As per Relevance of the word destination, we have this rfc below:
Request for Comments: 878
Obsoletes RFCs: 851, 802
The ARPANET 1822L Host Access
RFC 878
Andrew G.
ARPANET Mail: malis@bbn-
BBN Communications Corp
50 Moulton St
Cambridge, MA 02238
December 1983
This RFC specifies the ARPANET 1822L Host Access Protocol,
is a successor to the existing 1822 Host Access Protocol. 1822
allows ARPANET hosts to use logical names as well as 1822'
physical port locations to address each other
1822L Host Access Protocol December 1983
RFC 878
Table of
1 INTRODUCTION.......................................... 1
2 THE ARPANET 1822L HOST ACCESS PROTOCOL................ 3
2.1 Addresses and Names................................. 5
2.2 Name Translations................................... 7
2.2.1 Authorization and Effectiveness................... 7
2.2.2 Translation Policies............................. 11
2.2.3 Reporting Destination Host Downs................. 13
2.2.4 1822L and 1822 Interoperability.................. 15
2.3 Uncontrolled Packets............................... 16
2.4 Establishing Host-IMP Communications............... 19
2.5 Counting RFNMs When Using 1822L.................... 20
2.6 1822L Name Server.................................. 23
3 1822L LEADER FORMATS................................. 25
3.1 Host-to-IMP 1822L Leader Format.................... 26
3.2 IMP-to-Host 1822L Leader Format.................... 34
4 REFERENCES........................................... 42
A 1822L-IP ADDRESS MAPPINGS............................ 43
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2.1 1822 Address Format.................................. 5
2.2 1822L Name Format.................................... 6
2.3 1822L Address Format................................. 6
3.1 Host-to-IMP 1822L Leader Format..................... 27
3.2 NDM Message Format.................................. 30
3.3 IMP-to-Host 1822L Leader Format..................... 35
3.4 Name Server Reply Format............................ 38
A.1 1822 Class A Mapping................................ 44
A.2 1822L Class A Mapping............................... 44
A.3 1822L Class B Mapping............................... 45
A.4 1822L Class C Mapping............................... 46
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RFC 878
1
This RFC specifies the ARPANET 1822L Host Access Protocol,
will allow hosts to use logical addressing (i.e., host names
are independent of their physical location on the ARPANET)
communicate with each other. This new host access protocol
known as the ARPANET 1822L (for Logical) Host Access Protocol
and is a successor to the current ARPANET 1822 Host
Protocol, which is described in sections 3.3 and 3.4 of
Report 1822 [1]. Although the 1822L protocol uses
Host-IMP leaders than the 1822 protocol, the IMPs will
to support the 1822 protocol, and hosts using either protocol
readily communicate with each other (the IMPs will handle
translation automatically).
The RFC's terminology is consistent with that used in
1822, and any new terms will be defined when they are first used
Familiarity with Report 1822 (section 3 in particular)
assumed. As could be expected, the RFC makes many references
Report 1822. As a result, it uses, as a convenient abbreviation
"see 1822(x)" instead of "please refer to Report 1822, section x
for further details".
This RFC updates, and obsoletes, RFC 851. The changes from
RFC are
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o Section 2.2.4 was rewritten for clarity
o Section 2.5 was expanded to further discuss the effects
using 1822L names on host-to-host virtual circuits
o In section 3.2, the type 1 IMP-to-host message has two
subtypes, the type 9 message has one new subtype, and the
15, subtype 4 message is no longer defined
o An appendix describing the mapping between 1822L names
internet (IP) addresses has been added
All of these changes to RFC 851 are marked by revision bars (as |
shown here) in the right margin. |
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2 THE ARPANET 1822L HOST ACCESS
The ARPANET 1822L Host Access Protocol allows a host to
logical addressing to communicate with other hosts on
ARPANET. Basically, logical addressing allows hosts to refer
each other using an 1822L name (see section 2.1) which
independent of a host's physical location in the network.
183 (also published as BBN Report 4473) [2] gives the use
logical addressing considerable justification. Among
advantages it cites are
o The ability to refer to each host on the network by a
independent of its location on the network
o Allowing different hosts to share the same host port on
time-division basis
o Allowing a host to use multi-homing (where a single host
more than one port to communicate with the network).
