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Network File System Version 4 C. Lever
Internet-Draft Oracle
Intended status: Standards Track 6 April 2021
Expires: 8 October 2021
Network File System (NFS) Upper-Layer Binding To RPC-Over-RDMA Version 2
draft-ietf-nfsv4-nfs-ulb-v2-04
Abstract
This document specifies Upper-Layer Bindings of Network File System
(NFS) protocol versions to RPC-over-RDMA version 2.
Note
Discussion of this draft takes place on the NFSv4 working group
mailing list (nfsv4@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/nfsv4/. Working Group
information can be found at https://datatracker.ietf.org/wg/nfsv4/
about/.
This note is to be removed before publishing as an RFC.
The source for this draft is maintained in GitHub. Suggested changes
can be submitted as pull requests at https://github.com/chucklever/
i-d-nfs-ulb-v2. Instructions are on that page as well.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 8 October 2021.
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Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Upper-Layer Binding for NFS Versions 2 and 3 . . . . . . . . 4
3.1. Reply Size Estimation . . . . . . . . . . . . . . . . . . 4
3.2. RPC Binding Considerations . . . . . . . . . . . . . . . 5
3.3. Transport Considerations . . . . . . . . . . . . . . . . 5
4. Upper-Layer Bindings for NFS Version 2 and 3 Auxiliary
Protocols . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. MOUNT, NLM, and NSM Protocols . . . . . . . . . . . . . . 7
4.2. NFSACL Protocol . . . . . . . . . . . . . . . . . . . . . 7
5. Upper-Layer Binding For NFS Version 4 . . . . . . . . . . . . 7
5.1. DDP-Eligibility . . . . . . . . . . . . . . . . . . . . . 7
5.2. Reply Size Estimation . . . . . . . . . . . . . . . . . . 9
5.3. RPC Binding Considerations . . . . . . . . . . . . . . . 10
5.4. NFS COMPOUND Requests . . . . . . . . . . . . . . . . . . 10
5.5. NFS Callback Requests . . . . . . . . . . . . . . . . . . 12
5.6. Session-Related Considerations . . . . . . . . . . . . . 13
5.7. Transport Considerations . . . . . . . . . . . . . . . . 14
6. Extending NFS Upper-Layer Bindings . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Normative References . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . 17
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 18
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
The RPC-over-RDMA version 2 transport may employ direct data
placement to convey data payloads associated with RPC transactions,
as described in [I-D.ietf-nfsv4-rpcrdma-version-two]. RPC client and
server implementations using RPC-over-RDMA version 2 must agree which
XDR data items and RPC procedures are eligible to use direct data
placement (DDP) to ensure successful interoperation.
An Upper-Layer Binding specifies this agreement for one or more
versions of one RPC program. Other operational details, such as RPC
binding assignments, pairing Write chunks with result data items, and
reply size estimation, are also specified by such a Binding.
This document contains material required of Upper-Layer Bindings, as
specified in Appendix A of [I-D.ietf-nfsv4-rpcrdma-version-two], for
the following NFS protocol versions:
* NFS version 2 [RFC1094]
* NFS version 3 [RFC1813]
* NFS version 4.0 [RFC7530]
* NFS version 4.1 [RFC8881]
* NFS version 4.2 [RFC7862]
The current document also provides Upper-Layer Bindings for auxiliary
protocols used with NFS versions 2 and 3 (see Section 4).
This document assumes the reader is already familiar with concepts
and terminology defined throughout
[I-D.ietf-nfsv4-rpcrdma-version-two] and the documents it references.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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3. Upper-Layer Binding for NFS Versions 2 and 3
The Upper-Layer Binding specification in this section applies to NFS
version 2 [RFC1094] and NFS version 3 [RFC1813]. For brevity, in
this document, a "Legacy NFS client" refers to an NFS client using
version 2 or version 3 of the NFS RPC program (100003) to communicate
with an NFS server. Likewise, a "Legacy NFS server" is an NFS server
communicating with clients using NFS version 2 or NFS version 3.
The following XDR data items in NFS versions 2 and 3 are DDP-
eligible:
* The opaque file data argument in the NFS WRITE procedure
* The pathname argument in the NFS SYMLINK procedure
* The opaque file data result in the NFS READ procedure
* The pathname result in the NFS READLINK procedure
All other argument or result data items in NFS versions 2 and 3 are
not DDP-eligible.
