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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                     October 15, 2007
Expires: September 2007

                           The DCCP Service Code

Status of this Memo

   By submitting this Internet-Draft, each author represents that
   any applicable patent or other IPR claims of which he or she is
   aware have been or will be disclosed, and any of which he or she
   becomes aware will be disclosed, in accordance with Section 6 of
   BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   The list of current Internet-Drafts can be accessed at

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   This Internet-Draft will expire on April 15, 2008.


   This document describes the usage of Service Codes by the Datagram
   Congestion Control Protocol, RFC 4340. This document motivates the
   setting of Service Codes 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). It updates the description provided in RFC 4340.

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Table of Contents

   1. Introduction...................................................3
      1.1. History...................................................3
      1.2. Conventions used in this document.........................6
   2. An Architecture for Service Codes..............................6
      2.1. IANA Port Numbers.........................................6
      2.2. DCCP Service Code Values..................................7
      2.3. Service Code Registry.....................................8
      2.4. Zero Service Code.........................................8
      2.5. SDP for describing Service Codes..........................9
   3. Use of the DCCP Service Code...................................9
      3.1. Setting Service Codes at the Sender......................10
      3.2. Using Service Codes in the Network.......................10
      3.3. Using Service Codes at the Receiver......................11
         3.3.1. Reception of a DCCP-Request.........................12
         3.3.2. Multiple Associations of Service Codes and Ports....13
         3.3.3. Automatically launching a Server....................13
   4. Benchmarking Services Described in this document..............13
      4.1. Echo.....................................................14
      4.2. Daytime..................................................14
      4.3. Character generator......................................14
      4.4. Time service.............................................14
      4.5 PerfTest service.........................................15
   5. Security Considerations.......................................15
      5.1. Interactions of Service Codes and port numbers...........16
      5.2. Interactions with IPsec..................................16
   6. IANA Considerations...........................................17
      6.1. Port number values allocated by this document............17
      6.2. Service Code values allocated by this document...........18
   7. Acknowledgments...............................................19
   8. References....................................................19
      8.1. Normative References.....................................19
      8.2. Informative References...................................19
   9. Author's Addresses............................................21
      9.1. Intellectual Property Statement..........................21
      9.2. Disclaimer of Validity...................................22
      9.3. Copyright Statement......................................22
   APPENDIX A: API support for Service Codes........................23

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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.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 (section 2.2).

   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. An application identifies the requested service by
   the Service Code value in a DCCP-REQUEST. Each application may listen
   on one or more ports associated with one or more Service Codes
   ([RFC4340], 8.1.2).

   The use of Service Codes can assist in identifying the intended
   service when the server by a Middleboxes (a network address
   translator (NAT) [RFC2663], NAT-PT [RFC2766], Firewalls, etc).
   Middleboxes that desire to identify the type of data being
   transported by a flow, 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 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 describe properly how well-known 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 [RFC2960], UDP-Lite [RFC3828]) used "well-known" port
   numbers [RFC814]. These 16-bit values indicate the application
   service associated with a connection or message. The server port must
   be known to the client to allow a connection to be established.  This

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   may be achieved using out-of-band signaling (e.g. described using SDP
   [RFC4566]), but more commonly a well-known 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 well-
   known [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].  This fixed space of port numbers is globally reserved

   In the earliest draft of DCCP the authors wanted to address the issue
   of well-known 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 on 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. Firewall writers are encouraged 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
   "well-known", 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 well-known port.  Ideally, it should
   be sufficiently easy that every application-writer can request a
   well-known port and get one instantly with no questions asked. The
   16-bit port space traditionally used is not large enough to support
   such a trivial allocation of well-known 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 the use of a 32-bit Service
   Code [RFC4340] that is included only in the DCCP-Request packet. This
   was intended to perform the primary role of a well-known server port,
   in that it would be trivially simply to obtain a unique value for
   each application. Placing the value in a request packet, requires no
   additional overhead for the actual data flow.  It is however
   sufficient for both the end-systems, and provides any stateful
   middleboxe(s) along the path with additional information to
   understand what applications are being used.

   The original draft of the DCCP specification did not use traditional
   ports; instead the client allocated a 32-bit identifier to uniquely
   identified the 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 to allow it to
   reach the corresponding listening application.  This design 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
   favour of two traditional 16-bit ports, one chosen by the server and
   one by the client. This allows middleboxes to utilize similar
   techniques for DCCP, UDP, TCP, etc. (e.g. NAT).  This also has the
   advantage that two servers associated with the same Service Code
   could co-exist on the same server host.  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 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.

   The solution is to register well-known DCCP ports.  The limited
   availability of well-known ports appears to contradict the benefits
   of DCCP service codes, because although it may be trivial to obtain a

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   service code, it has not traditionally been trivial to obtain a well-
   known port from IANA and in the long-run it may not be possible to
   uniquely allocate a well-known 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 well-known port, and need to
   run on the same host at the same time). No protocols issues arise
   from a port being associated with two Service Codes, each bound to
   different applications does not raise any protocol issues. An
   incoming DCCP-Request is directed to the correct application.

