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Versions: 00 01 02 03 draft-ietf-taps-transports-usage-udp

Internet Engineering Task Force                             G. Fairhurst
Internet-Draft                                                  T. Jones
Intended status: Informational                    University of Aberdeen
Expires: April 8, 2017                                  October 05, 2016


 Features of the User Datagram Protocol (UDP) and Lightweight UDP (UDP-
                       Lite) Transport Protocols
              draft-fairhurst-taps-transports-usage-udp-03

Abstract

   This document describes how the User Datagram Protocol (UDP) and the
   Lightweight User Datagram Protocol (UDP-Lite) transport protocols
   expose services to applications and how an application can configure
   and use the features offered by the transport service.  The document
   is intended as a contribution to the Transport Services (TAPS)
   working group to assist in analysis of the UDP and UDP-Lite transport
   interface.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 8, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  UDP and UDP-Lite Primitives . . . . . . . . . . . . . . . . .   3
     3.1.  Primitives Provided by UDP  . . . . . . . . . . . . . . .   3
       3.1.1.  Excluded Primitives . . . . . . . . . . . . . . . . .   8
     3.2.  Primitives Provided by UDP-Lite . . . . . . . . . . . . .   9
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Appendix A.  Revision Notes . . . . . . . . . . . . . . . . . . .  13
   Appendix B.  Notes Based on Typical Usage . . . . . . . . . . . .  14
   Appendix C.  UDP Multicast  . . . . . . . . . . . . . . . . . . .  14
     C.1.  Multicast Primitives  . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Terminology

   This document uses common terminology defined in
   [I-D.ietf-taps-transports-usage].  This document also refers to the
   terminology of [RFC2119], but does not itself define new terms using
   this terminology.

2.  Introduction

   This document presents defined interactions between transport
   protocols and applications in the form of 'primitives' (function
   calls).  Primitives can be invoked by an application or a transport
   protocol; the latter type is called an "event".  The list of
   transport service features and primitives in this document is
   strictly based on the parts of protocol specifications that relate to
   what the protocol provides to an application using it and how the
   application interacts with it.  It does not cover parts of a protocol
   that are explicitly stated as optional to implement.

   This follows the methodology defined in
   [I-D.ietf-taps-transports-usage], specifically it provides the first
   pass of this process.  It discusses the relevant RFC text describing
   primitives for each protocol.  This also provides documentation that
   may help users of UDP and UDP-Lite.



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3.  UDP and UDP-Lite Primitives

   This summarizes the relevant text parts of the RFCs describing the
   UDP and UDP-Lite protocols, focusing on what the transport protocols
   provide to the application and how the transport is used (based on
   abstract API descriptions, where they are available).

3.1.  Primitives Provided by UDP

   The User Datagram Protocol (UDP) [RFC0768] States: "This User
   Datagram Protocol (UDP) is defined to make available a datagram mode
   of packet-switched computer communication in the environment of an
   interconnected set of computer networks."  It "provides a procedure
   for application programs to send messages to other programs with a
   minimum of protocol mechanism (..)".

   The User Interface section of [RFC0768] specifies that the user
   interface to an application should be able to create receive ports,
   source and destination ports and addresses, and provide operations to
   receive data based on ports with an indication of source port and
   address.  Operations should be provided that allows datagrams be sent
   specifying the source and destination ports and addresses to be sent.

   UDP for IPv6 is defined by [RFC2460], and API extensions to support
   this in [RFC3493].  [RFC6935] and [RFC6936] defines an update to the
   UDP transport specified in RFC 2460.  This enables use of a zero UDP
   checksum mode with a tunnel protocol, providing that the method
   satisfies the requirements in [RFC6936].

   UDP offers only a basic transport interface.  UDP datagrams may be
   directly sent and received, without exchanging messages between the
   endpoints to setup a connection (i.e., there is no handshake prior to
   communication).  Using the sockets API, applications can receive
   packets from more than one IP source address on a single UDP socket.
   Common support allows specification of the local IP address,
   destination IP address, local port and destination port values.  Any
   or all of these can be indicated, with defaults supplied by the local
   system when these are not specified.  The local endpoint is set using
   the BIND call and set on the remote endpoint using the CONNECT call.
   The CLOSE function has local significance only.  This does not impact
   the status of the remote endpoint.