Whether or not an NFS operation is considered non-idempotent, a
transport error might not indicate whether the server has processed
the arguments of the RPC Call, or whether the server has accessed or
modified client memory associated with that RPC.
3.1. Reply Size Estimation
During the construction of each RPC Call message, a Requester is
responsible for allocating appropriate transport resources to receive
the corresponding Reply message. These resources must be capable of
holding the entire Reply, therefore the Requester needs to estimate
the maximum possible size of the expected Reply message.
* In many cases, the expected Reply can fit in one or a few RDMA
Send messages. The Requester need not provision any RDMA
resources, relying instead on message continuation to handle the
entire Reply message.
* In cases where the Requester deems direct data placement to be the
most efficient transfer mechanism, it provisions Write chunks
wherein the Responder can place results. In these cases, the
Requester must reliably estimate the maximum size of each result
that is to be placed in a Write chunk.
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* When the Requester expects an especially large Reply message, it
can provision a combination of a Reply chunk and Write chunks for
result data items. In such cases, the Requester must reliably
estimate the maximum size of each result that is to be placed in a
Write chunk and the maximum size of the remainder to be placed in
the Reply chunk.
A legacy NFS client needs to make every effort to avoid
retransmission of non-idempotent NFS requests due to underestimated
Reply resources. Thanks to the mechanism of message continuation in
RPC-over-RDMA version 2, the need for such retransmission is greatly
reduced.
3.2. RPC Binding Considerations
Legacy NFS servers traditionally listen for clients on UDP and TCP
port 2049. Additionally, they register these ports with a local
portmapper service [RFC1833].
A Legacy NFS server supporting RPC-over-RDMA version 2 and
registering itself with the RPC portmapper MAY choose an arbitrary
port, or MAY use the alternative well-known port number for its RPC-
over-RDMA service (see Section 8). The chosen port MAY be registered
with the RPC portmapper using the netids assigned in Section 12 of
[I-D.ietf-nfsv4-rpcrdma-version-two].
3.3. Transport Considerations
Legacy NFS client implementations often rely on a transport-layer
keep-alive mechanism to detect when a legacy server has become
unresponsive. When an NFS server is no longer responsive, client-
side keep-alive terminates the connection, which in turn triggers
reconnection and retransmission of outstanding RPC transactions.
3.3.1. Keep-Alive
Some RDMA transports (such as the Reliable Connected QP type on
InfiniBand) have no keep-alive mechanism. Without a disconnect or
new RPC traffic, such connections can remain alive long after an NFS
server has become unresponsive or unreachable. Once an NFS client
has consumed all available RPC-over-RDMA version 2 credits on that
transport connection, it awaits a reply indefinitely before sending
another RPC request.
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Legacy NFS clients SHOULD reserve one RPC-over-RDMA version 2 credit
to use for periodic server or connection health assessment. Either
peer can use this credit to drive an RPC request on an otherwise idle
connection, triggering either an affirmative server response or a
connection termination.
3.3.2. Replay Detection
Legacy NFS servers typically employ request replay detection to
reduce the risk of data and file namespace corruption that could
result when an NFS client retransmits a non-idempotent NFS request.
A legacy NFS server can send a cached response when a replay is
detected, rather than executing the request again. Replay detection
is not perfect, but it is usually adequate.
For legacy NFS servers, replay detection commonly utilizes heuristic
indicators such as the IP address of the NFS client, the source port
of the connection, the transaction ID of the request, and the
contents of the request's RPC and upper-layer protocol headers. In
short, replay detection is typically based on a connection tuple and
the request's XID. A legacy NFS client is careful to re-use the same
source port, if practical, when reconnecting so that legacy NFS
servers are better able to detect retransmissions.
However, a legacy NFS client operating over an RDMA transport has no
control over connection source ports. It is almost certain that an
RPC request that is retransmitted on a new connection can never be
detected as a replay if the legacy NFS server includes the connection
source port in its replay detection heuristics.
Therefore a legacy NFS server using an RDMA transport should never
use a legacy NFS client connection's source port as part of its NFS
request replay detection mechanism.