o Allowing several hosts that provide the same service to
the same name
The main differences between the 1822 and 1822L protocols are
format of the leaders that are used to introduce messages
a host and an IMP, and the specification in those leaders of
source and/or destination host(s). Hosts have the choice
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using the 1822 or the 1822L protocol. When a host comes up on
IMP, it declares itself to be an 1822 host or an 1822L host
the type of NOP message (see section 3.1) it uses. Once up
hosts can switch from one protocol to the other by issuing
appropriate NOP. Hosts that do not use the 1822L protocol
still be addressable by and can communicate with hosts that do
and vice-versa
Another difference between the two protocols is that the 1822
leaders are symmetric, while the 1822L leaders are not. The
symmetric means that in the 1822 protocol, the exact same
format is used for messages in both directions between the
and IMPs. For example, a leader sent from a host over a
that was looped back onto itself (via a looping plug or
hardware) would arrive back at the host and appear to be a
message from a real host (the destination host of the
message). In contrast, the 1822L headers are not symmetric,
a host can detect if the connection to its IMP is looped
receiving a message with the wrong leader format. This
the host to take appropriate action upon detection of the loop
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2.1 Addresses and
The 1822 protocol defines one form of host specification, and
1822L protocol defines two additional ways to identify
hosts. These three forms are 1822 addresses, 1822L names,
1822L addresses
1822 addresses are the 24-bit host addresses found in 1822
leaders. They have the following format
1 8 9 24
+----------------+---------------------------------+
| | |
| Host number | IMP number |
| | |
+----------------+---------------------------------+
1822 Address
Figure 2.1
These fields are quite large, and the ARPANET will never use
than a fraction of the available address space. 1822
are used in 1822 leaders only
1822L names are 16-bit unsigned numbers that serve as a
identifier for one or more hosts. 1822L names have a
simpler format
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1 16
+--------------------------------+
| |
| 1822L name |
| |
+--------------------------------+
1822L Name
Figure 2.2
The 1822L names are just 16-bit unsigned numbers, except
bits 1 and 2 are not both zeros (see below). This allows
49,000 hosts to be specified
1822 addresses cannot be used in 1822L leaders, but there may
a requirement for an 1822L host to be able to address a
physical host port or IMP fake host. 1822L addresses are
for this function. 1822L addresses form a subset of the 1822
name space, and have both bits 1 and 2 off
1 2 3 8 9 16
+---+---+------------+----------------+
| | | | |
| 0 | 0 | host # | IMP number |
| | | | |
+---+---+------------+----------------+
1822L Address
Figure 2.3
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This format allows 1822L hosts to directly address hosts 0-63
IMPs 1-255 (IMP 0 does not exist). Note that the highest
numbers are reserved for addressing the IMP's internal
hosts. At this writing, the IMP has seven fake hosts, so
numbers 57-63 address the IMP fake hosts, while host numbers 0-56
address real hosts external to the IMP. As the number of
fake hosts changes, this boundary point will also change
2.2 Name
There are a number of factors that determine how an 1822L name
translated by the IMP into a physical address on the network
These factors include which translations are legal; in what
different translations for the same name should be attempted
which legal translations shouldn't be attempted because
particular host port is down; and the interoperability
1822 and 1822L hosts. These issues are discussed in
following sections
2.2.1 Authorization and
Every host on a C/30 IMP, regardless of whether it is using
1822 or 1822L protocol to access the network, can have one
more 1822L names (logical addresses). Hosts using 1822L can
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use these names to address the hosts in the network
of their physical locations. Because of the
constraints mentioned in the introduction, hosts on non-C/30
cannot be assigned 1822L names. To circumvent this restriction
however, 1822L hosts can also use 1822L addresses to access
of the other hosts
At this point, several questions arise: How are these
assigned, how do they become known to the IMPs (so
translations to physical addresses can be made), and how do
IMPs know which host is currently using a shared port? To
each question in order
Names are assigned by a central network administrator. When
name is created, it is assigned to a host (or a group of hosts
at one or more specific host ports. The host(s) are allowed
reside at those specific host ports, and nowhere else. If a
moves, it will keep the same name, but the administrator has
update the central database to reflect the new host port
Changes to this database are distributed to the IMPs by
Network Operations Center (NOC). For a while, the host may
allowed to reside at either of (or both) the new and old ports
Once the correspondence between a name and one or more
ports where it may be used has been made official by
administrator, that name is said to be authorized. 1822
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addresses, which actually refer to physical host ports,
always authorized in this sense
Once a host has been assigned one or more names, it has to
the IMPs know where it is and what name(s) it is using.
are two cases to consider, one for 1822L hosts and another
1822 hosts. The following discussion only pertains to hosts
C/30 IMPs
When an IMP sees an 1822L host come up on a host port, the
has no way of knowing which host has just come up (several
may share the same port, or one host may prefer to be known
different names at different times). This requires the host
declare itself to the IMP before it can actually send and
messages. This function is performed by a new host-to-
message, the Name Declaration Message (NDM), which lists
names that the host would like to be known by. The IMP
its tables to see if each of the names is authorized, and
an NDM Reply to the host saying which names were
authorized and can now be used for sending and receiving
(i.e., which names are effective). A host can also use an
message to change its list of effective names (it can add to
delete from the list) at any time. The only constraint on
host is that any names it wishes to use can become effective
if they are authorized
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In the second case, if a host comes up on a C/30 IMP using
1822 protocol, the IMP automatically makes the first name the
finds in its tables for that host become effective when
receives the first 1822 NOP from the host. Thus, even though
host is using the 1822 protocol, it can still receive
from 1822L hosts via its 1822L name. Of course, it can
receive messages from an 1822L host via its 1822L address
well. (Remember, the distinction between 1822L names
addresses is that the addresses correspond to physical
on the network, while the names are strictly
identifiers). The IMPs translate between the different
and send the proper leader in each case (see section 2.2.4).