   UDP and UDP-Lite do not provide congestion control, retransmission,
   nor support to optimise fragmentation etc.  This means that
   applications using UDP need to provide additional functions on top of
   the UDP transport API.  This requires parameters to be passed through
   the API to control the network layer (IPv4 or IPv6).  These
   additional primitives could be considered a part of the network layer



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   (e.g., control of the setting of the Don't Fragment flag on a
   transmitted datagram), but are nonetheless essential to allow a user
   of the UDP API to implement functions that are normally associated
   with the transport layer (such as probing for Path maximum
   transmission size).  Although this adds complexity to the analysis of
   the API, this document includes such primitives.

   [I-D.ietf-tsvwg-rfc5405bis] also states "many operating systems also
   allow a UDP socket to be connected, i.e., to bind a UDP socket to a
   specific pair of addresses and ports.  This is similar to the
   corresponding TCP sockets API functionality.  However, for UDP, this
   is only a local operation that serves to simplify the local send/
   receive functions and to filter the traffic for the specified
   addresses and ports.  Binding a UDP socket does not establish a
   connection - UDP does not notify the remote end when a local UDP
   socket is bound.  Binding a socket also allows configuring options
   that affect the UDP or IP layers, for example, use of the UDP
   checksum or the IP Timestamp option.  On some stacks, a bound socket
   also allows an application to be notified when ICMP error messages
   are received for its transmissions [RFC1122]."

   The [POSIX] API offers mechanisms for an application to receive
   asynchronous data events at the socket layer.  Calls such as poll,
   select or queue allow an application to be notified when data has
   arrived at a socket or a socket has flushed its buffers.  It is
   possible to structure a callback-driven API to the network interface
   on top of these calls.  There are protocols that allow a macro
   interface to network primitives, [RFC6458] describes implicit
   association setup for sending datagram messages using SCTP.  Implicit
   connection setup allows an application to delegate connection life
   management to the transport API.  The transport API uses protocol
   primitives to offer the automated service to the application via the
   socket API.  By combining UDP primitives (CONNECT.UDP, SEND.UDP), a
   higher level API could offer a similar service.

   Guidance on the use of services provided by UDP is provided in
   [I-D.ietf-tsvwg-rfc5405bis].

   The following primitives are specified:

   CONNECT:  The CONNECT primitive allows the association of source and
      port sets to a socket to enable creation of a 'connection' for UDP
      traffic.  This UDP connection allows an application to be notified
      of errors received from the network stack and provides a shorthand
      access to the send and receive primitives.  Since UDP is itself
      connectionless, no datagrams are sent because this primitive is
      executed.  A further connect call can be used to change the
      association to a source/port pair.



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      Two forms of usage may be identified for the CONNECT primitive:



      1.  bind(): A bind operation sets the local port, either
          implicitly, triggered by a send to operation on an unbound,
          unconnected socket using an ephemeral port.  Or by an explicit
          bind to makes use of a configured or well-known port.

      2.  bind(); connect(): A bind operation followed by a CONNECT
          primitive.  The bind operation establishes the use of a known
          local port for datagrams, rather than using an ephemeral port.
          The connect operation specifies a known address port
          combination to be used by default for future datagrams.  This
          form is used either after receiving a datagram from an
          endpoint causing the creation of a connection or can be
          triggered by third party configuration or a protocol trigger
          (such as reception of a UDP Service Description Protocol, SDP
          [RFC4566], record).

   LISTEN:  The roles of a client and a server are often not appropriate
      for UDP, where connections can be peer-to-peer.  The listening
      functions are performed using one of the forms of CONNECT
      primitive described above.

   SEND:  The SEND primitive hands over a provided number of bytes that
      UDP should send to the other side of a UDP connection in a UDP
      datagram.  The primitive can be used by an application to directly
      send datagrams to an endpoint defined by an address/port pair.  If
      a connection has been created, then the address/port pair is
      inferred from the current connection for the socket.  A connection
      created on the socket will allow network errors to be returned to
      the application as a notification on the send primitive.  Messages
      passed to the send primitive that cannot be sent atomically in a
      datagram will not be sent by the network layer, generating an
      error.

   RECEIVE:  The RECEIVE primitive allocates a receiving buffer to
      accommodate a received datagram.  The primitive returns the number
      of bytes provided from a received UDP datagram.  Section 4.1.3.5
      of [RFC1122] states "When a UDP datagram is received, its
      specific-destination address MUST be passed up to the application
      layer."

