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Network Working Group                                           K. MooreRequest for Comments: 3205                       University of TennesseeBCP: 56                                                    February 2002Category: Best Current PracticeOn the use of HTTP as a SubstrateStatus of this Memo   This document specifies an Internet Best Current Practices for the   Internet Community, and requests discussion and suggestions for   improvements.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2002).  All Rights Reserved.Abstract   Recently there has been widespread interest in using Hypertext   Transfer Protocol (HTTP) as a substrate for other applications-level   protocols.  This document recommends technical particulars of such   use, including use of default ports, URL schemes, and HTTP security   mechanisms.1. Introduction   Recently there has been widespread interest in using Hypertext   Transfer Protocol (HTTP) [1] as a substrate for other applications-   level protocols.  Various reasons cited for this interest have   included:   o  familiarity and mindshare,   o  compatibility with widely deployed browsers,   o  ability to reuse existing servers and client libraries,   o  ease of prototyping servers using CGI scripts and similar      extension mechanisms,   o  ability to use existing security mechanisms such as HTTP digest      authentication [2] and SSL or TLS [3],   o  the ability of HTTP to traverse firewalls, and   o  cases where a server often needs to support HTTP anyway.Moore                    Best Current Practice                  [Page 1]

RFC 3205                     HTTP Layering                 February 2002   The Internet community has a long tradition of protocol reuse, dating   back to the use of Telnet [4] as a substrate for FTP [5] and SMTP   [6].  However, the recent interest in layering new protocols over   HTTP has raised a number of questions when such use is appropriate,   and the proper way to use HTTP in contexts where it is appropriate.   Specifically, for a given application that is layered on top of HTTP:   o  Should the application use a different port than the HTTP default      of 80?   o  Should the application use traditional HTTP methods (GET, POST,      etc.) or should it define new methods?   o  Should the application use http: URLs or define its own prefix?   o  Should the application define its own MIME-types, or use something      that already exists (like registering a new type of MIME-directory      structure)?   This memo recommends certain design decisions in answer to these   questions.   This memo is intended as advice and recommendation for protocol   designers, working groups, implementors, and IESG, rather than as a   strict set of rules which must be adhered to in all cases.   Accordingly, the capitalized key words defined inRFC 2119, which are   intended to indicate conformance to a specification, are not used in   this memo.2. Issues Regarding the Design Choice to use HTTP   Despite the advantages listed above, it's worth asking the question   as to whether HTTP should be used at all, or whether the entire HTTP   protocol should be used.2.1 Complexity   HTTP started out as a simple protocol, but quickly became much more   complex due to the addition of several features unanticipated by its   original design.  These features include persistent connections, byte   ranges, content negotiation, and cache support.  All of these are   useful for traditional web applications but may not be useful for the   layered application.  The need to support (or circumvent) these   features can add additional complexity to the design and   implementation of a protocol layered on top of HTTP.  Even when HTTP   can be "profiled" to minimize implementation overhead, the effort of   specifying such a profile might be more than the effort of specifying   a purpose-built protocol which is better suited to the task at hand.Moore                    Best Current Practice                  [Page 2]

RFC 3205                     HTTP Layering                 February 2002   Even if existing HTTP client and server code can often be re-used,   the additional complexity of layering something over HTTP vs. using a   purpose-built protocol can increase the number of interoperability   problems.2.2 Overhead   Further, although HTTP can be used as the transport for a "remote   procedure call" paradigm, HTTP's protocol overhead, along with the   connection setup overhead of TCP, can make HTTP a poor choice.  A   protocol based on UDP, or with both UDP and TCP variants, should be   considered if the payloads are very likely to be small (less than a   few hundred bytes) for the foreseeable future.  This is especially   true if the protocol might be heavily used, or if it might be used   over slow or expensive links.   On the other hand, the connection setup overhead can become   negligible if the layered protocol can utilize HTTP/1.1's persistent   connections, and if the same client and server are likely to perform   several transactions during the time the HTTP connection is open.2.3 Security   Although HTTP appears at first glance to be one of the few "mature"   Internet protocols that can provide good security, there are many   applications for which neither HTTP's digest authentication nor TLS   are sufficient by themselves.   Digest authentication requires a secret (e.g., a password) to be   shared between client and server.  This further requires that each   client know the secret to be used with each server, but it does not   provide any means of securely transmitting such secrets between the   parties.  Shared secrets can work fine for small groups where   everyone is physically co-located; they don't work as well for large   or dispersed communities of users.  Further, if the server is   compromised a large number of secrets may be exposed, which is   especially dangerous if the same secret (or password) is used for   several applications.  (Similar concerns exist with TLS based clients   or servers - if a private key is compromised then the attacker can   impersonate the party whose key it has.)   TLS and its predecessor SSL were originally designed to authenticate   web servers to clients, so that a user could be assured (for example)   that his credit card number was not being sent to an imposter.   However, many applications need to authenticate clients to servers,   or to provide mutual authentication of client and server.  TLS doesMoore                    Best Current Practice                  [Page 3]

