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).
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1822L Host Access Protocol December 1983
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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 Server
Request host-to-IMP message contains, following the
leader and any leader padding, 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
1822L address, and the second word contains a bit
signifying whether or not that particular translation
is effective and the routing distance (expected network
transmission delay, in 6.4 ms units) to the address's
IMP. In figure 3.4, which includes the leader without
any leader padding, EFF is 1 for effective and 0 for
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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.
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 Format
Figure 3.4
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1822L Host Access Protocol December 1983
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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
(see figure 3.2).
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.
5: The multi-homed Destination Host name is authorized,
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1822L Host Access Protocol December 1983
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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
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 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.
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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
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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1822L Host Access Protocol December 1983
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4 REFERENCES
[1] "Specifications for the Interconnection of a Host and an
IMP", BBN Report 1822, December 1981 Revision.
[2] 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.
[3] J. Reynolds and J. Postel, "Assigned Numbers", Request For
Comments 870, October 1983, p. 14.
[4] J. Postel, ed., "Internet Protocol - DARPA Internet Program
Protocol Specification", Request for Comments 791, September
1981.
[5] J. Postel, "Address Mappings", Request for Comments 796,
September 1981.
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1822L Host Access Protocol December 1983
RFC878
APPENDIX A
1822L-IP ADDRESS MAPPINGS
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 RFC796, |
Address Mappings [5]. The current ARPANET-style class A mapping |
is as follows (from RFC796): |
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1822L Host Access Protocol December 1983
RFC878
+--------+ +--------+--------+
| HOST | | ZERO | IMP | 1822 Address
+--------+ +--------+--------+
8 8 8
+--------+--------+--------+--------+
| net # | HOST | LH | IMP | IP Address
+--------+--------+--------+--------+
8 8 8 8
1822 Class A Mapping
Figure A.1
For 1822L names and addresses, the mapping would be: |
+--------+--------+
| upper | lower | 1822L Name or Address
+--------+--------+
8 8
+--------+--------+--------+--------+
| net # | upper | LH | lower | IP Address
+--------+--------+--------+--------+
8 8 8 8
1822L Class A Mapping
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 |
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RFC878
functions onto one physical host port. |
This mapping extends to class B networks: |
+--------+--------+
| upper | lower | 1822L Name or Address
+--------+--------+
8 8
+----------------+--------+--------+
| network number | upper | lower | IP Address
+----------------+--------+--------+
16 8 8
1822L Class B Mapping
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: |
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+--------+--------+
|01000000| lower | 1822L Name
+--------+--------+
8 8
+------------------------+--------+
| network number | lower | IP Address
+------------------------+--------+
24 8
1822L Class C Mapping
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. |
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1822L Host Access Protocol December 1983
RFC878
INDEX
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
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RFC878
uncontrolled packet.................................. 16, 28
virtual circuit connection............................... 20