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Internet
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...
The Internet Protocol is designed for use in interconnected systems of
packet-switched computer communication networks. Such a system has
...
... networks. Such a system has
been called a "catenet" [1]. The internet protocol provides for
transmitting blocks of data called datagrams ...
... hosts identified by
fixed length addresses. The internet protocol also provides for
fragmentation and reassembly of long datagrams ...
...
The internet protocol is specifically limited in scope to provide the
functions necessary to deliver a package of bits (an internet ...
... internet protocol is specifically limited in scope to provide the
functions necessary to deliver a package of bits (an internet
datagram) from a source to a destination ...
... services commonly
found in host-to-host protocols. The internet protocol can capitalize
on the services of its supporting networks ...
...
This protocol is called on by host-to-host protocols in an internet
environment. This protocol calls on local network protocols to carry
the internet ...
... internet
environment. This protocol calls on local network protocols to carry
the internet datagram to the next gateway or destination host ...
... TCP header and user data) as the data
portion of an internet datagram. The TCP module would provide the
...
... TCP module would provide the
addresses and other parameters in the internet header to the internet
...
... addresses and other parameters in the internet header to the internet
module as arguments of the call. The internet module would then
...
... header to the internet
module as arguments of the call. The internet module would then
create an internet ...
... internet module would then
create an internet datagram and call on the local network interface to
...
...
In the ARPANET case, for example, the internet module would call on a
local net module which would add the 1822 leader [2] to the internet ...
... internet module would call on a
local net module which would add the 1822 leader [2] to the internet
datagram creating an ARPANET ...
... ARPANET address would be derived from the internet address by the
local network interface and would be the address ...
... header to fragment and
reassemble internet datagrams when necessary for transmission through
"small packet" networks ...
... internet module resides in each host
engaged in internet communication and in each gateway that
interconnects networks ...
... interpreting address fields and for fragmenting and assembling
internet datagrams. In addition, these modules (especially in
gateways ...
... datagram as an independent
entity unrelated to any other internet datagram. There are no
connections ...
... service choices provided in the
networks that make up the internet. This type of service indication
is to be used by gateways ...
... Time to Live is an indication of an upper bound on the lifetime of
an internet datagram. It is set by the sender of the datagram ...
... route where it is processed. If the
time to live reaches zero before the internet datagram reaches its
destination ...
... Header Checksum provides a verification that the information used
in processing internet datagram has been transmitted correctly. The
data may contain errors. If the header checksum ...
... datagram has been transmitted correctly. The
data may contain errors. If the header checksum fails, the internet
datagram is discarded at once by the entity ...
...
The internet protocol does not provide a reliable communication
facility. There are no acknowledgments either end-to-end or
...
...
Errors detected may be reported via the Internet Control Message
Protocol (ICMP) [3] which is implemented in the internet protocol ...
... Internet Control Message
Protocol (ICMP) [3] which is implemented in the internet protocol
module.
...
...
The following diagram illustrates the place of the internet protocol
in the protocol hierarchy:
...
... | | |
+--------------------------+----+
| Internet Protocol & ICMP |
+--------------------------+----+
...
...
The sending application program prepares its data and calls on its
local internet module to send that data as a datagram and passes the
destination address ...
... datagram header and attaches the data
to it. The internet module determines a local network address for
...
... header, and
turns the datagram over to the internet module. The internet module
determines from the internet address ...
... turns the datagram over to the internet module. The internet module
determines from the internet address that the datagram ...
... internet module. The internet module
determines from the internet address that the datagram is to be
forwarded to another host ...
... forwarded to another host in a second network. The internet module
determines a local net address for the destination host ...
...
The function or purpose of Internet Protocol is to move datagrams
through an interconnected set of networks ...
... networks. This is done by passing
the datagrams from one internet module to another until the
destination is reached. The internet ...
... internet module to another until the
destination is reached. The internet modules reside in hosts and
gateways ...
