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Network Working Group                                      R. SrinivasanRequest for Comments: 1831                              Sun MicrosystemsCategory: Standards Track                                    August 1995RPC: Remote Procedure Call Protocol Specification Version 2Status of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.ABSTRACT   This document describes the ONC Remote Procedure Call (ONC RPC   Version 2) protocol as it is currently deployed and accepted.  "ONC"   stands for "Open Network Computing".TABLE OF CONTENTS      1. INTRODUCTION                                              2      2. TERMINOLOGY                                               2      3. THE RPC MODEL                                             2      4. TRANSPORTS AND SEMANTICS                                  4      5. BINDING AND RENDEZVOUS INDEPENDENCE                       5      6. AUTHENTICATION                                            5      7. RPC PROTOCOL REQUIREMENTS                                 5      7.1 RPC Programs and Procedures                              6      7.2 Authentication                                           7      7.3 Program Number Assignment                                8      7.4 Other Uses of the RPC Protocol                           8      7.4.1 Batching                                               8      7.4.2 Broadcast Remote Procedure Calls                       8      8. THE RPC MESSAGE PROTOCOL                                  9      9. AUTHENTICATION PROTOCOLS                                 12      9.1 Null Authentication                                     13      10. RECORD MARKING STANDARD                                 13      11. THE RPC LANGUAGE                                        13      11.1 An Example Service Described in the RPC Language       13      11.2 The RPC Language Specification                         14      11.3 Syntax Notes                                           15      APPENDIX A: SYSTEM AUTHENTICATION                           16      REFERENCES                                                  17      Security Considerations                                     18      Author's Address                                            18Srinivasan                  Standards Track                     [Page 1]

RFC 1831        Remote Procedure Call Protocol Version 2     August 19951. INTRODUCTION   This document specifies version two of the message protocol used in   ONC Remote Procedure Call (RPC).  The message protocol is specified   with the eXternal Data Representation (XDR) language [9].  This   document assumes that the reader is familiar with XDR.  It does not   attempt to justify remote procedure calls systems or describe their   use.  The paper by Birrell and Nelson [1] is recommended as an   excellent background for the remote procedure call concept.2. TERMINOLOGY   This document discusses clients, calls, servers, replies, services,   programs, procedures, and versions.  Each remote procedure call has   two sides: an active client side that makes the call to a server,   which sends back a reply.  A network service is a collection of one   or more remote programs.  A remote program implements one or more   remote procedures; the procedures, their parameters, and results are   documented in the specific program's protocol specification.  A   server may support more than one version of a remote program in order   to be compatible with changing protocols.   For example, a network file service may be composed of two programs.   One program may deal with high-level applications such as file system   access control and locking.  The other may deal with low-level file   input and output and have procedures like "read" and "write".  A   client of the network file service would call the procedures   associated with the two programs of the service on behalf of the   client.   The terms client and server only apply to a particular transaction; a   particular hardware entity (host) or software entity (process or   program) could operate in both roles at different times.  For   example, a program that supplies remote execution service could also   be a client of a network file service.3. THE RPC MODEL   The ONC RPC protocol is based on the remote procedure call model,   which is similar to the local procedure call model.  In the local   case, the caller places arguments to a procedure in some well-   specified location (such as a register window).  It then transfers   control to the procedure, and eventually regains control.  At that   point, the results of the procedure are extracted from the well-   specified location, and the caller continues execution.Srinivasan                  Standards Track                     [Page 2]

