Internet Info 1997 December/Internet_Info_CD-ROM_Walnut_Creek_December_1997.iso/ien/ien-61

Text File | 1988-12-02 | 12KB | 458 lines

IEN 61
Section 2.5.6.1


                          Internet Name Server





                               Jon Postel

















                            27 October 1978





                     Information Sciences Institute
                   University of Southern California
                           4676 Admiralty Way
                   Marina del Rey, California  90291

                             [phone]
















                          INTERNET NAME SERVER
                          --------------------

NAME SYNTAX

It is strongly  recommended  that the use of host names  in programs  be
consistent  for both input and output across all hosts.  To promote such
consistency of the internet level, the following syntax is specified:

The SYNTAX  of names as presented to the user and as entered by the user
is:

  ! NET ! REST

  where:

    NET is a network name or number as defined in [1]

  and

    REST is a host name within  that network  expressed  as a  character
    string  or as a number.   When  a number is used, it is expressed in
    decimals and is prefixed with a sharpsign (e.g., #1234).

  Note that this syntax  has minimal  impact  on the allowable character
  strings for host names within a network.  The only restriction is that
  a REST string cannot begin with an exclaimation point (!).

  The !NET!  may be omitted when specifying a host in the local network.
  That is "!" indicates the network portion of a name string.

NAME SERVER

To aid in the translation  of names to internet  addresses, several name
server  processes will be provided.  The name server process will accept
a name in the above form and will return a name, address pair.

The name server processes will have well-known addresses; addresses that
are constant  over long periods  of time and published in documents such
as [1].

A request sent to a name server is sent as an internet datagram [2] with
the following content:

    +--------+--------+--------+--------+--------+--------+---\\---+
    !        !        !                                            !
    !  NAME  ! LENGTH !                NAME STRING                 !
    !        !        !                                            !
    +--------+--------+--------+--------+--------+--------+---\\---+





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                                                               27 Oct 78
Internet Name Server                                              IEN 61



  where:

    NAME is a one octet code indicating that the following is a name,

    LENGTH  is a one octet  count  of the number  of octets  in the name
    string, and

    NAME STRING is an ASCII character string of the form ! NET ! REST.

A reply to a successful translation is sent as an internet datagram with
the following content:

    +--------+--------+--------+--------+--------+--------+---\\---+
    !        !        !                                            !
    !  NAME  ! LENGTH !                NAME STRING                 !
    !        !        !                                            !
    +--------+--------+--------+--------+--------+--------+---\\---+
    !        !        !                                   !
    ! ADDRESS! LENGTH !         INTERNET ADDRESS          !
    !        !        !                                   !
    +--------+--------+--------+--------+--------+--------+

  where:

    ADDRESS  is a one octet  code indicating  that the following  is  an
    internet address,

    LENGTH  is a one octet  count  (=4)  of the length  of the  internet
    address, and

    INTERNET ADDRESS is the internet address.

Actually  a particular  name might map to several internet addresses, in
this case the response would include a list of internet addresses.















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27 Oct 78
IEN 61                                              Internet Name Server



When a name is not found,  an error is reported via an internet datagram
as follows:

    +--------+--------+--------+--------+--------+--------+---\\---+
    !        !        !                                            !
    !  NAME  ! LENGTH !                NAME STRING                 !
    !        !        !                                            !
    +--------+--------+--------+--------+--------+--------+---\\---+
    !        !        !  ERROR !                                   !
    ! ERROR  ! LENGTH !  CODE  !       ERROR STRING                !
    !        !        !        !                                   !
    +--------+--------+--------+--------+--------+--------+---\\---+

  where:

    ERROR CODE specifies the error.

    ERROR STRING explains the error.

Error Codes

  The following error codes are defined:

    CODE          MEANING
    ----          -------
     0            Undetermined or undefined error
     1            Name not found
     2            Improper name syntax
     3            Name not found, but the following similar names exist

  Note Error 3 is followed by a list of name strings.

Communication with a Name Server Process

  Communication  with a name server  process  is via internet datagrams.
  Internet  datagrams  do not guarantee  reliable  communication.  Thus,
  some requests or replies may be lost.

  The  name  server   process   is  a  transaction   oriented   process;
  furthermore,  the  nature  of  the  transactions  allows  them  to  be
  processed in any order and even to be duplicated.  This allows the use
  of a very simple communication protocol.