... internet system. The datagrams are routed from one
internet module to another through individual networks based on the
interpretation of an internet address ...
... internet module to another through individual networks based on the
interpretation of an internet address. Thus, one important mechanism
of the internet protocol is the internet address ...
... interpretation of an internet address. Thus, one important mechanism
of the internet protocol is the internet address.
...
... internet address. Thus, one important mechanism
of the internet protocol is the internet address.
...
...
In the routing of messages from one internet module to another,
datagrams may need to traverse a network ...
... datagram. To overcome this difficulty, a
fragmentation mechanism is provided in the internet protocol.
...
... address indicates where it is. A
route indicates how to get there. The internet protocol deals
primarily with addresses. It is the task of higher level (i.e.,
...
... host-to-host or application) protocols to make the mapping from
names to addresses. The internet module maps internet addresses to
local net addresses ...
... names to addresses. The internet module maps internet addresses to
local net addresses. It is the task of lower level (i.e., local net
...
... local address (called the
"rest" field). There are three formats or classes of internet
addresses: in class a, the high order bit is zero, the next 7 bits ...
... several distinct hosts to the extent of using several distinct
internet addresses. Some hosts will also have several physical
interfaces (multi-homing ...
... host to have several physical
interfaces to the network with each having several logical internet
addresses.
...
...
Fragmentation of an internet datagram is necessary when it
originates in a local net that allows a large packet ...
... internet datagram can be marked "don't fragment." Any internet
datagram so marked is not to be internet ...
... internet
datagram so marked is not to be internet fragmented under any
circumstances. If internet datagram ...
... datagram so marked is not to be internet fragmented under any
circumstances. If internet datagram marked don't fragment cannot be
...
... Fragmentation, transmission and reassembly across a local network
which is invisible to the internet protocol module is called
intranet fragmentation ...
... datagram from those of another. The originating protocol module of
an internet datagram sets the identification field to a value that
must be unique for that source-destination ...
... time the datagram will be active in the internet system. The
originating protocol module of a complete datagram sets the
...
... fragment a long internet datagram, an internet protocol module
(for example, in a gateway), creates ...
... (for example, in a gateway), creates two new internet datagrams and
copies the contents of the internet ...
... internet datagrams and
copies the contents of the internet header fields from the long
datagram ...
... header fields from the long
datagram into both new internet headers. The data of the long
datagram ...
... first portion NFB (for Number of Fragment Blocks). The first
portion of the data is placed in the first new internet datagram,
and the total length field is set to the length of the first
...
... datagram. The more-fragments flag is set to one. The second
portion of the data is placed in the second new internet datagram,
and the total length field is set to the length of the second
...
... datagram. The fragment offset field of the second new internet
datagram is set to the value of that field in the long datagram ...
...
To assemble the fragments of an internet datagram, an internet
protocol module (for example at a destination host ...
... fragments of an internet datagram, an internet
protocol module (for example at a destination host) combines
internet ...
... internet
protocol module (for example at a destination host) combines
internet datagrams that all have the same value for the four fields:
identification, source, destination ...
... fragment offset in that fragment's
internet header. The first fragment will have the fragment ...
...
+-------------------------------+
| Internet Protocol & ICMP & GGP|
+-------------------------------+
...
... Internet Header Format ...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Example Internet Datagram Header
...
...
The Version field indicates the format of the internet header. This
document describes version 4 ...
... type of service is used to specify the treatment of the datagram
during its transmission through the internet system. Example
mappings of the internet type of service ...
... during its transmission through the internet system. Example
mappings of the internet type of service to the actual service
...
... Total Length is the length of the datagram, measured in octets,
including internet header and data. This field allows the length of
a datagram ...
... header
octets to fit in a datagram. The maximal internet header is 60
octets, and a typical internet ...
... This field indicates the maximum time the datagram is allowed to
remain in the internet system. If this field contains the value
zero, then the datagram must be destroyed. This field is modified
...