The third question above has by now already been answered.
an 1822L host comes up, it uses the NDM message to tell the
which host it is (which names it is known by). Even if this is
shared port, the IMP knows which host is currently connected
Whenever a host goes down, its names automatically become non
effective. When it comes back up, it has to make them
again
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2.2.2 Translation
Several hosts can share the same 1822L name. If more than one
these hosts is up at the same time, any messages sent to
1822L name will be delivered to just one of the hosts
that name, and a RFNM will be returned as usual. However,
sending host will not receive any indication of which
received the message, and subsequent messages to that name
not guaranteed to be sent to the same host. Typically,
providing exactly the same service could share the same 1822
name in this manner
Similarly, when a host is multi-homed, the same 1822L name
refer to more than one host port (all connected to the
host). If the host is up on only one of those ports, that
will be used for all messages addressed to the host. However,
the host were up on more than one port, the message would
delivered over just one of those ports, and the subnet
choose which port to use. This port selection could change
message to message. If a host wanted to insure that
messages were delivered to it on specific ports, these
could use either the port's 1822L address or a specific 1822
name that referred to that port alone
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Three different address selection policies are available for
name mapping process. When translated, each name uses one of
three policies (the policy is pre-determined on a per-
basis). The three policies are
o Attempt each translation in the order in which the
addresses are listed in the IMP's translation tables, to
the first reachable physical host address. This list
always searched from the top whenever an uncontrolled
is to be sent or a new virtual circuit connection has to
created (see section 2.5). This is the most commonly
policy
o Selection of the closest physical address, which uses
IMP's routing tables to find the translation to
destination IMP with the least delay path whenever
uncontrolled packet is to be sent or a new virtual
connection has to be created
o Use load leveling. This is similar to the second policy,
differs in that searching the address list for a
translation starts at the address following where the
translation search ended whenever an uncontrolled packet is
be sent or a new virtual circuit connection has to be created
This attempts to spread out the load from any one IMP's
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to the various host ports associated with a particular name
Note that this is NOT network-wide load leveling, which
require a distributed algorithm and tables
2.2.3 Reporting Destination Host
As was explained in report 1822, and as will be discussed
greater detail in section 2.5, whenever regular messages are
by a host, the IMP opens a virtual circuit connection to
destination host from the source host. A connection will
open at least as long as there are any outstanding (un-RFNMed
messages using it and both the source and destination hosts
up
However, the destination host may go down for some reason
the lifetime of a connection. If the host goes down while
are no outstanding messages to it in the network, then
connection is closed and no other action is taken until
source host submits the next message for that destination.
that time, ONE of the following events will occur
A1. If 1822 or an 1822L address is being used to specify
destination host, then the source host will receive a type 7
(Destination Host Dead) message from the IMP
A2. If an 1822L name is being used to specify the
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host, and the name maps to only one authorized host port
then a type 7 message will also be sent to the source host
A3. If an 1822L name is being used to specify the
host, and the name maps to more than one authorized
port, then the IMP attempts to open a connection to
authorized and effective host port for that name. If
such connection can be made, the host will receive a type 15
(1822L Name or Address Error), subtype 5 (no
translations) message (see section 3.2). Note that a type 7
message cannot be returned to the source host, since type 7
messages refer to a particular destination host port,
the name maps to more than one destination port
Things get a bit more complicated if there are any
messages on the connection when the destination host goes down
The connection will be closed, and one of the following
occur
B1. If 1822 or an 1822L address is being used to specify
destination host, then the source host will receive a type 7
message for each outstanding message
B2. If an 1822L name is being used to specify the
host, then the source host will receive a type 9 (Incomplete |
Transmission), subtype 6 (message lost due to logically |
addressed host going down) message for each outstanding |
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1822L Host Access Protocol December 1983
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message. The next time the source host submits
message for that same destination name, the
algorithm will be used (either step A2 or step A3).
The above two algorithms also apply when a host stays up,
declares the destination name for an existing connection to
longer be effective. In this case, however, the type 7
above will be replaced by type 15, subtype 3 (name not effective
messages
Section 2.3 discusses how destination host downs are handled
uncontrolled packets
2.2.4 1822L and 1822
As has been previously stated, 1822 and 1822L hosts
intercommunicate, and the IMPs will automatically handle
necessary leader and address format conversions. However,
every combination of 1822 and 1822L hosts allows
interoperability with regard to the use of 1822L names,
1822 hosts are restricted to using physical addresses
There are two possible situations where any incompatibility could |
arise: |
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o An 1822 host sending a message to an 1822L host: The 1822 |
host specifies the destination host by its 1822 address. The |
destination host will receive the message with an 1822L leader |
containing the 1822L addresses of the source and destination |
hosts. |
o An 1822L host sending a message to an 1822 host: The 1822L |
host can use 1822L names or addresses to specify both the |
source and destination hosts. The destination host will |
receive the message with an 1822 leader containing the 1822 |
address of the source host. |
2.3 Uncontrolled
Uncontrolled packets (see 1822(3.6)) present a unique problem
the 1822L protocol. Uncontrolled packets use none of the
ordering and error-control mechanisms in the IMP, and do not
the normal virtual circuit connection facilities. As a result
uncontrolled packets need to carry all of their overhead
them, including source and destination names. If 1822L names
used when sending an uncontrolled packet, additional
is now required by the subnetwork when the packet is
to the destination IMP. This means that less host-to-host
can be contained in the packet than is possible between 1822
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1822L Host Access Protocol December 1983
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hosts
Uncontrolled packets that are sent between 1822 hosts may
not more than 991 bits of data. Uncontrolled packets that
sent to and/or from 1822L hosts are limited to 32 bits less,
not more than 959 bits. Packets that exceed this length
result in an error indication to the host, and the packet
not be sent. This error indication represents an enhancement
the previous level of service provided by the IMP, which
simply discard an overly long uncontrolled packet
notification
Other enhancements that are provided for uncontrolled
service are a notification to the host of any errors that
detected by the host's IMP when it receives the packet. A
will be notified if an uncontrolled packet contains an error
the 1822L name specification, such as if the name is
authorized or effective, if the remote host is unreachable (
is indicated by none of its names being effective), if
congestion control throttled the packet before it left the
IMP, or for any other reason the source IMP was not able to
the packet on its way
In most cases, the host will not be notified if the
packet was lost once it was transmitted by the source IMP
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However, the IMP will attempt to notify the source host if
logically-addressed uncontrolled packet was mistakenly sent to
host that the source IMP thought was effective, but which
out to be dead or non-effective at the destination IMP.