   DISABLE_CHECKSUM:  The CHECKSUM function controls whether a sender
      disables the UDP checksum when sending datagrams.  [RFC0768] and
      IPv6 [RFC6935] [RFC6936] [I-D.ietf-tsvwg-rfc5405bis].  When set it
      overrides the default UDP behaviour disabling the checksum on



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      sending.  Section 4.1.3.4 of [RFC1122] states "An application MAY
      optionally be able to control whether a UDP checksum will be
      generated, but it MUST default to checksumming on."

   REQUIRE_CHECKSUM:  The REQUIRE_CHECKSUM function determines whether
      UDP datagrams received with a zero checksum are permitted or
      discarded.  Section 4.1.3.4 of [RFC1122] states "An application
      MAY optionally be able to control whether UDP datagrams without
      checksums should be discarded or passed to the application."
      Section 3.1 of [RFC3828] requires that the checksum field is non-
      zero, and hence UDP-Lite need to discard all datagrams received
      with a zero checksum.

   SET_IP_OPTIONS:  The SET_IP_OPTIONS function enables a datagram to be
      sent with the specified IP options.  Section 4.1.3.2 of[RFC1122]
      states that an "application MUST be able to specify IP options to
      be sent in its UDP datagrams, and UDP MUST pass these options to
      the IP layer."

   GET_IP_OPTIONS:  The GET_IP_OPTIONS function is a network-layer
      function that enables a receiver to read the IP options of a
      received datagram.  Section 4.1.3.2 of[RFC1122] states that a UDP
      receiver "MUST pass any IP option that it receives from the IP
      layer transparently to the application layer".

   SET_DF:  The SET_DF function is a network-layer function that sets
      the Don't Fragment (DF) flag to be used in the field of an IP
      header of a packet that carries a UDP datagram.  A UDP application
      should implement a method that avoids IP fragmentation ( section 4
      of [I-D.ietf-tsvwg-rfc5405bis]).  It can use Packetization-Layer-
      Path MTU Discovery (PLPMTUD) [RFC4821] or Path MTU Discovery
      [RFC1191].  NOTE: In many other IETF transports (e.g.  TCP) the
      transport provides the support needed to use DF, when using UDP,
      the application is responsible for the techniques needed to
      discover the path MTU, coordinating with the network layer.

   GET_INTERFACE_MTU:  The GET_INTERFACE_MTU function a network-layer
      function that indicates the largest unfragmented IP packet that
      may be sent.  A UDP endpoint can subtract the size of all network
      and transport headers to determine the maximum size of
      unfragmented UDP payload.  UDP applications should use this value
      as part of a method to avoid sending UDP datagrams that would
      result in IP packets that exceed the effective path maximum
      transmission unit (PMTU) allowed on the network path.  The
      effective PMTU specified in Section 1 of [RFC1191] is equivalent
      to the "effective MTU for sending" specified in [RFC1122].
      [RFC4821] states: "If PLPMTUD updates the MTU for a particular
      path, all Packetization Layer sessions that share the path



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      representation (as described in Section 5.2) SHOULD be notified to
      make use of the new MTU and make the required congestion control
      adjustments."

   SET_TTL:  The SET_TTL function a network-layer function that sets the
      hop limit (TTL field) to be used in the field of an IPv4 header of
      a packet that carries an UDP datagram.  This is used to limit the
      scope of unicast datagrams.  Section 3.2.2.4 of [RFC1122] states
      an "incoming Time Exceeded message MUST be passed to the transport
      layer".

   GET_TTL:  The GET_TTL function is a network-layer function that reads
      the value of the TTL field from the IPv4 header of a received UDP
      datagram.  Section 3.2.2.4 of [RFC1122] states that a UDP receiver
      "MAY pass the received TOS up to the application layer" When used
      for applications such as the Generalized TTL Security Mechanism
      (GTSM) [RFC5082], this needs the UDP receiver API to pass the
      received value of this field to the application.

   SET_IPV6_UNICAST_HOPS:  The SET_IPV6_UNICAST_HOPS function is a
      network-layer function that sets the hop limit field to be used in
      the field of an IPv6 header of a packet that carries a UDP
      datagram.  For IPv6 unicast datagrams, this is functionally
      equivalent to the SET_TTL IPv4 function.

