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Versions: 00 01 02 03 draft-ietf-dccp-serv-codes

DCCP WG                                                     G.Fairhurst
Internet Draft                                   University of Aberdeen
Expires: September 2007                                   March 2, 2007



                           The DCCP Service Code
                  draft-fairhurst-dccp-serv-codes-03.txt


Status of this Memo

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   This Internet-Draft will expire on September 2, 2007.

Abstract

   This document describes the usage of Service Codes by the Datagram
   Congestion Control Protocol, RFC 4340. Service Codes provide a method
   to identify the intended service/application to process a DCCP
   Connection Request. This provides improved flexibility in the use and
   assignment of port numbers for connection multiplexing. The DCCP
   Service Code can also enable more explicit coordination of services
   behind NATs and firewalls. This document motivates the setting of
   Service Codes by applications, rather than assigning a default
   Service Code value of zero.




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Table of Contents

   1. Introduction...................................................3
      1.1. Conventions used in this document.........................4
   2. An Architecture for supporting Service Codes...................5
      2.1. IANA Port Numbers.........................................5
      2.2. DCCP Service Code Values..................................6
      2.3. Zero Service Code.........................................6
      2.4. Reception of a DCCP-Request with a bound Service Code.....6
      2.5. Reception of a DCCP-Request with an unbound Service Code..7
      2.6. SDP for describing Service Codes..........................7
      2.7. Service Code Registry.....................................7
   3. Use of the DCCP Service Code...................................7
      3.1. Setting Service Codes at the Sender.......................8
      3.2. Using Service Codes in the Network........................8
      3.3. Using Service Codes at the Receiver.......................8
      3.4. Multiple Associations of Service Codes and Ports at the
      Sender.........................................................9
      3.5. Summary of Service Code and Port Handling................10
   4. Implementation Support for Service Codes......................11
      4.1. Minimal Support..........................................11
      4.2. Standard Support.........................................11
      4.3. Enhanced Support.........................................11
   5. Changes required to the API to support Service Codes..........12
      5.1. Interactions with IPsec..................................12
   6. Service Code Registry.........................................13
   7. Benchmarking Services Described in this document..............13
      7.1. Echo.....................................................13
      7.2. Daytime..................................................13
      7.3. Character generator......................................13
      7.4. Time service.............................................14
      7.5. PerfTest service.........................................14
   8. Security Considerations.......................................15
      8.1. Interactions of Service Codes and port numbers...........15
   9. IANA Considerations...........................................16
      9.1. Port number values allocated by this document............16
      9.2. Service Code values allocated by this document...........16
   10. Conclusions..................................................17
   11. Acknowledgments..............................................17
   12. References...................................................18
      12.1. Normative References....................................18
      12.2. Informative References..................................18
   Author's Addresses...............................................19
   Intellectual Property Statement..................................20
   Disclaimer of Validity...........................................20
   Copyright Statement....................Error! Bookmark not defined.
   Acknowledgment...................................................21


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1. Introduction

   Most Internet transport protocols use "well-known" port numbers
   [RFC814] to indicate which application service is associated with a
   connection or message; this includes TCP [RFC793], UDP [RFC768], SCTP
   [RFC2960], UDP-Lite [RFC3828], and DCCP [RFC4340]. Making a port
   number well-known involves registration with the Internet Assigned
   Numbers Authority (IANA), which includes defining a service by a
   unique keyword and reserving a port number from among a fixed pool
   [IANA].

   DCCP specifies a Service Code as a 4-byte value (32 bits). This
   describes the application-level service to which a client application
   wishes to connect ([RFC4340], Section 8.1.2). A service code
   identifies the protocol (or a standard profile, e.g. [ID.DCCP.RTP])
   to be used at the application layer. It is not intended to be used to
   specify a variant of an application, or a specific variant of a
   protocol.

   Service Codes allow a flexible correspondence between application-
   layer services and port numbers, which affects how applications
   interact with DCCP. This decouples the use of ports for connection
   demultiplexing and state management from their use to indicate a
   desired service.

   The use of Service Codes can assist in identifying the correct
   intended service when the server is located behind a NAT that
   modifies the port numbers associated with a flow.

   Middle-boxes (e.g. NATs, Firewalls) that desire to identify the type
   of data being transported by a flow, can utilize the Service Code for
   this purpose. When consistently used, the Service Code can provide a
   more specific indication of the actual service (e.g. indicating the
   type of multimedia flow, or intended application behaviour).