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995   The remote procedure call model is similar.  One thread of control   logically winds through two processes: the caller's process, and a   server's process.  The caller process first sends a call message to   the server process and waits (blocks) for a reply message.  The call   message includes the procedure's parameters, and the reply message   includes the procedure's results.  Once the reply message is   received, the results of the procedure are extracted, and caller's   execution is resumed.   On the server side, a process is dormant awaiting the arrival of a   call message.  When one arrives, the server process extracts the   procedure's parameters, computes the results, sends a reply message,   and then awaits the next call message.   In this model, only one of the two processes is active at any given   time.  However, this model is only given as an example.  The ONC RPC   protocol makes no restrictions on the concurrency model implemented,   and others are possible.  For example, an implementation may choose   to have RPC calls be asynchronous, so that the client may do useful   work while waiting for the reply from the server.  Another   possibility is to have the server create a separate task to process   an incoming call, so that the original server can be free to receive   other requests.   There are a few important ways in which remote procedure calls differ   from local procedure calls:      1. Error handling: failures of the remote server or network must      be handled when using remote procedure calls.      2. Global variables and side-effects: since the server does not      have access to the client's address space, hidden arguments cannot      be passed as global variables or returned as side effects.      3. Performance:  remote procedures usually operate one or more      orders of magnitude slower than local procedure calls.      4. Authentication: since remote procedure calls can be transported      over unsecured networks, authentication may be necessary.      Authentication prevents one entity from masquerading as some other      entity.   The conclusion is that even though there are tools to automatically   generate client and server libraries for a given service, protocols   must still be designed carefully.Srinivasan                  Standards Track                     [Page 3]

RFC 1831        Remote Procedure Call Protocol Version 2     August 19954. TRANSPORTS AND SEMANTICS   The RPC protocol can be implemented on several different transport   protocols.  The RPC protocol does not care how a message is passed   from one process to another, but only with specification and   interpretation of messages.  However, the application may wish to   obtain information about (and perhaps control over) the transport   layer through an interface not specified in this document.  For   example, the transport protocol may impose a restriction on the   maximum size of RPC messages, or it may be stream-oriented like TCP   with no size limit.  The client and server must agree on their   transport protocol choices.   It is important to point out that RPC does not try to implement any   kind of reliability and that the application may need to be aware of   the type of transport protocol underneath RPC.  If it knows it is   running on top of a reliable transport such as TCP [6], then most of   the work is already done for it.  On the other hand, if it is running   on top of an unreliable transport such as UDP [7], it must implement   its own time-out, retransmission, and duplicate detection policies as   the RPC protocol does not provide these services.   Because of transport independence, the RPC protocol does not attach   specific semantics to the remote procedures or their execution   requirements.  Semantics can be inferred from (but should be   explicitly specified by) the underlying transport protocol.  For   example, consider RPC running on top of an unreliable transport such   as UDP.  If an application retransmits RPC call messages after time-   outs, and does not receive a reply, it cannot infer anything about   the number of times the procedure was executed.  If it does receive a   reply, then it can infer that the procedure was executed at least   once.   A server may wish to remember previously granted requests from a   client and not regrant them in order to insure some degree of   execute-at-most-once semantics.  A server can do this by taking   advantage of the transaction ID that is packaged with every RPC   message.  The main use of this transaction ID is by the client RPC   entity in matching replies to calls.  However, a client application   may choose to reuse its previous transaction ID when retransmitting a   call.  The server may choose to remember this ID after executing a   call and not execute calls with the same ID in order to achieve some   degree of execute-at-most-once semantics.  The server is not allowed   to examine this ID in any other way except as a test for equality.   On the other hand, if using a "reliable" transport such as TCP, the   application can infer from a reply message that the procedure was   executed exactly once, but if it receives no reply message, it cannotSrinivasan                  Standards Track                     [Page 4]

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995   assume that the remote procedure was not executed.  Note that even if   a connection-oriented protocol like TCP is used, an application still   needs time-outs and reconnection to handle server crashes.   There are other possibilities for transports besides datagram- or   connection-oriented protocols.  For example, a request-reply protocol   such as VMTP [2] is perhaps a natural transport for RPC.  ONC RPC   uses both TCP and UDP transport protocols.Section 10 (RECORD   MARKING STANDARD) describes the mechanism employed by ONC RPC to   utilize a connection-oriented, stream-oriented transport such as TCP.5. BINDING AND RENDEZVOUS INDEPENDENCE   The act of binding a particular client to a particular service and   transport parameters is NOT part of this RPC protocol specification.   This important and necessary function is left up to some higher-level   software.   Implementors could think of the RPC protocol as the jump-subroutine   instruction ("JSR") of a network; the loader (binder) makes JSR   useful, and the loader itself uses JSR to accomplish its task.   Likewise, the binding software makes RPC useful, possibly using RPC   to accomplish this task.6. AUTHENTICATION   The RPC protocol provides the fields necessary for a client to   identify itself to a service, and vice-versa, in each call and reply   message.  Security and access control mechanisms can be built on top   of this message authentication.  Several different authentication   protocols can be supported.  A field in the RPC header indicates   which protocol is being used. More information on specific   authentication protocols is insection 9: "Authentication Protocols".7. RPC PROTOCOL REQUIREMENTS   The RPC protocol must provide for the following:      (1) Unique specification of a procedure to be called.      (2) Provisions for matching response messages to request messages.      (3) Provisions for authenticating the caller to service and          vice-versa.Srinivasan                  Standards Track                     [Page 5]

