rfc878.txt

RFC 相关的技术文档

     Bits 81-96: Unused, must be zero.










































                                  - 33 -



     1822L Host Access Protocol                          December 1983
     RFC 878



     3.2  IMP-to-Host 1822L Leader Format




                    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 Format
                                Figure 3.3





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     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  section

          3.1).   This field is only used in message types 0, 5-9, and

          15.


     Bits 17-20: Unused and set to zero.


     Bit 21: Trace Bit:

          If equal to one, the source host designated this message for

          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  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).  In addition to its  |

               already  defined  sub-types,  this  message has two new  |



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     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-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  3.2).   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).



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     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  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



                                  - 37 -



     1822L Host Access Protocol                          December 1983
     RFC 878



               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
     RFC 878



          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,



                                  - 39 -



     1822L Host Access Protocol                          December 1983
     RFC 878



                    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.



                                  - 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  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