   Use of a Service Code value, instead of binding a service to a
   particular publicly-known port number, also permits a larger number
   of concurrent connections for a particular service. For example, this
   may be useful for applications where servers need to handle very
   large numbers of simultaneous open ports to the same service.

   If an application does not set a Service Code, the connection is
   associated with a Service Code of zero, with the intended server
   identified only by the destination port number.



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1.1. 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].












































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2. An Architecture for supporting Service Codes

   DCCP defines the use of a combination of ports and Service Codes to
   identify the server application ([RFC4340], 8.1.2). These are
   described in the following sections. Section 3 describes the use of
   Service Codes by end hosts and network middleboxes.

2.1. IANA Port Numbers

   In DCCP, an endpoint address is associated with a port number,
   forming a socket; and a pair of sockets uniquely identifies each
   connection. Ports provide the fundamental de-multiplexing function.

   Like DCCP, most Internet Transport Protocols (e.g. TCP [RFC793], UDP
   [RFC768]) also define publicly-known ports for most services, whether
   intended for public access (e.g., telnet, DNS) or for services
   typically used between pre-arranged pairs (e.g., X11, SSL). In TCP
   and UDP these are the primary means of identifying the required
   service when a connection request is received.

   The Internet Assigned Numbers Authority currently manages the set of
   globally reserved port numbers [IANA]. The destination port value
   that is associated with a service is determined either by an
   operating system index to a copy of the IANA table (e.g.,
   getportbyname() in Unix, which indexes the /etc/services file), or
   directly mapped by the application.

   The UDP and TCP port number space: 0..65535, is split into three
   ranges [RFC2780]:

   o  0..1023 "well-known", also called "system" ports

   o  1024..49151 "registered", also called "user" ports

   o  49152..65535 "dynamic", also called "private" ports

   One challenge with the use of IANA-managed ports is that this
   allocates ports globally, for all hosts on the public Internet, even
   though the association between a port and a service is of interest
   only to the end hosts participating in a connection. As a result, the
   fixed space of port numbers is being globally reserved unnecessarily.
   It is more useful to allocate this name space on a per-host basis
   [ID.Portnames].

   Well-known/Reserved DCCP ports are described in a separate IANA
   registry [RFC4340]. This registry may also associate ports with a
   pre-defined set of Service Codes (see section 2.2).


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   The source port associated with a connection request, often known as
   the "ephemeral port", traditionally includes the range 49152-65535,
   and should also include the 1024-49151 range.   The value used for
   the ephemeral port is usually chosen by the client operating system.
   It has been suggested that a randomized choice of port number value
   can help defend against "blind" attacks [ID.TSVWG.RAND]. Such methods
   may also be applicable to IETF-defined transport protocols, including
   DCCP.

2.2. DCCP Service Code Values

   DCCP specifies a 4 byte Service Code [RFC4340]. Service codes may be
   represented in one of three forms: as a decimal number (the canonical
   method), as a 4 character ASCII string, or as a hexadecimal number.

   The Service Code identifies the application-level service to which a
   client application wishes to connect. It is present only in DCCP-
   Request and DCCP-Response packets and permits a more flexible
   correspondence between services and port numbers than is possible
   using the corresponding socket pair (4-tuple of layer-3 addresses and
   layer-4 ports). This decouples the use of ports for connection
   demultiplexing and state management, from their use to indicate a
   desired endpoint service.

   One method of operation is to assign one Service Code per Port,
   although multiple applications may be permitted on the same port (if
   a Server implementation permits this).

   Service Codes allow a larger number of concurrent connections for a
   particular service than possible using well-known port numbers, by
   allowing endpoints to allocate their own port numbers separately,
   based on services they deploy (c.f. section 2.1).

2.3. Zero Service Code

   A Service Code value of zero indicates that the Service Code function
   is not used by a client. A server uses only the destination port
   number to identify the required application (as in section 2.1).

2.4. Reception of a DCCP-Request with a bound Service Code

   A Service Code value may be associated by the client (initiator of
   the DCCP-Request), and is used by the server (recipient of the DCCP-
   Request) to associate the connection with the corresponding
   application. This association MUST be explicit (i.e. the requested
   Service Code MUST have been previously bound to the destination port
   at the server). Once connected, the server returns a copy of the


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   Service Code in the DCCP-Response packet completing the initial
   handshake [RFC4340].

