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Versions: (draft-fairhurst-dccp-serv-codes) 00 01 02 03 04 05 06 07 08 09 10 11 RFC 5595

DCCP WG                                                     G.Fairhurst
Internet-Draft                                   University of Aberdeen
Intended status: Proposed Standard                       April 28, 2009
Expires: October 31, 2009
Updates: RFC 4340

                           The DCCP Service Code
                     draft-ietf-dccp-serv-codes-09.txt


Status of this Memo

   This Internet-Draft is submitted to IETF 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 October 28, 2009.

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   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Abstract

   This document describes the usage of Service Codes by the Datagram
   Congestion Control Protocol, RFC 4340. It motivates the setting of a
   Service Code by applications. 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 use of a
   DCCP Service Code can also enable more explicit coordination of
   services with middleboxes (e.g. network address translators and
   firewalls). This document updates the specification provided in RFC
   4340.

Table of Contents

   1. Introduction...................................................4
      1.1. History...................................................4
      1.2. Conventions used in this document.........................7
   2. An Architecture for Service Codes..............................7
      2.1. IANA Port Numbers........................................78
      2.2. DCCP Service Code Values..................................8
         2.2.1. New versions of Applications or Protocols............9
      2.3. Service Code Registry.....................................9
      2.4. Zero Service Code........................................10
      2.5. Invalid Service Code.....................................10
      2.6. SDP for describing Service Codes.........................10
      2.7. A method to hash the Service Code to a Dynamic Port......10
   3. Use of the DCCP Service Code..................................11
      3.1. Setting Service Codes at the Client......................12
      3.2. Using Service Codes in the Network.......................12
      3.3. Using Service Codes at the Server........................13
         3.3.1. Reception of a DCCP-Request.........................14
         3.3.2. Multiple Service Codes associated with a Port...Error!
         Bookmark not defined.
         3.3.3. Automatically launching a Server....................15
   4. DCCP Benchmarking Services....................................15
      4.1. Echo.....................................................15
      4.2. Daytime..................................................15
      4.3. Character generator......................................15
      4.4. Time service.............................................16
      4.5. Generic PerfTest service.................................16
      4.6. PERF service.............................................16
   5. Security Considerations.......................................17


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      5.1. Server Port number re-use................................17
      5.2. Association of applications with Service Codes...........18
      5.3. Interactions with IPsec..................................18
      5.4. Security Considerations for Benchmarking Services........19
   6. IANA Considerations...........................................19
      6.1. IANA Assignments for Benchmarking Applications...........19
         6.1.1. Port number values allocated by this document.......19
         6.1.2. Service Code values allocated by this document......20
   7. Acknowledgments...............................................21
   8. References....................................................21
      8.1. Normative References.....................................21
      8.2. Informative References...................................21
   9. Author's Addresses............................................23
      9.1 Disclaimer    ............................................24



































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1. Introduction

   DCCP specifies a Service Code as a 4-byte value (32 bits) that
   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.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 (Section 2.2).

   The Service Code mechanism allows an application to declare the set
   of services that are associated with server port numbers. This can
   affect how an application interacts with DCCP. It allows decoupling
   the role of port numbers to indicate a desired service from the role
   in connection demultiplexing and state management. A DCCP application
   identifies the requested service by the Service Code value in a DCCP-
   Request packet. Each application therefore associates one or more
   Service Codes with each listening port ([RFC4340], section 8.1.2).

   The use of Service Codes can assist in identifying the intended
   service by a firewall and may assist other middleboxes (e.g., a proxy
   server, network address translator (NAT) [RFC2663]). Middleboxes that
   desire to identify the type of data a flow claims to transport,
   should 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).

   The more flexible use of server ports can also offer benefit to
   applications where servers need to handle very large numbers of
   simultaneous open ports to the same service.

   RFC 4340 omits to describe the motivation behind Service Codes, nor
   does it properly describe how Well Known and Registered server ports
   relate to Service Codes.  The intent of this document is to clarify
   these issues.

1.1. History

   It is simplest to understand the motivation for defining Service
   Codes by describing the history of the DCCP protocol.

   Most current Internet transport protocols (TCP [RFC793], UDP
   [RFC768], SCTP [RFC4960], UDP-Lite [RFC3828]) used "Published" port
   numbers from the Well Known or registered number spaces [RFC814].
   These 16-bit values indicate the application service associated with


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   a connection or message. The server port must be known to the client
   to allow a connection to be established.  This may be achieved using
   out-of-band signaling (e.g. described using SDP [RFC4566]), but more
   commonly a Published port is allocated to a particular protocol or
   application; for example HTTP commonly uses port 80 and SMTP commonly
   uses port 25. Making a port number Published [RFC1122] 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].