4. Upper-Layer Bindings for NFS Version 2 and 3 Auxiliary Protocols
Storage administrators typically deploy NFS versions 2 and 3 with
several other protocols, sometimes referred to as the "NFS auxiliary
protocols." These are distinct RPC programs that define procedures
that are not part of the NFS RPC program (100003). The Upper-Layer
Bindings in this section apply to:
* Versions 2 and 3 of the MOUNT RPC program (100005) [RFC1813]
* Versions 1, 3, and 4 of the NLM RPC program (100021) [RFC1813]
* Version 1 of the NSM RPC program (100024), described in Chapter 11
of [XNFS]
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* Versions 2 and 3 of the NFSACL RPC program (100227). The NFSACL
program does not have a public definition. In this document it is
treated as a de facto standard, as there are several
interoperating implementations.
4.1. MOUNT, NLM, and NSM Protocols
Historically, NFS/RDMA implementations have chosen to convey the
MOUNT, NLM, and NSM protocols via TCP. A legacy NFS server
implementation MUST provide support for these protocols via TCP to
enable interoperation of these protocols when NFS/RDMA is in use.
4.2. NFSACL Protocol
Often legacy clients and servers that support the NFSACL RPC program
convey NFSACL procedures on the same transport connection and port as
the NFS RPC program (100003). Utilizing the same port obviates the
need for separate a rpcbind query to discover server support for this
RPC program.
ACLs are typically small, but even large ACLs must be encoded and
decoded to some degree before being made available to users. Thus no
data item in this Upper-Layer Protocol is DDP-eligible.
For procedures whose replies do not include an ACL object, the size
of a reply is determined directly from the NFSACL RPC program's XDR
definition. However, legacy client implementations should choose a
maximum size for ACLs based on internal limits, and can rely on
message continuation to handle the a priori unknown size of large ACL
objects in Replies.
5. Upper-Layer Binding For NFS Version 4
The Upper-Layer Binding specification in this section applies to
versions of the NFS RPC program defined in NFS version 4.0 [RFC7530]
NFS version 4.1 [RFC8881] and NFS version 4.2 [RFC7862].
5.1. DDP-Eligibility
Only the following XDR data items in the COMPOUND procedure of all
NFS version 4 minor versions are DDP-eligible:
* The opaque data field in the WRITE4args structure
* The linkdata field of the NF4LNK arm in the createtype4 union
* The opaque data field in the READ4resok structure
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* The linkdata field in the READLINK4resok structure
5.1.1. The NFSv4.2 READ_PLUS operation
NFS version 4.2 introduces an enhanced READ operation called
READ_PLUS [RFC7862]. READ_PLUS enables an NFS server to perform data
reduction of READ results so that the returned READ data is more
compact.
In a READ_PLUS result, returned file content appears as a list of one
or more of the following items:
* Regular data content: the same as the result of a traditional READ
operation.
* Unallocated space in a file: where no data has yet been written or
previously-written data has been removed via a hole-punch
operation.
* A counted pattern.
Upon receipt of a READ_PLUS result, an NFSv4.2 client expands the
returned list into the preferred local representation of the original
file content.
Before receiving that result, an NFSv4.2 client typically does not
know how the file's content is organized on the NFS server. Thus it
is not possible to predict the size or structure of a READ_PLUS Reply
in advance. The use of direct data placement is therefore
challenging.
A READ_PLUS content list containing more than one segment of regular
file data could be conveyed using multiple Write chunks, but only if
the client knows in advance where those chunks appear in the Reply
Payload stream. Moreover, the usual benefits of hardware-assisted
data placement are entirely waived if the client-side transport must
parse the result of each read I/O.
Therefore this Upper Layer Binding does not make any element of an
NFSv4.2 READ_PLUS Reply DDP-eligible. Further, this Upper Layer
Binding recommends that implementations avoid the use of the
READ_PLUS operation on NFS/RDMA mount points.
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5.2. Reply Size Estimation
Within NFS version 4, there are certain variable-length result data
items whose maximum size cannot be estimated by clients reliably
because there is no protocol-specified size limit on these result
arrays. These include:
* The attrlist4 field
* Fields containing ACLs such as fattr4_acl, fattr4_dacl, and
fattr4_sacl
* Fields in the fs_locations4 and fs_locations_info4 data structures
* Fields which pertain to pNFS layout metadata, such as loc_body,
loh_body, da_addr_body, lou_body, lrf_body, fattr_layout_types,
and fs_layout_types
5.2.1. Reply Size Estimation for Minor Version 0
The NFS version 4.0 protocol itself does not impose any bound on the
size of NFS calls or replies.