   GET_IPV6_UNICAST_HOPS:  The GET_IPV6_UNICAST_HOPS function is a
      network-layer function that reads the value from the hop count
      field in the IPv6 header from the IP header information of a
      received UDP datagram.  For IPv6 unicast datagrams, this is
      functionally equivalent to the GET_TTL IPv4 function.

   SET_DSCP:  The SET_DSCP function is a network-layer function that
      sets the DSCP (or legacy TOS) value to be used in the field of an
      IP header of a packet that carries a UDP Datagram.  Section 2.4 of
      [RFC1122] states that "Applications MUST select appropriate TOS
      values when they invoke transport layer services, and these values
      MUST be configurable.".  The application should be able to change
      the TOS during the connection lifetime, and the TOS value should
      be passed to the IP layer unchanged.  Section 4.1.4 of [RFC1122]
      also states that on reception the "UDP MAY pass the received TOS
      value up to the application layer".  [RFC2475] [RFC3260] replaces
      this field in the IP Header assigning the six most significant
      bits to carry the Differentiated Services Code Point (DSCP) field.
      Preserving the intention of [RFC1122] to allow the application to
      specify the "Type of Service", this should be interpreted to mean
      that an API should allow the application to set the DSCP.
      Section 3.1.6 of [I-D.ietf-tsvwg-rfc5405bis] describes the way UDP
      applications should use this field.  Normally a UDP socket will



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      assign a single DSCP value to all Datagrams in a flow, but it is
      allowed to use different DSCP values for datagrams within the same
      flow in some cases, as described in [I-D.ietf-tsvwg-rfc5405bis].
      Guidelines for WebRTC that illustrate this use are provided in
      [RFC7657].

   SET_ECN:  The SET_ECN function is a network-layer function that sets
      the ECN field in the IP Header of a UDP Datagram.  When use of the
      TOS field was redefined [RFC3260], 2 bits of the field were
      assigned to support Explicit Congestion Notification (ECN)
      [RFC3168].  Section 3.1.5 [I-D.ietf-tsvwg-rfc5405bis] describes
      the way UDP applications should use this field.  NOTE: In many
      other IETF transports (e.g.  TCP) the transport provides the
      support needed to use ECN, when using UDP, the application itself
      is responsible for the techniques needed to use ECN.

   GET_ECN:  The GET_ECN function is a network-layer function that
      returns the value of the ECN field in the IP Header of a received
      UDP Datagram.  Section 3.1.5 [I-D.ietf-tsvwg-rfc5405bis] states
      that a UDP receiver "MUST check the ECN field at the receiver for
      each UDP datagram that it receives on this port", requiring the
      UDP receiver API to pass to pass the received ECN field up to the
      application layer to enable appropriate congestion feedback.

   ERROR_REPORT  The ERROR_REPORT event informs an application of "soft
      errors", including the arrival of an ICMP or ICMPv6 error message.
      Section 4.1.4 of [RFC1122] states "UDP MUST pass to the
      application layer all ICMP error messages that it receives from
      the IP layer."  For example, this event is required to implement
      ICMP-based Path MTU Discovery [RFC1191] [RFC1981].

   CLOSE:  The close primitive closes a connection.  No further
      datagrams may be sent/received.  Since UDP is itself
      connectionless, no datagrams are sent because this command is
      executed.

3.1.1.  Excluded Primitives

   Section 3.4 of [RFC1122] also describes "GET_MAXSIZES: - replaced,
   GET_SRCADDR (Section 3.3.4.3) and ADVISE_DELIVPROB:".  These
   mechanisms are no longer used.  It also specifies use of the Source
   Quench ICMP message, which has since been deprecated [RFC6633].  The
   IPV6_V6ONLY function defined in Section 5.3 of [RFC3493] restricts
   the use of information from the name resolver to only allow
   communication of AF_INET6 sockets to use IPv6 only.  This is not
   considered part of the transport service.





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3.2.  Primitives Provided by UDP-Lite

   The Lightweight User Datagram Protocol (UDP-Lite) [RFC3828] provides
   similar services to UDP.  It changed the semantics of the UDP
   "payload length" field to that of a "checksum coverage length" field.
   UDP-Lite requires the pseudo-header checksum to be computed at the
   sender and checked at a receiver.  Apart from the length and coverage
   changes, UDP-Lite is semantically identical to UDP.

