

   In this document, the characters ">>" preceding an indented line(s)
   indicates a compliance requirement statement using the key words
   listed above. This convention aids reviewers in quickly identifying
   or finding the explicit compliance requirements of this RFC.

3. History

   The term 'port' was first used in RFC33 to describe a simplex
   communication path from a process [RFC33]. At a meeting described in
   [RFC37], an idea was presented to decouple connections between
   processes and links that they use as paths, and thus to include
   source and destination socket identifiers in packets. RFC38 explains
   this in detail, in which processes might have more than one of these
   paths, and that more than one may be active at a time [RFC38]. As a
   result, there was the need to add a process identifier to the header
   of each message, so that the incoming data could be demultiplexed to
   the appropriate process. RFC38 further suggested that 32 bits would
   be used for these identifiers. RFC48 discusses the current notion of
   listening on a given port, but does not discuss how the issue of
   port determination [RFC48]. RFC61 notes that the challenge of
   knowing the appropriate port numbers is "left to the processes" in
   general, but introduces the concept of a "well-known" port for
   common services [RFC61].

   RFC76 addresses this issue more constructively, proposing a
   "telephone book" by which an index would allow ports to be used by
   name, but still assumes that both source and destination ports are
   fixed by such a system [RFC76]. RFC333 suggests that the port pair,
   rather than an individual port, would be used on both sides of the
   connection for demultiplexing messages [RFC333]. This is the final
   view in RFC793 (and its predecessors, including IEN 112 [IEN112]),
   and brings us to their current meaning. RFC739 introduces the notion
   of generic reserved ports, used for groups of protocols, such as
   "any private RJE server" [RFC739]. Although the overall range of
   such ports was (and remains) 16 bits, only the first 256 (high 8
   bits cleared) in the range were considered assigned.

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   RFC758 is the first to describe a list of such well-known ports, as
   well as describing ranges used for different purposes [RFC758]:

      Binary    Octal


      0-63      0-77      Network Wide Standard Function

      64-127    100-177   Hosts Specific Functions

      128-223   200-337   Reserved for Future Use

      224-255   340-377   Any Experimental Function

   In RFC820, those range meanings disappeared, and a single list of
   assignments is presented [RFC820]. By RFC900, they appeared as
   decimal numbers rather than the octal ranges used previously
   [RFC900]. RFC1340 increased this range from 0..255 to 0..1023, and
   began to list TCP and UDP port assignments individually (although
   the assumption was, and remains, that once assigned a port applies
   to all transport protocols, including TCP, UDP, recently SCTP and
   DCCP, as well as ISO-TP4 for a brief period in the early 1990s)
   [RFC1340]. RFC1340 also established the Registered space of 1024-
   59151, though it notes that it is not controlled by the IANA at that
   point. The list provided by RFC1700 in 1994 remained the standard
   until it was declared replaced by an on-line version, as of RFC3232
   in 2002 [RFC1700][RFC3232].

4. Current Port Use

   The current IANA website (www.iana.org) indicates three ranges of
   port assignments:

      Binary         Hex


      0-1023         0x03FF         Well-Known (a.k.a. 'system')

      1024-49151     0x0400-0xBFFF  Registered (a.k.a. 'user')

      49152-65535    0xC000-0xFFFF  Dynamic/Private

   Well-known encompasses the range 0..1023. On some systems, use of
   these ports requires privileged access, e.g., that the process run
   as 'root', which is why these are referred to as 'system' ports. The

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   ports from 1024..49151 denotes non-privileged services, known as
   'registered'; because these ports do not run with special
   privileges, they are often referred to as 'user' ports. Dynamic or
   Private ports are not assigned through IANA.

   Both Well-Known and Registered ports are assigned through IANA, so
   both are sometimes called "registered ports". As a result, the term
   'registered' is ambiguous, referring either to the entire range 0-
   49151 or to the user ports. Complicating matters further, 'system'
   ports do not always require special (i.e., 'root') privilege.
   Regardless, for clarity, throughout the remainder of this document
   we will refer to the port ranges as 'system', 'user', and 'private'.