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995   Besides these requirements, features that detect the following are   worth supporting because of protocol roll-over errors, implementation   bugs, user error, and network administration:      (1) RPC protocol mismatches.      (2) Remote program protocol version mismatches.      (3) Protocol errors (such as misspecification of a procedure's          parameters).      (4) Reasons why remote authentication failed.      (5) Any other reasons why the desired procedure was not called.7.1 RPC Programs and Procedures   The RPC call message has three unsigned integer fields -- remote   program number, remote program version number, and remote procedure   number -- which uniquely identify the procedure to be called.   Program numbers are administered by a central authority   (rpc@sun.com).  Once implementors have a program number, they can   implement their remote program; the first implementation would most   likely have the version number 1.  Because most new protocols evolve,   a version field of the call message identifies which version of the   protocol the caller is using.  Version numbers enable support of both   old and new protocols through the same server process.   The procedure number identifies the procedure to be called.  These   numbers are documented in the specific program's protocol   specification.  For example, a file service's protocol specification   may state that its procedure number 5 is "read" and procedure number   12 is "write".   Just as remote program protocols may change over several versions,   the actual RPC message protocol could also change.  Therefore, the   call message also has in it the RPC version number, which is always   equal to two for the version of RPC described here.   The reply message to a request message has enough information to   distinguish the following error conditions:      (1) The remote implementation of RPC does not support protocol      version 2.  The lowest and highest supported RPC version numbers      are returned.      (2) The remote program is not available on the remote system.      (3) The remote program does not support the requested version      number.  The lowest and highest supported remote program version      numbers are returned.Srinivasan                  Standards Track                     [Page 6]

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995      (4) The requested procedure number does not exist.  (This is      usually a client side protocol or programming error.)      (5) The parameters to the remote procedure appear to be garbage      from the server's point of view.  (Again, this is usually caused      by a disagreement about the protocol between client and service.)7.2 Authentication   Provisions for authentication of caller to service and vice-versa are   provided as a part of the RPC protocol.  The call message has two   authentication fields, the credential and verifier.  The reply   message has one authentication field, the response verifier.  The RPC   protocol specification defines all three fields to be the following   opaque type (in the eXternal Data Representation (XDR) language [9]):      enum auth_flavor {         AUTH_NONE       = 0,         AUTH_SYS        = 1,         AUTH_SHORT      = 2         /* and more to be defined */      };      struct opaque_auth {         auth_flavor flavor;         opaque body<400>;      };   In other words, any "opaque_auth" structure is an "auth_flavor"   enumeration followed by up to 400 bytes which are opaque to   (uninterpreted by) the RPC protocol implementation.   The interpretation and semantics of the data contained within the   authentication fields is specified by individual, independent   authentication protocol specifications.  (Section 9 defines the   various authentication protocols.)   If authentication parameters were rejected, the reply message   contains information stating why they were rejected.Srinivasan                  Standards Track                     [Page 7]