non-delivery notice is sent back to the source IMP as
uncontrolled packet from the destination IMP, so the source
is not guaranteed to receive this indication
If the source IMP successfully receives the non-delivery notice
then the source host will receive a type 15 (1822L Name
Address Error), subtype 6 (down or non-effective port) message
If the packet is resubmitted or another packet is sent to
same destination name, and there are no available
translations, then the source host will receive a type 15,
subtype 5 (no effective translations) message if the
name has more than one mapping; or will receive either a type 7
(Destination Host Dead) or a type 15, subtype 3 (name
effective) message if the destination name has a
translation
Those enhancements to the uncontrolled packet service that
not specific to logical addressing will be available to
using 1822 as well as 1822L. However, uncontrolled packets
be sent using 1822L leaders in order to receive any
that the packet was lost once it has left the source IMP
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2.4 Establishing Host-IMP
When a host comes up on an IMP, or after there has been a
in the communications between the host and its IMP (
1822(3.2)), the orderly flow of messages between the host and
IMP needs to be properly (re)established. This allows the
and host to recover from most any failure in the other or
their communications path, including a break in mid-message
The first messages that a host should send to its IMP are
NOP messages. Three messages are required to insure that
least one message will be properly read by the IMP (the first
could be concatenated to a previous message if communications
been broken in mid-stream, and the third provides redundancy
the second). These NOPs serve several functions:
synchronize the IMP with the host, they tell the IMP how
padding the host requires between the message leader and
body, and they also tell the IMP whether the host will be
1822 or 1822L leaders
Similarly, the IMP will send three NOPs to the host when
detects that the host has come up. Actually, the IMP will
six NOPs, alternating three 1822 NOPs with three 1822L NOPs
Thus, the host will see three NOPs no matter which protocol it
using. The NOPs will be followed by two Interface
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messages, one of each style. If the IMP receives a NOP from
host while the above sequence is occurring, the IMP will
send the remainder of the NOPs and the Interface Reset in
proper style. The 1822 NOPs will contain the 1822 address of
host interface, and the 1822L NOPs will contain the
1822L address
Once the IMP and the host have sent each other the
messages, regular communications can commence. See 1822(3.2)
further details concerning the ready line, host tardiness,
other issues
2.5 Counting RFNMs When Using 1822
When a host submits a regular message using an 1822 leader,
IMP checks for an existing simplex virtual circuit
(see 1822(3.1)) from the source host to the destination host.
such a connection already exists, it is used. Otherwise, a
connection from the source host port to the destination host
is opened. In either case, there may be at most eight
outstanding on that connection at any one time. If a
submits a ninth message on that connection before it receives
reply for the first message, then the host will be blocked
the reply is sent for the first message
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Such connections can stay open for some time, but are timed
after three minutes of no activity, or can be closed if there
contention for the connection blocks in either the source
destination IMP. However, a connection will never be closed
long as there are any outstanding messages on it. This allows
source host to count the number of replies it has received
messages to each destination host address in order to avoid
blocked by submitting a ninth outstanding message on
connection
When a host submits a regular message using an 1822L leader,
similar process occurs, except that in this case, connections
distinguished by the source port/source name/destination
combination. When the message is received from a host, the
first looks for an open connection for that same port and
name/destination name pair. If such a connection is found,
it is used, and no further name translation is performed. If
however, no open connection was found, then the destination
is translated, and a connection opened to the physical host port
As long as there are any outstanding messages on the
it will stay open, and it will have the same restriction
only eight messages may be outstanding at any one time. Thus,
source host can still count replies to avoid being blocked,
they must be counted on a source port and source name/
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name pair basis, instead of just by source port and
host address as before
Since connections are based on the source name as well as
destination name, this implies that there may be more than
open connection from physical host port A to physical host
B, which would allow more than 8 outstanding
simultaneously from the first to the second port. However,
this to occur, either the source or destination names, or both
must differ from one connection to the next. For example, if
names "543" and "677" both translate to physical port 3 on
51, then the host on that port could open four connections
itself by sending messages from "543" to "543", from "543"
"677", from "677" to "543", and from "677" to "677".