   The sending interface of UDP-Lite differs from that of UDP by the
   addition of a single (socket) option that communicates the checksum
   coverage length.  This specifies the intended checksum coverage, with
   the remaining unprotected part of the payload called the "error-
   insensitive part".

   The receiving interface of UDP-Lite differs from that of UDP by the
   addition of a single (socket) option that specifies the minimum
   acceptable checksum coverage.

   The UDP-Lite Management Information Base (MIB) further defines the
   checksum coverage method [RFC5097].  Guidance on the use of services
   provided by UDP-Lite is provided in [I-D.ietf-tsvwg-rfc5405bis].

   UDP-Lite requires use of the UDP or UDP-Lite checksum, and hence it
   is not permitted to use the "DISABLE_CHECKSUM:" function to disable
   use of a checksum, nor is it possible to disable receiver checksum
   processing using the "REQUIRE_CHECKSUM:" function . All other
   primitives and functions for UDP are permitted.

   In addition, the following are defined:

   SET_CHECKSUM_COVERAGE:  The SET_CHECKSUM_COVERAGE function sets the
      coverage area for a sent datagram.  UDP-Lite traffic uses this
      primitive to set the coverage length provided by the UDP checksum.
      Section 3.3 of [RFC5097] states that "Applications that wish to
      define the payload as partially insensitive to bit errors ...
      Should do this by an explicit system call on the sender side."
      The default is to provide the same coverage as for UDP.

   SET_MIN_COVERAGE  The SET_MIN_COVERAGE function sets the minimum a
      acceptable coverage protection for received datagrams.  UDP-Lite
      traffic uses this primitive to set the coverage length that is
      checked on receive (section 1.1 of [RFC5097] describes the
      corresponding MIB entry as udpliteEndpointMinCoverage).
      Section 3.3 of [RFC3828] states that "applications that wish to
      receive payloads that were only partially covered by a checksum
      should inform the receiving system by an explicit system call".




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      The default is to require only minimal coverage of the datagram
      payload.

4.  Acknowledgements

   This work was partially funded by the European Union's Horizon 2020
   research and innovation programme under grant agreement No. 644334
   (NEAT).  The views expressed are solely those of the author(s).
   Thanks to all who have commented or contributed, including Joe Touch,
   Ted Hardie, Aaron Falk.

5.  IANA Considerations

   This memo includes no request to IANA.

   If there are no requirements for IANA, the section will be removed
   during conversion into an RFC by the RFC Editor.

6.  Security Considerations

   Security considerations for the use of UDP and UDP-Lite are provided
   in the referenced RFCs.  Security guidance for application usage is
   provide in the UDP-Guidelines [I-D.ietf-tsvwg-rfc5405bis].

7.  References

7.1.  Normative References

   [I-D.ietf-taps-transports-usage]
              Welzl, M., Tuexen, M., and N. Khademi, "On the Usage of
              Transport Service Features Provided by IETF Transport
              Protocols", draft-ietf-taps-transports-usage-01 (work in
              progress), July 2016.

   [I-D.ietf-tsvwg-rfc5405bis]
              Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
              Guidelines", draft-ietf-tsvwg-rfc5405bis-07 (work in
              progress), November 2015.

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <http://www.rfc-editor.org/info/rfc768>.

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122,
              DOI 10.17487/RFC1122, October 1989,
              <http://www.rfc-editor.org/info/rfc1122>.




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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <http://www.rfc-editor.org/info/rfc2460>.

   [RFC2553]  Gilligan, R., Thomson, S., Bound, J., and W. Stevens,
              "Basic Socket Interface Extensions for IPv6", RFC 2553,
              DOI 10.17487/RFC2553, March 1999,
              <http://www.rfc-editor.org/info/rfc2553>.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, DOI 10.17487/RFC3168, September 2001,
              <http://www.rfc-editor.org/info/rfc3168>.

   [RFC3493]  Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
              Stevens, "Basic Socket Interface Extensions for IPv6",
              RFC 3493, DOI 10.17487/RFC3493, February 2003,
              <http://www.rfc-editor.org/info/rfc3493>.

   [RFC3828]  Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., Ed.,
              and G. Fairhurst, Ed., "The Lightweight User Datagram
              Protocol (UDP-Lite)", RFC 3828, DOI 10.17487/RFC3828, July
              2004, <http://www.rfc-editor.org/info/rfc3828>.

