Internet Engineering Task Force G. Fairhurst
Internet-Draft T. Jones
Intended status: Informational University of Aberdeen
Expires: November 12, 2017 May 11, 2017
Features of the User Datagram Protocol (UDP) and Lightweight UDP (UDP-
Lite) Transport Protocols
draft-ietf-taps-transports-usage-udp-01
Abstract
This is an informational document that describes the transport
protocol interface primitives provided by the User Datagram Protocol
(UDP) and the Lightweight User Datagram Protocol (UDP-Lite) transport
protocols. It identifies the datagram services exposed to
applications and how an application can configure and use the
features offered by the Internet datagram transport service. The
resulting road map to documentation may be of help to users of the
UDP and UDP-Lite protocols.
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 November 12, 2017.
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document authors. All rights reserved.
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to this document. Code Components extracted from this document must
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. UDP and UDP-Lite Primitives . . . . . . . . . . . . . . . . . 3
3.1. Primitives Provided by UDP . . . . . . . . . . . . . . . 4
3.1.1. Excluded Primitives . . . . . . . . . . . . . . . . . 10
3.2. Primitives Provided by UDP-Lite . . . . . . . . . . . . . 10
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Multicast Primitives . . . . . . . . . . . . . . . . 15
Appendix B. Revision Notes . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
This document presents defined interactions between transport
protocols and applications in the form of 'primitives' (function
calls) for the User Datagram Protocol (UDP) [RFC0768] and the
Lightweight User Datagram Protocol (UDP-Lite) [RFC3828]. In this
usage, the word application refers to any program built on the
datagram interface, and including tunnels and other upper layer
protocols that use UDP and UDP-LIte.
The de facto standard application programming interface (API) for
TCP/IP applications is the "socket" interface [POSIX]. An
application can use the recv() and send() POSIX functions as well as
the recvfrom() and sendto() and recvmsg() and sendmsg() functions.
The UDP and UDP-Lite sockets API differs from that for TCP in several
key ways. (Examples of usage of this API are provided in [STEVENS].)
Additional functions in the sockets API are provided by socket
options, examples include:
o SO_REUSEADDR specifies the rules for validating addresses supplied
to bind() should allow reuse of local addresses
o SO_REUSEPORT specifies that the rules for validating ports
supplied to bind() should allow reuse of a local port
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o IP_RECVTTL returns the IP Time To Live (TTL) field from IP header
of a received datagram.
Some platforms also offer applications the ability to directly
assemble and transmit IP packets through "raw sockets" or similar
facilities. The raw socket API is a second, more cumbersome method
of using UDP. The use of this API is discussed in the RFC series in
the UDP Guidelines [RFC8085].
The list of transport service features and primitives in this
document is strictly based on the parts of protocol specifications in
RFC-series that relate to what the transport protocol provides to an
application that uses it and how the application interacts with the
transport protocol. Primitives can be invoked by an application or a
transport protocol; the latter type is called an "event".
The description in the next section follows the methodology defined
by the IETF TAPS working group [I-D.ietf-taps-transports-usage].
Specifically, it provides the first pass of this process, which
discusses the relevant RFC text describing primitives for each
protocol.
The presented road map to documentation of the transport interface
may also help developers working with UDP and UDP-Lite.
2. Terminology
This 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. It uses common terminology defined in "Usage of
Transport Features Provided by IETF Transport Protocols"
[I-D.ietf-taps-transports-usage]. This document also refers to the
terminology of RFC 2119 [RFC2119], but does not itself define new
terms using this terminology.
3. UDP and UDP-Lite Primitives
This section 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 (in and how the
transport is used (based on abstract API descriptions, where they are
available).
This section describes unicast usage, but UDP and UDP-Lite also
support IPv4 broadcast and IPv4/IPv6 multicast [RFC8085]. Many
primitives also apply when the transports are used with IP broadcast
and multicast. Appendix Appendix A describes where to find
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documentation for network-layer primitives required to use UDP or
UDP-Lite with IP multicast.
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 RFC768 states that the user interface
to an application should be able to create receive, 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 has been defined for IPv6 [RFC2460], together with API extensions
for a Basic Socket Interface Extensions for IPv6 [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 the corresponding applicability statement [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., no handshake is performed by
the transport protocol 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. It does not impact the status of the remote
endpoint.
Neither UDP nor UDP-Lite provide congestion control, retransmission,
nor do they have support to optimise fragmentation and other
transport functions. This means that applications using UDP need to
provide additional functions on top of the UDP transport API
[RFC8085]. Some transport functions require 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
(e.g., control of the setting of the Don't Fragment (DF) flag on a
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transmitted IPv4 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 the path
maximum transmission size). This document includes such primitives.
