Network Working Group D. Bernstein INTERNET DRAFT IR June 1991, revised May 1992 TAP Status of This Memo This document is an Internet Draft. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a "working draft" or "work in progress." Please check the I-D abstract listing contained in each Internet Draft directory to learn the current status of this or any other Internet Draft. Document Expiration Date: November 15, 1992. 1. Introduction It is common for Internet hosts to associate a relatively long-lived identifier, commonly a "username" or "owner name," to each TCP connection. TAP announces the identifier associated with a particular TCP connection to the host on the other end of the connection. TAP may be used on any host which associates a relatively long-lived identifier to each connection. 2. Overview This is a connection-based application which runs over TCP. The TAP server listens for TCP connections on port 113 (decimal). After a connection is established, the server reads one line of data which specifies the connection of interest. If that connection exists and is associated with a system-dependent identifier, the server sends the identifier. Otherwise it sends an error line. After sending the identifier or error line, the server closes its connection. The server will give information about TCP connections between the server's host and host H only to host H itself. The two hosts (i.e., IP addresses) involved are not transmitted explicitly by the protocol; they are implicit in the connection made to the server. 3. Request format The server accepts simple text query requests of the form , where is the TCP port on the server's host and is the TCP port on the client's host. All numbers are expressed in decimal without a sign, and all text is ASCII. If the request is not in this format, the server may immediately drop the connection. For example, say user joe@rose connects to the standard TELNET port on host tulip, through TCP ports 6191 on rose and 23 on tulip. (In other words, let's say this connection exists, and rose associates the identifier joe to it. Note that rose and tulip are simply names used in this document to identify two IP-connected machines. They are not fully qualified domain names.) tulip connects to the TAP server at port 113 on rose. It sends this line: 6191 , 23 Here 6191 is the TCP port on the server's host (rose) and 23 is the TCP port on the client's host (tulip). This uniquely specifies the given TELNET connection. The precise format of the request line is as follows: , followed by any amount of whitespace, followed by a comma and any amount of whitespace, followed by , followed by carriage return and line feed. Whitespace means space or tab; "any amount" means zero or more, though a client should not print excessively many spaces. The client should not send anything after the line feed; the server should ignore everything after the line feed. The client should not add initial zeros to its decimal numbers, but the server must accept such numbers. Future revisions of this standard may assign additional meaning to decimals with a leading 0. 4. Response format The server sends a response line in one of these two formats: , : USERID : : or , : ERROR : Here and are the same numbers as in the query. (If the client uses initial zeros, the server may do so as well, but otherwise it should not use initial zeros.) is an operating system name for the server's host as described in Assigned Numbers, RFC 1060 or its successors. is a system-dependent identifier. is text describing an error as outlined below. may also be OTHER to specify any other operating system not yet listed in Assigned Numbers. Even if the server's system is listed in Assigned Numbers, the server may use OTHER for any reason, including operating system type privacy. is in some format defined by the system. This standard does not define the format or meaning of . is typically in the same format as a system-dependent mailbox name, which is typically in the same format as a system-dependent username, but these equivalences are not required. For example, some possible responses to the 6191 , 23 query might be the following: 6191 , 23 : USERID : UNIX : joe 6191 , 23 : USERID : MULTICS : StJohns.DODCSC.a 6191 , 23 : USERID : OTHER : StJohns.DODCSC.a 6191 , 23 : USERID : TAC : MCSJ-MITMUL 6191,23 :USERID:OTHER:wewishyouamerrychristmasandahappynewyear 6191 , 23 : ERROR : NO-USER An ERROR line means that the server could not determine the identifier associated to the TCP connection. tells why. may be any of the following: INVALID-PORT or was improperly specified---out of the range 0 to 65535, for example---or the request was otherwise nonstandard. In this case the server may drop the connection without replying. NO-USER The connection specified by the port pair is not currently in use. UNKNOWN-ERROR Cannot determine the identifier associated to the connection, for an unknown reason. The server may give this in any case and for any reason, including privacy, whether or not another applies. Other values may be specified as necessary. The server may also report an beginning with the letter X; all such s are reserved for experimental or nonstandard use. The precise format of the response line is as follows: , followed by any amount of whitespace, followed by a comma and any amount of whitespace, followed by , followed by any amount of whitespace, followed by a colon and any amount of whitespace. In the USERID case, it is then followed by USERID and any amount of whitespace, a colon and any amount of whitespace, and any amount of whitespace, one or more characters giving , and finally carriage return and line feed. In the ERROR case, it is followed by ERROR and any amount of whitespace, a colon and any amount of whitespace, one or more characters giving , and finally carriage return and line feed. Note that this format is ambiguous if contains colons or whitespace. Assigned Numbers does not currently list any with colons or whitespace, but if it ever does, the TAP server must use OTHER for the on such a machine. The server should also not use a containing carriage return or line feed. Similarly, if or begins with whitespace or contains carriage return-line feed, the response line format is ambiguous. The server must never use containing whitespace, carriage return, or line feed, and future revisions of this RFC will never provide for such an . The server cannot send beginning with whitespace or containing carriage return-line feed; it should not send containing whitespace, carriage return, or linefeed. ERROR : UNKNOWN-ERROR is preferable. Finally, , , and cannot be empty strings, and cannot contain ASCII nul (character 0). Later revisions of this protocol specification may further restrict the octets which may be transmitted. In light of this, servers should, if possible, limit to at most ASCII codes 33 through 126. Clients should, however, be prepared to handle all octets. Note that there is no limit on line lengths: in particular, on the length of . The client may drop the connection at any time to avoid overflow. The server should, if possible, place the most useful information within the first 512 characters of . 5. Security The scope of this document is limited to the definition of TAP. Applications are not discussed here. You are advised that this document makes no guarantees as to the validity, security, authenticity, or usefulness of the data transmitted via TAP. You are also advised that there is no a priori reason to believe that a server running on port 113 of an Internet host is, in fact, a TAP server. 6. Notes This section is not part of the TAP description proper. It provides historical information and pointers to further information. TAP is derived from the protocol defined in RFC 931. It was first implemented by this author in early 1990, then again in February 1991, and distributed via the USENET network under the name authd. Later in 1991 two more independent interoperable implementations were distributed through the Internet. TAP, as defined in this document, is the same as the authd protocol, which has not changed since its first implementation in early 1990. At the time of publication of this document, there is a non-IETF mailing list for people who want to use TAP to solve problems. To join, send mail to rfc931-users-request@kramden.acf.nyu.edu. Official discussions of the standardization of TAP do not currently have a home, as the IESG has refused to create a working group or mailing list for TAP. The author would like to thank Chris Davis for his helpful suggestions. Document Expiration Date: November 15, 1992. (See the Status of This Memo section for explanation.) Author's Address Daniel J. Bernstein 5 Brewster Lane Bellport, NY 11713 Email: brnstnd@nyu.edu