INTERNET-DRAFT Robert Thurlow
Expires: August 1, 2008 January 30, 2008
Intended status: Informational
RPC: Remote Procedure Call Protocol Specification Version 2
draft-ietf-nfsv4-rfc1831bis-07.txt
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Abstract
This document describes the ONC (Open Network Computing) Remote
Procedure Call (ONC RPC Version 2) protocol as it is currently
deployed and accepted. It is meant to supersede [RFC1831].
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The RPC Model . . . . . . . . . . . . . . . . . . . . . . . 3
4. Transports and Semantics . . . . . . . . . . . . . . . . . . 5
5. Binding and Rendezvous Independence . . . . . . . . . . . . 6
6. Authentication . . . . . . . . . . . . . . . . . . . . . . . 6
7. RPC Protocol Requirements . . . . . . . . . . . . . . . . . 6
7.1. RPC Programs and Procedures . . . . . . . . . . . . . . . 7
7.2. Authentication . . . . . . . . . . . . . . . . . . . . . . 8
7.3. Program Number Assignment . . . . . . . . . . . . . . . . 9
7.4. Other Uses of the RPC Protocol . . . . . . . . . . . . . . 9
7.4.1. Batching . . . . . . . . . . . . . . . . . . . . . . . . 9
7.4.2. Broadcast Remote Procedure Calls . . . . . . . . . . . . 9
8. The RPC Message Protocol . . . . . . . . . . . . . . . . . 10
9. Authentication Protocols . . . . . . . . . . . . . . . . . 13
9.1. Null Authentication . . . . . . . . . . . . . . . . . . 14
10. Record Marking Standard . . . . . . . . . . . . . . . . . 14
11. The RPC Language . . . . . . . . . . . . . . . . . . . . 14
11.1. An Example Service Described in the RPC Language . . . 15
11.2. The RPC Language Specification . . . . . . . . . . . . 16
11.3. Syntax Notes . . . . . . . . . . . . . . . . . . . . . 16
12. IANA Considerations . . . . . . . . . . . . . . . . . . . 17
12.1. Numbering Requests to IANA . . . . . . . . . . . . . . 17
12.2. Protecting Past Assignments . . . . . . . . . . . . . . 17
12.3. RPC Number Assignment . . . . . . . . . . . . . . . . . 17
12.3.1. To be assigned by IANA . . . . . . . . . . . . . . . 18
12.3.2. Defined by local administrator . . . . . . . . . . . 18
12.3.3. Transient block . . . . . . . . . . . . . . . . . . . 18
12.3.4. Reserved block . . . . . . . . . . . . . . . . . . . 19
12.3.5. RPC Number Sub-Blocks . . . . . . . . . . . . . . . . 19
12.4. RPC Authentication Flavor Number Assignment . . . . . . 20
13. Security Considerations . . . . . . . . . . . . . . . . . 21
14. Appendix A: System Authentication . . . . . . . . . . . . 21
15. Appendix B: Requesting RPC program or authentication
numbers . . . . . . . . . . . . . . . . . . . . . . . . . 22
16. Full Copyright Statement . . . . . . . . . . . . . . . . 24
17. Intellectual property . . . . . . . . . . . . . . . . . . 24
18. Acknowledgment . . . . . . . . . . . . . . . . . . . . . 24
19. Normative References . . . . . . . . . . . . . . . . . . 26
20. Informative References . . . . . . . . . . . . . . . . . 26
21. Author's Address . . . . . . . . . . . . . . . . . . . . 28
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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 [RFC4506]. 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 [XRPC] 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.
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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:
o Error handling: failures of the remote server or network must be
handled when using remote procedure calls.
o 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.
o Performance: remote procedures usually operate one or more
orders of magnitude slower than local procedure calls.
o 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
[RFC793] 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, 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 [RFC768], 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
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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] is perhaps a natural transport for RPC. ONC RPC
currently 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. The mechanism by which future transports having different
structural characteristics should be used to transfer ONC RPC
messages should be specified by means of a standards-track RFC, once
such additional transports are defined.
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 in section 9: "Authentication Protocols".
7. RPC Protocol Requirements
The RPC protocol must provide for the following:
o Unique specification of a procedure to be called.
o Provisions for matching response messages to request messages.
o Provisions for authenticating the caller to service and vice-
versa.
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Besides these requirements, features that detect the following are
worth supporting because of protocol roll-over errors, implementation
bugs, user error, and network administration:
o RPC protocol mismatches.
o Remote program protocol version mismatches.
o Protocol errors (such as misspecification of a procedure's
parameters).
o Reasons why remote authentication failed.
o 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). 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:
o The remote implementation of RPC does not support protocol
version 2. The lowest and highest supported RPC version numbers
are returned.
o The remote program is not available on the remote system.