   [RFC6935]  Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
              UDP Checksums for Tunneled Packets", RFC 6935,
              DOI 10.17487/RFC6935, April 2013,
              <http://www.rfc-editor.org/info/rfc6935>.

7.2.  Informative References

   [POSIX]    "IEEE Std. 1003.1-2001, , "Standard for Information
              Technology - Portable Operating System Interface (POSIX)",
              Open Group Technical Standard: Base Specifications Issue
              6, ISO/IEC 9945:2002", December 2001.

   [RFC1191]  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
              DOI 10.17487/RFC1191, November 1990,
              <http://www.rfc-editor.org/info/rfc1191>.

   [RFC1981]  McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
              for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August
              1996, <http://www.rfc-editor.org/info/rfc1981>.



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   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
              <http://www.rfc-editor.org/info/rfc2475>.

   [RFC3260]  Grossman, D., "New Terminology and Clarifications for
              Diffserv", RFC 3260, DOI 10.17487/RFC3260, April 2002,
              <http://www.rfc-editor.org/info/rfc3260>.

   [RFC3678]  Thaler, D., Fenner, B., and B. Quinn, "Socket Interface
              Extensions for Multicast Source Filters", RFC 3678,
              DOI 10.17487/RFC3678, January 2004,
              <http://www.rfc-editor.org/info/rfc3678>.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
              July 2006, <http://www.rfc-editor.org/info/rfc4566>.

   [RFC4821]  Mathis, M. and J. Heffner, "Packetization Layer Path MTU
              Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
              <http://www.rfc-editor.org/info/rfc4821>.

   [RFC5082]  Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
              Pignataro, "The Generalized TTL Security Mechanism
              (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
              <http://www.rfc-editor.org/info/rfc5082>.

   [RFC5097]  Renker, G. and G. Fairhurst, "MIB for the UDP-Lite
              protocol", RFC 5097, DOI 10.17487/RFC5097, January 2008,
              <http://www.rfc-editor.org/info/rfc5097>.

   [RFC5790]  Liu, H., Cao, W., and H. Asaeda, "Lightweight Internet
              Group Management Protocol Version 3 (IGMPv3) and Multicast
              Listener Discovery Version 2 (MLDv2) Protocols", RFC 5790,
              DOI 10.17487/RFC5790, February 2010,
              <http://www.rfc-editor.org/info/rfc5790>.

   [RFC6458]  Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
              Yasevich, "Sockets API Extensions for the Stream Control
              Transmission Protocol (SCTP)", RFC 6458,
              DOI 10.17487/RFC6458, December 2011,
              <http://www.rfc-editor.org/info/rfc6458>.

   [RFC6633]  Gont, F., "Deprecation of ICMP Source Quench Messages",
              RFC 6633, DOI 10.17487/RFC6633, May 2012,
              <http://www.rfc-editor.org/info/rfc6633>.





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   [RFC6936]  Fairhurst, G. and M. Westerlund, "Applicability Statement
              for the Use of IPv6 UDP Datagrams with Zero Checksums",
              RFC 6936, DOI 10.17487/RFC6936, April 2013,
              <http://www.rfc-editor.org/info/rfc6936>.

   [RFC7657]  Black, D., Ed. and P. Jones, "Differentiated Services
              (Diffserv) and Real-Time Communication", RFC 7657,
              DOI 10.17487/RFC7657, November 2015,
              <http://www.rfc-editor.org/info/rfc7657>.

   [STEVENS]  "Stevens, W., Fenner, B., and A. Rudoff, "UNIX Network
              Programming, The sockets Networking API", Addison-
              Wesley.", 2004.

Appendix A.  Revision Notes

   Note to RFC-Editor: please remove this entire section prior to
   publication.

   Individual draft -00:

   o  This is the first version.  Comments and corrections are welcome
      directly to the authors or via the IETF TAPS working group mailing
      list.

   Individual draft -01:

   o  Includes ability of a UDP receiver to disallow zero checksum
      datagrams.

   o  Fixes to references and some connect on UDP usage.

   Individual draft -02:

   o  Fixes to address issues noted by WG.

   o  Completed Multicast section to specify modern APIs.

   o  Noted comments on API usage for UDP.

   o  Feedback from various reviewers.

