FTPEXT Working Group Mark Allman Internet Draft NASA Lewis/Sterling Software Expires: July 14, 1998 Shawn Ostermann Ohio University January 14, 1998 FTP Extensions for IPv6 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 and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Distribution of this document is unlimited. Please send comments to the FTP Extension working group (FTPEXT-WG) of the Internet Engineering Task Force (IETF) at . Subscription address is . Discussions of the group are archived at . Abstract The specification for the File Transfer Protocol assumes that the underlying network protocol uses a 32-bit network address (specifically IP version 4). With the deployment of version 6 of the Internet Protocol, network addresses will no longer be 32-bits. This paper specifies extensions to FTP that will allow the protocol to work over IPv4 and IPv6. In addition, the framework defined can support additional network protocols in the future. 1. Introduction The keywords, such as MUST and SHOULD, found in this document are used as defined in RFC 2119 [Bra97]. The File Transfer Protocol [PR85] only provides the ability to open data connections on networks using the IPv4 protocol [Pos81a]. FTP assumes network addresses will be 32 bits in length. However, with Allman and Ostermann [Page 1] INTERNET-DRAFT FTP Extensions for IPv6 January 14, 1998 the deployment of version 6 of the Internet Protocol [DH96] this will no longer be the case. RFC 1639 [Pis94] specifies extensions to FTP to enable its use over various network protocols. However, the mechanism can fail in a multiple protocol environment. During the transition between IPv4 and IPv6, FTP needs the ability to negotiate the network protocol that will be used for data transfer. This document provides a specification which makes no assumptions regarding the underlying network protocol. In this specification, the FTP commands PORT and PASV are replaced with EPRT and EPSV, respectively. 2. The EPRT Command The EPRT command allows for the specification of an extended address for the data connection. The extended address consists of the network protocol as well as the network and transport addresses. The format of EPRT is: EPRT The EPRT command keyword must be followed by a single space. Following the space, a delimiter character () must be specified. The delimiter character MUST be one of the ASCII characters in range 33-126 inclusive. The character "|" (ASCII 124) is recommended unless it coincides with a character needed to encode the network address. The argument MUST be an upper-case string indicating the protocol to be used (and, implicitly, the address length). This specification defines keywords for the following network protocols: Keyword Protocol ------- -------- IP4 Internet Protocol, Version 4 [Pos81a] IP6 Internet Protocol, Version 6 [DH96] It is expected that keywords for additional network protocols will be specified as needed in later documents. The is a protocol specific string representation of the network address. For each of the following keywords, addresses MUST be in the following format: Keyword Address Format Example ------- -------------- ------- IP4 dotted decimal 132.235.1.2 IP6 IPv6 string 1080::8:800:200C:417A representations defined in [HD96] The argument must be the string representation of the number of the TCP port on which the host is listening for the data connection. Allman and Ostermann [Page 2] INTERNET-DRAFT FTP Extensions for IPv6 January 14, 1998 The and fields are optional. If left blank, their default values are as follows: Field Default Value If Omitted ----- ------------------------ Network protocol of the control connection Network address of the control connection The following are sample EPRT commands: EPRT |IP4|132.235.1.2|6275| EPRT |||5282| The first command specifies that the server should use IPv4 to open a data connection to the host "132.235.1.2" on TCP port 6275. The second command specifies that the server should use the network protocol and network address used by the control connection to open a TCP data connection on port 5282. Upon receipt of a valid EPRT command, the server MUST return a code of 200 (Command OK). The standard negative error code 500 and 501 [PR85] are sufficient to handle most errors (e.g., syntax errors) involving the EPRT command. However, an additional error codes is needed. The response code 522 indicates that the server does not support the requested network protocol. The interpretation of this new error code is: 5yz Negative Completion x2z Connections xy2 Extended Port Failure - unknown network protocol The text portion of the response MUST indicate