rfc1492.txt
来自「RFC 的详细文档！」· 文本 代码 · 共 1,179 行 · 第 1/3 页
TXT
1,179 行
Network Working Group C. Finseth
Request for Comments: 1492 University of Minnesota
July 1993
An Access Control Protocol, Sometimes Called TACACS
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard. Distribution of this memo is
unlimited.
Background
There used to be a network called ARPANET. This network consisted of
end nodes (hosts), routing nodes (IMPs) and links. There were (at
least) two types of IMPs: those that connected dedicated lines only
and those that could accept dial up lines. The latter were called
"TIPs."
People being what they were, there was a desire to control who could
use the dial up lines. Someone invented a protocol, called "TACACS"
(Terminal Access Controller Access Control System?), which allowed a
TIP to accept a username and password and send a query to a TACACS
authentication server, sometimes called a TACACS daemon or simply
TACACSD. This server was normally a program running on a host. The
host would determine whether to accept or deny the request and sent a
response back. The TIP would then allow access or not, based upon
the response.
While TIPs are -- shall we say? -- no longer a major presence on the
Internet, terminal servers are. Cisco Systems terminal servers
implement an extended version of this TACACS protocol. Thus, the
access control decision is delegated to a host. In this way, the
process of making the decision is "opened up" and the algorithms and
data used to make the decision are under the complete control of
whoever is running the TACACS daemon. For example, "anyone with a
first name of Joe can only login after 10:00 PM Mon-Fri, unless his
last name is Smith or there is a Susan already logged in."
The extensions to the protocol provide for more types of
authentication requests and more types of response codes than were in
the original specification.
The original TACACS protocol specification does exist. However, due
to copyright issues, I was not able to obtain a copy of this document
Finseth [Page 1]
RFC 1492 TACACS July 1993
and this lack of access is the main reason for the writing of this
document. This version of the specification was developed with the
assistance of Cisco Systems, who has an implementation of the TACACS
protocol that is believed to be compatible with the original
specification. To be precise, the Cisco Systems implementation
supports both the simple (non-extended) and extended versions. It is
the simple version that would be compatible with the original.
Please keep in mind that this is an informational RFC and does not
specify a standard, and that more information may be uncovered in the
future (i.e., the original specification may become available) that
could cause parts of this document to be known to be incorrect.
This RFC documents the extended TACACS protocol use by the Cisco
Systems terminal servers. This same protocol is used by the
University of Minnesota's distributed authentication system.
1. Protocol Semantics
This section will describe the requests and responses. The following
two sections will describe two different ways of encoding the
protocol.
A request/response pair is the basic unit of interaction. In this
pair, the client sends a request and the server replies with a
response. All requests must be acknowledged with a response. This
requirement implies that all requests can be denied, although it is
probably futile to attempt to deny a "logout" request.
1.1 Connections
In some cases, a string of request/response pairs forms a larger
unit, called a "connection."
There are three types of connections:
1) Authenticate only, no connection:
client: sends an AUTH packet
server: responds with a REPLY
Finseth [Page 2]
RFC 1492 TACACS July 1993
2) Login connection:
client: sends a LOGIN packet
server: responds with a REPLY
repeat zero or more times:
client: sends a CONNECT packet
server: responds with a REPLY
client: sends a LOGOUT packet
server: responds with a REPLY
3) SLIP connection:
client: sends a LOGIN packet
server: responds with a REPLY
repeat zero or more times:
client: sends a CONNECT packet
server: responds with a REPLY
client: sends a SLIPADDR packet
server: responds with a REPLY
repeat zero or more times:
client: sends a CONNECT packet
server: responds with a REPLY
client: sends a SLIPON packet
server: responds with a REPLY
client: sends a LOGOUT packet (immediate)
server: responds with a REPLY
client: sends a SLIPOFF packet
server: responds with a REPLY
1.2 Requests
This section lists the requests supported by the protocol. The
responses are described in the later encodings sections.
AUTH(username, password, line, style)
This request asks for an authentication. The parameters are:
Finseth [Page 3]
RFC 1492 TACACS July 1993
- the username
- the password
- an indication of which line the request is for, and
- a style of authentication
The username is a string that identifies the user. In principle,
it can be of any length and contain any characters. In practice,
it should be no longer than 128 characters and should contain only
the ASCII characters "!" (33 decimal) through "~" (126 decimal),
inclusive.
The password is a string that is used to authenticate the user
identified by the username. In principle, it can be of any length
and contain any characters. In practice, it should be no longer
than 128 characters and should contain only the ASCII characters
"!" (33 decimal) through "~" (126 decimal), inclusive.
The line is a non-negative decimal integer. If the client
supports multiple physical access channels, this value identifies
the particular channel. By convention, lines are numbered
starting from one, although this should be taken with a grain of
salt. For example, Cisco Systems' implementation uses zero to
designate the console port, then continues with one for the "main"
serial lines. Clients that support only one channel should use
line zero.
The authentication style is a possibly empty string. It
identifies the particular style of authentication to be performed.
Its syntax and semantics are local.