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o The remote program does not support the requested version
number. The lowest and highest supported remote program version
numbers are returned.
o The requested procedure number does not exist. (This is usually
a client side protocol or programming error.)
o 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
[RFC4506]):
enum auth_flavor {
AUTH_NONE = 0,
AUTH_SYS = 1,
AUTH_SHORT = 2,
AUTH_DH = 3,
RPCSEC_GSS = 6
/* 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 Reserved
1 - 0x1fffffff To be assigned by IANA
0x20000000 - 0x3fffffff Defined by local administrator
(some blocks assigned here)
0x40000000 - 0x5fffffff Transient
0x60000000 - 0x7effffff Reserved
0x7f000000 - 0x7fffffff Assignment outstanding
0x80000000 - 0xffffffff Reserved
The first group is a range of numbers administered by IANA 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 methods
described in Appendix B. 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
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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 [RFC4506].
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 /* e.g. 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 */
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/*
* 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 */
/*
* kerberos errors
*/
AUTH_KERB_GENERIC = 8, /* kerberos generic error */
AUTH_TIMEEXPIRE = 9, /* time of credential expired */
AUTH_TKT_FILE = 10, /* problem with ticket file */
AUTH_DECODE = 11, /* can't decode authenticator */
AUTH_NET_ADDR = 12, /* wrong net address in ticket */
/*
* GSS related errors
*/
RPCSEC_GSS_NOCRED = 13, /* no credentials for user */
RPCSEC_GSS_FAILED = 14 /* GSS failure, creds deleted */
};
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;
};
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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 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;
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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:
/*
* 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
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numbers, are also administered centrally, and developers may assign
new flavor numbers by methods described in Appendix B. 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 (AUTH_SYS) is described in Appendix A. It is strongly
recommended that implementors include AUTH_SYS in their
implementations to promote interoperability, since many applications
make use of this flavor. See "Security Considerations" for
information about other, more secure, authentication flavors.
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.
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
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"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:
proc-return identifier "(" proc-firstarg
("," type-specifier )* ")" "=" constant ";"
proc-return: "void" | type-specifier
proc-firstarg: "void" | type-specifier
11.3. Syntax Notes
o The following keywords are added and cannot be used as
identifiers: "program" and "version";
o 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.
o 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.
o Program identifiers are in the same name space as constant and
type identifiers.
o Only unsigned constants can be assigned to programs, versions
and procedures.
o Current RPC language compilers do not generally support more
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than one type-specifier in procedure argument lists; the usual
practice is to wrap arguments into a structure.
12. IANA Considerations
The assignment of RPC program numbers and authentication flavor
numbers has in the past been performed by Sun Microsystems, Inc.
This is inappropriate for an IETF standard protocol, as such work is
done well by the Internet Assigned Numbers Authority (IANA). This
document proposes the transfer of authority over RPC program numbers
and authentication flavor numbers described here from Sun
Microsystems, Inc. to IANA and proposes how IANA will maintain and
assign RPC program numbers and authentication flavor numbers. Users
of RPC protocols will benefit by having an independent body
responsible for RPC number assignments.
12.1. Numbering Requests to IANA
Appendix B of this document describes the information to be sent to
IANA to request one or more RPC numbers and the rules that apply.
IANA should review this part of the document as well.
12.2. Protecting Past Assignments
Sun has made assignments in both number spaces since the original
deployment of RPC. The assignments made by Sun Microsystems are
still valid, and will be preserved. Sun will communicate all current
assignments in both number spaces to IANA before final handoff of
number assignment is done.
12.3. RPC Number Assignment
Future IANA practice should deal with the following partitioning of
the 32-bit number space:
0 Reserved
1 - 0x1fffffff To be assigned by IANA
0x20000000 - 0x3fffffff Defined by local administrator
(see note1)
0x40000000 - 0x5fffffff Transient
0x60000000 - 0x7effffff Reserved
0x7f000000 - 0x7fffffff Assignment outstanding
0x80000000 - 0xffffffff Reserved
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Detailed information for the administration of these blocks is given
below.
12.3.1. To be assigned by IANA
The first block will be administered by IANA, with previous
assignments by Sun protected. Previous assignments were restricted
to the range decimal 100000-399999 (0x000186a0 to 0x00061a7f),
therefore IANA should begin assignments at decimal 400000.
Individual numbers should be grated on a first-come, first-served
basis, and blocks should be granted under rules related to the size
of the block.
12.3.2. Defined by local administrator
The "Defined by local administrator" block is available for any local
administrative domain to use, in a similar manner to IP address
ranges reserved for private use. The expected use would be through
the establishment of a local domain "authority" for assigning numbers
from this range. This authority would establish any policies or
procedures to be used within that local domain for use or assignment
of RPC numbers from the range. The local domain should be
sufficiently isolated that it would be unlikely that RPC applications
developed by other local domains could communicate with the domain.
