IEN 116 J. Postel
ISI
August 1979
Obsoletes: 89, 61
INTERNET NAME SERVER
--------------------
INTRODUCTION
------------
This memo defines the procedure to access an Internet Name Server. Such
a server provides the actual addresses of hosts in the internet when
supplied with a host name. An Internet Name Server is a dynamic
name-to-number translation service.
This server utilizes the User Datagram Protocol (UDP) [2], which in turn
calls on the Internet Protocol (IP) [3].
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 "Assigned Numbers" [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
decimal and is prefixed with a sharp sign (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 exclamation point (!).
The !NET! may be omitted when specifying a host in the local network.
That is "!" indicates the network portion of a name string.
Postel [page 1]
August 1979
Internet Name Server IEN 116
BASIC 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 "Assigned Numbers" [1].
A request sent to a name server is sent as a user datagram [2] with the
following content:
+--------+--------+--------+--------+--------+--------+---\\---+
| | | |
| NAME | LENGTH | NAME STRING |
| | | |
+--------+--------+--------+--------+--------+--------+---\\---+
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 a user datagram with the
following content:
+--------+--------+--------+--------+--------+--------+---\\---+
| | | |
| NAME | LENGTH | NAME STRING |
| | | |
+--------+--------+--------+--------+--------+--------+---\\---+
| | | |
| ADDRESS| LENGTH | INTERNET ADDRESS |
| | | |
+--------+--------+--------+--------+--------+--------+
[page 2] Postel
August 1979
IEN 116 Internet Name Server
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.
When a name is not found, an error is reported via a user 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
Communication with a Name Server Process
Communication with a name server process is via user datagrams. User
datagrams do not guarantee reliable communication. Thus, some
requests or replies may be lost.
Postel [page 3]
August 1979
Internet Name Server IEN 116
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 requester should make the
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 user datagram protocol does provide a checksum for the detection
of errors.
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. The item-length includes in its count the item-count and
the item-length octets.
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.
+--------+--------+--------+--------+
|ItemCode|Item Len|... Item Data ...|
+--------+--------+--------+--------+
| ......... Item Data cont ........ |
+--------+--------+--------+--------+
| Item Data cont. |ItemCode|Item Len|
+--------+--------+--------+--------+
| ........... Item Data ........... |
+--------+--------+--------+--------+
[page 4] Postel
August 1979
IEN 116 Internet Name Server
Item Code Value Assignments:
NAME = 1
ADDRESS = 2
ERROR = 3
Example
a typical request:
+-----------------+--------+--------+
| 1 | 12 | ! | A |
+--------+--------+--------+--------+
| R | P | A | ! |
+--------+--------+--------+--------+
| I | S | I | B |
+--------+--------+--------+--------+
and the reply:
+-----------------+--------+--------+
| 1 | 12 | ! | A |
+--------+--------+--------+--------+
| R | P | A | ! |
+--------+--------+--------+--------+
| I | S | I | B |
+--------+--------+--------+--------+
| 2 | 6 | 10 | 3 |
+--------+--------+--------+--------+
| 0 | 52 |
+--------+--------+
Postel [page 5]
August 1979
Internet Name Server IEN 116
EXTENDED NAME SERVER
--------------------
Several extensions have been proposed [4], the following two are
adopted: partially specified names, and a service field.
In the first extension partially specified names are allowed and are
indicated by the use of "wild card" fields or characters.
Wild Card Field Meaning
--------------- -------
* All
~ Local (Same as that of the requestor)
Wild Card Character Meaning
--------------- -------
* Any substring
Examples:
!~!* all hosts on the net of the requestor.
!*!SRI* all hosts with names whose first three characters
are SRI on all nets
In general, there are three cases for each of the net and host fields.
Using the symbols N for named network and H for named host the 9 cases
are:
!~!~ local net, local host
!~!* local net, all hosts
!~!H local net, named host
!*!~ all nets, local host
!*!* all nets, all hosts
!*!H all nets, named host
!N!~ named net, local host
!N!* named net, all hosts
!N!H named net, named host
[page 6] Postel
August 1979
IEN 116 Internet Name Server
When such a request is processed and the result is more than one
name/address pair, the response is all the pairs.
Examples:
1)
request:
!ARPA!ISI*
response:
!ARPA!ISIA 10 1 0 22
!ARPA!ISIB 10 3 0 52
!ARPA!ISIC 10 2 0 22
!ARPA!ISID 10 3 0 22
!ARPA!ISIE 10 1 0 52
2)
request:
!~!SRI-R2D2
response:
!ARPA!SRI-R2D2 10 3 0 51
!SF-PR-1!SRI-R2D2 2 0 0 11
3)
request:
!*!ISIA
response:
!ARPA!ISIA 10 1 0 22
The second extension is that a third field may be appended to the name.
This is the SERVICE field.
Postel [page 7]
August 1979
Internet Name Server IEN 116
! NET ! HOST ! SERVICE
To reply to a request of this form the name server must provide the
internet address (net and host), the protocol number, and the port
number.
+--------+--------+--------+--------+--------+--------+---\\---+
| | | |
| NAME | LENGTH | NAME STRING |
| | | |
+--------+--------+--------+--------+--------+--------+---\\---+
| | | |
| ADDRESS| LENGTH | INTERNET ADDRESS |
| | | |
+--------+--------+--------+--------+--------+--------+
| | | |
|PROTOCOL| PORT |
| | | |
+--------+--------+--------+
Examples:
1)
request:
!ARPA!ISIA!TELNET
response:
!ARPA!ISIA!TELNET 10 1 0 22 6 0 23
2)
request:
!ARPA!*!NAME-SERVER
response:
!ARPA!SRI-KL!NAME-SERVER 10 1 0 2 17 42
[page 8] Postel
August 1979
IEN 116 Internet Name Server
References
References
----------
[1] J. Postel. "Assigned Numbers," IEN 117, USC/Information Sciences
Institute, August 1979.
[2] J. Postel. "User Datagram Protocol," IEN 88, USC/Information
Sciences Institute, May 1979.
[3] J. Postel. "Internet Protocol," IEN 111, USC/Information
Sciences Institute, August 1979.
[4] J. Pickens, E. Feinler, and J. Mathis. "The NIC Name Server -- A
Datagram Based Information Utility," Proceedings of the Fourth
Berkeley Conference on Distributed Data Management and Computer
Networks, pp. 275-283, August 1979.
Acknowledgments
---------------
John Pickens contributed the ideas for the Extended Name Server.
Postel [page 9]