... zero, then the datagram must be destroyed. This field is modified
in internet header processing. The time is measured in units of
seconds, but since every module that processes a datagram ...
...
This field indicates the next level protocol used in the data
portion of the internet datagram. The values for various protocols
are specified in "Assigned Numbers" [9 ...
... (e.g., time to live), this is recomputed and verified at each point
that the internet header is processed.
...
... 3 = reserved for future use
The following internet options are defined:
CLASS NUMBER ...
...
This option indicates the end of the option list. This might
not coincide with the end of the internet header according to
the internet ...
... internet header according to
the internet header length. This is used at the end of all
options, not the end of each option, and need only be used if
...
... options, not the end of each option, and need only be used if
the end of the options would not otherwise coincide with the end
of the internet header.
...
... loose source and record route (LSRR) option provides a means
for the source of an internet datagram to supply routing
information to be used by the gateways ...
...
A route data is composed of a series of internet addresses.
Each internet address is 32 bits ...
... route data is composed of a series of internet addresses.
Each internet address is 32 bits or 4 octets. If the pointer is
...
... The recorded route address is the internet module's own internet
address as known in the environment into which this datagram is
...
... route address is the internet module's own internet
address as known in the environment into which this datagram is
being forwarded.
...
... as a whole) remains a constant length as the datagram progresses
through the internet.
This option is a loose source route ...
... strict source and record route (SSRR) option provides a
means for the source of an internet datagram to supply routing
information to be used by the gateways ...
...
A route data is composed of a series of internet addresses.
Each internet address is 32 bits ...
... route data is composed of a series of internet addresses.
Each internet address is 32 bits or 4 octets. If the pointer is
...
... The recorded route address is the internet module's own internet
address as known in the environment into which this datagram is
...
... route address is the internet module's own internet
address as known in the environment into which this datagram is
being forwarded.
...
... as a whole) remains a constant length as the datagram progresses
through the internet.
This option is a strict source route ...
...
A recorded route is composed of a series of internet addresses.
Each internet address is 32 bits ...
... route is composed of a series of internet addresses.
Each internet address is 32 bits or 4 octets. If the pointer is
...
... route data area must be zero.
When an internet module routes a datagram it checks to see if
the record route ...
... the record route option is present. If it is, it inserts its
own internet address as known in the environment into which this
datagram is being forwarded into the recorded route ...
... |01000100| length | pointer|oflw|flg|
+--------+--------+--------+--------+
| internet address |
+--------+--------+--------+--------+
| timestamp ...
... timestamp if it matches its own
address with the next specified internet address.
The Timestamp ...
... timestamps. The intitial contents of the timestamp data area
must be zero or internet address/zero pairs.
If the timestamp ...
... gateways, with reassembly taking place
at the destination internet protocol module in the destination host.
Of course, fragmentation ...
... gateways of a network is also
allowed since this is transparent to the internet protocols and the
higher-level protocols. This transparent type of fragmentation and
...
... single physical host to act as several distinct internet hosts.
That is, there must be a mapping between internet ...
... network/host interfaces that allows several internet addresses to
correspond to one interface. It must also be allowed for a host ...
...
The internet identification field (ID) is used together with the
source and destination address, and the protocol fields ...
... MF = 0, fragment offset =
0). If an internet datagram is fragmented, its data portion must be
...
...
Every internet module must be able to forward a datagram of 68
octets without further fragmentation ...
... datagram of 68
octets without further fragmentation. This is because an internet
header may be up to 60 octets, and the minimum fragment ...
... To produce the first fragment:
(1) Copy the original internet header;
(2) OIHL <- IHL; OTL <- TL; OFO <- FO ...
... To produce the second fragment:
(7) Selectively copy the internet header (some options
are not copied, see option definitions);
...
... The type of service (TOS) is for internet service quality selection.