Guidance on the use of the services provided by UDP is provided in
the UDP Guidelines [RFC8085]. This 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 endpoint 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 Internet Control
Message (ICMP) error messages are received for its transmissions
[RFC1122]."
The POSIX Base Specifications [POSIX] define an API that 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 when
a socket has flushed its buffers.
A callback-driven API to the network interface can be structured on
top of these calls. 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 sockets API. By combining UDP primitives
(CONNECT.UDP, SEND.UDP), a higher level API could offer a similar
service.
The following datagram primitives are specified:
CONNECT: The CONNECT primitive allows the association of source and
destination 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.
Two forms of usage may be identified for the CONNECT primitive:
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1. bind(): A bind operation sets the local port, either
implicitly, triggered by a "sendto" operation on an unbound,
unconnected socket using an ephemeral port. Or by an explicit
"bind" to use a configured or well-known port.
2. bind(); connect(): A bind operation that is 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 that causes 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 the 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. Connecting a
socket allows 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 the requirements of Internet hosts [RFC1122] states "When a UDP
datagram is received, its specific-destination address MUST be
passed up to the application layer."
CHECKSUM_ENABLED: The optional CHECKSUM primitive controls whether a
sender enables the UDP checksum when sending datagrams ( [RFC0768]
and [RFC6935] [RFC6936] [RFC8085]). When unset, this overrides
the default UDP behaviour, disabling the checksum on sending.
Section 4.1.3.4 of the requirements for Internet hosts [RFC1122]
states "An application MAY optionally be able to control whether a
UDP checksum will be generated, but it MUST default to
checksumming on."
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REQUIRE_CHECKSUM: The optional REQUIRE_CHECKSUM primitive determines
whether UDP datagrams received with a zero checksum are permitted
or discarded, UDP defaults to requiring checksums.
Section 4.1.3.4 of the requirements for Internet hosts [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 the specification for UDP-Lite
[RFC3828] requires that the checksum field is non-zero, and hence
the UDP-Lite API must discard all datagrams received with a zero
checksum.
SET_IP_OPTIONS: The SET_IP_OPTIONS primitive request the network-
layer to send a datagram with the specified IP options.
Section 4.1.3.2 of the requirements for Internet hosts[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 primitive retrieves the IP
options of a datagram recieved at the network-layer.
Section 4.1.3.2 of the requirements for Internet hosts[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 primitive allows the network-layer to fragment
packets using the Fragment Offset in IPv4 [RFC6864] and a host to
use Fragment Headers in IPv6 [RFC2460], IPv4 allows routers to
fragments packets. The SET_DF primitive sets the Don't Fragment
(DF) flag in the IPv4 packet header that carries a UDP datagram.
Although some specific applications rely on fragmentation support,
in general, a UDP application should implement a method that
avoids IP fragmentation (section 4 of [RFC8085]). NOTE: In many
other IETF transports (e.g., TCP) the transport provides the
support needed to use DF. However, when using UDP, the
application is responsible for the techniques needed to discover
the effective path maximum transmission unit (PMTU) allowed on the
network path, coordinating with the network layer. The acceptable
maximum packet size can be determined using Packetization-Layer-
Path MTU Discovery (PLPMTUD) [RFC4821] or Path MTU Discovery
[RFC1191] [RFC1981].
GET_INTERFACE_MTU: The GET_INTERFACE_MTU primitive retrieves a
network-layer value that indicates the largest non-fragmented IP
packet that may be sent from the configured interface. A UDP
endpoint can subtract the size of all network and transport
headers to determine the maximum size of non-fragmented UDP
payload. UDP applications should use this value as part of a
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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 PATH (specified
in Section 1 of [RFC1191]) is equivalent to the "effective MT for
sending" (specified in [RFC1122]). The specification of PLPMTUD
[RFC4821] states: "If PLPMTUD updates the MT for a particular
path, all Packetization Layer sessions that share the path
representation (as described in Section 5.2) SHOULD be notified to
make use of the new MT and make the required congestion control
adjustments." To determine an appropriate UDP payload size,
applications MUST subtract the size of the IP header (which
includes any IPv4 optional headers or IPv6 extension headers) as
well as the length of the UDP header (8 bytes) from the PMTU size.
SET_TTL: The SET_TTL primitive sets the hop limit (TTL field) in the
network-layer that is used in the 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 the requirements for
Internet hosts [RFC1122] states an "incoming Time Exceeded message
MUST be passed to the transport layer".
GET_TTL: The GET_TTL primitive retrieves the value of the TTL field
in a network packet received at the network-layer.