Some of the data items enumerated in Section 5.2 (in particular, the
items related to ACLs and fs_locations) make it difficult to predict
the maximum size of NFS version 4.0 replies that interrogate
variable-length fattr4 attributes. Client implementations might rely
upon internal architectural limits to constrain the reply size, but
such limits are not always guaranteed to be reliable.
When an NFS version 4.0 client expects an especially sizeable fattr4
result, it can rely on message continuation or provision a Reply
chunk to enable that server to return that result via explicit RDMA.
5.2.2. Reply Size Estimation for Minor Version 1 and Newer
In NFS version 4.1 and newer minor versions, the csa_fore_chan_attrs
argument of the CREATE_SESSION operation contains a
ca_maxresponsesize field. The value in this field can be taken as
the absolute maximum size of replies generated by an NFS version 4.1
server.
An NFS version 4 client can use this value in cases where it is not
possible to estimate a reply size upper bound precisely. In
practice, objects such as ACLs, named attributes, layout bodies, and
security labels are much smaller than this maximum.
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5.3. RPC Binding Considerations
NFS version 4 servers are required to listen on TCP port 2049, and
are not required to register with an rpcbind service [RFC7530].
Therefore, an NFS version 4 server supporting RPC-over-RDMA version 2
MUST use the alternative well-known port number for its RPC-over-RDMA
service (see Section 8 Clients SHOULD connect to this well-known port
without consulting the RPC portmapper (as for NFS version 4 on TCP
transports).
5.4. NFS COMPOUND Requests
5.4.1. Multiple DDP-eligible Data Items
An NFS version 4 COMPOUND procedure can contain more than one
operation that carries a DDP-eligible data item. An NFS version 4
client provides XDR Position values in each Read chunk to
disambiguate which chunk is associated with which argument data item.
However, NFS version 4 server and client implementations must agree
in advance on how to pair Write chunks with returned result data
items.
In the following lists, a "READ operation" refers to any NFS version
4 operation that has a DDP-eligible result data item. An NFS version
4 client applies the mechanism specified in Section 4.3.2 of
[I-D.ietf-nfsv4-rpcrdma-version-two] to this class of operations as
follows:
* If an NFS version 4 client wishes all DDP-eligible items in an NFS
reply to be conveyed inline, it leaves the Write list empty.
An NFS version 4 server acts as follows:
* The first chunk in the Write list MUST be used by the first READ
operation in an NFS version 4 COMPOUND procedure. The next Write
chunk is used by the next READ operation, and so on.
* If an NFS version 4 client has provided a matching non-empty Write
chunk, then the corresponding READ operation MUST return its DDP-
eligible data item using that chunk.
* If an NFS version 4 client has provided an empty matching Write
chunk, then the corresponding READ operation MUST return all of
its result data items inline.
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* If a READ operation returns a union arm which does not contain a
DDP-eligible result, and the NFS version 4 client has provided a
matching non-empty Write chunk, an NFS version 4 server MUST
return an empty Write chunk in that Write list position.
* If there are more READ operations than Write chunks, then
remaining NFS Read operations in an NFS version 4 COMPOUND that
have no matching Write chunk MUST return their results inline.
5.4.2. Chunk List Complexity
By default, the RPC-over-RDMA version 2 protocol places limits on the
number of chunks or segments that may appear in Read or Write lists
(see Section 5.2 of [I-D.ietf-nfsv4-rpcrdma-version-two]).
These implementation limits are especially important when Kerberos
integrity or privacy is in use [RFC7861]. GSS services increase the
size of credential material in RPC headers, potentially requiring the
use of a Long message, which increases the complexity of chunk lists
independent of the particular NFS version 4 COMPOUND being conveyed.
In the absence of an explicit transport property exchange that alters
these limits, NFS version 4 clients SHOULD follow the prescriptions
listed below when constructing RPC-over-RDMA version 2 messages. NFS
version 4 servers MUST accept and process all such requests.
