TSVWG J. Touch
Internet Draft USC/ISI
Intended status: Best Current Practice July 15, 2013
Expires: January 2014
Recommendations for Transport Port Uses
draft-ietf-tsvwg-port-use-02.txt
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warranty as described in the Simplified BSD License.
Abstract
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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. 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:
http://www.example.com:51509/
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
FTP.
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
associations.
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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
service?
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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
counterindicated:
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
namespace.
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
continues.
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
message.
>> 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
delimiters.
>> 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., 255.255.255.255
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
broadcast.
Designers should be very careful in creating services over
transports that do not support congestion control or error recovery,
notably UDP. There are several issues that should be considered in
such cases [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
completed.
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
1970.
[RFC37] Crocker, S., "Network Meeting Epilogue", RFC 37, March
1970.
[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
1980.
[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
1984.
[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
2011.
[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
TBD
This document was prepared using 2-Word-v2.0.template.dot.
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Authors' Addresses
Joe Touch
USC/ISI
4676 Admiralty Way
Marina del Rey, CA 90292-6695
U.S.A.
Phone: +1 (310) 448-9151
EMail: touch@isi.edu
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