   In the earliest draft of DCCP, the authors wanted to address the
   issue of Published ports in a future-proof manner, since this method
   suffers from several problems:

   o  The port space is not sufficiently large for ports to be easily
      allocated (e.g. in an unregulated manner).  Thus, many
      applications operate using unregistered ports, possibly colliding
      with use by other applications.

   o  The use of port-based firewalls encourages application-writers to
      disguise one application as another in an attempt to bypass
      firewall filter rules. This motivates firewall writers to use deep
      packet inspection in an attempt to identify the service associated
      with a port number.

   o  ISPs often deploy transparent proxies, primarily to improve
      performance and reduce costs.  For example, TCP requests destined
      to TCP port 80 are often redirected to a web proxy.

   These issues are coupled.  When applications collide on the same
   Published, but unregistered port, there is no simple way for network
   security equipment to tell them apart, with the likelihood of
   introducing problems with interaction of features.

   There is little that a transport protocol designer can do about
   applications that attempt to masquerade as other applications. For
   ones that are not attempting to hide, the problem may be simply that
   they cannot trivially obtain a Published port.  Ideally, it should be
   sufficiently easy that every application-writer can request a Well
   Known or registered port and receive one instantly with no questions
   asked. The 16-bit port space traditionally used is not large enough
   to support such a trivial allocation of ports.

   Thus, the design of DCCP sought an alternative solution.  The idea
   was simple. A 32-bit server port space should be sufficiently large
   that it enables use of very simple allocation policies.  However,



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   overhead considerations made a 32-bit port value undesirable (DCCP
   needed to be useful for low rate applications).

   The solution in DCCP to this problem was to use a 32-bit Service Code
   [RFC4340] that is included only in the DCCP-Request packet. The use
   of a 32-bit value was intended to make it trivially simply to obtain
   a unique value for each application. Placing the value in a DCCP-
   Request packet, requires no additional overhead for the actual data
   flow.  It is however sufficient for both the end systems, and
   provides any stateful middleboxes along the path with additional
   information to understand what applications are being used.

   Early discussion of the DCCP protocol considered an alternative to
   the use of traditional ports; instead it was suggested that a client
   used a 32-bit identifier to uniquely identify each connection. The
   server listened on a socket bound only to a Service Code.  This
   solution was unambiguous; the Service Code was the only identifier
   for a listening socket at the server side. The DCCP client included a
   Service Code in the request, allowing it to reach the corresponding
   listening application. One downside was that this prevented
   deployment of two servers for the same service on a single machine,
   something that is trivial with ports. The design also suffered from
   the downside of being sufficiently different from existing protocols
   that there were concerns that it would hinder the use of DCCP through
   NATs and other middleboxes.

   RFC 4340 abandoned the use of a 32-bit connection identifier in favor
   of two traditional 16-bit port values, one chosen by the server and
   one by the client. This allows middleboxes to utilize similar
   techniques for DCCP, UDP, TCP, etc. However, it introduced a new
   problem: "How does the server port relate to the Service Code?"  The
   intent was that the Service Code identified the application or
   protocol using DCCP, providing middleboxes with information about the
   intended use of a connection, and that the pair of ports effectively
   formed a 32-bit connection identifier, which was unique between a
   pair of end-systems.

   The large number of available unique Service Code values allows all
   applications to be assigned a unique Service Code. However, there
   remains a current problem:  The server port is chosen by the server,
   but the client needs to know this to establish a connection.  It was
   undesirable to mandate out-of-band communication to discover the
   server port.  A solution is to register DCCP server ports.  The
   limited availability of DCCP server ports appears to contradict the
   benefits of DCCP Service Codes, because although it may be trivial to
   obtain a Service Code, it has not traditionally been trivial to
   obtain a registered port from IANA and in the long-run it may not be


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   possible to uniquely allocate a unique registered DCCP port to new
   applications. As port numbers become scarce, this motivates the need
   to associate more than one Service Code with a listening port (e.g.
   two different applications could be assigned the same server port,
   and need to run on the same host at the same time, differentiated by
   their different associated Service Codes.

   Service Codes provide flexibility in the way clients identify the
   server application to which they wish to communicate. The mechanism
   allows a server to associate a set of server ports with a service.
   The set may be common with other services available at the same
   server host, allowing a larger number of concurrent connections for a
   particular service than possible when the service is identified by a
   single Published port number.