   Service Codes provide flexibility in the way clients identify the
   server application to which they wish to communicate. The Service
   Code 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 well-known port number.

   There has been confusion concerning how well-known ports relate to
   well-known Service Codes. The goal of this document is to clarify the
   issues concerning the use and allocation 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",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   All protocol code points and values are transmitted in network byte
   order (most significant byte first), with the most significant bit of
   each byte is placed in the left-most position of an 8-bit field.

2. An Architecture for 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.

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

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   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",
   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] in TCP. This method may be applicable
   to other IETF-defined transport protocols, including DCCP.

   Traditionally, the destination (server) 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

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

2.2. DCCP Service Code Values

   DCCP specifies a 4 byte Service Code ([RFC4340],8.1.2) represented in
   one of three forms as: a decimal number (the canonical 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,
   TIME, ECHO. In a different example, DTLS provides a transport-service
   (not an application-layer service), therefore applications using DTLS
   are individually identified by a set of corresponding service codes.

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   A single passive listening port may be associated with more than one
   Service Code value, which may be associated with one or different
   server applications.

   Endpoints MUST associate a Service Code with every DCCP socket
   [RFC4340], both actively and passively opened. The application will
   generally supply this Service Code. It 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). This decouples the use of ports for connection
   demultiplexing and state management, from their use to indicate a
   desired endpoint service. The Service Code value is present only in
   DCCP-Request ([RFC4340],5.2)and DCCP-Response packets

   Applications/protocols that provide version negotiation or indication
   in the protocol operating over DCCP do not require a new server port
   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 well-known ports, the DCCP Well-Known Ports
   registry MUST also be updated to include the new Service Code value.

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],
   19.8, updated by this document). Private service codes are not
   centrally allocated and are denoted by the range 1056964608-
   1073741823 (i.e. whose first hexadecimal digit has the ASCII value
   for '?').

   Associations of Service Code with Well-Known Ports may also be
   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 stated 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

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   This document clarifies section 19.8 of RFC 4340:

   "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 for their protocols from
   the IANA."

2.5. Invalid Service Code

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

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.DCCP.RTP].

3. Use of the DCCP Service Code

   The basic operation of Service Codes is as follows:

   o  A sending host:

       .  issues a DCCP-Request with a Service Code and chooses a
          destination 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.

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

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   This section explicitly updates RFC 4340 as follows:

   "A DCCP implementation SHOULD allow multiple applications using
   different DCCP service codes to listen on the same server port.

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

   The remainder of this section describes processing of DCCP Service
   Codes at the sending and receiving hosts and within the network by

3.1. Setting Service Codes at the Sender

   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

3.2. Using Service Codes in the Network

   Port numbers and IP addresses are the traditional methods to identify
   a flow within an IP network. When the DCCP header has not been
   encrypted, Middleboxes [RFC3234] SHOULD use the Service Code to
   identify the application-service (even when running on a non-standard
   port). When consistently used, the Service Code can provide a more
   specific indication of the actual service (e.g. indicate the type of
   multimedia flow, or intended application behaviour). Middlebox
   devices are therefore expected to check Service Code values as well
   as, or even instead of port numbers for DCCP.

   DCCP connections identified by the Service Code continue to use IP
   addresses and ports, although neither port number may be well-
   known/reserved. Network address and port translators, known
   collectively as NATs [RFC2663][RFC2766], not only interpret DCCP
   ports, but may also translate/modify them [RFC2993]. Interpreting
   DCCP Service Codes can reduce the need to correctly interpret port
   numbers, leading to new opportunities for network address and port
   translators. The DCCP Service Code may allow services to be
   identified behind NATs, if NATs are not further extended to translate
   Service Codes.

   Although Service Codes label a connection and can (and is encouraged
   to) associate specific delivery properties (e.g. use Service Codes 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

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   therefore desire to 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 recommendations are provided:

   o  A middlebox SHOULD use the Service Code value to assist in
      determining the behaviour to be applied to a packet flow (e.g.
      default keep-alive interval, NAT translation, etc).

   o  A middlebox SHOULD NOT modify the Service Code, unless they also
      change the service that a connection is accessing.

   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 Receiver

   A Service Code is used by a host that receives a DCCP-Request to
   associate a DCCP connection with the corresponding application
   service. At the server, this association must be explicit, i.e. if
   the connection is accepted, the requested Service Code must have been
   previously associated with the listening port at the server.

   A number of options are presented for servers using passively
   listening sockets.  As an example, consider the four cases that could
   arise when two DCCP server applications listen on the same host:

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

   o  The two servers may be associated with the same DCCP Service Code,
      but be bound to different server ports (section 3.3.1).

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

   o  The two servers could attempt to use the same DCCP Service Code
      and bind to the same 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 ([RFC4340, 8.1.2) states that an implementation:

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

   o  MAY, at the discretion of an implementation, associate more than
      one Service Code with a passive socket.

   This document updates RFC4340 in the following way:

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

   o  MUST also allow a server to use a single Service Code for more
      than one server port.

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

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], 8.1.3).