RFC 3205                     HTTP Layering                 February 2002   have a capability to provide authentication in each direction, but   such authentication may or may not be suitable for a particular   application.   Web browsers which support TLS or SSL are typically shipped with the   public keys of several certificate authorities (CAs) "wired in" so   that they can verify the identity of any server whose public key was   signed by one of those CAs.  For this to work well, every secure web   server's public key has to be signed by one of the CAs whose keys are   wired into popular browsers.  This deployment model works when there   are a (relatively) small number of servers whose identities can be   verified, and their public keys signed, by the small number of CAs   whose keys are included in a small number of different browsers.   This scheme does not work as well to authenticate millions of   potential clients to servers.  It would take a much larger number of   CAs to do the job, each of which would need to be widely trusted by   servers.  Those CAs would also have a more difficult time verifying   the identities of (large numbers of) ordinary users than they do in   verifying the identities of (a smaller number of) commercial and   other enterprises that need to run secure web servers.   Also, in a situation where there were a large number of clients   authenticating with TLS, it seems unlikely that there would be a set   of CAs whose keys were trusted by every server.  A client that   potentially needed to authenticate to multiple servers would   therefore need to be configured as to which key to use with which   server when attempting to establish a secure connection to the   server.   For the reasons stated above, client authentication is rarely used   with TLS.  A common technique is to use TLS to authenticate the   server to the client and to establish a private channel, and for the   client to authenticate to the server using some other means - for   example, a username and password using HTTP basic or digest   authentication.   For any application that requires privacy, the 40-bit ciphersuites   provided by some SSL implementations (to conform to outdated US   export regulations or to regulations on the use or export of   cryptography in other countries) are unsuitable.  Even 56-bit DES   encryption, which is required of conforming TLS implementations, has   been broken in a matter of days with a modest investment in   resources.  So if TLS is chosen it may be necessary to discourage use   of small key lengths, or of weak ciphersuites, in order to provide   adequate privacy assurance.  If TLS is used to provide privacy for   passwords sent by clients then it is especially important to support   longer keys.Moore                    Best Current Practice                  [Page 4]

RFC 3205                     HTTP Layering                 February 2002   None of the above should be taken to mean that either digest   authentication or TLS are generally inferior to other authentication   systems, or that they are unsuitable for use in other applications   besides HTTP.  Many of the limitations of TLS and digest   authentication also apply to other authentication and privacy   systems.  The point here is that neither TLS nor digest   authentication is a "magic pixie dust" solution to authentication or   privacy.  In every case, an application's designers must carefully   determine the application's users' requirements for authentication   and privacy before choosing an authentication or privacy mechanism.   Note also that TLS can be used with other TCP-based protocols, and   there are SASL [7] mechanisms similar to HTTP's digest   authentication.  So it is not necessary to use HTTP in order to   benefit from either TLS or digest-like authentication.  However, HTTP   APIs may already support TLS and/or digest.2.4 Compatibility with Proxies, Firewalls, and NATs   One oft-cited reason for the use of HTTP is its ability to pass   through proxies, firewalls, or network address translators (NATs).   One unfortunate consequence of firewalls and NATs is that they make   it harder to deploy new Internet applications, by requiring explicit   permission (or even a software upgrade of the firewall or NAT) to   accommodate each new protocol.  The existence of firewalls and NATs   creates a strong incentive for protocol designers to layer new   applications on top of existing protocols, including HTTP.   However, if a site's firewall prevents the use of unknown protocols,   this is presumably a conscious policy decision on the part of the   firewall administrator.  While it is arguable that such policies are   of limited value in enhancing security, this is beside the point -   well-known port numbers are quite useful for a variety of purposes,   and the overloading of port numbers erodes this utility.  Attempting   to circumvent a site's security policy is not an acceptable   justification for doing so.   It would be useful to establish guidelines for "firewall-friendly"   protocols, to make it easier for existing firewalls to be compatible   with new protocols.2.5 Questions to be asked when considering use of HTTP   o  When considering payload size and traffic patterns, is HTTP an      appropriate transport for the anticipated use of this protocol?Moore                    Best Current Practice                  [Page 5]