2.5. Reception of a DCCP-Request with an unbound Service Code

   DCCP defines a number of possible error conditions that may arise in
   processing of a Connection Request:

   o  Connection Refused (Invalid port)

   o  Too Busy (Service Code/Port may be valid)

   o  Bad Service Code (Invalid Service Code for specified port)

   Reception of a DCCP-Request with an invalid destination port MUST
   result in the DCCP-Request being rejected, and sending a DCCP-Reset
   with Reset Code "Connection Refused". A server MAY also use the Reset
   Code "Too Busy" ([RFC4340], 8.1.3).

   Reception of a DCCP-Request for a port number where the Service Code
   that is not bound MUST result in the DCCP-Request being rejected, and
   returning a DCCP-Reset with Reset Code "Bad Service Code" ([RFC4340],
   8.1.2).

2.6. SDP for describing Service Codes

   Methods that currently signal the use of port numbers, such as the
   Session Description Protocol (SDP) require extension to support DCCP
   Service Codes [ID.DCCP.RTP].

2.7. Service Code Registry

   The set of Service Codes currently specified for use within the
   general Internet are defined in an IANA-controlled name space. IANA
   manages new allocations of Service Codes in this space [RFC4340].
   Service Code bindings to Ports may also be defined in the IANA DCCP
   Port Registry.





3. Use of the DCCP Service Code

   Like UDP, DCCP uses port numbers to demultiplex connections. Upon
   receipt of a DCCP-Request including the Service Code, the Code is
   matched against a list of available services.


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3.1. Setting Service Codes at the Sender

   Applications SHOULD specify an appropriate Service Code when sending
   a DCCP-Request packet. Valid Service Codes should be selected from
   the set of values assigned in the DCCP Service Code Registry
   maintained by IANA [IANA-SC], or from the uncoordinated private space
   ([RFC4340], 8.1.2.). An application that does not set a Service Code,
   SHOULD be associated with a Service Code value of zero.

3.2. Using Service Codes in the Network

   Port numbers and IP addresses are the accepted methods to identify a
   flow within an IP network. When the DCCP header has not been
   encrypted, Middleboxes [RFC3234], such as firewalls, can instead use
   the Service Code to identify the application (even when running on a
   non-standard port). Middlebox devices are therefore expected to check
   Service Code values before port numbers for DCCP. The Service Code
   values on DCCP-Requests should be used for supplementary checks
   [RFC4340]. Section 4.1 describes some issues that may arise in this
   case.

   The use of the DCCP Service Code can potentially lead to interactions
   with other protocols that interpret or modify DCCP port numbers. This
   includes IPsec and other firewall systems, other security mechanisms,
   other in-band exchange of port numbers, and network address
   translators (NATs).

   Network address and port translators, known collectively as NATs, not
   only interpret DCCP ports, but may also translate/modify them
   [RFC2993]. This interferes with the use of ports for service
   identification [RFC3234]. The DCCP Service Code may allow services to
   be identified behind NATs if NATs are not further extended to
   translate Service Codes. Middleboxes should not modify the Service
   Code unless they change the service that a connection is accessing.

   DCCP connections identified by the Service Code continue to use IP
   addresses and ports, although neither port number may be well-
   known/reserved. Translation of these ports need to be considered in
   the operation of NATs. In addition, DCCP Service Codes can reduce the
   need to correctly interpret port numbers, leading to new
   opportunities for network address and port translators.

3.3. Using Service Codes at the Receiver

   An implementation MUST allow a server application to bind to a
   Service Code on a fixed port. The Service Code of zero may be the
   default, indicating that no specific Service Code is in use.


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   An implementation MAY allow server applications to bind to a Service
   Code specifying a set of acceptable ports.

   The DCCP Service Codes associates a DCCP Connection with the service
   that the client expects to be running at the server.  This value MUST
   take precedence over any service bound to the port number. Two cases
   can occur:

   o  When a DCCP-Request packet is received with a Service Code value
      of zero, the connection is associated with an application using
      the destination port number specified in the DCCP-Request. If
      there is no specific application associated with the destination
      port, then the connection MUST be aborted and a DCCP-RESET packet
      is returned. If the port is not associated with a zero Service
      Code, then the connection is aborted.

   o  A DCCP-Request that is received with a non-zero Service Code MUST
      be checked to validate that the server has associated the Service
      Code with the specified destination port. If the Service Code is
      associated with the port, the corresponding server application is
      used. If there is no associated application, the server MUST abort
      the connection by issuing a DCCP-Reset with the reset code "Bad
      Service Code".