The type of service is specified along the abstract parameters
...
... service parameter). The uncontrolled messages tend
to be less reliably delivered and suffer less delay. Suppose an
internet datagram is to be sent through the ARPANET. Let the
...
... priority bit on since
the Internet precedence is in the upper half of its range, to select
standard messages since the throughput ...
... sender to the maximum time the
datagram is allowed to be in the internet system. If the datagram
is in the internet ...
... internet system. If the datagram
is in the internet system longer than the time to live, then the
datagram ...
...
This field must be decreased at each point that the internet header
is processed to reflect the time spent processing the datagram ...
... implementations. That is, the presence or absence of an option is
the choice of the sender, but each internet module must be able to
parse every option. There can be several options present in the
option field.
...
...
The options might not end on a 32-bit boundary. The internet header
must be filled out with octets of zeros. The first of these would
...
... must be filled out with octets of zeros. The first of these would
be interpreted as the end-of-options option, and the remainder as
internet header padding.
...
...
Every internet module must be able to act on every option. The
Security Option is required if classified, restricted, or
...
... The internet header checksum is recomputed if the internet header is
changed. For example, a reduction of the time to live ...
... changed. For example, a reduction of the time to live, additions or
changes to internet options, or due to fragmentation. This checksum
...
... fragmentation. This checksum
at the internet level is intended to protect the internet header
fields from transmission errors.
...
... checksum
at the internet level is intended to protect the internet header
fields from transmission errors.
...
... bit errors are
acceptable while retransmission delays are not. If the internet
protocol enforced data correctness such applications could not be
supported.
...
... program (or even a gateway program) will be called the "user" since it
is using the internet module. Since internet protocol is a datagram
...
... gateway program) will be called the "user" since it
is using the internet module. Since internet protocol is a datagram
protocol, there is minimal memory or state ...
... state maintained between datagram
transmissions, and each call on the internet protocol module by the
user supplies all information necessary for the IP to perform the
...
... The following two example calls satisfy the requirements for the user
to internet protocol module communication ("=>" means returns):
...
... datagram, it executes the SEND call supplying
all the arguments. The internet protocol module, on receiving this
call, checks the arguments and prepares and sends the message. If the
...
...
When a datagram arrives at the internet protocol module from the local
network, either there is a pending RECV call from the user addressed
...
... physical connections or logical
addresses). The internet module must check to see that the source
address is one of the legal address for this host ...
...
An implementation may also allow or require a call to the internet
module to indicate interest in or reserve exclusive use of a class of
...
... version 4 of internet protocol; the
internet header consists of five 32 bit words, and the total length of
...
...
In this example, we show first a moderate size internet datagram (452
data octets), then two internet ...
... internet datagram (452
data octets), then two internet fragments that might result from the
fragmentation ...
...
Internet Protocol
...
... An internet header field carrying various control flags. ...
... Internet Control Message Protocol, implemented in the internet
module, the ICMP is used from gateways ...
... Internet Address ...
... The unit of data exchanged between a pair of internet modules
(includes the internet header). ...
... host within a network. The actual mapping of
an internet local address on to the host addresses ...
... Fragment Blocks in a the data portion of an
internet fragment. That is, the length of a portion of data
measured in 8 octet ...
... The local address portion of an Internet Address. ...
... Transmission Control Protocol: A host-to-host protocol for
reliable communication in internet environments. ...
... internet header field which indicates the upper bound on
how long this internet datagram may exist. ...
... header field Total Length is the length of the
datagram in octets including internet header and data. ...
... The user of the internet protocol. This may be a higher level
protocol module, an application program, or a gateway program. ...
... Postel, J., "Internet Control Message Protocol - DARPA Internet Program Protocol Specification ...
... Postel, J., "Internet Control Message Protocol - DARPA Internet Program Protocol Specification," RFC 792std5, USC/Information Sciences Institute, September 1981. ...