RFC 1831        Remote Procedure Call Protocol Version 2     August 19957.3 Program Number Assignment   Program numbers are given out in groups of hexadecimal 20000000   (decimal 536870912) according to the following chart:              0 - 1fffffff   defined by rpc@sun.com       20000000 - 3fffffff   defined by user       40000000 - 5fffffff   transient       60000000 - 7fffffff   reserved       80000000 - 9fffffff   reserved       a0000000 - bfffffff   reserved       c0000000 - dfffffff   reserved       e0000000 - ffffffff   reserved   The first group is a range of numbers administered by rpc@sun.com and   should be identical for all sites.  The second range is for   applications peculiar to a particular site.  This range is intended   primarily for debugging new programs.  When a site develops an   application that might be of general interest, that application   should be given an assigned number in the first range.  Application   developers may apply for blocks of RPC program numbers in the first   range by sending electronic mail to "rpc@sun.com".  The third group   is for applications that generate program numbers dynamically.  The   final groups are reserved for future use, and should not be used.7.4 Other Uses of the RPC Protocol   The intended use of this protocol is for calling remote procedures.   Normally, each call message is matched with a reply message.   However, the protocol itself is a message-passing protocol with which   other (non-procedure call) protocols can be implemented.7.4.1 Batching   Batching is useful when a client wishes to send an arbitrarily large   sequence of call messages to a server.  Batching typically uses   reliable byte stream protocols (like TCP) for its transport.  In the   case of batching, the client never waits for a reply from the server,   and the server does not send replies to batch calls.  A sequence of   batch calls is usually terminated by a legitimate remote procedure   call operation in order to flush the pipeline and get positive   acknowledgement.7.4.2 Broadcast Remote Procedure Calls   In broadcast protocols, the client sends a broadcast call to the   network and waits for numerous replies.  This requires the use of   packet-based protocols (like UDP) as its transport protocol.  ServersSrinivasan                  Standards Track                     [Page 8]

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995   that support broadcast protocols usually respond only when the call   is successfully processed and are silent in the face of errors, but   this varies with the application.   The principles of broadcast RPC also apply to multicasting - an RPC   request can be sent to a multicast address.8. THE RPC MESSAGE PROTOCOL   This section defines the RPC message protocol in the XDR data   description language [9].      enum msg_type {         CALL  = 0,         REPLY = 1      };   A reply to a call message can take on two forms: The message was   either accepted or rejected.      enum reply_stat {         MSG_ACCEPTED = 0,         MSG_DENIED   = 1      };   Given that a call message was accepted, the following is the status   of an attempt to call a remote procedure.      enum accept_stat {         SUCCESS       = 0, /* RPC executed successfully             */         PROG_UNAVAIL  = 1, /* remote hasn't exported program        */         PROG_MISMATCH = 2, /* remote can't support version #        */         PROC_UNAVAIL  = 3, /* program can't support procedure       */         GARBAGE_ARGS  = 4, /* procedure can't decode params         */         SYSTEM_ERR    = 5  /* errors like memory allocation failure */      };   Reasons why a call message was rejected:      enum reject_stat {         RPC_MISMATCH = 0, /* RPC version number != 2          */         AUTH_ERROR = 1    /* remote can't authenticate caller */      };   Why authentication failed:      enum auth_stat {         AUTH_OK           = 0,  /* success                          */Srinivasan                  Standards Track                     [Page 9]

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995         /*          * failed at remote end          */         AUTH_BADCRED      = 1,  /* bad credential (seal broken)     */         AUTH_REJECTEDCRED = 2,  /* client must begin new session    */         AUTH_BADVERF      = 3,  /* bad verifier (seal broken)       */         AUTH_REJECTEDVERF = 4,  /* verifier expired or replayed     */         AUTH_TOOWEAK      = 5,  /* rejected for security reasons    */         /*          * failed locally          */         AUTH_INVALIDRESP  = 6,  /* bogus response verifier          */         AUTH_FAILED       = 7   /* reason unknown                   */      };   The RPC message:   All messages start with a transaction identifier, xid, followed by a   two-armed discriminated union.  The union's discriminant is a   msg_type which switches to one of the two types of the message.  The   xid of a REPLY message always matches that of the initiating CALL   message.  NB: The xid field is only used for clients matching reply   messages with call messages or for servers detecting retransmissions;   the service side cannot treat this id as any type of sequence number.      struct rpc_msg {         unsigned int xid;         union switch (msg_type mtype) {         case CALL:            call_body cbody;         case REPLY:            reply_body rbody;         } body;      };   Body of an RPC call:   In version 2 of the RPC protocol specification, rpcvers must be equal   to 2.  The fields prog, vers, and proc specify the remote program,   its version number, and the procedure within the remote program to be   called.  After these fields are two authentication parameters:  cred   (authentication credential) and verf (authentication verifier).  The   two authentication parameters are followed by the parameters to the   remote procedure, which are specified by the specific program   protocol.   The purpose of the authentication verifier is to validate the   authentication credential.  Note that these two items areSrinivasan                  Standards Track                    [Page 10]