As has already been stated, the destination names in
messages are only translated when connections are first opened
Once a connection is open, that connection, and its
physical host port, will continue to be used until it is closed
If, in the meantime, a "better" destination host port
to the same destination name became available, it would not
used until the next time a new connection is opened to
destination name
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Also, the act of making an 1822L name be non-effective will not |
automatically cause any connections using that name to be closed. |
However, they will be closed after at most three minutes of |
inactivity. A host can, if it wishes, make all of its names at a |
port be noneffective and close all of its connections to and from |
the port by flapping the host's ready line to that IMP port. |
2.6 1822L Name
There may be times when a host wants to perform its
translations, or might need the full list of physical
to which a particular name maps. For example, a connection-
host-to-host protocol may require that the same physical
port on a multi-homed host be used for all messages using
host-to-host connection, and the host does not wish to trust
IMP to always deliver messages using a destination name to
same host port
In these cases, the host can submit a type 11 (Name
Request) message to the IMP, which requests the IMP to
the destination 1822L name and return a list of the addresses
which it maps. The IMP will respond with a type 11 (Name
Reply) message, which contains the selection policy in use
that name, the number of addresses to which the name maps,
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addresses themselves, and for each address, whether it
effective and its routing distance from the IMP. See section 3.2
for a complete description of the message's contents
Using this information, the source host could make an
decision on which of the physical host ports corresponding to
1822L name to use and then send the messages to that port,
than to the name
The IMP also supports a different type of name service. A
needs to issue a Name Declaration Message to the IMP in order
make its names effective, but it may not wish to keep its
in some table or file in the host. In this case, it can ask
IMP to tell it which names it is authorized to use
In this case, the host submits a type 12 (Port List Request
message to the IMP, and the IMP replies with a type 12 (Port
Reply) message. It contains, for the host port over which
IMP received the request and sent the reply, the number of
that map to the port, the list of names, and whether or not
name is effective. The host can then use this information
order to issue the Name Declaration Message. Section 3.2
contains a complete description of the reply's contents
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3 1822L LEADER
The following sections describe the formats of the leaders
precede messages between an 1822L host and its IMP. They
designed to be as compatible with the 1822 leaders as possible
The second, fifth, and sixth words are identical in the
leaders, and all of the existing functionality of the 1822
leaders has been retained. In the first word, the 1822
Format Flag is now also used to identify the two types of 1822
leaders, and the Handling Type has been moved to the second byte
The third and fourth words contain the Source and
1822L Name, respectively
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3.1 Host-to-IMP 1822L Leader
1 4 5 8 9 16
+--------+--------+----------------+
| | 1822L | |
| Unused | H2I | Handling Type |
| | Flag | |
+--------+--------+----------------+
17 20 21 22 24 25 32
+--------+-+------+----------------+
| |T|Leader| |
| Unused |R|Flags | Message Type |
| |C| | |
+--------+-+------+----------------+
33 48
+----------------------------------+
| |
| Source Host |
| |
+----------------------------------+
49 64
+----------------------------------+
| |
| Destination Host |
| |
+----------------------------------+
65 76 77 80
+-------------------------+--------+
| | |
| Message ID |Sub-type
| | |
+-------------------------+--------+
81 96
+----------------------------------+
| |
| Unused |
| |
+----------------------------------+
Host-to-IMP 1822L Leader
Figure 3.1
- 26 -
1822L Host Access Protocol December 1983
RFC 878
Bits 1-4: Unused, must be set to zero
Bits 5-8: 1822L Host-to-IMP Flag
This field is set to decimal 13 (1101 in binary).
Bits 9-16: Handling Type
This field is bit-coded to indicate the
characteristics of the connection desired by the host.
1822(3.3).
Bit 9: Priority Bit
Messages with this bit on will be treated as
messages
Bits 10-16: Unused, must be zero
Bits 17-20: Unused, must be zero
Bit 21: Trace Bit
If equal to one, this message is designated for tracing
it proceeds through the network. See 1822(5.5).
Bits 22-24: Leader Flags
Bit 22: A flag available for use by the destination host
See 1822(3.3) for a description of its use by the IMP'
TTY Fake Host
Bits 23-24: Reserved for future use, must be zero
- 27 -
1822L Host Access Protocol December 1983
RFC 878
Bits 25-32: Message Type
Type 0: Regular Message - All host-to-host
occurs via regular messages, which have several sub
types, found in bits 77-80. These sub-types are
0: Standard - The IMP uses its full message and
control facilities, and host blocking may occur
3: Uncontrolled Packet - The IMP will perform
message-control functions for this type
message, and network flow and congestion
may cause loss of the packet. Also see 1822(3.6)
and section 2.3.
1-2,4-15: Unassigned
Type 1: Error Without Message ID - See 1822(3.3).
Type 2: Host Going Down - see 1822(3.3).
Type 3: Name Declaration Message (NDM) - This message
used by the host to declare which of its 1822L names
or is not effective (see section 2.2.1), or to make
of its names non-effective. The first 16 bits of
data portion of the NDM message, following the
and any leader padding, contains the number of 1822
names contained in the message. This is followed
the 1822L name entries, each 32 bits long, of which
first 16 bits is a 1822L name and the second 16
contains either of the integers zero or one.
- 28 -
1822L Host Access Protocol December 1983
RFC 878
indicates that the name should not be effective,
one indicates that the name should be effective.