* The Read list can contain either a Position-Zero Read chunk, one
Read chunk with a non-zero Position, or both.
* The Write list can contain no more than one Write chunk.
NFS version 4 clients wishing to send more complex chunk lists can
provide configuration interfaces to bound the complexity of NFS
version 4 COMPOUNDs, limit the number of elements in scatter-gather
operations, and avoid other sources of chunk overruns at the
receiving peer.
If an NFS version 4 server receives an RPC request via RPC-over-RDMA
version 2 that it cannot process due to chunk list complexity limits,
it SHOULD return one of the following responses to the client:
* A problem is detected by the transport layer while parsing the
transport header in an RPC Call message. The server responds with
an RDMA2_ERROR message with the err field set to ERR_CHUNK.
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* A problem is detected during XDR decoding of the RPC Call message
while the RPC layer reassembles the call's XDR stream. The server
responds with an RPC reply with its "reply_stat" field set to
MSG_ACCEPTED and its "accept_stat" field set to GARBAGE_ARGS.
After receiving one of these errors, an NFS version 4 client SHOULD
NOT retransmit the failing request, as the result would be the same
error. It SHOULD terminate the RPC transaction associated with the
XID in the reply without further processing, and report an error to
the RPC consumer.
5.4.3. NFS Version 4 COMPOUND Example
The following example shows a Write list with three Write chunks, A,
B, and C. The NFS version 4 server consumes the provided Write
chunks by writing the results of the designated operations in the
compound request (READ and READLINK) back to each chunk.
Write list:
A --> B --> C
NFS version 4 COMPOUND request:
PUTFH LOOKUP READ PUTFH LOOKUP READLINK PUTFH LOOKUP READ
| | |
v v v
A B C
If the NFS version 4 client does not want to have the READLINK result
returned via RDMA, it provides an empty Write chunk for buffer B to
indicate that the READLINK result must be returned inline.
5.5. NFS Callback Requests
The NFS version 4 family of protocols support server-initiated
callbacks to notify NFS version 4 clients of events such as recalled
delegations.
5.5.1. NFS Version 4.0 Callback
An NFS version 4.0 client uses the SETCLIENTID operation to advertise
the IP address, port, and netid of its NFS version 4.0 callback
service. When an NFS version 4.0 server provides a backchannel
service to an NFS version 4.0 client that uses RPC-over-RDMA version
2 for its forward channel, the server MUST advertise the backchannel
service using either the "tcp" or "tcp6" netid.
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Because the backchannel does not operate on RPC-over-RDMA, no XDR
data item in the NFS version 4.0 callback RPC program is DDP-
eligible.
5.5.2. NFS Version 4.1 Callback
In NFS version 4.1 and newer minor versions, callback operations may
appear on the same connection that is in use for NFS version 4
forward channel client requests. NFS version 4 clients and servers
MUST use the mechanisms described in Section 4.5 of
[I-D.ietf-nfsv4-rpcrdma-version-two] to convey backchannel operations
on an RPC-over-RDMA version 2 transport.
The csa_back_chan_attrs argument of the CREATE_SESSION operation
contains a ca_maxresponsesize field. The value in this field is the
absolute maximum size of backchannel replies generated by a replying
NFS version 4 client.
There are no DDP-eligible data items in callback procedures defined
in NFS version 4.1 or NFS version 4.2. However, some callback
operations, such as messages that convey device ID information, can
be sizeable. A sender can use Message Continuation or a Long message
in this situation.
When an NFS version 4.1 client can support Long Calls in its
backchannel, it reports a backchannel ca_maxrequestsize that is
larger than the connection's inline thresholds. Otherwise, an NFS
version 4 server MUST use only Short messages to convey backchannel
operations.
5.6. Session-Related Considerations
The presence of an NFS version 4 session (as defined in [RFC8881])
does not effect the operation of RPC-over-RDMA version 2. None of
the operations introduced to support NFS sessions (e.g., the SEQUENCE
operation) contain DDP-eligible data items. There is no need to
match the number of session slots with the number of available RPC-
over-RDMA version 2 credits.
However, there are a few new cases where an RPC transaction can fail.
For example, a Requester might receive, in response to an RPC
request, an RDMA2_ERROR message with a rdma_err value of ERR_CHUNK.
