Internet
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... requirements for host system implementations of the Internet protocol
suite. This RFC covers the communication protocol layers: link
layer, IP layer, and transport layer ...
... transport layer. Its companion RFC,
"Requirements for Internet Hosts -- Application and Support"
[INTRO:1 ...
... vendors,
implementors, and users of Internet communication software. They
represent the consensus of a large body of technical experience and
wisdom, contributed by the members of the Internet ...
... Internet communication software. They
represent the consensus of a large body of technical experience and
wisdom, contributed by the members of the Internet research and
vendor communities.
...
... This RFC enumerates standard protocols that a host connected to the
Internet must use, and it incorporates by reference the RFCs and
other documents describing the current specifications for these
protocols. It corrects errors in the referenced documents and adds
...
... incomplete by itself; the complete set of requirements for an
Internet host is primarily defined in the standard protocol
specification documents, with the corrections, amendments, and
...
... A good-faith implementation of the protocols that was produced after
careful reading of the RFC's and with some interaction with the
Internet technical community, and that followed good communications
software engineering practices, should differ from the requirements ...
... the general goal of arbitrary host interoperation across the
diversity and complexity of the Internet system. Although most
current implementations fail to meet these requirements in various
...
...
These requirements are based on the current level of Internet
architecture. This document will be updated as required to provide
additional clarifications or to include additional information in
those areas in which specifications are still evolving.
...
...
This introductory section begins with a brief overview of the
Internet architecture as it relates to hosts, and then gives some
general advice to host ...
... The Internet Architecture ...
...
General background and discussion on the Internet architecture and
supporting protocol suite can be found in the DDN Protocol
Handbook [INTRO:3 ...
... INTRO:11]. Reference [INTRO:5] describes the
procedure for obtaining Internet protocol documents, while
[INTRO:6] contains a list of the numbers assigned within Internet
protocols ...
... Internet protocol documents, while
[INTRO:6] contains a list of the numbers assigned within Internet
protocols.
...
... programs on behalf of user(s), employing network and/or
Internet communication services in support of this function.
An Internet ...
... Internet communication services in support of this function.
An Internet host corresponds to the concept of an "End-System"
used in the OSI ...
...
An Internet communication system consists of interconnected
packet networks supporting communication among host ...
... networks supporting communication among host computers
using the Internet protocols. The networks are interconnected
using packet-switching computers called "gateways ...
... using packet-switching computers called "gateways" or "IP
routers" by the Internet community, and "Intermediate Systems"
by the OSI world [INTRO:13 ...
... Gateways" [INTRO:2] contains the official
specifications for Internet gateways. That RFC together with
the present document and its companion [INTRO:1 ...
... the present document and its companion [INTRO:1] define the
rules for the current realization of the Internet architecture.
...
...
The current Internet architecture is based on a set of
assumptions about the communication system. The assumptions
most relevant to hosts ...
... network(s); its connection to the Internet is only
conceptual. Two hosts on the same network ...
... objective is to insulate host software from changes caused
by the inevitable evolution of the Internet routing
architecture ...
... network variation.
A basic objective of the Internet design is to tolerate a
wide range of network characteristics -- e.g., bandwidth ...
... bandwidth is still available. Finally, the goal is full
"open system interconnection": an Internet host must be
able to interoperate robustly and effectively with any
...
... host must be
able to interoperate robustly and effectively with any
other Internet host, across diverse Internet paths.
...
... ambitious goals. For example, the LAN environment is
typically much more benign than the Internet as a whole;
LANs have low packet loss ...
... for long; they are soon gatewayed to each other, to
organization-wide internets, and eventually to the global
Internet system. In the end, neither the customer nor the
vendor ...
... The requirements spelled out in this document are designed
for a full-function Internet host, capable of full
interoperation over an arbitrary Internet ...
... Internet Protocol Suite ...
...
To communicate using the Internet system, a host must implement
the layered set of protocols comprising the Internet protocol
suite ...
... Internet system, a host must implement
the layered set of protocols comprising the Internet protocol
suite. A host typically must implement at least one protocol
from each layer ...
...
The protocol layers used in the Internet architecture are as
follows [INTRO:4]:
...
... The application layer is the top layer of the Internet
protocol suite. The Internet suite does not further
subdivide the application layer ...
... application layer is the top layer of the Internet
protocol suite. The Internet suite does not further
subdivide the application layer, although some of the
...
... subdivide the application layer, although some of the
Internet application layer protocols do contain some
internal sub-layering. The application layer ...
... internal sub-layering. The application layer of the
Internet suite essentially combines the functions of the
top two layers -- Presentation and Application -- of the
OSI ...
...
The most common Internet user protocols are:
...
... Other transport protocols have been developed by the
research community, and the set of official Internet
transport protocols may be expanded in the future.
...
... All Internet transport protocols use the Internet Protocol
(IP) to carry data from source host ...