3.4. Multiple Associations of Service Codes and Ports at the Sender

   A single Service Code MAY be bound to more than one destination port
   (wildcarding a set of port values). Also a single destination port
   MAY be bound to multiple Service Codes (wildcarding a set of Service
   Codes), although an active connection may only be associated with a
   single Service Code [RFC4340].

   o  An end host implementation may provide a method that only allows a
      single Service Code to be associated with each listening port.
      This means that a single port may be used only for a pre-specified
      service; however this service does not need to be permanently
      running at the Server. The arrival of a DCCP-Request may therefore
      require launching an application to accept messages from the DCCP
      connection. This operation could resemble that of "portmapper" or
      "inetd".









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   o  When a Connection Request is received with a port number that is
      associated with multiple Service Codes, the listening server needs
      to provide a method to ensure that the DCCP-Request is associated
      with an application server that handles the corresponding Service
      Code. This may require launching an application to accept messages
      from the DCCP connection. This use may allow a server to offer
      more than the limit of 65,536 services determined by the size of
      the Port field (fewer if system/user/dynamic boundaries are
      preserved). The limit is based solely on the number of unique
      connections between two hosts (i.e., 4,294,967,296).

   As in the previous section, when the specified Service Code is not
   associated with the specified port, the server MUST abort the
   connection and send a DCCP Reset message.

3.5. Summary of Service Code and Port Handling

   The basic operation of the Service Codes is as follows:

   o  A source host may issue a DCCP-Request with a Service Code of zero
      and chooses either a well-known/reserved destination port or a
      port number announced by some other means.

   o  A source host may issue a DCCP-Request with a non-zero Service
      Code and chooses a destination port number that is associated with
      the specified Service Code at the destination.

   o  The destination host, upon receiving a DCCP-Request with a zero
      Service Code, validates that the port supports a Service Code of
      zero and then uses the destination port to identify the associated
      server.

   o  The destination host, upon receiving a DCCP-Request with a non-
      zero Service Code, determines whether an available service
      matching the Service Code is supported for the specified
      destination port.

   o  If the service is available, the session is associated with a
      corresponding server, and a DCCP-Response is returned.

   o  If the service is not available, the session is aborted and a
      DCCP-Reset packet is returned.







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4. Implementation Support for Service Codes

   This document does not define how to implement Service Codes on a
   particular platform or using a specific operating system. It does
   define three levels of support that may be offered.

   >>> This section needs further work, ideas are welcome! <<<

4.1. Minimal Support

   All Servers MUST be capable of accepting a DCCP-Request that contains
   a zero Service Code. These may be handled in the same way as other
   transport connections (e.g. UDP, TCP). In this level, a DCCP-Request
   with a non-zero Service Code MUST result in the connection being
   aborted. This limits interoperability with other levels. This model
   is suitable for platforms with limited capability, but is NOT
   RECOMMENDED for general use.

4.2. Standard Support

   In this level of support, a server MAY accept a DCCP-Request that
   contains a zero Service Code. Each Service Code specified in a DCCP-
   Request message is checked against an internal database to determine
   the permitted port range that may be associated with the Service
   Code. This model is RECOMMENDED for general use.

   The design could be simplified if one Default Service code were to be
   associated with a set of specific well-known ports, allowing a port
   to be mapped via a library or operating system function to their
   default Service Code (simplifying the binding). Such a system needs
   however also MUST provide a way to allow a sending and/or receiving
   application to bind to a none-default Service Code (specified by the
   application). It should also be noted that some higher layer
   protocols are not associated with a single well-known port and that
   they must therefore use this latter method.

4.3. Enhanced Support

   A server operating at the enhanced level provides finer and more
   flexible control of the use of Service Codes and Port numbers. This
   permits a receiver to accept DCCP-Requests with arbitrary mappings
   between Service Codes and port ranges, associating each connection
   with the appropriate application server. This level of support may
   require operating systems to use a modified process to handle in-
   coming DCCP requests and may allow policies to be defined.




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5. Changes required to the API to support Service Codes

   The use of Service Codes requires an API that allows a service to
   bind to a Service Code as well as a port number. One approach is to
   use separate commands as follows:

   o  Extend the existing port number indicator command (e.g., Unix
      bind() or connect() calls) to select a specific port number where
      desired.

   o  Extend the existing socket parameterization command (e.g., Unix
      setsockopt()) to set a service-code option.

   o  An information base (table) may be used by servers to identify the
      set of Service Codes that are associated with each port and the
      corresponding set of server applications.