This could result in RPC number contention, which would cause one of
the applications to fail. In the absence of a local administrator,
this block can be utilized in a "Private Use" manner per [RFC2434].
12.3.3. Transient block
The "Transient" block can be used by any RPC application on a "as
available" basis. This range is intended for services that can
communicate a dynamically selected RPC program number to clients of
the service. Any mechanism can be used to communicate the number.
Examples include shared memory when the client and server are located
on the same system, or a network message (either RPC or otherwise)
that disseminates the selected number.
The transient block is not administered. An RPC service uses this
range by selecting a number in the transient range and attempting to
register that number with the local system's RPC bindery (see the
RPCBPROC_SET or PMAPPROC_SET procedures in "Binding Protocols for ONC
RPC", [RFC1833]). If successful, no other RPC service was using that
number and the RPC Bindery has assigned that number to the requesting
RPC application. The registration is valid until the RPC Bindery
terminates, which normally would only happen if the system reboots
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causing all applications, including the RPC service using the
transient number, to terminate. If the transient number registration
fails, another RPC application is using the number and the requestor
must select another number and try again. To avoid conflicts, the
recommended method is to select a number randomly from the transient
range.
12.3.4. Reserved block
The "Reserved" blocks are available for future use. RPC applications
must not use numbers in these ranges unless their use is allowed by
future action by the IESG.
12.3.5. RPC Number Sub-Blocks
RPC numbers are usually assigned for specific RPC services. Some
applications, however, require multiple RPC numbers for a service.
The most common example is an RPC service that needs to have multiple
instances of the service active simultaneously at a specific site.
RPC does not have an "instance identifier" in the protocol, so either
a mechanism must be implemented to multiplex RPC requests amongst
various instances of the service, or unique RPC numbers must be used
by each instance.
In these cases, the RPC protocol used with the various numbers may be
different or the same. The numbers may be assigned dynamically by
the application, or as part of a site-specific administrative
decision. If possible, RPC services that dynamically assign RPC
numbers should use the "Transient" RPC number block defined in
section 2. If not possible, RPC number sub-blocks may be requested.
Assignment of RPC Number Sub-Blocks is controlled by the size of the
sub-block being requested. "Specification Required" and "IESG
Approval" are used as defined by [RFC2434] Section 2.
Size of sub-block Assignment Method Authority
----------------- ----------------- ---------
Up to 100 numbers First Come First Served IANA
Up to 1000 numbers Specification Required IANA
More than 1000 numbers IESG Approval required IESG
Note: sub-blocks can be any size. The limits given above are
maximums and smaller size sub-blocks are allowed.
Sub-blocks sized up to 100 numbers may be assigned by IANA on a First
Come First Served basis. The RPC Service Description included in the
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range must include an indication of how the sub-block is managed. At
minimum, the statement should indicate whether the sub-block is used
with a single RPC protocol or multiple RPC protocols, and whether the
numbers are dynamically assigned or statically (through
administrative action) assigned.
Sub-blocks of up to 1000 numbers must be documented in detail. The
documentation must describe the RPC protocol or protocols that are to
be used in the range. It must also describe how the numbers within
the sub-block are to be assigned or used.
Sub-blocks sized over 1000 numbers must be documented as described
above, however an Internet Draft must be submitted as an
Informational or Standards Track RFC. If accepted as either, IANA
will assign the requested number sub-block.
In order to avoid multiple requests of large blocks of numbers the
following rule is proposed.
Requests up to and including 100 RPC numbers are handled via the
First Come First Served assignment method. This 100 number
threshhold applies to the total number of RPC numbers assigned to an
individual or entity. For example, if an individual or entity first
requests say 70 numbers, and then later requests 40 numbers, then the
request for the 40 numbers will be assigned via the Specification
Required method. As long as the total number of numbers assigned
does not exceed 1000, IANA is free to waive the Specification
Required assignment for incremental requests of less than 100
numbers.
If an individual or entity has under 1000 numbers and later requests
an additional set of numbers such that the individual or entity would
over 1000 numbers, then the individual or entity will have the
additional request submitted to the IESG. IESG is free to waive the
IESG Action Required assignment method for incremental requests of
less than 1000 numbers.
12.4. RPC Authentication Flavor Number Assignment
The second number space is the authentication mechanism identifier,
or "flavor", number. This number is used to distinguish between
various authentication mechanisms which can be optionally used with
an RPC message. An authentication identifier is used in the "flavor"
field of the "opaque_auth" structure.
Recent progress in RPC security has moved away from new auth flavors
as used by AUTH_DH [DH], and focused on using the existing RPCSEC_GSS
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[RFC2203] flavor and inventing novel GSS-API mechanisms which can be
used with it, such as Even though RPCSEC_GSS is an assigned
authentication flavor, use of a new RPCSEC_GSS mechanism with NFS
([RFC1094] [RFC1813] and [RFC3530]) will require the registration of
'pseudo-flavors' which are used to negotiate security mechanisms in
an unambiguous way, as defined by [RFC2623]. Existing pseudo-flavors
have been granted in the decimal range 390000-390255 as described in
2.2.