... IP protocol
is a fundamental and characteristic feature of the
Internet architecture. Internet IP was the model for the
...
... is a fundamental and characteristic feature of the
Internet architecture. Internet IP was the model for the
OSI ...
...
There are varying opinions in the Internet community about
embedded gateway functionality. The main arguments are as
...
... Gateway algorithms and protocols are still changing,
and they will continue to change as the Internet system
grows larger. Attempting to include a general gateway
...
...
There are two important lessons that vendors of Internet host
software have learned and which a new vendor ...
... Continuing Internet Evolution ...
...
The enormous growth of the Internet has revealed problems of
management and scaling in a large datagram ...
... persist for some years. A vendor who develops computer
communication software for the Internet protocol suite (or any
other protocol suite!) and then fails to maintain and update
...
... that software for changing specifications is going to leave a
trail of unhappy customers. The Internet is a large
communication network, and the users are in constant contact
...
... deficiencies in vendor software propagates quickly through the
Internet technical community.
...
... designed to have the worst possible effect. This assumption
will lead to suitable protective design, although the most
serious problems in the Internet have been caused by
unenvisaged mechanisms triggered by low-probability events;
mere human malice would never have taken so devious a course!
...
...
Adaptability to change must be designed into all levels of
Internet host software. As a simple example, consider a
protocol specification ...
... systems, each implementing many protocols and protocol layers,
and some of these contain bugs and mis-features in their
Internet protocol software. As a result of complexity,
diversity, and distribution of function, the diagnosis of
Internet ...
... Internet protocol software. As a result of complexity,
diversity, and distribution of function, the diagnosis of
Internet problems is often very difficult.
...
...
It would be ideal if a host implementation of the Internet
protocol suite could be entirely self-configuring. This would
allow the whole suite to be implemented in ROM or cast into
silicon, it would simplify diskless workstations, and it would
...
... with obsolete or incorrect implementations of the protocols,
distributed without sources, that unfortunately persist in many
parts of the Internet. To make correct systems coexist with
these faulty systems, administrators often have to "mis-
...
... some cases. The choice of default is a sensitive issue when
the configuration item controls the accommodation to existing
faulty systems. If the Internet is to converge successfully to
complete interoperability, the default values ...
... by application protocol data. To be transmitted end-to-
end through the Internet, a message must be encapsulated
inside a datagram ...
... A packet is the unit of data passed across the interface
between the internet layer and the link layer. It
...
... This document incorporates contributions and comments from a large
group of Internet protocol experts, including representatives of
university and research labs, vendors, and government agencies.
...
... Higher-layer Advice -- Provide a call from the
Internet layer to the link layer to indicate a
...
... "ADVISE_DELIVPROB()" call from the transport layer
to the Internet layer (see Section 3.4), and in
fact the ADVISE_DELIVPROB routine might in turn
...
... SNAP") which can be used to hold the Ether-Type field.
An Internet system MUST NOT send 802 packets using K1=6.
...
...
Address translation from Internet addresses to link-layer
addresses on Ethernet and IEEE 802 networks ...
... INTERNET LAYER PROTOCOLS ...
... Robustness Principle: "Be liberal in what you accept, and
conservative in what you send" is particularly important in the
Internet layer, where one misbehaving host can deny Internet
service ...
... RFC-1112std5 [IP:4] defines the Internet Group Management
Protocol IGMP, as part of a recommended extension to hosts
...
... IP multicast may be an arbitrary group of
Internet hosts. IP multicasting is designed as a natural
...
... expect that IP layer functions may increase somewhat in the
future, as further Internet control and management facilities are
developed.
...
... Multihoming introduces considerable confusion and complexity into
the protocol suite, and it is an area in which the Internet
architecture falls seriously short of solving all problems. There
are two distinct problem areas in multihoming:
...
... Internet Protocol -- IP ...
... permanent or transient. Permanent multicast addresses are
allocated by the Internet Assigned Number Authority
[INTRO:6], while transient addresses ...
...
The Internet model requires that every host support
reassembly. See Sections 3.3.2 and 3.3.3 for the
...
...
Some Internet protocol experts have maintained that
when a host sends an identical copy of an earlier
...
... However, the observed patterns of datagram loss in the
Internet do not favor the probability of retransmitted
fragments filling reassembly gaps, while other
...
... The Precedence field is intended for Department of Defense
applications of the Internet protocols. The use of non-zero
values in this field is outside the scope of this document
...
... order to implement an "expanding scope" search for some
Internet resource. This is used by some diagnostic
tools, and is expected to be useful for locating the
...
...
A fixed value must be at least big enough for the
Internet "diameter," i.e., the longest possible path.
A reasonable value is about twice the diameter ...
... timestamp in a
Timestamp option whose Internet address fields are
not pre-specified or whose first pre-specified
address ...
... Internet Control Message Protocol -- ICMP ...