   XXX Author note:

   May need to discuss:

   get_port_and_service_code_by_name(char *what_service_do_you_want)

   char *get_service_code_by_number(unsigned sc)

   and interactions with getadddrinfo() address/port lookup routine,
   which has been introduced to simplify the migration to IPv6
   ([RFC3493], 6.1).

   XXX End Author Note.

5.1. Interactions with IPsec

   IPsec uses port numbers to perform access control in transport mode
   [RFC4301].  Security policies can define port-specific access control
   (PROTECT, BYPASS, DISCARD), as well as port-specific algorithms and
   keys. Similarly, firewall policies allow or block traffic based on
   port numbers.

   Use of port numbers in IPsec selectors and firewalls may assume that
   the numbers correspond to well-known services. It is useful to note
   that there is no such requirement; any service may run on any port,
   subject to mutual agreement between the endpoint hosts.  Use of the
   Service Code may interfere with this assumption both within IPsec and
   in other firewall systems, but it does not add a new vulnerability.
   New implementations of IPsec and firewall systems may interpret the



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   Service Code when implementing policy rules, but should not rely on
   either port numbers or Service Codes to indicate a specific service.

   This is not an issue for IPsec because the entire DCCP header and
   payload are protected by all IPsec modes. None of the DCCP header is
   protected by application-layer security, e.g., DTLS [ID.DTLS.DCCP],
   so again this is not an issue [RFC4347].



6. Service Code Registry

   The set of Service Codes currently specified for use within the
   general Internet are defined in an IANA-controlled name space. IANA
   manages new allocations of Service Codes in this space [RFC4340].
   Service Code bindings to Ports may also be defined in the IANA DCCP
   Port Registry.



7. Benchmarking Services Described in this document

   A number of simple services are commonly supported by systems using
   DCCP and UDP, this section defines corresponding services for DCCP.
   These services are useful to debug and benchmark bidirectional DCCP
   connections. The IANA section of this document allocates a
   corresponding set of code points for these services.

7.1. Echo

   The operation of the DCCP Echo service follows that specified for UDP
   [RFC862]: a server listens for DCCP connections; once a client has
   set up a connection, each data packet sent to the server will be
   copied (echoed) back to the client.

7.2. Daytime

   The DCCP daytime service is operationally equivalent to the
   connection-based TCP daytime service [RFC867]: any data received is
   discarded by the server; and generates a response sent in a DCCP data
   packet containing the current time and data as an ASCII string; after
   which the connection is closed.

7.3. Character generator

   The operation of the DCCP chargen service corresponds to the
   connection-based TCP chargen protocol [RFC864]: A server listens for


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   incoming requests and, once a client has established a connection,
   continuously sends datagrams containing a random number (between 0
   and 512, up to the current path MTU) of characters. The service
   terminates when the user either closes or aborts the connection.
   Congestion control is enforced using the mechanisms [RFC4340] and
   related documents.

   If necessary the receiver can enforce flow control on this service by
   using either or both of the Slow Receiver ([RFC4340], 11.6) and Data
   Dropped ([RFC4340], 11.7) options to signal the server to slow down.

   The chargen protocol provides a useful service that may be used for
   testing and measurement of bidirectional DCCP connectivity, as well
   as congestion control responsiveness. The datagram-based variant of
   chargen can be emulated with the DCCP ECHO service by changing the
   format of the datagrams sent by the client, hence these services
   complement each other.

7.4. Time service

   The format of timestamps and the operation of the DCCP time service
   is equivalent with the TCP time protocol variant [RFC868]: a server
   listens for incoming connections; after a client has established a
   new connection, the server sends a 4-byte timestamp; whereupon the
   client closes the connection.

7.5. PerfTest service

   The PerfTest concept specified by this document provides a generic
   service that may be used to benchmark and measure both unidirectional
   and bidirectional DCCP connections, as well as server and host DCCP
   stacks.

   This document defines a generic PerfTest service. The payload of DCCP
   packets associated with the DCCP PerfTest service are silently
   discarded by the receiver, and used only for gathering numerical
   performance data.

   The PerfTest server is identified by a combination of the port number
   and DCCP Service Code. It does not recommend a specific benchmarking
   software to use, but does allocate a port number specified that
   currently coincides with that of the open-source iperf benchmarking
   program [iperf].