  If a request  is made to the name server  process  and no response  is
  received  within a reasonable time, then the requestor should make the




Postel                                                          [page 3]


                                                               27 Oct 78
Internet Name Server                                              IEN 61



  request  again.   This recovers  from communication errors which cause
  the loss of either the request or the reply.

  In order  to use this simple  strategy,  care must be taken  to  allow
  replies to be properly matched with requests.  The name server process
  does this by including in each reply a copy of the entire request.

  The internet  datagram  does not even guarantee the correctness of the
  data.   The name server  protocol  must provide  measures  to  prevent
  incorrect  data from being used.   For example,  an  interent  address
  field could be affected by transmission errors.

  For this reason, the name server protocol includes a checksum over the
  information  of the requests  and replies.   The checksum algorithm is
  the same as is used in the internet  protocol  (which  covers only the
  internet header).

Format

  The requests and replies to and from a name server process are encoded
  as "items".   An item consists  of an item-code an item-length and the
  item-data.

    Item  :=  Item-Code  Item-Length  Item-Data

    +--------+--------+--------+--------+--------+--------+---\\---+
    !        !        !                                            !
    !  Item  !  Item  !               Item                         !
    !  Code  ! Length !                      Data                  !
    !        !        !                                            !
    +--------+--------+--------+--------+--------+--------+---\\---+

  A request  is typically  one item, and a reply is typically two items.
  In any case the items  communicated  at one time are  grouped  into  a
  "block".   A block consists  of an octet of zero, an octet identifying
  this as an name server  block,  a two octet  block length, a two octet
  checksum field, and some items.

    Block  :=  BHead  Items
    BHead  :=  Zero  NS-id  Block-Length  Checksum
    Items  :=  Item  !  Items  Item








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27 Oct 78
IEN 61                                              Internet Name Server



                 +--------+--------+-----------------+
                 !        !  Name  !      Block      !
                 !  Zero  ! Server !      Length     !
                 +-----------------+--------+--------+
                 !     Checksum    !ItemCode!Item Len!
                 +--------+--------+--------+--------+
                 ! ........... Item Data ........... !
                 +--------+--------+--------+--------+
                 ! ......... Item Data cont ........ !
                 +--------+--------+--------+--------+
                 ! Item Data cont. !ItemCode!Item Len!
                 +--------+--------+--------+--------+
                 ! ........... Item Data ........... !
                 +--------+--------+--------+--------+

  This format  is chosen to be compatible with the proposed multiplexing
  format for internet protocol.  Also the name server is one application
  using raw  internet  datagrams  as  the  transmission  media,  so  the
  internet  header  protocol field should carry the value indicating raw
  datagram.  An additional  field is needed  somewhere  to multiplex the
  various applications using raw datagrams.

Item Code Value Assignments:

  NAME    = 1

  ADDRESS = 2

  ERROR   = 3

Example

  a typical request:

                 +--------+--------+-----------------+
                 !        !  NAME  !                 !
                 !   0    ! SERVER !        14       !
                 +-----------------+--------+--------+
                 !     CHECKSUM    !   1    !   10   !
                 +--------+--------+--------+--------+
                 !   !    !   A    !   R    !   P    !
                 +--------+--------+--------+--------+
                 !   A    !   !    !   I    !   S    !
                 +--------+--------+--------+--------+
                 !   I    !   B    !
                 +--------+--------+



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                                                               27 Oct 78
Internet Name Server                                              IEN 61



  and the reply:

                 +--------+--------+-----------------+
                 !        !  NAME  !                 !
                 !   0    ! SERVER !        20       !
                 +-----------------+--------+--------+
                 !     CHECKSUM    !   1    !   10   !
                 +--------+--------+--------+--------+
                 !   !    !   A    !   R    !   P    !
                 +--------+--------+--------+--------+
                 !   A    !   !    !   I    !   S    !
                 +--------+--------+--------+--------+
                 !   I    !   B    !   2    !   4    !
                 +--------+--------+--------+--------+
                 !   10   !   3    !   0    !   52   !
                 +--------+--------+--------+--------+

































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27 Oct 78
IEN 61                                              Internet Name Server
                                                              References



References

[1]     J.  Postel. "Assigned Numbers," RFC 750, NIC 45500, 26 September
        1978.

[2]     J.  Postel.  "Internetwork Protocol Specification -- Version 4,"
        IEN 54, USC-Information Sciences Institute, September 1978.









































Postel                                                          [page 7]