   There has been confusion concerning how server ports relate to
   Service Codes. The goal of this document is to clarify this and the
   issues concerning the use of Service Codes.

   RFC4340 states that Service Codes are not intended to be DCCP-
   specific. Service Codes, or similar concepts may therefore also be
   useful to other IETF transport protocols.

1.2. 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].

2. An Architecture for Service Codes

   DCCP defines the use of a combination of ports and Service Codes to
   identify the server application ([RFC4340], section 8.1.2). These are
   described in the following Sections.

2.1. IANA Port Numbers

   In DCCP, the packets belonging to a connection are de-multiplexed
   based on a combination of four values {source IP address, source
   port, dest IP address, dest port}, as in TCP. An endpoint address is
   associated with a port number, (e.g. forming a socket); and a pair of
   associations uniquely identifies each connection. Ports provide the
   fundamental per-packet de-multiplexing function.

   The Internet Assigned Numbers Authority currently manages the set of
   globally reserved port numbers [IANA]. The source port associated
   with a connection request, often known as the "ephemeral port", is


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   traditionally in the range 49152-65535, and also includes the range
   1024-49151.  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.Rand] in TCP. This method may be applicable to
   other IETF-defined transport protocols, including DCCP.

   Traditionally, the destination (server) port value 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.

   DCCP supports Well Known and registered ports. These are allocated in
   the DCCP IANA port numbers registry ([RFC4340], Section 19.9). Each
   registered DCCP port MUST be associated with at least one pre-defined
   Service Code.

   Applications that do not need to use a server port in the Well Known
   or registered range SHOULD use a dynamic server port (i.e. that does
   not require to be registered in the DCCP port registry). Clients can
   identify the server port value for the services to which they wish to
   connect using a range of methods. One common method is by reception
   of a SDP record (Section 2.6) exchanged out-of-band (e.g. using SIP
   [RFC3261] or RTSP [RFC2326]). DNS SRV resource records also provide a
   way to identify a server port for a particular service based on the
   services string name [RFC2782].

   Applications that do not use out-of-band signalling can still
   communicate, providing that both client and server agree the port
   value to be used. This eliminates the need for each registered
   Service Code to be allocated an IANA-assigned server port (see also
   Section 2.7).

2.2. DCCP Service Code Values

   DCCP specifies a 4 byte Service Code ([RFC4340], section 8.1.2)
   represented in one of three forms: a decimal number (the canonical



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   method), a four character ASCII string, or an eight digit hexadecimal
   number.

   The Service Code identifies the application-level service to which a
   client application wishes to connect. Examples of services are RTP
   [ID.RTP], TIME (this document), ECHO (this document). In a different
   example, DTLS [RFC5238] provides a transport-service (not an
   application-layer service), therefore applications using DTLS are
   individually identified by a set of corresponding Service Code
   values.

   Endpoints MUST associate a Service Code with every DCCP socket
   [RFC4340], both actively and passively opened. The application will
   generally supply this Service Code. A single passive listening port
   may be associated with more than one Service Code value. The set of
   Service Codes could be associated with one or more server
   applications. This permits a more flexible correspondence between
   services and port numbers than possible using the corresponding
   socket pair (4-tuple of layer-3 addresses and layer-4 ports). In the
   currently defined set of packet types, the Service Code value is
   present only in DCCP-Request ([RFC4340], section 5.2) and DCCP-
   Response packets ([RFC4340], section 5.3). Note new DCCP packet types
   (e.g. [ID.Simul]) could also carry a Service Code value.

2.2.1. New versions of Applications or Protocols

   Applications/protocols that provide version negotiation or indication
   in the protocol operating over DCCP do not require a new server port
   or new Service Code for each new protocol version. New versions of
   such applications/protocols SHOULD continue to use the same Service
   Code. If the application developers feel that the new version
   provides significant new capabilities (e.g. that will change the
   behavior of middleboxes), they MAY allocate a new Service Code
   associated with the same or a different set of Well Known ports. If
   the new Service Code is associated with a Well Known or registered
   port, the DCCP Ports registry MUST also be updated to include the new
   Service Code value, but MAY share the same server port assignment(s).

2.3. Service Code Registry

   The set of registered Service Codes 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]).
   Private Service Codes are not centrally allocated and are denoted by
   the decimal range 1056964608-1073741823 (i.e. 32-bit values with the
   high-order byte equal to a value of 63, corresponding to the ASCII
   character '?').


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   Associations of Service Code with Well Known Ports are also defined
   in the IANA DCCP Port Registry (section 2.1).