which network protocols the server does support. If the network protocol is unsupported, the format of the response string MUST be: \ (prot1,prot2,...,protn) In this document, any text enclosed within "<>" is informational text that can be written in any language. In the above case, the text SHOULD indicate that the network protocol in the EPRT command is not supported by the server. Two example response strings follow: Supported network protocols (IP6) Supported network protocols (IP4,IP6) 3. The EPSV Command The EPSV command requests that a server listen on a data port and wait for a connection. The EPSV command takes an optional Allman and Ostermann [Page 3] INTERNET-DRAFT FTP Extensions for IPv6 January 14, 1998 argument. The response to this command includes all information needed to setup a connection using the EPRT command. The response code for entering passive mode using an extended address MUST be 229. The interpretation of this code, according to [PR85] is: 2yz Positive Completion x2z Connections xy9 Extended Passive Mode Entered The text returned in response to the EPSV command MUST be: \ () The portion of the string enclosed in parentheses MUST be the exact string needed by the EPRT command to open the data connection, as specified above. As with the EPRT command, the first two fields in the EPSV response are optional. Similar to the EPRT commands, when left blank these fields default to the values used for the control connection. An example response string follows: Entering Extended Passive Mode (|IP4|132.235.1.2|6446|) The standard negative error codes 500 and 501 are sufficient to handle all errors involving the EPSV command (e.g., syntax errors). When the EPSV command is issued with no argument, the server will choose the network protocol for the data connection. However, since it is possible for the server to return an unsupported protocol in the EPSV response, the client needs to be able to request a specific protocol. If the server returns a protocol that the client does not support, the client will not be able to open a data connection to the server. In this situation, the client MUST issue an ABOR (abort) command to allow the server to close down the listening connection. The client can then send an EPSV command requesting the use of a specific network protocol, as follows: EPSV If the requested protocol is supported by the server, it SHOULD use the protocol. If not, the server MUST return the 522 error messages as outlined in section 2. The client may issue either form of the EPSV command at any time. In other words, the version without arguments need not be issued before the version with arguments. 4. IPv6 Transition Issues To aid in transition from IPv4 to IPv6 it is RECOMMENDED that the network address be omitted from the EPRT command and the EPSV response whenever possible. This will allow the end hosts to utilize standard IPv6 mechanisms to communicate (such as network Allman and Ostermann [Page 4] INTERNET-DRAFT FTP Extensions for IPv6 January 14, 1998 address translators), rather than forcing FTP to negotiate the network protocol. 5. Security Issues The above changes to FTP do not introduce new FTP security problems. A companion Internet Draft [AO96] is a more general discussion of FTP security issues and techniques to reduce these security problems. 6. Conclusions The extensions specified in this paper will enable FTP to operate over a variety of network protocols. References [AO97] Mark Allman and Shawn Ostermann. FTP Security Considerations, January 1998. I-D draft-ietf-ftpext-sec-consider-00.txt (work in progress). [Bra97] Scott Bradner. Key words for use in RFCs to Indicate Requirement Levels, March 1997. RFC 2119. [DH96] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6) Specification, January 1996. RFC 1883. [HD96] R. Hinden and S. Deering. IP Version 6 Addressing Architecture, January 1996. RFC 1884. [Pis94] D. Piscitello. FTP Operation Over Big Address Records (FOOBAR), June 1994. RFC 1639. [Pos81a] J. Postel. Internet Protocol, September 1981. RFC 791. [Pos81b] J. Postel. Transmission Control Protocol, September 1981. RFC 793. [PR85] J. Postel and J. Reynolds. File Transfer Protocol (FTP), October 1985. RFC 959. Allman and Ostermann [Page 5] INTERNET-DRAFT FTP Extensions for IPv6 January 14, 1998 Author's Addresses: Mark Allman NASA Lewis Research Center/Sterling Software 21000 Brookpark Rd. MS 54-2 Cleveland, OH 44135 mallman@lerc.nasa.gov http://gigahertz.lerc.nasa.gov/~mallman/ Shawn Ostermann School of Electrical Engineering and Computer Science Ohio University 416 Morton Hall Athens, OH 45701 ostermann@cs.ohiou.edu Allman and Ostermann [Page 6]