Section 3.2.2.4 of the requirements for Internet hosts [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 primitive sets the
network-layer hop limit field in an IPv6 packet header [RFC2460]
carrying 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 primitive is a
network-layer function that reads the hop count in the IPv6 header
[RFC2460] 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 primitive is a network-layer function that
sets the Differentiated Services (diffserv) Code Point, DSCP, (or
the legacy Type of Service, ToS) value [RFC2474] to be used in the
field of an IP header of a packet that carries a UDP datagram.
Section 2.4 of the requirements for Internet hosts[RFC1123] states
that "Applications MUST select appropriate ToS values when they
invoke transport layer services, and these values MUST be
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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". The Differentiated Services (diffuser)
model [RFC2475] [RFC3260] replaces this field in the IP Header
assigning the six most significant bits to carry the
Differentiated Services Code Point (DSCP) field [RFC2474].
Preserving the intention of the hist requirements [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 the UDP Guidelines
[RFC8085] describes the way UDP applications should use this
field. Normally a UDP socket will assign a single DSCP value to
all datagrams in a flow, but a sender is allowed to use different
DSCP values for datagrams within the same flow in certain
cases[RFC8085]. There are guidelines for WebRTC that illustrate
this use [RFC7657].
SET_ECN: The SET_ECN primitive is a network-layer function that sets
the ECN field in the IP Header of a UDP datagram. The ECN field
defaults to a value of 00. When the use of the ToS field was
redefined by diffserv [RFC3260], 2 bits of the field were assigned
to support Explicit Congestion Notification (ECN) [RFC3168].
Section 3.1.5 of the UDP Guidelines [RFC8085] 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 or higher layer
protocol is itself responsible for the techniques needed to use
ECN.
GET_ECN: The GET_ECN primitive 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 of the UDP Guidelines [RFC8085]
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 the host requirements [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 MT Discovery [RFC1191] [RFC1981].
UDP applications must perform a CONNECT to receive ICMP errors.
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CLOSE: The close primitive closes a connection. No further
datagrams can be sent or received. Since UDP is itself
connectionless, no datagrams are sent when this primitive is
executed.
3.1.1. Excluded Primitives
Section 3.4 of the host requirements [RFC1122] also describes
"GET_MAXSIZES, 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 the basic socket
interface for IPv6 [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.
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) [RFC5097] further defines the checksum coverage method.
Guidance on the use of services provided by UDP-Lite is provided in
the UDP Guidelines [RFC8085].
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:
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SET_CHECKSUM_COVERAGE: The SET_CHECKSUM_COVERAGE primitive 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 the UDP-Lite MIB [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 primitive sets the minimum
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 the UDP-Lite MIB [RFC5097]
describes the corresponding MIB entry as
udpliteEndpointMinCoverage). Section 3.3 of the UDP-Lite
specification [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".
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 and Aaron Falk.
5. IANA Considerations
This memo includes no request to IANA.
The authors request the section to 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
provided in the UDP-Guidelines [RFC8085].
7. References
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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.
[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>.
[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123,
DOI 10.17487/RFC1123, October 1989,
<http://www.rfc-editor.org/info/rfc1123>.
[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>.
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[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>.
[RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field",
RFC 6864, DOI 10.17487/RFC6864, February 2013,
<http://www.rfc-editor.org/info/rfc6864>.
[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>.
[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>.
[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <http://www.rfc-editor.org/info/rfc8085>.
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>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<http://www.rfc-editor.org/info/rfc2474>.
[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>.
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[RFC3260] Grossman, D., "New Terminology and Clarifications for
Diffserv", RFC 3260, DOI 10.17487/RFC3260, April 2002,
<http://www.rfc-editor.org/info/rfc3260>.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, DOI 10.17487/RFC3376, October 2002,
<http://www.rfc-editor.org/info/rfc3376>.
[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>.
[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<http://www.rfc-editor.org/info/rfc3810>.
[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>.
[RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet
Group Management Protocol Version 3 (IGMPv3) and Multicast
Listener Discovery Protocol Version 2 (MLDv2) for Source-
Specific Multicast", RFC 4604, DOI 10.17487/RFC4604,
August 2006, <http://www.rfc-editor.org/info/rfc4604>.
[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>.
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[RFC6633] Gont, F., "Deprecation of ICMP Source Quench Messages",
RFC 6633, DOI 10.17487/RFC6633, May 2012,
<http://www.rfc-editor.org/info/rfc6633>.
[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. Multicast Primitives
This appendix describes primitives that are used when UDP and UDP-
Lite support IPv4/IPv6 Multicast. Guidance on the use of UDP and
UDP-Lite for multicast services is provided in the UDP
Guidelines[RFC8085].