2.4. Zero Service Code

   A Service Code of zero is "permanently reserved (it represents the
   absence of a meaningful Service Code)" [RFC4340]. This indicates that
   no application information was provided. RFC 4340 states that
   applications MAY be associated with this Service Code in the same way
   as other Service Code values. This use is permitted for any server
   port.

   This document clarifies section 19.8 of RFC 4340, by adding the
   following:

   "Applications SHOULD NOT use a Service Code of zero.

   Application writers that need a temporary Service Code value SHOULD
   choose a value from the private range (section 2.3).

   Applications intended for deployment in the Internet are encouraged
   to use an IANA-defined Service Code. If no specific Service Code
   exists, they SHOULD request a new assignment from the IANA."

2.5. Invalid Service Code

   RFC4340 defines the Service Code value of 0xFFFFFFFF as Invalid. This
   is provided so implementations can use a special four-byte value to
   indicate "no valid Service Code". Implementations MUST NOT accept a
   DCCP-Request with this value, and SHOULD NOT allow applications to
   bind to this Service Code value [RFC4340].

2.6. SDP for describing Service Codes

   Methods that currently signal destination port numbers, such as the
   Session Description Protocol (SDP) [RFC4566] require extension to
   support DCCP Service Codes [ID.RTP].

2.7. A method to hash the Service Code to a Dynamic Port

   Applications that do not use out-of-band signalling, or an IANA-
   assigned port still require both the client and server to agree the
   server port value to be used. This Section describes an optional
   method that allows an application to derive a default server port
   number from the Service Code. The returned value is in the dynamic
   port range [RFC4340]:



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     int s_port; /* server port */
     s_port = (sc[0]<<7)^(sc[1]<<5)^(sc[2]<<3)^sc[3] | 0xC000;
     if (s_port==0xFFFF) {s_port = 0xC000}

   Where sc[] represents the four bytes of the Service Code, and sc[3]
   is the least significant byte, for example this function associates
   SC:fdpz with the server port 64634.

   This algorithm has the following properties:

   o  It identifies a default server port for each service.

   o  It seeks to assign different Service Codes to different ports, but
      does not guarantee an assignment is unique.

   o  It preserves the four bits of the final bytes of the Service Code,
      allowing mapping common series of Service Codes to adjacent ports,
      e.g. Foo1, and Foo2; and Fooa and Foob would be assigned adjacent
      ports.

   o  It avoids the port 0xFFFF, which is not accessible on all host
      platforms.

   Applications and higher-layer protocols that have been assigned a
   Service Code (or use a Service Code from the unassigned private
   space) may use this method. It does not preclude other applications
   using the selected server port, since DCCP servers are
   differentiated by the Service Code value.


3. Use of the DCCP Service Code

   The basic operation of Service Codes is as follows:

   A client initiating a connection:

       .  issues a DCCP-Request with a Service Code and chooses a
          destination (server) port number that is expected to be
          associated with the specified Service Code at the destination.

   o  A server that receives a DCCP-Request:

       .  determines whether an available service matching the Service
          Code is supported for the specified destination server port.
          The session is associated with the Service Code and a
          corresponding server. A DCCP-Response is returned.



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       .  if the service is not available, the session is rejected and a
          DCCP-Reset packet is returned.

3.1. Setting Service Codes at the Client

   A client application MUST associate every DCCP connection (and hence
   every DCCP active socket) with a single Service Code value
   [RFC4340]). This value is used in the corresponding DCCP-Request
   packet.

3.2. Using Service Codes in the Network

   DCCP connections identified by the Service Code continue to use IP
   addresses and ports, although neither port number may be Published.

   Port numbers and IP addresses are the traditional methods to identify
   a flow within an IP network. Middlebox [RFC3234] implementors
   therefore need to note that new DCCP connections are identified by
   the pair of Server Port and Service Code in addition to the IP
   address. This means that the IANA may allocate a server port to more
   than one DCCP application [RFC4340].

   Network address and port translators, known collectively as NATs
   [RFC2663], may interpret DCCP ports [RFC2993] [ID.Behave-DCCP]. They
   may also interpret DCCP Service Codes. Interpreting DCCP Service
   Codes can reduce the need to correctly interpret port numbers,
   leading to new opportunities for network address and port
   translators. Although it is encouraged to associate specific delivery
   properties with the Service Code, e.g. to identify the real-time
   nature of a flow that claims to be using RTP, there is no guarantee
   that the actual connection data corresponds to the associated Service
   Code.  A middlebox implementor may still use deep packet inspection,
   and other means, in an attempt to verify the content of a connection.