These situations are not different from existing RPC errors, which an
NFS session implementation can already handle for other transport
types. Moreover, there might be no SEQUENCE result available to the
Requester to distinguish whether failure occurred before or after the
Responder executed the requested operations.
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When a transport error occurs (e.g., an RDMA2_ERROR type message is
received), the Requester proceeds, as usual, to match the incoming
XID value to a waiting RPC Call. The Requester terminates the RPC
transaction and reports the result status to the RPC consumer. The
Requester's session implementation then determines the session ID and
slot for the failed request and performs slot recovery to make that
slot usable again. Otherwise, that slot could be rendered
permanently unavailable.
When an NFS session is not present (for example, when NFS version 4.0
is in use), a transport error does not indicate whether the server
has processed the arguments of the RPC Call, or whether the server
has accessed or modified client memory associated with that RPC.
5.7. Transport Considerations
5.7.1. Congestion Avoidance
Section 3.1 of [RFC7530] states:
Where an NFS version 4 implementation supports operation over the
IP network protocol, the supported transport layer between NFS and
IP MUST be an IETF standardized transport protocol that is
specified to avoid network congestion; such transports include TCP
and the Stream Control Transmission Protocol (SCTP).
Section 2.9.1 of [RFC8881] further states:
Even if NFS version 4.1 is used over a non-IP network protocol, it
is RECOMMENDED that the transport support congestion control.
It is permissible for a connectionless transport to be used under
NFS version 4.1; however, reliable and in-order delivery of data
combined with congestion control by the connectionless transport
is REQUIRED. As a consequence, UDP by itself MUST NOT be used as
an NFS version 4.1 transport.
RPC-over-RDMA version 2 utilizes only reliable, connection-oriented
transports that guarantee in-order delivery, meeting all the above
requirements for NFS version 4.0 and 4.1. See Section 4.2.1 of
[I-D.ietf-nfsv4-rpcrdma-version-two] for more details.
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5.7.2. Retransmission and Keep-alive
NFS version 4 client implementations often rely on a transport-layer
keep-alive mechanism to detect when an NFS version 4 server has
become unresponsive. When an NFS server is no longer responsive,
client-side keep-alive terminates the connection, which in turn
triggers reconnection and RPC retransmission.
Some RDMA transports (such as the Reliable Connected QP type on
InfiniBand) have no keep-alive mechanism. Without a disconnect or
new RPC traffic, such connections can remain alive long after an NFS
server has become unresponsive. Once an NFS client has consumed all
available RPC-over-RDMA version 2 credits on that transport
connection, it indefinitely awaits a reply before sending another RPC
request.
NFS version 4 clients SHOULD reserve one RPC-over-RDMA version 2
credit to use for periodic server or connection health assessment.
Either peer can use this credit to drive an RPC request on an
otherwise idle connection, triggering either a quick affirmative
server response or immediate connection termination.
In addition to network partition and request loss scenarios, RPC-
over-RDMA version 2 transport connections can be terminated when a
Transport header is malformed, Reply messages exceed receive
resources, or when too many RPC-over-RDMA messages are sent at once.
In such cases:
* If a transport error occurs (e.g., an RDMA2_ERROR type message is
received) before the disconnect or instead of a disconnect, the
Requester MUST respond to that error as prescribed by the
specification of the RPC transport. Then the NFS version 4 rules
for handling retransmission apply.
* If there is a transport disconnect and the Responder has provided
no other response for a request, then only the NFS version 4 rules
for handling retransmission apply.
6. Extending NFS Upper-Layer Bindings
RPC programs such as NFS are required to have an Upper-Layer Binding
specification to interoperate on RPC-over-RDMA version 2 transports
[I-D.ietf-nfsv4-rpcrdma-version-two]. Via standards action, the
Upper-Layer Binding specified in this document can be extended to
cover versions of the NFS version 4 protocol specified after NFS
version 4 minor version 2, or to cover separately published
extensions to an existing NFS version 4 minor version, as described
in [RFC8178].