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

   o  If the receiving host is listening on the specified destination
      port number and the Service Code of the DCCP-Request matches one
      of the Service Codes associated with this 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 port is not associated with the requested Service Code, the
      server MUST reject the request by sending a DCCP-Reset packet with
      Reset Code 8, "Bad Service Code" ([RFC4340], 8.1.2).

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

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3.3.2. Multiple Associations of Service Codes and Ports at the Server

   RFC4340 states that a single passively opened (listening) port MAY be
   associated with multiple Service Codes, although an active (open)
   connection can only be associated with a single Service Code. This
   document updates RFC4340 to add:

   "A Service Code MAY be associated with more than one destination port
   (corresponding to a specified set of server port values)."

   A single application may wish to accept connections for more than one
   Service Code using the same port.  This approach can simplify
   middlebox processing, e.g. it should not be necessary to create more
   than one hole in a firewall for this to be the case; for example DTLS
   connections and unencrypted connections for the same application will
   normally use different Service Codes to distinguish them, but because
   this is the same application, it makes sense to use the same port.

3.3.3. Automatically launching a Server

   A host implementation may permit a service to be associated with a
   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". This 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 upper 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 connection MUST be aborted
   and a DCCP Reset message sent [RFC4340].

4. 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.

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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 data 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, 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.

4.4. 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.

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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

   The payload of DCCP packets associated with this service does 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).

   >>> Note from Eddie on suggested alternative text:  This Service Code
   is for benchmarking applications that transmit data in one-direction
   only. An benchmarking application that does expect responses to
   messages it sends requires 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
   stacks. This service is identified by a Service Code "PERF" and is
   associated with a well-known port number that currently coincides
   with that used by the iperf benchmarking program [iperf].

5. 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 (section 3.2 describes
      middlebox behaviour).

   2. Interpretation of DCCP Service Codes over-riding traditional use
      of reserved/well-known port numbers (section 5.1)

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   3. Interaction with IPsec and DTLS security (section 5.2).

   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.

5.1. Interactions of Service Codes and port numbers

   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. 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. Care needs to be exercised when interpreting the mapping
   of a 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.

5.2. 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
   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].

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6. IANA Considerations

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

   >>> Author Note: This section requires consideration by the IANA and
   the DCCP WG -                    - issues need to be identified.

   >>> Author Note: Which port-numbering space should this apply to? -                                                                          -
   Free-allocation may be easier to manage in the dynamic port-space
   using a separate DCCP registry that is independent of TCP, UDP, and
   other IETF-defined transport protocols?

   To encourage application writers to register their applications, and
   to avoid restricting DCCP service codes to a 16-bit space, we revise
   RFC 4340 as follows:

   "IANA should allocate well-known DCCP ports on demand to anyone to
   applies, without requiring a specification or additional
   justification. Each well-known port request MUST be for a specific
   registered DCCP Service Code. The procedure may allow both to be
   assigned in the same request.

   IANA MUST use an allocation policy that attempts to minimize server
   port collisions, but it is expected that the same well-known port
   will sometimes be allocated to more than one Service Code."

6.1. Port number values allocated by this document

   IANA action is required to assign 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]

6.2. 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 replace tbd by the assigned a port number in section

    | 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 |  - |                               |    [*]   |
    |0x58504552|      |    |                               |          |
     Table 1: Allocation of Service Codes by this document.

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

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   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 (e.g.

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, review of the document, and compilation
   of useful test applications defined in the IANA section of this
   document. Mark Handley provided significant input to the 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

   [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

8.2. Informative References

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

   [IANA-SC] IANA DCCP Service Code Registry

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

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   [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-xx.txt.

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

   [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).

   [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.

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

   [RFC2766] Tsirtsis, G. and P. Srisuresh, "Network Address Translation
             - Protocol Translation (NAT-PT)", RFC 2766, February 2000.

   [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.

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   [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.

   [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.

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

9. Author's Addresses

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

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

9.1. Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

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   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at

9.2. Disclaimer of Validity

   This document and the information contained herein are provided on

9.3. 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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APPENDIX A: API support for Service Codes

   A potential issue in defining an API for DCCP arises when an
   application binds to a port it needs to specify the associated DCCP
   Service Code. This requires an API that allows a service to be
   associated with a Service Code in addition to 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 also select a specific Service Code
      where desired.

   o  Extend the existing socket parameterization command (e.g., Unix
      setsockopt()) to set a service-code option. This is implemented in
      the present Linux API for a DCCP socket (where the Service Code
      should be wrapped by htonl/ntohl to ensure network byte order).

   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.

   The current socket API generally requires separate requests to bind
   the port and to set the Service Code for the socket.  This is not a
   problem, providing that an implementation requires both to be
   specified before the socket is allowed to accept connections.

   The host API SHOULD provide a method that returns the Service code of
   an incoming connection request to the application. This may be used
   by an application to correctly process a connection that arrives at a
   port for which it has registered more than one Service Code.

   >>> 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).

   Functions such as getnameinfo and getservent may also need to be
   updated. >>> End Author Note.

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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.

   >>> Need to check changes relative to RFC4340!

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