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8. Security Considerations

   This document does not describe new protocol functions.

   The document discusses the usage of Service Codes. There are three
   areas of security that are important:

   1. Interaction with NATs and firewalls (see section 3.2, on middlebox
      behaviour).

   2. Interaction with IPsec and DTLS security (see section 4.1, on use
      of IPsec).

   3. Interpretation of DCCP Service Codes over-riding traditional use
      of reserved/well-known port numbers (see section 7.1)

   4. Services used for benchmarking and testing may also be used to
      generate traffic for other purposes, and pose an opportunity for a
      Denial of Service attack. Care needs to be exercised when enabling
      these services in an operational network, or appropriate rate-
      limits should be provided to mitigate these effects.



8.1. Interactions of Service Codes and port numbers

   The Service Code value may be used to over-ride the traditional way
   that operating systems consider low-numbered ports as privileged.
   This represents a change in the way operating systems respect this
   range of DCCP port numbers.

   The same service (application) may be potentially accessed using more
   than one Service Code. Examples include the use of separate Service
   Codes for an application layered directly upon DCCP and one using
   DTLS transport over DCCP. Other possibilities include the use of a
   private Service Code point that maps to the same application as
   assigned to an IANA-defined Service Code value. Different versions of
   a service (application) may also be mapped to a corresponding set of
   Service Code values. Care needs to be exercised when interpreting the
   mapping the Service Code value to the corresponding service.

   Processing of Service Codes may imply more processing than currently
   associated with incoming port numbers. Implementers need to guard
   against increasing opportunities for Denial of Service attack.





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9. IANA Considerations

   A set of new services are defined in section 6 and are summarized in
   this section.

9.1. Port number values allocated by this document

   This document requests allocation of the following code points from
   the IANA DCCP Port numbers registry:

   >>>>>> IANA ACTION Please replace IANA THIS RFC, with the allocated
   RFC  number. <<<

   echo      7/dccp   Echo SC:ECHO
   # IETF dccp WG, [IANA - THIS RFC]
   daytime   13/dccp  DayTime    SC:DTIM
   # IETF dccp WG, [IANA - THIS RFC]
   chatgen   19/dccp  Chargen    SC:CHAR
   # IETF dccp WG, [IANA - THIS RFC]
   time      37/dccp  Timeserver SC:TIME
   # IETF dccp WG, [IANA - THIS RFC]
   perf    5001/dccp  PerfTest   SC:PERF
   # IETF dccp WG, [IANA - THIS RFC]


9.2. Service Code values allocated by this document

   This document solicits IANA action to allocate the following code
   points from the Service Code registry [IANA-SC]. The requested
   assignments are listed below and summarized in table 1. This set of
   Service Codes may be utilized for testing DCCP implementations and
   transmission paths.

    +----------+------+----+-------------------------------+----------+
    | Service  | ASCII|Port|          Description          |   Ref    |
    | Code (SC)| Code |    |                               |          |
    +----------+------+----+-------------------------------+----------+
    |0x4543484f| ECHO |   7| Echo service                  | [RFC862] |
    |0x4454494d| DTIM |  13| Daytime server                | [RFC867] |
    |0x43484152| CHAR |  19| Character generator (chargen) | [RFC864] |
    |0x54494d45| TIME |  37| Timeserver                    | [RFC868] |
    |0x50455246| PERF |5001| Performance tests (e.g.       | *        |
    |          |      |    | iperf, ttcp, ...)             |          |
    +----------+------+----+-------------------------------+----------+
     Table 1: Allocation of Service Codes by this document.




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     Notes:
     1)  Port is the default port associated with this service.
     2)  * Reference is this document.


   The document notes that it is NOT required to supply an approved
   document (e.g. a published RFC) to support an application for a DCCP
   Service Code or port number value, although RFCs may be used to
   request Service Code values via the IANA Considerations section (e.g.
   [ID.DTLS.DCCP], [ID.DCCP.RTP]).


10. Conclusions

   This document discusses the operation of service codes by the DCCP
   transport protocol [RFC4340] and motivates their use. The document
   augments and clarifies the way in which DCCP applications should use
   the Service Code Feature. It does not update or obsolete the protocol
   defined in RFC4340.

   Service Codes, or similar concepts may also be useful to other IETF
   Transport Protocols [ID.Portnames]).