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7. Security Considerations
RPC-over-RDMA version 2 supports all RPC security models, including
RPCSEC_GSS security and transport-level security [RFC7861]. The
choice of what Direct Data Placement mechanism to convey RPC argument
and results does not affect this since it changes only the method of
data transfer. Because the current document defines only the binding
of the NFS protocols atop RPC-over-RDMA version 2
[I-D.ietf-nfsv4-rpcrdma-version-two], all relevant security
considerations are, therefore, described at that layer.
8. IANA Considerations
The use of direct data placement in NFS introduces a need for an
additional port number assignment for networks that share traditional
UDP and TCP port spaces with RDMA services. The iWARP protocol is
such an example [RFC5040] [RFC5041].
For this purpose, the current document specifies a set of transport
protocol port number assignments. IANA has assigned the following
ports for NFS/RDMA in the IANA port registry, according to the
guidelines described in [RFC6335].
nfsrdma 20049/tcp Network File System (NFS) over RDMA
nfsrdma 20049/udp Network File System (NFS) over RDMA
nfsrdma 20049/sctp Network File System (NFS) over RDMA
The current document should be added as a reference for the nfsrdma
port assignments. The current document does not alter these
assignments.
9. References
9.1. Normative References
[I-D.ietf-nfsv4-rpcrdma-version-two]
Lever, C. and D. Noveck, "RPC-over-RDMA Version 2
Protocol", Work in Progress, Internet-Draft, draft-ietf-
nfsv4-rpcrdma-version-two-03, 10 August 2020,
<https://tools.ietf.org/html/draft-ietf-nfsv4-rpcrdma-
version-two-03>.
[RFC1833] Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
RFC 1833, DOI 10.17487/RFC1833, August 1995,
<https://www.rfc-editor.org/info/rfc1833>.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011,
<https://www.rfc-editor.org/info/rfc6335>.
[RFC7530] Haynes, T., Ed. and D. Noveck, Ed., "Network File System
(NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
March 2015, <https://www.rfc-editor.org/info/rfc7530>.
[RFC7861] Adamson, A. and N. Williams, "Remote Procedure Call (RPC)
Security Version 3", RFC 7861, DOI 10.17487/RFC7861,
November 2016, <https://www.rfc-editor.org/info/rfc7861>.
[RFC7862] Haynes, T., "Network File System (NFS) Version 4 Minor
Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
November 2016, <https://www.rfc-editor.org/info/rfc7862>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8881] Noveck, D., Ed. and C. Lever, "Network File System (NFS)
Version 4 Minor Version 1 Protocol", RFC 8881,
DOI 10.17487/RFC8881, August 2020,
<https://www.rfc-editor.org/info/rfc8881>.
9.2. Informative References
[RFC1094] Nowicki, B., "NFS: Network File System Protocol
specification", RFC 1094, DOI 10.17487/RFC1094, March
1989, <https://www.rfc-editor.org/info/rfc1094>.
[RFC1813] Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
Version 3 Protocol Specification", RFC 1813,
DOI 10.17487/RFC1813, June 1995,
<https://www.rfc-editor.org/info/rfc1813>.
[RFC5040] Recio, R., Metzler, B., Culley, P., Hilland, J., and D.
Garcia, "A Remote Direct Memory Access Protocol
Specification", RFC 5040, DOI 10.17487/RFC5040, October
2007, <https://www.rfc-editor.org/info/rfc5040>.
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[RFC5041] Shah, H., Pinkerton, J., Recio, R., and P. Culley, "Direct
Data Placement over Reliable Transports", RFC 5041,
DOI 10.17487/RFC5041, October 2007,
<https://www.rfc-editor.org/info/rfc5041>.
[RFC8178] Noveck, D., "Rules for NFSv4 Extensions and Minor
Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017,
<https://www.rfc-editor.org/info/rfc8178>.
[XNFS] The Open Group, "Protocols for Interworking: XNFS, Version
3W", February 1998.
Acknowledgments
Thanks to Tom Talpey, who contributed the text of Section 5.4.2.
David Noveck contributed the text of Section 5.6 and Section 6. The
author also wishes to thank Bill Baker and Greg Marsden for their
support of this work.
Special thanks go to Transport Area Director Magnus Westerlund, NFSV4
Working Group Chairs Brian Pawlowski, and David Noveck, and NFSV4
Working Group Secretary Thomas Haynes for their support.
Author's Address
Charles Lever
Oracle Corporation
United States of America
Email: chuck.lever@oracle.com
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