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995   historically separate, but are always used together as one logical   entity.      struct call_body {         unsigned int rpcvers;       /* must be equal to two (2) */         unsigned int prog;         unsigned int vers;         unsigned int proc;         opaque_auth  cred;         opaque_auth  verf;         /* procedure specific parameters start here */      };   Body of a reply to an RPC call:      union reply_body switch (reply_stat stat) {      case MSG_ACCEPTED:         accepted_reply areply;      case MSG_DENIED:         rejected_reply rreply;      } reply;   Reply to an RPC call that was accepted by the server:   There could be an error even though the call was accepted.  The first   field is an authentication verifier that the server generates in   order to validate itself to the client.  It is followed by a union   whose discriminant is an enum accept_stat.  The SUCCESS arm of the   union is protocol specific.  The PROG_UNAVAIL, PROC_UNAVAIL,   GARBAGE_ARGS, and SYSTEM_ERR arms of the union are void.  The   PROG_MISMATCH arm specifies the lowest and highest version numbers of   the remote program supported by the server.      struct accepted_reply {         opaque_auth verf;         union switch (accept_stat stat) {         case SUCCESS:            opaque results[0];            /*             * procedure-specific results start here             */          case PROG_MISMATCH:             struct {                unsigned int low;                unsigned int high;             } mismatch_info;          default:             /*Srinivasan                  Standards Track                    [Page 11]

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995              * Void.  Cases include PROG_UNAVAIL, PROC_UNAVAIL,              * GARBAGE_ARGS, and SYSTEM_ERR.              */             void;          } reply_data;      };   Reply to an RPC call that was rejected by the server:   The call can be rejected for two reasons: either the server is not   running a compatible version of the RPC protocol (RPC_MISMATCH), or   the server rejects the identity of the caller (AUTH_ERROR). In case   of an RPC version mismatch, the server returns the lowest and highest   supported RPC version numbers.  In case of invalid authentication,   failure status is returned.      union rejected_reply switch (reject_stat stat) {      case RPC_MISMATCH:         struct {            unsigned int low;            unsigned int high;         } mismatch_info;      case AUTH_ERROR:         auth_stat stat;      };9. AUTHENTICATION PROTOCOLS   As previously stated, authentication parameters are opaque, but   open-ended to the rest of the RPC protocol.  This section defines two   standard "flavors" of authentication.  Implementors are free to   invent new authentication types, with the same rules of flavor number   assignment as there is for program number assignment.  The "flavor"   of a credential or verifier refers to the value of the "flavor" field   in the opaque_auth structure. Flavor numbers, like RPC program   numbers, are also administered centrally, and developers may assign   new flavor numbers by applying through electronic mail to   "rpc@sun.com".  Credentials and verifiers are represented as variable   length opaque data (the "body" field in the opaque_auth structure).   In this document, two flavors of authentication are described.  Of   these, Null authentication (described in the next subsection) is   mandatory - it must be available in all implementations.  System   authentication is described inAppendix A.  It is strongly   recommended that implementors include System authentication in their   implementations.  Many applications use this style of authentication,   and availability of this flavor in an implementation will enhance   interoperability.Srinivasan                  Standards Track                    [Page 12]

