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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

(213) 822-1511

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 !
! ! ! !
+--------+--------+--------+--------+--------+--------+---\\---+

Postel [page 1]

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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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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

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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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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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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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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]