IP multicast may be supported using the Any Source Multicast (ASM)
model or by the Source-Specific Multicast (SSM) model. The latter
requires use of a Multicast Source Filter (MSF) when specifying an IP
multicast group destination address.
Use of multicast requires additional primitives at the transport API
that need to be called to coordinate operation of the IPv4 and IPv6
network layer protocols. For example, to receive datagrams sent to a
group, an endpoint must first become a member of a multicast group at
the network layer. Local multicast reception is signalled for IPv4
by the Internet Group Management Protocol (IGMP) [RFC3376] [RFC4604].
IPv6 uses the equivalent Multicast Listener Discovery (MLD) protocol
[RFC3810] [RFC5790], carried over ICMPv6. A lightweight version of
these protocols has also been specified [RFC5790].
The following are defined:
JoinLocalGroup: 1 of the basic socket extensions for IPv6 [RFC3493]
provides a function that allows receivi9ng traffic from a local
IPv4 multicast group.
IPV6_MULTICAST_IF: Section 5.2 of the basic socket extensions for
IPv6 [RFC2553] states that this sets the interface that will be
used for outgoing multicast packets.
IP_MULTICAST_TTL: This sets the time to live field t to use for
outgoing IPv4 multicast packets. This is used to limit scope of
multicast datagrams. Methods such as GTSM [RFC5082], set this
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value to ensure link-local transmission. GTSM also requires the
UDP receiver API to pass the received value of this field to the
application.
IPV6_MULTICAST_HOPS: Section 5.2 of the basic socket extensions for
IPv6 [RFC2553] states that sets the hop count to use for outgoing
multicast IPv6 packets. (This is equivalent to IP_MULTICAST_TTL
used for IPv4 multicast).
IPV6_MULTICAST_LOOP: Section 5.2 of the basic socket extensions for
IPv6 [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 the basic socket extensions for IPv6
[RFC2553] provides a function that allows an endpoint to join an
IPv6 multicast group.
SIOCGIPMSFILTER: Section 8.1 of the socket interface for MSF
[RFC3678] provides a function that allows reading the multicast
source filters.
SIOCSIPMSFILTER: Section 8.1 of the socket interface for MSF
[RFC3678] provides a function that allows setting/modifying the
multicast source filters.
IPV6_LEAVE_GROUP: Section 5.2 of the basic socket extensions for
IPv6 [RFC2553] provides a function that allows leaving an IPv6
multicast group.
LeaveHostGroup: Section 7.1 of the basic socket extensions for IPv6
[RFC3493] provides a function that allows leaving an IPv4
multicast group.
LeaveLocalGroup: Section 7.1 of the basic socket extensions for IPv6
[RFC3493] provides a function that allows leaving a local IPv4
multicast group.
Section 4.1.1 of the Socket Interface Extensions for MSF [RFC3678]
updates the multicast interface to add support for MSF for IPv4 and
IPv6 required by IGMPv3. Three sets of API functionality are
defined:
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."
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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 MSF can block data from a given multicast
source to a given ASM or SSM group.
IP_UNBLOCK_SOURCE: This updates an MSF to undo a previous call to
IP_UNBLOCK_SOURCE for an ASM or SSM group.
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 the socket interface for MSF [RFC3678] updates the
interface to add IPv4 MSF support to IGMPv3 using ASM:
IP_ADD_SOURCE_MEMBERSHIP: This is used to join an SSM group.
IP_DROP_SOURCE_MEMBERSHIP: This is used to leave an SSM group.
Section 4.1.2 of the socket interface for MSF [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 the socket interface for MSF [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.
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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 an ASM or SSM group.
Section 5.2 of the socket interface for MSF [RFC3678] specifies the
Protocol-Independent Advanced MSF (Full-state) API applicable for
both IPv4 and IPv6:
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.
The Lightweight IGMPv3 (LW_IGMPv3) and MLDv2 protocol [RFC5790]
updates this interface (in Section 7.2 of RFC5790).
Appendix B. 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.
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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.
o Fixed Typos.
TAPS WG draft -00:
o Expected to progress with draft-ietf-taps-transports-usage of the
TAPS WG.
TAPS WG draft -01:
o No intentional changes were made to the specification of
primitives, this update is editorial
o Reorganised text to eliminate the appendices.
o Editorial changes were make to complete the document for a WGLC.
o Rephrasing to eliminate using references as nouns, and to make
text more consistent.
o One appendix was incorporated.
o This appendix was moved to the end (for later deletion by the RFC-
Ed).
Authors' Addresses
Godred Fairhurst
University of Aberdeen
School of Engineering
Fraser Noble Building
Fraser Noble Building Aberdeen AB24 3UE
UK
Email: gorry@erg.abdn.ac.uk
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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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