...
Every ICMP error message includes the Internet header and at
least the first 8 data octets of the datagram ...
... conjunction with a multicast routing protocol, to support IP
multicasting across the Internet.
...
... route cache entry defines the endpoints of an
Internet path. Although the connecting path may change
dynamically in an arbitrary way, the transmission
characteristics of the path tend to remain
...
... destination address to be used as a pure 32-bit
number, which may allow the Internet architecture
to be more easily extended in the future without
any change to the hosts ...
... To avoid pinging, the layers above and/or below the
Internet layer SHOULD be able to give "advice" on the
status of route cache ...
... discarded unnecessarily, and communication may fail. The
timeout needs to be at least as large as the typical
maximum delay across the Internet. A realistic minimum
reassembly timeout would be 60 seconds.
...
...
Since nearly all networks in the Internet currently
support an MTU of 576 or greater, we strongly recommend
...
... entity") has no address of its own, but instead
uses a single Internet Protocol (IP) address. This has
...
... With respect to (A), proponents of the Strong ES
model note that automatic Internet routing
mechanisms could not route ...
...
(a) If the remote Internet address lies on one of the
(sub-) nets to which the host is directly
...
... Applications are urged to make use of these mechanisms where
applicable, even when the mechanisms are not currently
effective in the Internet (e.g., TOS). This will allow these
mechanisms to be immediately useful when they do become
...
... For an ICMP error message, the data that is passed up MUST
include the original Internet header plus all the octets of
the original message that are included in the ICMP message ...
... virtual-circuit transport protocol for the Internet suite. TCP
provides reliable, in-sequence delivery ...
... ports, used to access services that are
standardized across the Internet. The remainder of the
port space can be freely allocated to application
...
... IP layer the task of
determining a suitable MTU for the Internet path. We
therefore recommend that TCP always send the option (if
...
... segments that contain one
data octet each, which makes very inefficient use of
the Internet and contributes to Internet congestion.
...
... data octet each, which makes very inefficient use of
the Internet and contributes to Internet congestion.
The Nagle Algorithm ...
... threshold is chosen to compensate for the maximum
likely segment reordering in the Internet. There is
not yet enough experience with the fast retransmit
algorithm to determine how useful it is.
...
... TCP data segments can
increase efficiency in both the Internet and the hosts by
sending fewer than one ACK ...
... TCP
indicates some failure of the remote host or the Internet
path. This failure may be of short or long duration. The
following procedure MUST be used to handle excessive
...
...
Some Internet paths have significant setup times, and
the number of such paths is likely to increase in the
future.
...
... because it could: (1) cause perfectly good connections
to break during transient Internet failures; (2)
consume unnecessary bandwidth ("if no one is using the
...
... connection, who cares if it is still good?"); and (3)
cost money for an Internet path that charges for
packets.
...
... "Requirements for Internet Gateways," R. Braden and J. Postel, RFC-1009hist(-> 1812prop), June 1987. ...
... "Official Internet Protocols," J. Reynolds and J. Postel, RFC-1011, May 1987.
This document is republished periodically with new RFC ...
This document is republished periodically with new RFC ...
... "The ARPA Internet Protocol," J. Postel, C. Sunshine, and D. Cohen, Computer Networks, Vol. 5, No. 4, July 1981. ...
... "The DARPA Internet Protocol Suite," B. Leiner, J. Postel, R. Cole and D. Mills, Proceedings INFOCOM 85, IEEE, Washington DC, March 1985. Also in: IEEE ...
... 1042std43, February 1988.
This RFC contains a great deal of information of importance to Internet implementers planning to use IEEE 802 networks. ...
This RFC contains a great deal of information of importance to Internet implementers planning to use IEEE 802 networks. ...
... Defense, August 1983.
This specification, as amended by RFC-963, is intended to describe the Internet Protocol but has some serious omissions (e.g., the mandatory subnet extension [IP:3] and the optional multicasting ...
This specification, as amended by RFC-963, is intended to describe the Internet Protocol but has some serious omissions (e.g., the mandatory subnet extension [IP:3] and the optional multicasting ...
... "Some Problems with the Specification of the Military Standard Internet Protocol," D. Sidhu, RFC-963, November 1985. ...
... Fragmentation Considered Harmful," C. Kent and J. Mogul, ACM SIGCOMM-87, August 1987. Published as ACM Comp Comm Review, Vol. 17, no. 5.
This useful paper discusses the problems created by Internet fragmentation and presents alternative solutions. ...
This useful paper discusses the problems created by Internet fragmentation and presents alternative solutions. ...
... "Computing the Internet Checksum," R. Braden, D. Borman, and C. Partridge, RFC-1071, September 1988. ...
...
The Internet architecture generally provides little protection
against spoofing of IP source addresses ...
... LAN whose gateway to the rest of the
Internet discarded any incoming datagram with a source address that
...