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INTERNET-DRAFT Stephen X. Nahm
August 28, 1996 Sun Microsystems
RPC: Remote Procedure Call Protocol Specification Version 2
draft-ietf-oncrpc-remote-02.txt
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".
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.
This Internet-Draft expires on February 28, 1996. 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 "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 memo is unlimited.
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CONTENTS
1. INTRODUCTION
2. TERMINOLOGY
3. THE RPC MODEL
4. TRANSPORTS AND SEMANTICS
5. BINDING AND RENDEZVOUS INDEPENDENCE
6. AUTHENTICATION
7. RPC PROTOCOL REQUIREMENTS
7.1 RPC Programs and Procedures
7.2 Authentication
7.3 Program Number Assignment
7.4 Other Uses of the RPC Protocol
7.4.1 Batching
7.4.2 Broadcast Remote Procedure Calls
8. THE RPC MESSAGE PROTOCOL
9. AUTHENTICATION PROTOCOLS
9.1 Null Authentication
10. RECORD MARKING STANDARD
11. THE RPC LANGUAGE
11.1 An Example Service Described in the RPC Language
11.2 The RPC Language Specification
11.3 Syntax Notes
12. SECURITY CONSIDERATIONS
13. APPENDIX A: SYSTEM AUTHENTICATION
14. REFERENCES
15. AUTHOR'S ADDRESS
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1. 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 [10]. 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.
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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.
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.
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4. 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 cannot 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)
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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.
The recommended methods for binding are documented in "Binding Protocols
for ONC RPC Version 2" [8].
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 in section
9: "Authentication Protocols".
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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.
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 (iana@isi.edu). 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.
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(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 [10]):
enum auth_flavor {
AUTH_NONE = 0,
AUTH_SYS = 1,
AUTH_SHORT = 2,
AUTH_DH = 3, /* Diffie-Hellman Authentication */
AUTH_KERB4 = 4 /* Kerberos V4 Authentication */
/* 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.
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7.3 Program Number Assignment
Program numbers are given out in groups of hexadecimal 20000000 (decimal
536870912) according to the following chart:
0 - 1fffffff assigned by iana@isi.edu
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 the Internet Assigned
Number Authority, iana@isi.edu [9], 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 request 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 "iana@isi.edu". 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. Servers 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.
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8. THE RPC MESSAGE PROTOCOL
This section defines the RPC message protocol in the XDR data description
language [10].
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 */
/*
* 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 */
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/*
* failed locally
*/
AUTH_INVALIDRESP = 6, /* bogus response verifier */
AUTH_FAILED = 7, /* reason unknown */
/*
* kerberos errors
*/
AUTH_KERB_GENERIC = 8, /* kerberos generic error */
AUTH_TIMEEXPIRE = 9, /* time of credential expired */
AUTH_TKT_FILE = 10, /* something wrong with ticket file */
AUTH_DECODE = 11, /* can't decode authenticator */
AUTH_NET_ADDR = 12 /* wrong net address in ticket */
};
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.
From the client's perspective, XIDs associate RPC replys with calls which
the client has previously sent. From the server's perspective, XIDs are
used to detect retransmissions of RPC calls to which it has previously
replied. Implementations are advised to take precautions to ensure that an
XID is valid within a client-server RPC session by checking that other
parameters match, such as RPC program number and RPC version number.
Implementations may also want to check that the transport-layer end-points
agree, such as the IP address and port number in the TCP/IP protocol stack.
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 the XID as any type of sequence number.
struct rpc_msg {
unsigned int xid; /* Transaction identifier (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
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are specified by the specific program protocol.
The purpose of the authentication verifier is to validate the
authentication credential. Note that these two items are 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;
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default:
/*
* 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;
};
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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 "iana@isi.edu". 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 in Appendix 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.
Note that neither Null authentication nor System authentication provide any
security. A "flavor"-based authentication system is provided in ONC RPC so
that other, more secure, authentication protocols may be implemented in the
future.
9.1 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.
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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!)
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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;
/*
* 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.
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11.2 The RPC Language Specification
The RPC language is identical to the XDR language defined in RFC 1014,
except for the added definition of a "program-def" described below.
program-def:
"program" identifier "{"
version-def
version-def *
"}" "=" constant ";"
version-def:
"version" identifier "{"
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.
12. SECURITY CONSIDERATIONS
Security considerations are discussed in Section 9 and Section 13 (APPENDIX
A).
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13. APPENDIX 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).
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14. REFERENCES
[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:
Protocol Specification", RFC-1045, Stanford University, February
1988.
[3] Diffie & Hellman, "New Directions in Cryptography", IEEE
Transactions on Information Theory IT-22, November 1976.
[4] Mills, D., "Network Time Protocol (Version 3)", RFC-1305,
University of Delaware, 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", RFC-793, Information Sciences
Institute, September 1981.
[7] Postel, J., "User Datagram Protocol", RFC-768, Information
Sciences Institute, August 1980.
[8] Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
RFC-1833, Sun Microsystems, 1995.
[9] Reynolds, J., and Postel, J., "Assigned Numbers", STD-2, RFC-1700,
Information Sciences Institute, October 1994.
[10] Srinivasan, R., "XDR: External Data Representation Standard",
RFC-1832, Sun Microsystems, 1995.
15. AUTHOR'S ADDRESS
Stephen X. Nahm
Sun Microsystems, Inc.
2550 Garcia Avenue
Mountain View, CA 94043
Phone: +1 (415) 786-5086
E-mail: sxn@sun.com
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