IMP will reply with a NDM Reply message (see
3.2) indicating which of the names are now
and which are not. Pictorially, a NDM message has
following format (including the leader, which
printed in hexadecimal, and without any
padding):
- 29 -
1822L Host Access Protocol December 1983
RFC 878
1 16 17 32 33 48
+----------------+----------------+----------------+
| | | |
| 0D00 | 0003 | 0000 |
| | | |
+----------------+----------------+----------------+
49 64 65 80 81 96
+----------------+----------------+----------------+
| | | |
| 0000 | 0000 | 0000 |
| | | |
+----------------+----------------+----------------+
97 112 113 128 129 144
+----------------+----------------+----------------+
| | | |
| # of entries | 1822L name #1 | 0 or 1 |
| | | |
+----------------+----------------+----------------+
145 160 161 176
+----------------+----------------+
| | |
| 1822L name #2 | 0 or 1 | etc
| | |
+----------------+----------------+
NDM Message
Figure 3.2
An NDM with zero entries will cause all
effective names for the host to become non-effective
Type 4: NOP - This allows the IMP to know which style
leader the host wishes to use. A 1822L NOP
that the host wishes to use 1822L leaders, and an 1822
NOP signifies that the host wishes to use 1822 leaders
All of the other remarks concerning the NOP message
- 30 -
1822L Host Access Protocol December 1983
RFC 878
1822(3.3) still hold. The host should always
NOPs in groups of three to insure proper reception
the IMP. Also see section 2.4 for a further
on the use of the NOP message
Type 8: Error with Message ID - see 1822(3.3).
Type 11: Name Server Request - This allows the host to
the IMP's logical addressing tables as a name server
The destination name in the 1822L leader is translated
and the IMP replies with a Name Server Reply message
which lists the physical host addresses to which
destination name maps
Type 12: Port List Request - This allows the physical
to request the list of names that map to the host
over which this request was received by the IMP.
IMP replies with a Port List Reply message, which
the names that map to the port
Types 5-7,9-10,13-255: Unassigned
Bits 33-48: Source Host
This field contains one of the source host's 1822L
(or, alternatively, the 1822L address of the host port
message is being sent over). This field is
automatically filled in by the IMP, as in the 1822 protocol
because the host may be known by several names and may
- 31 -
1822L Host Access Protocol December 1983
RFC 878
to use a particular name as the source of this message.
messages from the same host need not use the same name
this field. Each source name, when used, is checked
authorization, effectiveness, and actually belonging to
host. Messages using names that do not satisfy all of
requirements will not be delivered, and will instead
in an error message being sent back into the source host
If the host places its 1822L address in this field,
address is checked to insure that it actually represents
host port where the message originated
Bits 49-64: Destination Host
This field contains the 1822L name or address of
destination host. If it contains a name, the name will
checked for effectiveness, with an error message returned
the source host if the name is not effective
Bits 65-76: Message ID
This is a host-specified identification used in all type 0
and type 8 messages, and is also used in type 2 messages
When used in type 0 messages, bits 65-72 are also known
the Link Field, and should contain values specified
Assigned Numbers [3] appropriate for the host-to-
protocol being used
- 32 -
1822L Host Access Protocol December 1983
RFC 878
Bits 77-80: Sub-type
This field is used as a modifier by message types 0, 2, 4,
and 8.
Bits 81-96: Unused, must be zero
- 33 -
1822L Host Access Protocol December 1983
RFC 878
3.2 IMP-to-Host 1822L Leader
1 4 5 8 9 16
+--------+--------+----------------+
| | 1822L | |
| Unused | I2H | Handling Type |
| | Flag | |
+--------+--------+----------------+
17 20 21 22 24 25 32
+--------+-+------+----------------+
| |T|Leader| |
| Unused |R|Flags | Message Type |
| |C| | |
+--------+-+------+----------------+
33 48
+----------------------------------+
| |
| Source Host |
| |
+----------------------------------+
49 64
+----------------------------------+
| |
| Destination Host |
| |
+----------------------------------+
65 76 77 80
+-------------------------+--------+
| | |
| Message ID |Sub-type
| | |
+-------------------------+--------+
81 96
+----------------------------------+
| |
| Message Length |
| |
+----------------------------------+
IMP-to-Host 1822L Leader
Figure 3.3
- 34 -
1822L Host Access Protocol December 1983
RFC 878
Bits 1-4: Unused and set to zero
Bits 5-8: 1822L IMP-to-Host Flag
This field is set to decimal 14 (1110 in binary).
Bits 9-16: Handling Type
This has the value assigned by the source host (see
3.1). This field is only used in message types 0, 5-9,
15.
Bits 17-20: Unused and set to zero
Bit 21: Trace Bit
If equal to one, the source host designated this message
tracing as it proceeds through the network. See 1822(5.5).
Bits 22-24: Leader Flags
Bit 22: Available as a destination host flag
Bits 23-24: Reserved for future use, set to zero
Bits 25-32: Message Type
Type 0: Regular Message - All host-to-host
occurs via regular messages, which have several sub
types. The sub-type field (bits 77-80) is the same
sent in the host-to-IMP leader (see section 3.1).
Type 1: Error in Leader - See 1822(3.4). In addition to its |
already defined sub-types, this message has two new |
- 35 -
1822L Host Access Protocol December 1983
RFC 878
sub-types: |
4: Illegal Leader Style - The host submitted a leader |
in which bits 5-8 did not contain the value 13, |
14, or 15 decimal. |
5: Wrong Leader Style - The host submitted an 1822L |
leader when the IMP was expecting an 1822 leader, |
or vice-versa. |
Type 2: IMP Going Down - See 1822(3.4).