   Individual draft -03:

   o  Removes pass 2 and 3 of the TAPS analysis from this revision.
      These are expected to be incorporated into a combined draft of the
      TAPS WG.




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   o  Fixed Typos.

Appendix B.  Notes Based on Typical Usage

   This appendix contains notes to assist in a later revision.

   The de facto standard application programming interface (API) for
   TCP/IP applications is the "sockets" interface[POSIX].  Some
   platforms also offer applications the ability to directly assemble
   and transmit IP packets through "raw sockets" or similar facilities.
   This is a second, more cumbersome method of using UDP.  The use of
   this API is discussed in the RFC series in
   [I-D.ietf-tsvwg-rfc5405bis].

   The UDP sockets API differs from that for TCP in several key ways.
   Because application programmers are typically more familiar with the
   TCP sockets API, this section discusses these differences.  [STEVENS]
   provides usage examples of the UDP sockets API.

   This section provides notes on some topics relating to implemented
   UDP APIs.

   A UDP application can use the recv() and send() POSIX functions as
   well as the recvfrom() and sendto() and recvmsg and sendmsg()
   functions.

   SO_REUSEADDR specifies that the rules used in validating addresses
   supplied to bind() should allow reuse of local addresses.

   SO_REUSEPORT specifies that the rules used in validating ports
   supplied to bind() should allow reuse of a local port

   Accessing TTL From applications: If the IP_RECVTTL option is enabled
   on a SOCK_DGRAM socket, the recvmsg(2) call will return the IP TTL
   (time to live) field for a UDP datagram.  The msg_control field in
   the msghdr structure points to a buffer that contains a cmsghdr
   structure followed by the TTL.

Appendix C.  UDP Multicast

   UDP and UDP-Lite Multicast may be considered in later versions of
   this document.  This appendix contains notes to assist in this later
   revision.

   A host must request the ability to broadcast before it can send/
   receive ipv4 broadcast traffic.  A host must become a member of a
   multicast group at the network layer before it can receive datagrams
   sent to the group.



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C.1.  Multicast Primitives

   UDP and UDP-Lite support IPv4 broadcast and IPv4/IPv6 Multicast.  Use
   of multicast requires additional functions at the transport API that
   must be called to coordinate operation of the IPv4 and IPv6 network
   layer protocols.

   Guidance on the use of UDP and UDP-Lite for multicast services is
   provided in [I-D.ietf-tsvwg-rfc5405bis].

   The following are defined:

   JoinLocalGroup:  1 of [RFC3493] provides a function that allows
      joining of a local IPv4 multicast group.

   IPV6_MULTICAST_IF:  Section 5.2 of [RFC2553] states that this sets
      the interface to use for outgoing multicast packets.

   IP_MULTICAST_TTL:  This sets the hop limit to use for outgoing
      multicast packets.  This is used to limit scope of multicast
      datagrams.  When used for applications such as GTSM, this needs
      the UDP receiver API to pass the received value of this field to
      the application.  (This is equivalent to IPV6_MULTICAST_HOPS for
      IPv6 multicast and TTL/IPV6_UNICAST_HOPS for unicast datagrams).

   IPV6_MULTICAST_HOPS:  Section 5.2 of [RFC2553] states that this sets
      the hop limit to use for outgoing multicast packets.  When used
      for applications such as GTSM, this needs the UDP receiver API to
      pass the received value of this field to the application.  (This
      is equivalent to IP_MULTICAST_TTL for IPv4 multicast and TTL/
      IPV6_UNICAST_HOPS for unicast datagrams).

   IPV6_MULTICAST_LOOP:  Section 5.2 of [RFC2553] states that this sets
      whether a copy of a datagram is looped back by the IP layer for
      local delivery when the datagram is sent to a group to which the
      sending host itself belongs).

   IPV6_JOIN_GROUP:  Section 5.2 of [RFC2553] provides a function that
      allows joining of an IPv6 multicast group.

   SIOCGIPMSFILTER:  Section 8.1 of [RFC3678] provides a function that
      allows reading the multicast source filters.

   SIOCSIPMSFILTER:  Section 8.1 of [RFC3678] provides a function that
      allows setting/modifying the multicast source filters.

   IPV6_LEAVE_GROUP:  Section 5.2 of [RFC2553] provides a function that
      allows leaving of a multicast group.



