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 communication
occurs via regular messages, which have several sub-
types. The sub-type field (bits 77-80) is the same as
sent in the host-to-IMP leader (see section 3.1).
Type 1: Error in Leader - See 1822(3.4).
Type 2: IMP Going Down - See 1822(3.4).
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Type 3: NDM Reply - This is a reply to the NDM host-to-IMP
message (see section 3.1). It will have the same
number of entries as the NDM message that is being
replying to, and each listed 1822L name will be
accompanied by a zero or a one (see figure 6). A zero
signifies that the name is not effective, and a one
means that the name is now effective.
Type 4: NOP - The host should discard this message. It is
used during initialization of the IMP/host
communication. The Destination Host field will contain
the 1822L Address of the host port over which the NOP
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) - See
1822(3.4).
Type 8: Error in Data - See 1822(3.4).
Type 9: Incomplete Transmission - See 1822(3.4).
Type 10: Interface Reset - See 1822(3.4).
Type 11: Name Server Reply - This reply to the Name Server
Request host-to-IMP message contains a word with the
selection policy and the number of physical addresses
to which the destination name maps, followed by two
words per physical address: the first word contains an
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1822L address, and the second word contains a bit
signifying whether or not that particular translation
is effective and the routing distance (in 6.4 ms units)
to the address's IMP. In figure 8, EFF is 1 for
effective and 0 for non-effective, and POL is a two-bit
number indicating the selection policy for the name
(see section 2.2.2):
0: First reachable.
1: Closest physical address.
2: Load leveling.
3: Unused.
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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| routine dist | etc.
| |F| |
+----------------+-+--------------+
Figure 8. Name Server Reply Format
Type 12: Port List Reply - This is the reply to the Port
List Request host-to-IMP message. It contains the
number of names that map to this physical host port,
followed by two words per name: the first word contains
an 1822L name that maps to this port, and the second
contains either a zero or a one, signifying whether or
not that particular translation is effective. The
format is identical to the type 3 NDM Reply message
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(see figure 6).
Type 15: 1822L Name or Address Error - This message is sent
in response to a type 0 message from a host that
contained an erroneous Source Host or Destination Host
field. Its sub-types are:
0: The Source Host 1822L name is not authorized or not
effective.
1: The Source Host 1822L address does not match the
host port used to send the message.
2: The Destination Host 1822L name is not authorized.
3: The physical host to which this singly-homed
Destination Host name translated is authorized and
up, but not effective. If the host was actually
down, a type 7 message would be returned, not a
type 15.
4: The Source or Destination Host field contains a
1822L name, but the host being addressed is on a
non-C/30 IMP (see figure 4 in section 2.2.4).
5: The multi-homed Destination Host name is authorized,
but has no available effective translations.
6: A logically-addressed uncontrolled packet was sent
to a dead or non-effective host port. However, if
it is resubmitted, there may be another effective
host port to which the IMP may be able to attempt
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to send the packet.
7: Logical addressing is not in use in this network.
8-15: Unassigned.
Types 13-14,16-255: Unassigned.
Bits 33-48: Source Host:
For type 0 messages, this field contains the 1822L name or
address of the host that originated the message. All
replies to the message should be sent to the host specified
herein. For message types 5-9 and 15, this field contains
the source host field used in a previous type 0 message sent
by this host.
Bits 49-64: Destination Host:
For type 0 messages, this field contains the 1822L name or
address that the message was sent to. This allows the
destination host to detect how it was specified by the
source host. For message types 5-9 and 15, this field
contains the destination host field used in a previous type
0 message sent by this host.
Bits 65-76: Message ID:
For message types 0, 5, 7-9, and 15, this is the value
assigned by the source host to identify the message (see
section 3.1). This field is also used by message types 2
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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 messages
only, and is the actual length in bits of the message
(exclusive of leader, leader padding, and hardware padding)
as computed by the IMP.
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4 REFERENCES
[1] Specifications for the Interconnection of a Host and an IMP,
BBN Report 1822, December 1981 Revision.
[2] A. Malis, The ARPANET Short Blocking Feature, Request For
Comments 852, April 1983.
[3] E. C. Rosen et. al., ARPANET Routing Algorithm Improvements,
Internet Experimenter's Note 183 (also published as BBN
Report 4473, Vol. 1), August 1980, pp. 55-107.
[4] J. Postel, Assigned Numbers, Request For Comments 820,
January 1983, p. 11.
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INDEX
1822...................................................... 4
1822 address.............................................. 6
1822 host................................................. 5
1822L..................................................... 4
1822L address............................................. 7
1822L host................................................ 5
1822L name................................................ 6
address selection policy................................. 12
authorized................................................ 9
blocking................................................. 22
closest physical address................................. 13
connection............................................... 22
destination host..................................... 33, 41
effective................................................ 10
first reachable.......................................... 12
handing type......................................... 29, 36
host downs............................................... 13
leader flags......................................... 29, 36
link field............................................... 34
load leveling............................................ 13
logical addressing........................................ 4
message ID........................................... 34, 41
message length........................................... 42
message type......................................... 30, 36
multi-homing.............................................. 4
name server...................................... 24, 32, 37
NDM.................................................. 10, 30
NDM reply............................................ 10, 37
NOC....................................................... 9
NOP........................................... 5, 20, 32, 37
priority bit............................................. 29
regular message...................................... 30, 36
RFNM................................................. 22, 37
source host.......................................... 33, 41
standard message......................................... 30
sub-type............................................. 34, 42
symmetric................................................. 5
trace bit............................................ 29, 36
uncontrolled packet.................................. 18, 30