   The use of the DCCP Service Code can potentially lead to interactions
   with other protocols that interpret or modify DCCP port numbers
   [RFC3234]. The following additional clarifications update the
   description provided in section 16 of RFC 4340:

   o  "A middlebox that intends to differentiate applications SHOULD
      test the Service Code in addition to the destination or source
      port of a DCCP-Request or DCCP-Response packet.

   o  A middlebox that does not modify the intended application (e.g.
      NATs [ID.Behave-DCCP] and Firewalls), MUST NOT change the Service
      Code.



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   o  A middlebox MAY send a DCCP-Reset in response to a packet with a
      Service Code that is considered unsuitable."

3.3. Using Service Codes at the Server

   A Service Code is used by a server that receives a DCCP-Request to
   associate a new DCCP connection with the corresponding application
   service. A number of options are presented for servers using
   passively listening sockets.  Four cases can arise when two DCCP
   server applications listen on the same host:

   o  The simplest case arises when two servers are associated with
      different Service Codes and are bound to different server ports
      (section 3.3.1).

   o  Two servers may be associated with the same DCCP Service Code
      value, but be bound to different server ports (Section 3.3.1).

   o  Two servers could use different DCCP Service Code values, and be
      bound to the same server port (section 3.3.2).

   o  Two servers could attempt to use the same DCCP Service Code and
      bind to the same server port.  A DCCP implementation MUST disallow
      this, since there is no way for the DCCP host to direct a new
      connection to the correct server application.

   RFC 4340 (section 8.1.2) states that an implementation:

   o  MUST associate each active socket with exactly one Service Code on
      a specified server port.

   In addition, section 8.1.2 also states:

   o  "Passive sockets MAY, at the implementation's discretion, be
      associated with more than one Service Code; this might let
      multiple applications, or multiple versions of the same
      application, listen on the same port, differentiated by Service
      Code."

   This document updates this text in RFC 4340 by replacing this with
   the following:

   o  "An implementation SHOULD allow more than one Service Code to be
      associated with a passive server port, enabling multiple
      applications, or multiple versions of an application, to listen on
      the same port, differentiated by the associated Service Code."



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   It also adds:

   o  "An implementation SHOULD provide a method that informs a server
      of the Service Code value that was selected by an active
      connection."

   A single passively opened (listening) port MAY therefore be
   associated with multiple Service Codes, although an active (open)
   connection can only be associated with a single Service Code. A
   single application may wish to accept connections for more than one
   Service Code using the same server port. This may allow a server to
   offer more than the limit of 65,536 services determined by the size
   of the Port field. The upper limit is based solely on the number of
   unique connections between two hosts (i.e., 4,294,967,296).

3.3.1. Reception of a DCCP-Request

   When a DCCP-Request is received, and the specified destination port
   is not bound to a server, the host MUST reject the connection by
   issuing a DCCP-Reset with Reset Code "Connection Refused". A host MAY
   also use the Reset Code "Too Busy" ([RFC4340], section 8.1.3).

   When the requested destination port is bound to a server, the host
   MUST also verify that the server port is associated with the
   specified Service Code. Two cases can occur:

   o  If the receiving host is listening on a server port and the DCCP-
      Request uses a Service Code that is associated with the port, the
      host accepts the connection. Once connected, the server returns a
      copy of the Service Code in the DCCP-Response packet completing
      the initial handshake [RFC4340].

   o  If the server port is not associated with the requested Service
      Code, the server SHOULD reject the request by sending a DCCP-Reset
      packet with Reset Code 8, "Bad Service Code" ([RFC4340], Section
      8.1.2), but MAY use the reason "Connection Refused".

   After a connection has been accepted, the protocol control block is
   associated with a pair of ports and a pair of IP addresses and a
   single Service Code value.

3.3.2. Multiple Associations of a Service Code with Ports

   DCCP Service Codes are not restricted to specific ports, although
   they may be associated with a specific well-known port.  This allows
   the same DCCP Service Code value to be associated with more than one
   server port (in either the active or passive state).


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3.3.3. Automatically launching a Server

   A host implementation may permit a service to be associated with a
   server port (or range of ports) that is not permanently running at
   the server. In this case, the arrival of a DCCP-Request may require a
   method to associate a DCCP-Request with a server that handles the
   corresponding Service Code. This operation could resemble that of
   "inetd" [inetd].

   As in the previous Section, when the specified Service Code is not
   associated with the specified server port, the connection MUST be
   aborted and a DCCP Reset message sent [RFC4340].