RFC 3205                     HTTP Layering                 February 2002      (In other words: will the payload size be worth the overhead      associated with TCP and HTTP?  Or will the application be able to      make use of HTTP persistent connections to amortize the cost of      that overhead over several requests?)   o  Is this new protocol usable by existing web browsers without      modification?      (For example: Is the request transmitted as if it were a filled-in      HTML form?  Is the response which is returned viewable from a web      browser, say as HTML?)   o  Are the existing HTTP security mechanisms appropriate for the new      application?   o  Are HTTP status codes and the HTTP status code paradigm suitable      for this application?  (seesection 8)   o  Does the server for this application need to support HTTP anyway?3. Issues Regarding Reuse of Port 80   IANA has reserved TCP port number 80 for use by HTTP.  It would not   be appropriate for a substantially new service, even one which uses   HTTP as a substrate, to usurp port 80 from its traditional use.  A   new use of HTTP might be considered a "substantially new service",   thus requiring a new port, if any of the following are true:   o  The "new service" and traditional HTTP service are likely to      reference different sets of data, even when they both operate on      the same host.   o  There is a good reason for the "new service" to be implemented by      a separate server process, or separate code, than traditional HTTP      service on the same host, at least on some platforms.   o  There is a good reason to want to easily distinguish the traffic      of the "new service" from traditional HTTP, e.g., for the purposes      of firewall access control or traffic analysis.   o  If none of the above are true, it is arguable that the new use of      HTTP is an "extension" to traditional HTTP, rather than a "new      service".  Extensions to HTTP which share data with traditional      HTTP services should probably define new HTTP methods to describe      those extensions, rather than using separate ports.  If separate      ports are used, there is no way for a client to know whether they      are separate services or different ways of accessing the same      underlying service.Moore                    Best Current Practice                  [Page 6]

RFC 3205                     HTTP Layering                 February 20024. Issues Regarding Reuse of the http: Scheme in URLs   A number of different URL schemes are in widespread use and many more   are in the process of being standardized.  In practice, the URL   scheme not only serves as a "tag" to govern the interpretation of the   remaining portion of the URL, it also provides coarse identification   of the kind of resource or service which is being accessed.  For   example, web browsers typically provide a different response when a   user mouse-clicks on an "http" URL, than when the user clicks on a   "mailto" URL.   Some criteria that might be used in making this determination are:   o  Whether this URL scheme is likely to become widely used, versus      used only in limited communities or by private agreement.   o  Whether a new "default port" is needed.  If reuse of port 80 is      not appropriate (see above), a new "default port" is needed.  A      new default port in turn requires that a new URL scheme be      registered if that URL scheme is expected to be widely used.      Explicit port numbers in URLs are regarded as an "escape hatch",      not something for use in ordinary circumstances.   o  Whether use of the new service is likely to require a      substantially different setup or protocol interaction with the      server, than ordinary HTTP service.  This could include the need      to request a different type of service from the network, or to      reserve bandwidth, or to present different TLS authentication      credentials to the server, or different kind of server      provisioning, or any number of other needs.   o  Whether user interfaces (such as web browsers) are likely to be      able to exploit the difference in the URL prefix to produce a      significant improvement in usability.   According to the rules in [8] the "http:" URI is part of the "IETF   Tree" for URL scheme names, and IETF is the maintainer of the "IETF   Tree".  Since IESG is the decision-making body for IETF, IESG has the   authority to determine whether a resource accessed by a protocol that   is layered on top of HTTP, should use http: or some other URL prefix.   Note that the convention of appending an "s" to the URL scheme to   mean "use TLS or SSL" (as in "http:" vs "https:") is nonstandard and   of limited value.  For most applications, a single "use TLS or SSL"   bit is not sufficient to adequately convey the information that a   client needs to authenticate itself to a server, even if it has the   proper credentials.  For instance, in order to ensure that adequate   security is provided with TLS an application may need to beMoore                    Best Current Practice                  [Page 7]