Type 3: NDM Reply - This is a reply to the NDM host-to-
message (see section 3.1). It will have the
number of entries as the NDM message that is
replying to, and each listed 1822L name will
accompanied by a zero or a one (see figure 3.2).
zero signifies that the name is not effective, and
one means that the name is now effective
Type 4: NOP - The host should discard this message. It
used during initialization of the IMP/
communication. The Destination Host field will
the 1822L Address of the host port over which the
is being sent. All other fields are unused
Type 5: Ready for Next Message (RFNM) - See 1822(3.4).
Type 6: Dead Host Status - See 1822(3.4).
Type 7: Destination Host or IMP Dead (or unknown) -
1822(3.4).
- 36 -
1822L Host Access Protocol December 1983
RFC 878
Type 8: Error in Data - See 1822(3.4).
Type 9: Incomplete Transmission - See 1822(3.4). In |
addition to its already defined sub-types, this message |
has one new sub-type: |
6: Logically Addressed Host Went Down - A logically |
addressed message was lost in the network because |
the destination host to which it was being |
delivered went down. The message should be |
resubmitted by the source host, since there may be |
another effective host port to which the message |
could be delivered (see section 2.2.3). |
Type 10: Interface Reset - See 1822(3.4).
Type 11: Name Server Reply - This reply to the Name
Request host-to-IMP message contains, following
leader and any leader padding, a word with
selection policy and the number of physical
to which the destination name maps, followed by
words per physical address: the first word contains
1822L address, and the second word contains a
signifying whether or not that particular
is effective and the routing distance (expected
transmission delay, in 6.4 ms units) to the address'
IMP. In figure 3.4, which includes the leader
any leader padding, EFF is 1 for effective and 0
- 37 -
1822L Host Access Protocol December 1983
RFC 878
non-effective, and POL is a two-bit number
the selection policy for the name (see section 2.2.2):
0: First reachable
1: Closest physical address
2: Load leveling
3: Unused
1 16 17 32 33 48
+----------------+----------------+----------------+
| | | |
| 0E00 | 000B | 0000 |
| | | |
+----------------+----------------+----------------+
49 64 65 80 81 96
+----------------+----------------+----------------+
| | | |
| dest. name | 0000 | 0000 |
| | | |
+----------------+----------------+----------------+
97 112 113 128 129 144
+-+--------------+----------------+-+--------------+
|P| | |E| |
|O| # of addrs | 1822L addr #1 |F| routing dist |
|L| | |F| |
+-+--------------+----------------+-+--------------+
145 160 161 176
+----------------+-+--------------+
| |E| |
| 1822L addr #2 |F| routing dist | etc
| |F| |
+----------------+-+--------------+
Name Server Reply
Figure 3.4
- 38 -
1822L Host Access Protocol December 1983
RFC 878
Type 12: Port List Reply - This is the reply to the
List Request host-to-IMP message. It contains
number of names that map to this physical host port
followed by two words per name: the first word
an 1822L name that maps to this port, and the
contains either a zero or a one, signifying whether
not that particular translation is effective.
format is identical to the type 3 NDM Reply
(see figure 3.2).
Type 15: 1822L Name or Address Error - This message is
in response to a type 0 message from a host
contained an erroneous Source Host or Destination
field. Its sub-types are
0: The Source Host 1822L name is not authorized or
effective
1: The Source Host 1822L address does not match
host port used to send the message
2: The Destination Host 1822L name is not authorized
3: The physical host to which this singly-
Destination Host name translated is authorized
up, but not effective. If the host was
down, a type 7 message would be returned, not
type 15.
5: The multi-homed Destination Host name is authorized
- 39 -
1822L Host Access Protocol December 1983
RFC 878
but has no available effective translations
6: A logically-addressed uncontrolled packet was
to a dead or non-effective host port. However,
it is resubmitted, there may be another
host port to which the IMP may be able to
to send the packet
7: Logical addressing is not in use in this network
8-15: Unassigned
Types 4,13-14,16-255: Unassigned
Bits 33-48: Source Host
For type 0 messages, this field contains the 1822L name
address of the host that originated the message.
replies to the message should be sent to the host
herein. For message types 5-9 and 15, this field
the source host field used in a previous type 0 message
by this host
Bits 49-64: Destination Host
For type 0 messages, this field contains the 1822L name
address that the message was sent to. This allows
destination host to detect how it was specified by
source host. For message types 5-9 and 15, this
contains the destination host field used in a previous
0 message sent by this host
- 40 -
1822L Host Access Protocol December 1983
RFC 878
Bits 65-76: Message ID
For message types 0, 5, 7-9, and 15, this is the
assigned by the source host to identify the message (
section 3.1). This field is also used by message types 2
and 6.
Bits 77-80: Sub-type
This field is used as a modifier by message types 0-2, 5-7,
9, and 15.
Bits 81-96: Message Length
This field is contained in type 0, 3, 11, and 12
only, and is the actual length in bits of the
(exclusive of leader, leader padding, and hardware padding
as computed by the IMP
- 41 -
1822L Host Access Protocol December 1983
RFC 878
4
[1] "Specifications for the Interconnection of a Host and
IMP", BBN Report 1822, December 1981 Revision
[2] E. C. Rosen et. al., "ARPANET Routing
Improvements", Internet Experimenter's Note 183 (
published as BBN Report 4473, Vol. 1), August 1980, pp. 55-
107.