For non-pseudo-flavor requests, IANA should begin granting RPC
authentication flavor numbers at 400000 to avoid conflicts with
currently granted numbers.
For authentication flavors to be used on the Internet, it is strongly
advised that an informational or standards-track RFC be published
describing the authentication mechanism behaviour and parameters.
13. Security Considerations
AUTH_SYS as described in Appendix A is known to be insecure due to
the lack of a verifier to permit the credential to be validated. Use
of AUTH_SYS is not recommended for services which permit clients to
modify data.
[RFC2203] defines a new security flavor, RPCSEC_GSS, which permits
GSS-API [RFC2743] mechanisms to be used for securing RPC. All non-
trivial RPC programs developed in future should implement
RPCSEC_GSS-based security appropriately. [RFC2623] describes how
this was done for a widely deployed RPC program.
14. 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.
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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).
15. Appendix B: Requesting RPC program or authentication numbers
RPC numbers which must be unique across all networks are assigned by
the Internet Assigned Number Authority. To apply for a single number
or a block of numbers, electronic mail must be sent to IANA
<iana@isi.edu> with the following information:
o The type of number(s) (program number or authentication flavor
number) sought
o How many numbers are sought
o The name of person or company which will use the number
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o An "identifier string" which associates the number with a
service
o Email address of the contact person for the service which will
be using the number.
o A short description of the purpose and use of the number
o If an authentication flavor number is sought, and the number
will be a 'pseudo-flavor' intended for use with RPCSEC_GSS and
NFS, mappings analogous to those in Section 4.2 of [RFC2623] are
required.
Specific numbers cannot be requested. Numbers are assigned on a
First Come First Served basis.
For all RPC authentication flavor numbers to used on the Internet, it
is strongly advised that an informational or standards-track RFC be
published describing the authentication mechanism behaviour and
parameters.
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16. Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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.
17. Intellectual property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
18. Acknowledgment
Funding for the RFC Editor function is provided by the IETF
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Administrative Support Activity (IASA).
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19. Normative References
[RFC4506]
Eisler, M., "XDR: External Data Representation Standard", RFC 4506,
May 2006
20. Informative References
[XRPC]
Birrell, A. D. & Nelson, B. J., "Implementing Remote Procedure
Calls", XEROX CSL-83-7, October 1983.
[VMTP]
Cheriton, D., "VMTP: Versatile Message Transaction Protocol",
Preliminary Version 0.3, Stanford University, January 1987.
[DH]
Diffie & Hellman, "New Directions in Cryptography", IEEE Transactions
on Information Theory IT-22, November 1976.
[RFC768]
Postel, J., "User Datagram Protocol", STD 6, RFC 768, USC/Information
Sciences Institute, August 1980.
[RFC793]
Postel, J., "Transmission Control Protocol - DARPA Internet Program
Protocol Specification", STD 7, RFC 793, USC/Information Sciences
Institute, September 1981.
[RFC1094]
Sun Microsystems, Inc., "NFS: Network File System Protocol
Specification", RFC 1094, March 1989.
[RFC1813]
Callaghan, B., Pawlowski, B., Staubach, P., "NFS Version 3 Protocol
Specification", RFC 1813, June 1995.
[RFC1831]
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R. Srinivasan, "RPC: Remote Procedure Call Protocol Specification
Version 2", RFC 1831, August 1995.
[RFC1833]
R. Srinivasan, "Binding Protocols for ONC RPC Version 2", RFC 1833,
August 1995.
[RFC2203]
Eisler, M., Chiu, A., Ling, L., "RPCSEC_GSS Protocol Specification",
RFC 2203, September 1997
[RFC2434]
Narten, T. and Alvestrand, H., "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 2434, October 1998.
[RFC2623]
Eisler, M., "NFS Version 2 and Version 3 Security Issues and the NFS
Protocol's Use of RPCSEC_GSS and Kerberos V5", RFC 2623, June 1999.
[RFC2743]
Linn. J., "Generic Security Service Application Program Interface
Version 2, Update 1", RFC 2743, January 2000.
[RFC3530]
Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame, C.,
Eisler, M., Noveck, D., "Network File System (NFS) version 4
Protocol", RFC 3530, April 2003.
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21. Author's Address
Address comments related to this memorandum to:
nfsv4@ietf.org
Robert Thurlow
Sun Microsystems, Inc.
500 Eldorado Boulevard, UBRM05-171
Broomfield, CO 80021
Phone: 877-718-3419
E-mail: robert.thurlow@sun.com
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