4. DCCP Benchmarking Services

   A number of simple services are commonly supported by systems using
   TCP and UDP, this Section defines corresponding services for DCCP
   [RFC4340]. These services are useful for debugging DCCP
   implementations and deployment, and for benchmarking bidirectional
   DCCP connections. The IANA Section of this document allocates a
   corresponding set of code points for these services.

4.1. 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.

4.2. 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 date as an ASCII string; after
   which the connection is closed.

4.3. Character generator

   The operation of the DCCP chargen service corresponds to the
   connection-based TCP chargen protocol [RFC864]: A server listens for
   incoming requests and, once a client has established a connection,
   continuously sends datagrams containing a random number (between 0
   and 512, not exceeding the current DCCP Maximum Packet Size, MPS) 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.


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

   The chargen protocol provides a 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.

4.4. Time service

   The format of timestamps and the operation of the DCCP time service
   is equivalent to 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.

4.5. Generic PerfTest service

   The PerfTest service 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. These services are identified by the Service Code "XPER".
   This document does not specify a specific port number for this
   service.

   The payload of DCCP packets associated with this service do not have
   a specified format. They are silently discarded by the receiver, and
   used only for gathering numerical performance data. Tools that have
   specific payload formats should register their own Service Code value
   with IANA (e.g., section 4.6).

   This Service Code is for benchmarking applications that transmit data
   in one direction only, with DCCP control traffic flowing in the
   opposite direction. A benchmarking application that expects data
   responses to the messages it sends would require a different Service
   Code. (This could result in different Middlebox treatment.)

4.6. PERF service

   The PERF service specified by this document describes the service
   supported by the open-source iperf benchmarking program [iperf].
   This may be used to benchmark and measure both unidirectional and
   bidirectional DCCP connections, as well as server and host DCCP


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   stacks. This service is identified by a Service Code "PERF" and is
   associated with a well-known port number that currently coincides
   with the UDP port used by the iperf benchmarking program [iperf].



5. Security Considerations

   The security considerations of RFC 4340 identifies and offers
   guidance on security issues relating to DCCP. This document discusses
   the usage of Service Codes. It does not describe new protocol
   functions.

   All IPsec modes protect the integrity of the DCCP header. This
   protects the Service Code field from undetected modification within
   the network. In addition, the IPsec Encapsulated Security Payload
   (ESP) mode may be used to encrypt the Service Code field, hiding the
   Service Code value within the network and also preventing
   interpretation by middleboxes. The DCCP header is not protected by
   application-layer security, (e.g., the use DTLS [RFC5238] as
   specified in DTLS/DCCP [RFC4347]).

   There are four areas of security that are important:

   1. Server Port number reuse (section 5.1).

   2. Interaction with NATs and firewalls (section 3.2 describes
      middlebox behaviour). Requirements relating to DCCP are described
      in [ID.Behave-DCCP].

   3. Interpretation of DCCP Service Codes over-riding traditional use
      of reserved/Well Known port numbers (Section 5.2).

   4. Interaction with IPsec and DTLS security (section 5.3).

5.1. Server Port number re-use

   Service Codes are used in addition to ports when demultiplexing
   incoming connections. This changes the service model to be used by
   applications and middleboxes.  The port-numbers registry already
   contains instances of multiple application registrations for a single
   port number for TCP and UDP. These are relatively rare.  Since the
   DCCP Service Code allows multiple applications to safely share the
   same port number, even on the same host, server port number reuse in
   DCCP may be more common than in TCP and UDP.




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5.2. Association of applications with Service Codes

   The use of Service Codes provides more ready feedback that a concrete
   service is associated with a given port on a servers, than for a
   service that does not employing service codes. By responding to an
   inbound connection request, systems not using these codes may
   indicate that some service is, or is not, available on a given port,
   but systems using this mechanism immediately provide confirmation (or
   denial) that a particular service is present. This may have
   implications in terms of port scanning and reconnaissance.

   Care needs to be exercised when interpreting the mapping of a Service
   Code value to the corresponding service. The same service
   (application) may be 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
   [RFC5238]. Other possibilities include the use of a private Service
   Code that maps to the same application as assigned to an IANA-defined
   Service Code value, or a single application that provides more than
   one service. Different versions of a service (application) may also
   be mapped to a corresponding set of Service Code values.

   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.

5.3. Interactions with IPsec

   The Internet Key Exchange protocol (IKEv2), does not currently
   specify a method to use DCCP Service Codes as a part of the
   information used to setup an IPsec security association.