11. Acknowledgments

   This work has been supported by the EC IST SatSix Project.
   Significant contributions to this document resulted from discussion
   with Joe Touch, and this is gratefully acknowledged. The author also
   thanks Ian McDonald and the DCCP WG for helpful comments on this
   topic, and Gerrit Renker for his help in determining DCCP behaviour,
   review of the document, and compilation of useful test applications
   defined in the IANA section of this document.















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12. References

12.1. Normative References

   [RFC1122] Braden, R. (ed.), "Requirements for Internet Hosts:
             Communication Layers, " STD 3, RFC 1122, Oct. 1989
             (STANDARD).

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

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

12.2. Informative References

   [IANA]    Internet Assigned Numbers Authority, www.iana.org

   [IANA-SC] IANA DCCP Service Code Registry
             http://www.iana.org/assignments/service-codes

   [ID.Portnames] J. Touch, "A TCP Option for Port Names", IETF Work in
             Progress, draft-touch-tcp-portnames-00.txt.

   [ID.DTLS.DCCP] T.Phelan, "Datagram Transport Layer Security (DTLS)
             over the Datagram Congestion Control Protocol (DCCP)", IETF
             Work in Progress, draft-phelan-dccp-dtls-01.txt.

   [ID.DCCP.RTP] C. Perkins, "RTP and the Datagram Congestion Control
             Protocol (DCCP)", IETF Work in Progress, draft-ietf-dccp-
             rtp-01.txt.

   [ID.TSVWG.RAND] M. Larsen, F. Gont, "Port Randomization", IETF Work
             in Progress, draft-larsen-tsvwg-port-randomization-00.

   [iperf]   http://dast.nlanr.net/Projects/Iperf/

   [RFC768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
             August 1980.

   [RFC793]  Postel, J., "Transmission Control Protocol", STD 7, RFC
             793, Sept. 1981 (STANDARD).

   [RFC814]  Clark, D., "NAME, ADDRESSES, PORTS, AND ROUTES", RFC 814,
             July 1982 (UNKNOWN).


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   [RFC862]  Postel, J., "Echo Protocol", STD 20, RFC 862, May 1983.

   [RFC864]  Postel, J., "Character Generator Protocol", STD 22, RFC
             864, May 1983.

   [RFC867]  Postel, J., "Daytime Protocol", STD 25, RFC 867, May 1983.

   [RFC868]  Postel, J. and K. Harrenstien, "Time Protocol", STD 26,
             RFC 868, May 1983.

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

   [RFC2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
             Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M., Zhang,
             L., and V. Paxson, "Stream Control Transmission Protocol",
             RFC 2960, October 2000.

   [RFC2993] Hain, T., "Architectural Implications of NAT", RFC 2993,
             November 2000 (INFORMATIONAL).

   [RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
             Issues", RFC 3234, February 2002.

   [RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
             Stevens, "Basic Socket Interface Extensions for IPv6", RFC
             3493, February 2003.

   [RFC3828] Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., and
             G. Fairhurst, "The Lightweight User Datagram Protocol (UDP-
             Lite)", RFC 3828, July 2004.

    [RFC4301] Kent, S. and K. Seo, "Security Architecture for the
             Internet Protocol", RFC 4301, December 2005.

   [RFC4347] Dierks, T. and E. Rescorla, "The Transport Layer Security
             (TLS) Protocol Version 1.1", RFC 4346, April 2006.










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13. Author's Addresses

   Godred (Gorry) Fairhurst
   Department of Engineering
   University of Aberdeen
   Kings College
   Aberdeen, AB24 3UE
   UK

   Email: gorry@erg.abdn.ac.uk
   URL:   http://www.erg.abdn.ac.uk/users/gorry


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    Copyright Statement

      Copyright (C) The IETF Trust (2007).

      This document is subject to the rights, licenses and restrictions
      contained in BCP 78, and except as set forth therein, the authors
      retain all their rights.










































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   Change Log.



   01 introduced:

   - a replacement of the word *range* when referring to sets of dccp
   ports (they are not necessarily contiguous), noted by E. Kohler.

   - Addition of some Service Codes in IANA section.

   02 introduced:

   - add the use of profiles with DCCP, identified by Service Code, but
   not the use of protocol variants.

   - further detail on implementation levels (more input would be good)

   - added security consideration for traffic generators

   - added ref to UDPL for completeness

   - Corrected NiTs found by Gerrit Renker


























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