RFC 3205                     HTTP Layering                 February 2002   configured with a list of acceptable ciphersuites, or with the client   certificate to be used to authenticate to a particular server.  When   it is necessary to specify authentication or other connection setup   information in a URL these should be communicated in URL parameters,   rather than in the URL prefix.5. Issues regarding use of MIME media types   Since HTTP uses the MIME media type system [9] to label its payload,   many applications which layer on HTTP will need to define, or select,   MIME media types for use by that application.  Especially when using   a multipart structure, the choice of media types requires careful   consideration.  In particular:   o  Should some existing framework be used, such as text/directory      [10], or XML [11,12], or should the new content-types be built      from scratch?  Just as with HTTP, it's useful if code can be      reused, but protocol designers should not be over-eager to      incorporate a general but complex framework into a new protocol.      Experience with ASN.1, for example, suggests that the advantage of      using a general framework may not be worth the cost.   o  Should MIME multipart or message types be allowed?  This can be an      advantage if it is desirable to incorporate (for example) the      multipart/alternative construct or the MIME security framework.      On the other hand, these constructs were designed specifically for      use in store-and-forward electronic mail systems, and other      mechanisms may be more appropriate for the application being      considered.      The point here is that a decision to use MIME content-type names      to describe protocol payloads (which is generally desirable if the      same payloads may appear in other applications) does not imply      that the application must accept arbitrary MIME content-types,      including MIME multipart or security mechanisms.  Nor does it      imply that the application must use MIME syntax or that it must      recognize or even tolerate existing MIME header fields.   o  If the same payload is likely to be sent over electronic mail, the      differences between HTTP encoding of the payload and email      encoding of the payload should be minimized.  Ideally, there      should be no differences in the "canonical form" used in the two      environments.  Text/* media types can be problematic in this      regard because MIME email requires CRLF for line endings of text/*      body parts, where HTTP traditionally uses LF only.Moore                    Best Current Practice                  [Page 8]

RFC 3205                     HTTP Layering                 February 2002   o  A MIME content-type label describes the nature of the object being      labeled.  It does not describe, and should not be used to      describe, the semantics which should be applied when the object is      received.  For instance, the transmission of an object with a      particular content-type using HTTP POST, should not be taken as a      request for some operation based solely on the type.  The request      should be separate from the content-type label and it should be      explicit.      When it is necessary for a protocol layered on HTTP to allow      different operations on the same type of object, this can be      communicated in a number of different ways: HTTP methods, HTTP      request-URI, HTTP request headers, the MIME Content-Disposition      header field, or as part of the payload.6. Issues Regarding Existing vs.New HTTP Methods   It has been suggested that a new service layered on top of HTTP   should define one or more new HTTP methods, rather than allocating a   new port.  The use of new methods may be appropriate, but is not   sufficient in all cases.  The definition of one or more new methods   for use in a new protocol, does not by itself alleviate the need for   use of a new port, or a new URL type.7. Issues regarding reuse of HTTP client, server, and proxy code   As mentioned earlier, one of the primary reasons for the use of HTTP   as a substrate for new protocols, is to allow reuse of existing HTTP   client, server, or proxy code.  However, HTTP was not designed for   such layering.  Existing HTTP client and code may have "http"   assumptions wired into them.  For instance, client libraries and   proxies may expect "http:" URLs, and clients and servers may send   (and expect) "HTTP/1.1", in requests and responses, as opposed to the   name of the layered protocol and its version number.   Existing client libraries may not understand new URL types.  In order   to get a new HTTP-layered application client to work with an existing   client library, it may be necessary for the application to convert   its URLs to an "http equivalent" form.  For instance, if service   "xyz" is layered on top of HTTP using port ###, the xyz client may   need, when invoking an HTTP client library, to translate its URLs   from "xyz://host/something" format to "http://host:###/something" for   the purpose of calling that library.  This should be done ONLY when   calling the HTTP client library - such URLs should not be used in   other parts of the protocol, nor should they be exposed to users.Moore                    Best Current Practice                  [Page 9]