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


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5.4. Security Considerations for Benchmarking Services

   Services used for benchmarking and testing may also be used to
   generate traffic for other purposes. They can therefore pose an
   opportunity for a Denial of Service attack. Care needs to be
   exercised when enabling these services in an operational network.
   Appropriate rate-limits should be provided to mitigate these effects
   for servers provided for testing. In this respect, the security
   considerations are the same as those for other IETF-defined transport
   protocols.



6. IANA Considerations

   This document does not update the IANA allocation procedures for the
   DCCP Port Number and DCCP Service Codes Registries as defined in RFC
   4340.

6.1. IANA Assignments for Benchmarking Applications

   A set of new services are defined in Section 4. Their corresponding
   IANA assignments are summarized in this Section.

   This 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. A
   specification is however required to allocate a Service Code that
   uses a combination of ASCII digits, uppercase letters, and character
   space, '-', '.', and '/') [RFC4340].

6.1.1. Port number values allocated by this document

   IANA action is required to assign server ports for use by DCCP. 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. <<<









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   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 iPerf  SC:PERF
   # IETF dccp WG, [IANA - THIS RFC]


6.1.2. 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.

   >>>IANA Please confirm these allocations. >>>

    +----------+------+----+-------------------------------+----------+
    | Service  | ASCII|Port|          Description          |   Ref    |
    | Code (SC)| Code |    |                               |          |
    +----------+------+----+-------------------------------+----------+
    |1162037327| ECHO |   7| Echo service                  | [RFC862] |
    |0x4543484f|      |    |                               |          |
    |1146374477| DTIM |  13| Daytime server                | [RFC867] |
    |0x4454494d|      |    |                               |          |
    |1128808786| CHAR |  19| Character generator (chargen) | [RFC864] |
    |0x43484152|      |    |                               |          |
    |1414090053| TIME |  37| Timeserver                    | [RFC868] |
    |0x54494d45|      |    |                               |          |
    |1346720326| PERF |5001| iPerf                         |    [*]   |
    |0x50455246|      |    |                               |          |
    |1481655634| XPER |  - | Generic Performance Service   |    [*]   |
    |0x58504552|      |    |                               |          |
    +----------+------+----+-------------------------------+----------+
     Table 1: Allocation of Service Codes by this document.

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





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7. 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, Fernando Gont, Eddie Kohler, and the DCCP WG for
   helpful comments on this topic, and Gerrit Renker for his help in
   determining DCCP behaviour and review of this document. Mark Handley
   provided significant input to the text on definition of Service Codes
   and their usage. He also contributed much of the material that has
   formed the historical background Section.

8. References

8.1. 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).

   [ID.Behave-DCCP] R. Denis-Courmont, "Network Address Translation
             (NAT) Behavioral Requirements for DCCP", IETF Work in
             Progress, draft-ietf-behave-dccp-05.txt.

8.2. 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.Simul] G. Fairhurst, G. Renker, "DCCP Simultaneous-Open Technique
             to Facilitate NAT/Middlebox Traversal", IETF Work in
             Progress, draft-ietf-dccp-simul-open-07.txt.

   [ID.RTP]  C. Perkins, "RTP and the Datagram Congestion Control
             Protocol (DCCP)", IETF Work in Progress, draft-ietf-dccp-
             rtp-07.txt.



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   [ID.Rand] M. Larsen, F. Gont, "Port Randomization", IETF Work in
             Progress, draft-larsen-tsvwg-port-randomization-02.txt

   [inetd]   The extended inetd project, http://xinetd.org/

   [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).

   [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.

   [RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time

             Streaming Protocol (RTSP)", RFC 2326, April 1998.

   [RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
             Translator (NAT) Terminology and Considerations", RFC 2663,
             August 1999.

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

   [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
             specifying the location of services (DNS SRV)", RFC 2782,
             February 2000.

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

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


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   [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
             A., Peterson, J., Sparks, R., Handley, M., and E. Schooler,
             "SIP: Session Initiation Protocol", RFC 3261, June 2002.

   [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] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
             Security", RFC 4347, April 2006.

   [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
             Description Protocol", RFC 4566, July 2006.

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

   [RFC5238] Phelan, T., "Datagram Transport Layer Security (DTLS) over
             the Datagram Congestion Control Protocol (DCCP)", RFC 5238,
             May 2008.



9. Author's Addresses

   Godred (Gorry) Fairhurst,
   School 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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9.1 Disclaimer

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s)
   controlling the copyright in such materials, this document may not
   be modified outside the IETF Standards Process, and derivative
   works of it may not be created outside the IETF Standards Process,
   except to format it for publication as an RFC or to translate it
   into languages other than English.



























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   >>> RFC Editor please remove this Section prior to publication.