RFC 1831        Remote Procedure Call Protocol Version 2     August 19959.1 Null Authentication   Often calls must be made where the client does not care about its   identity or the server does not care who the client is.  In this   case, the flavor of the RPC message's credential, verifier, and reply   verifier is "AUTH_NONE".  Opaque data associated with "AUTH_NONE" is   undefined.  It is recommended that the length of the opaque data be   zero.10. RECORD MARKING STANDARD   When RPC messages are passed on top of a byte stream transport   protocol (like TCP), it is necessary to delimit one message from   another in order to detect and possibly recover from protocol errors.   This is called record marking (RM).  One RPC message fits into one RM   record.   A record is composed of one or more record fragments.  A record   fragment is a four-byte header followed by 0 to (2**31) - 1 bytes of   fragment data.  The bytes encode an unsigned binary number; as with   XDR integers, the byte order is from highest to lowest.  The number   encodes two values -- a boolean which indicates whether the fragment   is the last fragment of the record (bit value 1 implies the fragment   is the last fragment) and a 31-bit unsigned binary value which is the   length in bytes of the fragment's data.  The boolean value is the   highest-order bit of the header; the length is the 31 low-order bits.   (Note that this record specification is NOT in XDR standard form!)11. THE RPC LANGUAGE   Just as there was a need to describe the XDR data-types in a formal   language, there is also need to describe the procedures that operate   on these XDR data-types in a formal language as well.  The RPC   Language is an extension to the XDR language, with the addition of   "program", "procedure", and "version" declarations.  The following   example is used to describe the essence of the language.11.1 An Example Service Described in the RPC Language   Here is an example of the specification of a simple ping program.   program PING_PROG {         /*          * Latest and greatest version          */         version PING_VERS_PINGBACK {            void            PINGPROC_NULL(void) = 0;Srinivasan                  Standards Track                    [Page 13]

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995            /*             * Ping the client, return the round-trip time             * (in microseconds). Returns -1 if the operation             * timed out.             */            int            PINGPROC_PINGBACK(void) = 1;         } = 2;         /*          * Original version          */         version PING_VERS_ORIG {            void            PINGPROC_NULL(void) = 0;         } = 1;      } = 1;      const PING_VERS = 2;      /* latest version */   The first version described is PING_VERS_PINGBACK with two   procedures, PINGPROC_NULL and PINGPROC_PINGBACK.  PINGPROC_NULL takes   no arguments and returns no results, but it is useful for computing   round-trip times from the client to the server and back again.  By   convention, procedure 0 of any RPC protocol should have the same   semantics, and never require any kind of authentication.  The second   procedure is used for the client to have the server do a reverse ping   operation back to the client, and it returns the amount of time (in   microseconds) that the operation used.  The next version,   PING_VERS_ORIG, is the original version of the protocol and it does   not contain PINGPROC_PINGBACK procedure. It is useful for   compatibility with old client programs, and as this program matures   it may be dropped from the protocol entirely.11.2 The RPC Language Specification   The RPC language is identical to the XDR language defined inRFC1014, except for the added definition of a "program-def" described   below.   program-def:      "program" identifier "{"         version-def         version-def *      "}" "=" constant ";"   version-def:      "version" identifier "{"Srinivasan                  Standards Track                    [Page 14]

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995          procedure-def          procedure-def *      "}" "=" constant ";"   procedure-def:      type-specifier identifier "(" type-specifier        ("," type-specifier )* ")" "=" constant ";"11.3 Syntax Notes   (1) The following keywords are added and cannot be used as   identifiers: "program" and "version";   (2) A version name cannot occur more than once within the scope of a   program definition. Nor can a version number occur more than once   within the scope of a program definition.   (3) A procedure name cannot occur more than once within the scope of   a version definition. Nor can a procedure number occur more than once   within the scope of version definition.   (4) Program identifiers are in the same name space as constant and   type identifiers.   (5) Only unsigned constants can be assigned to programs, versions and   procedures.Srinivasan                  Standards Track                    [Page 15]