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   LeaveHostGroup:  Section 7.1 of [RFC3493] provides a function that
      allows joining of an IPv4 multicast group.

   LeaveLocalGroup:  Section 7.1 of [RFC3493] provides a function that
      allows joining of a local IPv4 multicast group.

   Section 4.1.1 of [RFC3678] updates the interface to add support for
   Multicast Source Filters (MSF) to IGMPv3 for Any Source Multicast
   (ASM):

   This identifies three sets of API functionality:

   1.  IPv4 Basic (Delta-based) API.  "Each function call specifies a
       single source address which should be added to or removed from
       the existing filter for a given multicast group address on which
       to listen."

   2.  IPv4 Advanced (Full-state) API.  "This API allows an application
       to define a complete source-filter comprised of zero or more
       source addresses, and replace the previous filter with a new
       one."

   3.  Protocol-Independent Basic MSF (Delta-based) API

   4.  Protocol-Independent Advanced MSF (Full-state) API

   It specifies the following primitives:

   IP_ADD_MEMBERSHIP:  This is used to join an ASM group.

   IP_BLOCK_SOURCE:  This is a MSF that can be used to block data from a
      given multicast source to a given group for ASM or SSM.

   IP_UNBLOCK_SOURCE:  This updates an MSF to undo a previous call to
      IP_UNBLOCK_SOURCE for ASM or SSM.

   IP_DROP_MEMBERSHIP:  This is used to leave an ASM or SSM group.  (In
      SSM this drops all sources that have been joined for a particular
      group and interface.  The operations are the same as if the socket
      had been closed.)

   Section 4.1.2 of [RFC3678] updates the interface to add Multicast
   Source Filter (MSF) support for IGMPv3 with Any Source Multicast
   (ASM) using IPv4:

   IP_ADD_SOURCE_MEMBERSHIP:  This is used to join an SSM group.

   IP_DROP_SOURCE_MEMBERSHIP:  This is used to leave an SSM group.



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   Section 4.1.2 of [RFC3678] defines the Advanced (Full-state) API:

   setipv4sourcefilter  This is used to join an IPv4 multicast group, or
      to enable multicast from a specified source.

   getipv4sourcefilter:  This is used to leave an IPv4 multicast group,
      or to filter multicast from a specified source.

   Section 5.1 of [RFC3678] specifies Protocol-Independent Multicast API
   functions:

   MCAST_JOIN_GROUP  This is used to join an ASM group.

   MCAST_JOIN_SOURCE_GROUP  This is used to join an SSM group.

   MCAST_BLOCK_SOURCE:  This is used to block a source in an ASM group.

   MCAST_UNBLOCK_SOURCE:  This removes a previous MSF set by
      MCAST_BLOCK_SOURCE:

   MCAST_LEAVE_GROUP:  This leaves a SSM group.

   MCAST_LEAVE_GROUP:  This leaves a ASM or SSM group.

   Section 5.2 of [RFC3678] specifies the Protocol-Independent Advanced
   MSF (Full-state) API applicable for both IPv4 and IPv6 multicast:

   setsourcefilter  This is used to join an IPv4 or IPv6 multicast
      group, or to enable multicast from a specified source.

   getsourcefilter:  This is used to leave an IPv4 or IPv6 multicast
      group, or to filter multicast from a specified source.

   Section 7.2 of [RFC5790] updates the interface to specify support for
   Lightweight IGMPv3 (LW_IGMPv3) and MLDv2.

   According to the MSF API definition [RFC3678], "an LW-IGMPv3 host
   should implement either the IPv4 Basic MSF API or the Protocol-
   Independent Basic MSF API, and an LW-MLDv2 host should implement the
   Protocol- Independent Basic MSF API.  Other APIs, IPv4 Advanced MSF
   API and Protocol-Independent Advanced MSF API, are optional to
   implement in an LW-IGMPv3/LW-MLDv2 host."

Authors' Addresses







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   Godred Fairhurst
   University of Aberdeen
   School of Engineering
   Fraser Noble Building
   Fraser Noble Building Aberdeen  AB24 3UE
   UK

   Email: gorry@erg.abdn.ac.uk


   Tom Jones
   University of Aberdeen
   School of Engineering
   Fraser Noble Building
   Aberdeen  AB24 3UE
   UK

   Email: tom@erg.abdn.ac.uk

































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