   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

   +++++++++++++++++++++++++++

   WG 00 (first WG version)

   This introduced revisions to make it a WG document.

   - Corrected language and responded to many helpful comments from
   Fernando Gont and Ian McDonald.

   - Added a test for which server behaviour is used.

   - Added some speculative text on how to implement the SC.

   - More input and discussion is requested from the WG.

   - Added an informative appendix on host configuration.

   - Merging of some Sections to remove repetition and clarify wording.

   +++++++++++++++++++++++++++





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   WG 01

   Historical material was added.

   Comments from the list have been included.

   The concept of adding weak semantics to a SC=0 was removed. This was
   added at the request of implementers, with the aim of offering easier
   implementation on at least one target platform. It has been removed
   in this document because it weakens interoperability and complicates
   the Spec.

   The proposal to allow several levels of support was introduced in
   previous drafts following suggestions from the WG, but was removed in
   this revision. The method was seen to introduce complexity, and
   resulted in complex interoperability scenarios.

   Removed "test" method, this was no longer required.

   Draft was reorganized to improve clarity and simplify concepts.

   ----

   WG 02

   Updated following comments from Eddie Kohler.

   ----

   WG 03

   Fixed NiTs and addressed issues marked in previous version.

   Added 2 para at end of port Section saying how to use Well Known
   ports and that you do not need to register them.

   -----

   WG 04

   Cleaned English (removing duplication)

   Checked text that updates RFC4340 (and remove duplicates).

   Updated hash algorithm for SC->s_port

   Updated to IANA Section.


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   Edits in response to feedback from Tom Phelan, et al.

   -----

   WG-05:

   Various Sections were updated following feedback from the list, some
   specific comments were:

   Tom Phelan suggested clarification was needed for the usage of well-
   known ports in Section 1, and various other clarifications.

   Eddie Kohler suggested reworking the midbox Section.

   Eddie noted the hash function included the highest numbered port,
   which is not accessible on all OS.

   There was also discussion about the proper server port range to be
   used with this method. After previous concerns that using registered
   ports could have some (unknown) side effect, use was recommended in
   the dynamic range. Text was added to this Section.

   Discussions at IETF-71 lead to the idea to removing the IANA guidance
   on maintaining the registries to a new document that defines the
   policy across the set of transport registries.

   Eddie noted that port-reuse is likely to be more common with DCCP
   (security considerations).

   Lars noted that rate-limiting benchmarking tools may be somewhat
   undesirable, and this related to services for testing.

   The text recommending an update to the IANA procedures for ports and
   service codes has been moved to a TSV WG draft.

   -----

   WG-06:

   Updated the updating paragraphs to clarify the specific clauses of
   RFC 4340 are changed. Comments from Eddie and Colin.

   Very minor editorial corrections.

   -----

   WG-07:


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   Portname for Perf in registry changed to all lower case.

   Replaced para 2 of intro and updated later parts of the introduction
   (feedback in LC from Eddie).

   Added citation to the Behave WG Requirements for NATs (now in LC).

   -----

   WG-08:

   New text to address editorial corrections proposed by Alfred Hoenes.

   -----

   WG-09:Update following review feedback

   Gen-ART

   Section 3.2: Middlebox [RFC3234] implementors therefore need to note
   that new DCCP connections are identified by the pair of Server Port
   and Service Code. - Added "in addition to the IP address" to the end
   of the above sentence for clarity.

   Section 3.2: Updated sentence to read: This means that the IANA may
   allocate a server port to more than one DCCP application [RFC4340].

   Section 3.3.2 rewritten as: DCCP Service Codes are not restricted to
   specific ports, although they may be associated with a specific well-
   known port.  The same DCCP Service Code value may therefore be
   associated with more than one server port (in either the active or
   passive state).

   Section 5.3: Added: The Internet Key Exchange protocol (IKEv2), does
   not currently specify a method to use DCCP Service Codes as a part of
   the information used to setup an IPsec security association.

   Sec-Dir

   Section 5: Added: The security considerations of RFC 4340 identifies
   and offers guidance on security issues relating to DCCP.

   Section 5.2: Added new paragraph: The use of Service Codes provides
   more ready feedback that a concrete service is associated with a
   given port on a servers, than for a service that does not employing
   service codes. By responding to an inbound connection request,
   systems not using these codes may indicate that some service is, or


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   is not, available on a given port, but systems using this mechanism
   immediately provide confirmation (or denial) that a particular
   service is present. This may have implications in terms of port
   scanning and reconnaissance.

   Note: This I-D will be a normative reference in draft-ietf-dccp-
   simul-open.










































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