5. What is a Port?

   A port is a 16-bit number used for two distinct purposes:

      o  Demultiplexing transport connections within an end host

      o  Identifying a service

   The first reason requires that each transport connection between a
   given pair of IP addresses use a different pair of ports, but does
   not require either coordination or registration of port use. It is
   the second reason that drives the need for a common registry.

   Consider a user wanting to run a web server. That service could run
   on any port, provided that all clients knew what port to use to
   access that service at that host. Such information can be
   distributed out of band, e.g., in the URL, such as:


   Ultimately, it's important to keep in mind that the correlation of a
   service with a port number is an agreement between the two endpoints
   of the connection only. The rest of the world might think that
   you're sending DNS packets on port 53, but you can run a web server
   on that port just fine, provided the server and client both decide
   that port 53 is for HTTP web server traffic.

   Which brings us to the concept of a service. A service is the
   combination of ISO Layers 5-7 that represent an application protocol
   capability. For example www (port 80) is a service that uses HTTP as
   an application protocol, and provides a common web server [RFC2616].
   However, it is possible to use HTTP for other purposes, such as
   command and control. This is why some current service names (HTTP,

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   e.g.) are a bit overloaded - they describe not only the application
   protocol, but a particular service.

   IANA assigns ports so that endpoints on the Internet do not need to
   pairwise, explicitly coordinate the meaning of their port numbers.
   This is the primary reason for requesting assigned ports with IANA -
   to have a common agreement between all endpoints on the Internet as
   to the meaning of a port.

   Ports are used for other purposes as well, however. The other
   primary reason for requesting assigned ports with IANA is to
   simplify end system configuration, so individual installations do
   not need to coordinate their use of arbitrary ports. A similar
   reason is to simplify firewall management, so that a single, fixed
   firewall configuration can either permit or deny a service.

6. Conservation

   Ports are a scarce resource that are globally shared by the entire
   Internet community. As a result, every attempt should be made to
   conserve ports and request only those that are absolutely necessary.

   There are a variety of ways that systems can conserve port numbers:

      o  A single assigned port number can provide access to different
         capabilities over different connections (or equivalent, e.g.,
         for UDP [RFC768]), using in-band information.

      o  A single assigned port can indicate the dynamic port(s) on
         which different capabilities are supported, as is done for

      o  An existing service can indicate the dynamic port(s) on which
         services are supported, such as with mDNS and portmapper
         [RFC6762] [RFC6763].

      o  Copies of an existing service can be differentiated by using
         different IP addresses (even on the same host).

      o  Copies of some existing services can be differentiated using
         in-band information (e.g., HTTP).

      o  Different performance requirements or capabilities can already
         be supported using different connections or endpoint

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   The key observation is that port numbers are intended to
   differentiate services, not performance, replicas, connections, or
   payload types. Port numbers are a very small space, so it is never
   appropriate to consume port numbers to save larger spaces, such as
   IP addresses.

   Others have noted "think twice about modifying TCP, then don't"
   [RFC1263]. In this case, similar advice might be:

      o  Think twice before asking for a port, then try not to.

      o  If you need more than one port assignment, revise your
         architecture until you can get by with only one, or,
         preferably, none.

6.1. Firewall and NAT Considerations

   Assigned numbers are useful for configuring firewalls and other
   port-based systems for access control. Ultimately, these ports
   indicate services only to the endpoints, and any intermediate device
   that assigns meaning to a value can be incorrect. End systems might
   agree to run web services (HTTP) over port 53 (typically used for
   DNS) rather than port 80, at which point a firewall that blocks port
   80 would have no effect. However, assigned values often are
   important in helping configure firewalls to known values.

   Using dynamic ports, or dynamically-indicated ports over known ports
   (such as with FTP) often complicates firewall and NAT interactions.
   FTP over firewalls often requires direct support for deep-packet
   inspection (to snoop for the dynamic port to open) and "passive
   mode" FTP, in which both FTP connections are opened from the client
   to the server (useful for NAT traversal).

7. How to Use Assigned Ports

   The following section describes the steps users can take to help
   assist with the use of assigned ports.