RFC 3205                     HTTP Layering                 February 2002   Note that when a client is sending requests directly to an origin   server, the URL prefix ("http:") is not normally sent.  So   translating xyz: URLs to http: URLs when calling the client library   should not actually cause http: URLs to be sent over the wire.  But   when the same client is sending requests to a proxy server, the   client will normally send the entire URL (including the http: prefix)   in those requests.  The proxy will remove the http: prefix when the   request is communicated to the origin server.   Existing HTTP client libraries and servers will transmit "HTTP/1.1"   (or a different version) in requests and responses.  To facilitate   reuse of such libraries and servers by a new protocol, such a   protocol may therefore need to transmit and accept "HTTP/1.1" rather   than its own protocol name and version number.  Designers of   protocols which are layered on top of HTTP should explicitly choose   whether or not to accept "HTTP/1.1" in protocol exchanges.   For certain applications it may be necessary to require or limit use   of certain HTTP features, for example, to defeat caching of responses   by proxies.  Each protocol layered on HTTP must therefore specify the   specific way that HTTP will be used, and in particular, how the   client and server should interact with HTTP proxies.8.  Issues regarding use of HTTP status codes   HTTP's three-digit status codes were designed for use with   traditional HTTP applications (e.g., document retrieval, forms-based   queries), and are unlikely to be suitable to communicate the   specifics of errors encountered in dissimilar applications.  Even   when it seems like there is a close match between HTTP status codes   and the codes needed by the application, experience with reuse of   other protocols indicates that subtle variations in usage are likely;   and that this is likely to degrade interoperability of both the   original protocol (in this case HTTP) and any layered applications.   HTTP status codes therefore should not be used to indicate subtle   errors of layered applications.  At most, the "generic" HTTP codes   200 (for complete success) and 500 (for complete failure) should be   used to indicate errors resulting from the content of the request   message-body.  Under certain circumstances, additional detail about   the nature of the error can then be included in the response   message-body.  Other status codes than 200 or 500 should only appear   if the error was detected by the HTTP server or by an intermediary.   A layered application should not define new HTTP status codes.  The   set of available status codes is small, conflicts in code assignment   between different layered applications are likely, and they may be   needed by future versions of, or extensions to, mainstream HTTP.Moore                    Best Current Practice                 [Page 10]

RFC 3205                     HTTP Layering                 February 2002   Use of HTTP's error codes is problematic when the layered application   does not share same notion of success or failure as HTTP.  The   problem exists when the client does not connect directly to the   origin server, but via one or more HTTP caches or proxies.  (Since   the ability of HTTP to communicate through intermediaries is often   the primary motivation for reusing HTTP, the ability of the   application to operate in the presence of such intermediaries is   considered very important.)  Such caches and proxies will interpret   HTTP's error codes and may take additional action based on those   codes.  For instance, on receipt of a 200 error code from an origin   server (and under other appropriate conditions) a proxy may cache the   response and re-issue it in response to a similar request.  Or a   proxy may modify the result of a request which returns a 500 error   code in order to add a "helpful" error message.  Other response codes   may produce other behaviors.   A few guidelines are therefore in order:   o  A layered application should use appropriate HTTP error codes to      report errors resulting from information in the HTTP request-line      and header fields associated with the request.  This request      information is part of the HTTP protocol and errors which are      associated with that information should therefore be reported      using HTTP protocol mechanisms.   o  A layered application for which all errors resulting from the      message-body can be classified as either "complete success" or      "complete failure" may use 200 and 500 for those conditions,      respectively.  However, the specification for such an application      must define the mechanism which ensures that its successful (200)      responses are not cached by intermediaries, or demonstrate that      such caching will do no harm; and it must be able to operate even      if the message-body of an error (500) response is not transmitted      back to the client intact.   o  A layered application may return a 200 response code for both      successfully processed requests and errors (or other exceptional      conditions) resulting from the request message-body (but not from      the request headers).  Such an application must return its error      code as part of the response message body, and the specification      for that application protocol must define the mechanism by which      the application ensures that its responses are not cached by      intermediaries.  In this case a response other than 200 should be      used only to indicate errors with, or the status of, the HTTP      protocol layer (including the request headers), or to indicate the      inability of the HTTP server to communicate with the application      server.Moore                    Best Current Practice                 [Page 11]

