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
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include Simplified BSD License text as described in Section 4.e of
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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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