7.1. Do You Need a Port?

   First, ask whether you really need a port assignment. In many cases,
   a new assignment may not be needed, for example:

      o  Is this really a new service, or can you use an existing

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      o  Is this an experimental service [RFC3692]? If so, consider
         using the current experimental ports [RFC2780]

      o  Can this service use a dynamic port that is coordinated out-
         of-band, e.g.:

          o By explicit configuration of both endpoints.

          o By shared information within the same host (e.g., a
             configuration file).

          o Using an existing port discovery service: portmapper, mDNS,
             etc. [RFC6762] [RFC6763]

   There are a few good examples of reasons that more directly suggest
   that not only is a port not necessary, but it is directly

      o  Ports are not for performance. Performance enhancement can
         occur within separate connections.

      o  Additional ports are not to replicate an existing service. For
         example, if you have a device that is configured using a web
         browser, that is a copy of HTTP port 80, and does not warrant
         a new assignment. However, if you develop an automated system
         that happens to use HTTP framing, that could be a new service.
         A good way to tell is "can an unmodified client of the
         existing service interact with your service"? If so, that
         would be a copy, and should not request a new assignment.

      o  Ports are not for insecure versions of existing secure
         services. Consider that a service that includes required
         security would be made vulnerable by having the same
         capability accessible without security.

         Note that the converse is different, i.e., it can be useful to
         create a new, secure service that replicates an existing
         insecure service on a new port assignment. This can be
         necessary when the existing service is not backward-compatible
         with security enhancements, such as the use of TLS or SSL
         [Hi95] [RFC5246].

   Some users may not need assigned port numbers at all. Some systems
   can register services in the DNS, using SRV entries. These services
   can be discovered by a variety of means, including mDNS, or via
   direct query. In such cases, users can more easily request a SRV

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   name, which are assigned first-come, first-served from a much larger

   IANA assigns port numbers, but this assignment is typically used
   only for servers, i.e., the host that listens for incoming
   connections. Clients, i.e., hosts that initiate connections,
   typically refer to those assigned ports but do not need port
   assignments for their endpoint.

7.2. How Many Ports?

   As noted earlier, systems might require a single port assignment,
   but rarely require multiple ports. There are a variety of known ways
   to reduce port use. Although some may be cumbersome or inefficient,
   they are always preferable to consuming additional ports.

   Such techniques include:

      o  Use of a discovery service, either a shared service (mDNS), or
         a discovery service for a given system

      o  Multiplex packet types using in-band information, either on a
         per-message or per-connection basis. Such demultiplexing can
         even hand-off connections among different processes.

   There are some cases where it is still important to have assigned
   port numbers, largely to traverse either NATs or firewalls. Although
   automatic configuration protocols have been proposed and developed,
   system designers cannot yet their presence.

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

7.3. Picking a Port Number

   Given a demonstrated need for a port number assignment, the next
   question is how to pick the desired port number. An application for
   a port assignment does not need to include a desired port number; in
   that case, IANA will select from those currently available.

   Users should consider whether the requested port number is
   important. For example, would you accept an assignment if IANA
   picked the value? Would you want a TCP port number assignment if the

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   corresponding UDP one were unavailable (assuming your service needed
   only a TCP port) [RFC793]?

   The most critical issue in picking a number is selecting the desired
   range, i.e.., system vs. user ports. The distinction was intended to
   indicate a difference in privilege; system ports required privileged
   ('root') access, while user ports did not. That distinction has
   blurred because some current systems do not limit access control to
   system ports, and because some system services have been replicated
   on user numbers (e.g., IRC). Even so, system port assignments have
   continued at an average rate of 3-4 per year over the past 6 years
   (2007-2012), indicating that the desire to keep this distinction

   As a result, we recommend that the different between user and system
   ports be treated with caution. Developers are advised to treat
   services as if they are always run without privilege. As a result:

   >> Developers SHOULD NOT apply for system ports because the
   increased privilege they provide is not always enforced.

   Even when developers seek a system port, it may be very difficult to
   obtain. System port assignment requires IETF Review or IESG Approval
   and justification that both user and dynamic port ranges are
   insufficient [RFC6335].

   >> System implementers SHOULD enforce the need for privilege for
   processes to listen on system ports.