Example:
AUTH("fin@unet.umn.edu", "fake-password", 0, "staff")
This specifies a username of "fin@unet.umn.edu" (which happens to
be my e-mail address), a password, an indication that no line is
associated with this request, and a style of "staff". The
semantics for this style might be that I am required to be a staff
member (in addition, of course, to supplying a valid username and
password). The server would presumably consult an external
database to verify the staff status.
As a local option, the implementation may choose to encode the
style information by using alternate port numbers. E.g. port 4001
would mean style 1, 4002 would be style 2, etc.
Note that the AUTH request type cannot be sent using the UDP
encoding.
Finseth [Page 4]
RFC 1492 TACACS July 1993
LOGIN(username, password, line) returns (result1, result2, result3)
This request asks for an authentication and signals that -- if the
authentication succeeds -- a login connection is starting. The
parameters are:
- the username
- the password
- an indication of which line the request is for
The meanings of the input fields are the same as the AUTH request.
If the request is successful, this request returns three result
values in addition to the success status. The result values are
non-negative integers. Their interpretation is local. For
example, Cisco Systems terminal servers interpret result3 to be
the identifier of a local access list to use for additional
validation.
CONNECT(username, password, line, destinationIP, destinationPort)
returns (result1, result2, result3)
This request can only be issued when the username and line specify
an already-existing connection. As such, no authentication is
required and the password will in general be the empty string. It
asks, in the context of that connection, whether a TCP connection
can be opened to the specified destination IP address and port.
The return values are as for LOGIN.
SUPERUSER(username, password, line)
This request can only be issued when the username and line specify
an already-existing connection. As such, no authentication is
required and the password will in general be the empty string. It
asks, in the context of that connection, whether the user can go
into "super-user" or "enable" mode on the terminal server.
As an example of the flexibility inherint in this whole scheme,
the TACACSD supplied by Cisco Systems ignores the username part
and instead checks wether the password matches that of the special
user "$enable$".
LOGOUT(username, password, line, reason)
This request can only be issued when the username and line specify
an already-existing connection. As such, no authentication is
required and the password will in general be the empty string. It
indicates that the connection should be terminated (but see
Finseth [Page 5]
RFC 1492 TACACS July 1993
SLIPON). It must be acknowledged, but the success/fail status of
the acknowledgment is irrelevant. The reason value indicates why
the connection is terminating. A null reason value is supplied
when the connection is going into SLIP mode.
SLIPON(username, password, line, SLIPaddress) returns (result1,
result2, result3)
This request can only be issued when the username and line specify
an already-existing connection. As such, no authentication is
required and the password will in general be the empty string. It
asks, in the context of that connection, whether the specified
SLIPaddress can be used for the remote end of the connection.
If the server replies with a success, the client can proceed to a
SLIPON request. (It need not do so right away, however.)
Note that semantics of "username" can get hairy. For example, the
Cisco Systems implementation encodes information in this way:
- If the user just requested the default address be assigned, this
field holds the username in lower case.
- If the user requested a specific IP address or host name for the
SLIP connection, this field contains the requested host name in
UPPER case.
If the server replies with a success, the client will immediately
send a LOGOUT request. However, the connection will remain
established until a SLIPOFF request is sent. No other
authentication requests will be sent for that connection.
SLIPaddress specifies the IP address used by the remote host. If
a SLIPADDR request has been made, it will be that address.
Otherwise, it will be the default address assigned by the client
(e.g., Cisco terminal server).
The return values are as for LOGIN.
SLIPOFF(username, password, line, reason)
This request can only be issued when the username and line specify
an already-existing connection that is in "SLIP" mode. As such,
no authentication is required and the password will in general be
the empty string. It indicates that the connection should be
terminated. It must be acknowledged, but the success/fail status
of the acknowledgment is irrelevant. The reason value indicates
why the connection is terminating.
Finseth [Page 6]
RFC 1492 TACACS July 1993
2.0 UDP Encoding: TACACS
This section describes the UDP encoding of the requests that have
just been described. It also describes the responses. This UDP
encoding forms the basis of the historical TACACS protocol.
This protocol uses port 49. This assignment continues to be
confirmed by the IANA in the Assigned Numbers RFCs. (I can't say
that it was assigned by the IANA as the assignment preceded the
organization.)
The basic packet format is shown here. All multi-bytes values are in
network byte order. Unless otherwise specified, all values given are
in decimal. Unused fields should be set to zero, but the recipient
should not depend on that setting.
As was mentioned earlier, there are both simple and extended forms,
of which the simple form is a proper subset of the extended form. A
server should support both. I will describe both forms in parallel.
Simple Form
The fields are:
offset length field
0 1 version
1 1 type
2 2 nonce value
4 1 username length (to server) / response (to client)
5 1 password length (to server) / reason (to client)
in the usual packet layout format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Version : Type : Nonce :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: User len/Resp : PW len/Reason : data... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
⌨️ 快捷键说明
复制代码Ctrl + C
搜索代码Ctrl + F
全屏模式F11
增大字号Ctrl + =
减小字号Ctrl + -
显示快捷键?