RFC 3205                     HTTP Layering                 February 2002   o  A layered application which cannot operate in the presence of      intermediaries or proxies that cache and/or alter error responses,      should not use HTTP as a substrate.9. Summary of recommendations regarding reuse of HTTP   1. All protocols should provide adequate security.  The security      needs of a particular application will vary widely depending on      the application and its anticipated use environment.  Merely using      HTTP and/or TLS as a substrate for a protocol does not      automatically provide adequate security for all environments, nor      does it relieve the protocol developers of the need to analyze      security considerations for their particular application.   2. New protocols - including but not limited to those using HTTP -      should not attempt to circumvent users' firewall policies,      particularly by masquerading as existing protocols.      "Substantially new services" should not reuse existing ports.   3. In general, new protocols or services should not reuse http: or      other URL schemes.   4. Each new protocol specification that uses HTTP as a substrate      should describe the specific way that HTTP is to be used by that      protocol, including how the client and server interact with      proxies.   5. New services should follow the guidelines insection 8 regarding      use of HTTP status codes.10.  Security Considerations   Much of this document is about security.Section 2.3 discusses   whether HTTP security is adequate for the needs of a particular   application,section 2.4 discusses interactions between new HTTP-   based protocols and firewalls,section 3 discusses use of separate   ports so that firewalls are not circumvented, andsection 4 discusses   the inadequacy of the "s" suffix of a URL prefix for specifying   security levels.11.  References   [1]   Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,         Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --         HTTP/1.1",RFC 2616, June 1999.Moore                    Best Current Practice                 [Page 12]

RFC 3205                     HTTP Layering                 February 2002   [2]   Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,         Leach, P., Luotonen, A. and L. Stewart, "HTTP Authentication:         Basic and Digest Access Authentication",RFC 2617, June 1999.   [3]   Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",RFC2246, January 1999.   [4]   Postel, J. and J. Reynolds, "Telnet Protocol Specification",         STD 8,RFC 854, May 1983.   [5]   Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9,RFC 959, October 1985.   [6]   Klensin, J., "Simple Mail Transfer Protocol",RFC 2821, April         2001.   [7]   Myers, J., "Simple Authentication and Security Layer (SASL)",RFC 2222, October 1997.   [8]   Petke, R. and I. King, "Registration Procedures for URL Scheme         Names",BCP 35,RFC 2717, November 1999.   [9]   Freed, N. and N. Borenstein, "Multipurpose Internet Mail         Extensions (MIME) Part Two: Media Types",RFC 2046, November         1996.   [10]  Howes, T., Smith, M. and F. Dawson, "A MIME Content-Type for         Directory Information",RFC 2425, September 1998.   [11]  Bray, T., Paoli, J. and C. Sperberg-McQueen, "Extensible Markup         Language (XML)" World Wide Web Consortium Recommendation REC-         xml-19980210, February 1998.http://www.w3.org/TR/1998/REC-xml-19980210.   [12]  Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types",RFC3023, January 2001.12.  Author's Address   Keith Moore   University of Tennessee   Computer Science Department   1122 Volunteer Blvd, Suite 203   Knoxville TN, 37996-3450   USA   EMail: moore@cs.utk.eduMoore                    Best Current Practice                 [Page 13]

RFC 3205                     HTTP Layering                 February 200213.  Full Copyright Statement   Copyright (C) The Internet Society (2002).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Moore                    Best Current Practice                 [Page 14]