   At some future date, it might be useful to deprecate the distinction
   between system and user ports altogether. Services typically require
   elevated ('root') privileges to bind to a system port, but many such
   services go to great lengths to immediately drop those privileges to
   reduce the impact of an attack using their capabilities. As a result
   it can be more secure to run such services on user ports than on
   system ports. Further, avoiding system ports would potentially waste
   only approximately 180 of 1024 values (17%).

7.4. Support for Security

   Services represent a potential system vulnerability. Given the
   current state of cybersecurity in the Internet, we recommend that:

   >> New services SHOULD support security, either directly or via a
   secure transport such as TLS [RFC5246].

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   >> Insecure versions of new secure services SHOULD be avoided
   because of the vulnerability they create.

   >> Security SHOULD NOT rely on port number distinctions alone; every
   service, whether secure or not, SHOULD expect to be attacked.

   There is debate as to how to secure legacy insecure services
   [RFC6335]. Some argue that secure variants should share the existing
   port assignment, such that security is enabled on a per-connection
   basis [RFC2817]. Others argue that security should be supported on a
   new port assignment and be enabled by default. IANA currently
   permits either approach.

   Optional security can penalize performance, requiring additional
   round-trip exchanges before a connection can be established. As we
   discussed earlier, ports are a critical resource and it is
   inappropriate to consume assignments to increase performance.

   Note however that a new service might not be eligible for IANA
   assignment of both an insecure and a secure variant of the same
   service, and similarly IANA might be skeptical of an assignment for
   an insecure port for a secure service. In both cases, security of
   the service is compromised by adding the insecure port assignment.

7.5. Support for Future Versions

   Current IANA assignments are expected to support versioning
   [RFC6335]. Versions are typically indicated in-band, either at the
   beginning of a connection or association, or in each protocol

   >> Version support SHOULD be included in new services.

   >> Version numbers SHOULD NOT be included in either the service name
   or service description.

   Again, the port number space is far too limited to be used as an
   indicator of protocol version or message type. Although this has
   happened in the past (e.g., for NFS), it should be avoided.

7.6. Transport Protocols

   IANA assigns port numbers specific to one or more transport
   protocols, typically UDP and TCP, but also SCTP, DCCP, and any other
   standard transport protocol [RFC4340] [RFC4960]. Originally, IANA
   port assignments were made for both UDP and TCP together; other
   transports were not indicated. However, to conserve space, and to

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   reflect increasing use of other transports, assignments are now
   specific only to the transport requested.

   In general, a service should request assignments for multiple
   transports the same service name and description on the same port
   number only when they all reflect essentially the same service. Good
   examples of such use are DNS and NFS, where the difference between
   the UDP and TCP services are specific to supporting each transport.
   E.g., the UDP variant of a service might add sequence numbers, and
   the TCP variant of the same service might add in-band message

   >> Service names and descriptions for multiple transport port
   assignments SHOULD match only when they describe the same service,
   with the exception of enhancements for each supported transport.

   When the services differ, their service names and descriptions
   should reflect that difference. E.g., if TCP is used for the basic
   control protocol and UDP for an alarm protocol, then the services
   might be "name-ctl" and "name-alarm". A common example is when TCP
   is used for a service, and UDP is used to determine whether that
   service is active (via a multicast test message) [RFC1122]. The
   following convention has been used by IANA for several years to
   indicate this case:

   >> When UDP is used for multicast discovery of an active TCP
   service, the UDP service name SHOULD end in "-disc".

   Some services are used for discovery, either in conjunction with a
   TCP service, or as a stand-alone capability. Such services will be
   more reliable when using multicast rather than broadcast, because IP
   routers do not forward "all nodes" (all 1's, i.e.,
   for IPv4) broadcasts, and are have not been required to support
   subnet-directed broadcasts since 1999 [RFC1812] [RFC2644].

   >> UDP multi-host services SHOULD use multicast rather than

   Designers should be very careful in creating services over
   transports that do not support congestion control or error recovery,
   notably UDP. There are several issues that should be considered in
   such cases [RFC5405]:

   >> UDP services SHOULD be bandwidth limited, using only nominal
   network capacity. Users should keep in mind that "nominal" may vary
   depending on the deployment environment, and may be very low.