[3] J. Reynolds and J. Postel, "Assigned Numbers", Request
Comments 870, October 1983, p. 14.
[4] J. Postel, ed., "Internet Protocol - DARPA Internet
Protocol Specification", Request for Comments 791,
1981.
[5] J. Postel, "Address Mappings", Request for Comments 796,
September 1981.
- 42 -
1822L Host Access Protocol December 1983
RFC 878
APPENDIX
1822L-IP ADDRESS
Once logical addressing is in active (or universal) use in a |
network, to the extent that the "official" host tables for that |
network specify hosts by their logical names rather than by their |
physical network addresses, it would be desirable for hosts on |
other networks to also be able to use the same logical names to |
specify these hosts when sending traffic to them via the internet |
[4]. |
Happily, there exists a natural mapping between logical names and |
internet addresses that fits very nicely with the already |
standard ARPANET-style address mapping as specified in RFC 796, |
Address Mappings [5]. The current ARPANET-style class A mapping |
is as follows (from RFC 796): |
- 43 -
1822L Host Access Protocol December 1983
RFC 878
+--------+ +--------+--------+
| HOST | | ZERO | IMP | 1822
+--------+ +--------+--------+
8 8 8
+--------+--------+--------+--------+
| net # | HOST | LH | IMP | IP
+--------+--------+--------+--------+
8 8 8 8
1822 Class A
Figure A.1
For 1822L names and addresses, the mapping would be: |
+--------+--------+
| upper | lower | 1822L Name or
+--------+--------+
8 8
+--------+--------+--------+--------+
| net # | upper | LH | lower | IP
+--------+--------+--------+--------+
8 8 8 8
1822L Class A
Figure A.2
For 1822L addresses, this mapping is identical to the 1822 |
mapping. For 1822L names, the IP address would appear to be |
addressing a high-numbered (64-255) 1822 host. Although the LH |
(logical host) field is still defined, its use is discouraged; |
multiple logical names should now be used to multiplex multiple |
- 44 -
1822L Host Access Protocol December 1983
RFC 878
functions onto one physical host port. |
This mapping extends to class B networks: |
+--------+--------+
| upper | lower | 1822L Name or
+--------+--------+
8 8
+----------------+--------+--------+
| network number | upper | lower | IP
+----------------+--------+--------+
16 8 8
1822L Class B
Figure A.3
Finally, logical addressing will allow IMP-based class C networks |
for the first time. Previously, it was very hard to try to |
divide the 8 bits of host specification into some number of host |
bits and some number of IMP bits. However, if ALL of the |
internet-accessible hosts on the network have logical names, |
there is no reason why networks with up to 256 such logical names |
cannot now use class C addresses, as follows: |
- 45 -
1822L Host Access Protocol December 1983
RFC 878
+--------+--------+
|01000000| lower | 1822L
+--------+--------+
8 8
+------------------------+--------+
| network number | lower | IP
+------------------------+--------+
24 8
1822L Class C
Figure A.4
Those hosts on the network desiring internet access would be |
assigned logical names in the range 40000 to 40377 (octal), and |
the gateway(s) connected to that network would make the |
translation from IP addresses to 1822L names as specified above. |
Note that the network could have many more than 256 hosts, or 256 |
defined names; the only restriction is that hosts that desire |
internet support or access be addressable by a name in the range |
40000 - 40377. Traffic that was strictly local to the network |
could use other names or even 1822L addresses. |
- 46 -
1822L Host Access Protocol December 1983
RFC 878
1822...................................................... 3
1822 address.............................................. 5
1822 host................................................. 4
1822L..................................................... 3
1822L address............................................. 6
1822L and 1822 interoperability.......................... 15
1822L host................................................ 4
1822L name................................................ 5
address selection policy................................. 12
authorized................................................ 8
blocking................................................. 20
closest physical address................................. 12
connection............................................... 20
destination host..................................... 32, 40
effective............................................. 9, 23
first reachable.......................................... 12
handing type......................................... 27, 35
host downs............................................... 13
interoperability......................................... 15
leader flags......................................... 27, 35
link field............................................... 32
load leveling............................................ 12
logical addressing........................................ 3
message ID........................................... 32, 41
message length........................................... 41
message type......................................... 28, 35
multi-homing.............................................. 3
name server...................................... 23, 31, 37
NDM................................................... 9, 28
NDM reply............................................. 9, 36
NOC....................................................... 8
NOP........................................... 4, 19, 30, 36
priority bit............................................. 27
regular message...................................... 28, 35
RFNM................................................. 20, 36
source host.......................................... 31, 40
standard message......................................... 28
sub-type............................................. 33, 41
symmetric................................................. 4
trace bit............................................ 27, 35
- 47 -
1822L Host Access Protocol December 1983
RFC 878
uncontrolled packet.................................. 16, 28
virtual circuit connection............................... 20
- 48 -
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
RFC documents can be found at I.E.T.F.
Relevance System Copyright © 2002 Spectrum WorldResearch
other technical nosh by ServerMasters Corporation
collaboration of BobX