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995APPENDIX A: SYSTEM AUTHENTICATION   The client may wish to identify itself, for example, as it is   identified on a UNIX(tm) system.  The flavor of the client credential   is "AUTH_SYS".  The opaque data constituting the credential encodes   the following structure:      struct authsys_parms {         unsigned int stamp;         string machinename<255>;         unsigned int uid;         unsigned int gid;         unsigned int gids<16>;      };   The "stamp" is an arbitrary ID which the caller machine may generate.   The "machinename" is the name of the caller's machine (like   "krypton").  The "uid" is the caller's effective user ID.  The "gid"   is the caller's effective group ID.  The "gids" is a counted array of   groups which contain the caller as a member.  The verifier   accompanying the credential should have "AUTH_NONE" flavor value   (defined above).  Note this credential is only unique within a   particular domain of machine names, uids, and gids.   The flavor value of the verifier received in the reply message from   the server may be "AUTH_NONE" or "AUTH_SHORT".  In the case of   "AUTH_SHORT", the bytes of the reply verifier's string encode an   opaque structure.  This new opaque structure may now be passed to the   server instead of the original "AUTH_SYS" flavor credential.  The   server may keep a cache which maps shorthand opaque structures   (passed back by way of an "AUTH_SHORT" style reply verifier) to the   original credentials of the caller.  The caller can save network   bandwidth and server cpu cycles by using the shorthand credential.   The server may flush the shorthand opaque structure at any time.  If   this happens, the remote procedure call message will be rejected due   to an authentication error.  The reason for the failure will be   "AUTH_REJECTEDCRED".  At this point, the client may wish to try the   original "AUTH_SYS" style of credential.   It should be noted that use of this flavor of authentication does not   guarantee any security for the users or providers of a service, in   itself.  The authentication provided by this scheme can be considered   legitimate only when applications using this scheme and the network   can be secured externally, and privileged transport addresses are   used for the communicating end-points (an example of this is the use   of privileged TCP/UDP ports in Unix systems - note that not all   systems enforce privileged transport address mechanisms).Srinivasan                  Standards Track                    [Page 16]

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995REFERENCES   [1]  Birrell, A. D.  & Nelson, B. J., "Implementing Remote Procedure        Calls", XEROX CSL-83-7, October 1983.   [2]  Cheriton, D., "VMTP: Versatile Message Transaction Protocol",        Preliminary Version 0.3, Stanford University, January 1987.   [3]  Diffie & Hellman, "New Directions in Cryptography", IEEE        Transactions on Information Theory IT-22, November 1976.   [4]  Mills, D., "Network Time Protocol",RFC 1305, UDEL,        March 1992.   [5]  National Bureau of Standards, "Data Encryption Standard",        Federal Information Processing Standards Publication 46, January        1977.   [6]  Postel, J., "Transmission Control Protocol - DARPA Internet        Program Protocol Specification", STD 7,RFC 793, USC/Information        Sciences Institute, September 1981.   [7]  Postel, J., "User Datagram Protocol", STD 6,RFC 768,        USC/Information Sciences Institute, August 1980.   [8]  Reynolds, J., and Postel, J., "Assigned Numbers", STD 2,RFC 1700, USC/Information Sciences Institute, October 1994.   [9]  Srinivasan, R., "XDR: External Data Representation Standard",RFC 1832, Sun Microsystems, Inc., August 1995.   [10] Miller, S., Neuman, C., Schiller, J., and  J. Saltzer, "Section        E.2.1: Kerberos  Authentication and Authorization System",        M.I.T. Project Athena, Cambridge, Massachusetts, December 21,        1987.   [11] Steiner, J., Neuman, C., and J. Schiller, "Kerberos: An        Authentication Service for Open Network Systems", pp. 191-202 in        Usenix Conference Proceedings, Dallas, Texas, February 1988.   [12] Kohl, J. and C. Neuman, "The Kerberos Network Authentication        Service (V5)",RFC 1510, Digital Equipment Corporation,        USC/Information Sciences Institute, September 1993.Srinivasan                  Standards Track                    [Page 17]

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995Security Considerations   Security issues are not discussed in this memo.Author's Address   Raj Srinivasan   Sun Microsystems, Inc.   ONC Technologies   2550 Garcia Avenue   M/S MTV-5-40   Mountain View, CA  94043   USA   Phone: 415-336-2478   Fax:   415-336-6015   EMail: raj@eng.sun.comSrinivasan                  Standards Track                    [Page 18]