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   >> UDP services that use multipoint communication SHOULD be
   scalable, and SHOULD NOT rely solely on the efficiency of multicast
   transmission for scalability.

   >> UDP services SHOULD include congestion detection and backoff.

   >> UDP SHOULD NOT be used as a performance enhancement over TCP,
   i.e., to circumnavigate TCP's congestion control.

7.7. When to Request an Assignment

   Assignments are typically requested when a user has enough
   information to reasonably answer the questions in the IANA
   application. IANA applications typically take up to a few weeks to
   process, with some complex cases taking up to a month. The process
   typically involves a few exchanges between the IANA Ports Expert
   Review team and the applicant.

   An application needs to include a description of the service, as
   well as to address key questions designed to help IANA determine
   whether the assignment is justified.

   Services that are independently developed can be requested at any
   time, but are typically best requested in the last stages of design
   and initial experimentation, before any deployment has occurred that
   cannot easily be updated.

   >> Users MUST NOT deploy implementations that use ports prior their
   assignment by IANA.

   Deployments that use ports before deployment complicate IANA
   management of the port space. Keep in mind that this recommendation
   protects both other parties and you; it helps ensure that your
   desired number and service name are available when assigned. The
   list of currently unassigned numbers is just that - *currently*
   unassigned. It does not reflect pending applications, nor
   applications that might arrive before yours. Waiting for an official
   IANA assignment reduces the chance that your assignment will
   conflict with another deployed service.

   Applications made through Internet Draft / RFC publication typically
   use a placeholder ("PORTNUM") in the text, and use an experimental
   port number until a final assignment has been made [RFC6335]. That
   assignment is initially indicated in the IANA Considerations section
   of the document, and is tracked by the RFC Editor. When the RFC
   reaches the last stages of publication, that request is forwarded to
   IANA for handling. At that time, IANA typically requests that the

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   applicant fill out the application form on their website, because
   not every protocol document addresses the information required.
   Using this single application process also ensures that IANA has
   complete information even if the RFC publication is interrupted. For
   this reason as well, the application should be complete and not
   refer solely to the Internet Draft, RFC, a website, or any other
   external documentation.

   >> Users writing specifications SHOULD use symbolic names for port
   numbers and service names until an IANA assignment has been

7.8. Squatting

   "Squatting" describes the use of a number from the assigned range in
   deployed software without IANA assignment. It is hazardous because
   IANA cannot track such usage, and thus cannot avoid making
   legitimate assignments that conflict with such unauthorized usage.

   Note that there are numerous services that have squatted on such
   numbers that are in widespread use. Even such widespread de-facto
   use may not justify a later IANA assignment of that value,
   especially if either the value has already been assigned to a
   legitimate applicant or if the service would not qualify for an
   assignment of its own accord.

7.9. Other Considerations

   There are a few other points worth mentioning, which are summarized
   in this section.

   As noted earlier, system ports should be used sparingly, and it is
   better to avoid them altogether. This avoids the potentially
   incorrect assumption that the service on such ports run in a
   privileged mode.

   Port names and numbers are not intended to be changed. Once
   deployed, it can be very difficult to recall every implementation,
   so the assignment should be retained. However, in cases where the
   current assignee of a name or number has reasonable knowledge of the
   impact on such uses, and is willing to accept that impact, the name
   or number of an assignment can be changed [RFC6335]

   Aliases, or multiple service names for the same port number, are no
   longer considered appropriate [RFC6335].

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8. Security Considerations

   This document discusses ways to conserve port numbers, notably
   through encouraging demultiplexing within a single port.  As such,
   there may be cases where two variants of a protocol - insecure and
   secure, are suggested to share the same port (e.g., HTTP and HTTPS,
   though currently those are assigned different ports) [RFC2818].

   This document reminds protocol designers that port numbers are not a
   substitute for security, and should not alone be used to avoid
   denial of service or firewall traffic, notably because their use is
   not regulated or authenticated.

9. IANA Considerations

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

10. References

10.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

10.2. Informative References

   [Hi95]    Hickman, K., "The SSL Protocol", February 1995.

   [IEN112]  Postel, J., "Transmission Control Protocol", IEN 112,
             August 1979.

   [RFC33]   Crocker, S., "New Host-Host Protocol", RFC 33 February

   [RFC37]   Crocker, S., "Network Meeting Epilogue", RFC 37, March

   [RFC38]   Wolfe, S., "Comments on Network Protocol from NWG/RFC
             #36", RFC 38, March 1970.

   [RFC48]   Postel, J., S. Crocker, "Possible protocol plateau", RFC
             48, April 1970.

   [RFC61]   Walden, D., "Note on Interprocess Communication in a
             Resource Sharing Computer Network", RFC 61, July 1970.

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   [RFC76]   Bouknight, J., J. Madden, G. Grossman, "Connection by
             name: User oriented protocol", RFC 76, October 1970.

   [RFC333]  Bressler, R., D. Murphy, D. Walden. "Proposed experiment
             with a Message Switching Protocol", RFC 333, May 1972.

   [RFC739]  Postel, J., "Assigned numbers", RFC 739, November 1977.

   [RFC758]  Postel, J., "Assigned numbers", RFC 758, August 1979.

   [RFC768]  Postel, J., "User Datagram Protocol", RFC 768, August

   [RFC793]  Postel, J., "Transmission Control Protocol" RFC 793,
             September 1981

   [RFC820]  Postel, J., "Assigned numbers", RFC 820, August 1982.

   [RFC900]  Reynolds, J., J. Postel, "Assigned numbers", RFC 900, June

   [RFC1122] Deering, S., "Host extensions for IP multicasting", RFC
             1122, August 1989.

   [RFC1263] O'Malley, S., L. Peterson, "TCP Extensions Considered
             Harmful", RFC 1263, October 1991.

   [RFC1340] Reynolds, J., J. Postel, "Assigned numbers", RFC 1340,
             July 1992.

   [RFC1700] Reynolds, J., J. Postel, "Assigned numbers", RFC 1700,
             October 1994.

   [RFC1812] Baker, F. (Ed.), "Requirements for IP Version 4 Routers",
             RFC 1812, June 1995.

   [RFC2616] Fielding, R., J. Gettys, J. Mogul, H. Frystyk, L.
             Masinter, P. Leach, T. Berners-Lee, "Hypertext Transfer
             Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2644] Senie, D., "Changing the Default for Directed Broadcasts
             in Routers", RFC 2644, August 1999.

   [RFC2780] Bradner, S., V. Paxson, "IANA Allocation Guidelines For
             Values In the Internet Protocol and Related Headers", RFC
             2780, March 2000.

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   [RFC2817] Khare, R., S. Lawrence, "Upgrading to TLS Within
             HTTP/1.1", RFC 2817, May 2000.

   [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC3232] Reynolds, J. (Ed.), "Assigned Numbers: RFC 1700 is
             Replaced by an On-line Database", RFC 3232, January 2002.

   [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
             Considered Useful", BCP 82, RFC 3962, Jan. 2004.

   [RFC4340] Kohler, E., M. Handley, S. Floyd, "Datagram Congestion
             Control Protocol (DCCP)", RFC 4340, March 2006.

   [RFC4960] Stewart, R. (Ed.), "Stream Control Transmission Protocol",
             RFC 4960, September 2007.

   [RFC5246] Dierks, T., E. Rescorla, "The Transport Layer Security
             (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5405] Eggert, L., G. Fairhurst, "Unicast UDP Usage Guidelines
             for Application Designers," RFC 5405, Nov. 2008.

   [RFC6335] Cotton, M., L. Eggert, J. Touch, M. Westerlund, S.
             Cheshire, "Internet Assigned Numbers Authority (IANA)
             Procedures for the Management of the Service Name and
             Transport Protocol Port Number Registry", RFC 6335, August

   [RFC6762] Cheshire, S., M. Krochmal, "Multicast DNS", RFC 6762,
             February 2013.

   [RFC6763] Cheshire, S., M. Krochmal, "DNS-Based Service Discovery",
             RFC 6763, February 2013.

11. Acknowledgments


   This document was prepared using 2-Word-v2.0.template.dot.

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Authors' Addresses

   Joe Touch
   4676 Admiralty Way
   Marina del Rey, CA 90292-6695

   Phone: +1 (310) 448-9151
   EMail: touch@isi.edu

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