?? rfc4018.txt
字號:
Network Working Group M. Bakke
Request for Comments: 4018 Cisco
Category: Standards Track J. Hufferd
K. Voruganti
IBM
M. Krueger
HP
T. Sperry
Adaptec
April 2005
Finding Internet Small Computer Systems Interface (iSCSI) Targets
and Name Servers by Using Service Location Protocol version 2 (SLPv2)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The iSCSI protocol provides a way for hosts to access SCSI devices
over an IP network. This document defines the use of the Service
Location Protocol (SLP) by iSCSI hosts, devices, and management
services, along with the SLP service type templates that describe the
services they provide.
Table of Contents
1. Introduction................................................ 2
2. Notation Conventions........................................ 2
3. Terminology................................................. 3
4. Using SLP for iSCSI Service Discovery....................... 4
5. iSCSI SLP Templates......................................... 11
6. Security Considerations..................................... 18
7. IANA Considerations......................................... 19
8. Summary..................................................... 19
9. Normative References........................................ 19
10. Informative References...................................... 20
11. Acknowledgements............................................ 21
Bakke & Hufferd Standards Track [Page 1]
RFC 4018 iSCSI and SLPv2 April 2005
1. Introduction
iSCSI [RFC3720] is a protocol used to transport SCSI [SAM2] commands,
data, and status across an IP network. This protocol is connection-
oriented and is currently defined over TCP. iSCSI uses a client-
server relationship. The client end of the connection is an
initiator, and it sends SCSI commands; the server end of the
connection is called a target, and it receives and executes the
commands.
There are several methods an iSCSI initiator can use to find the
targets to which it should connect. Two of these methods can be
accomplished without the use of SLP:
- Each target and its address can be statically configured on the
initiator.
- Each address providing targets can be configured on the initiator;
iSCSI provides a mechanism by which the initiator can query the
address for a list of targets.
The above methods are further defined in "iSCSI Naming and Discovery
Requirements" [RFC3721].
Each of the above methods requires a small amount of configuration to
be done on each initiator. The ability to discover targets and name
services without having to configure initiators is a desirable
feature. The Service Location Protocol (SLP) [RFC2608] is an IETF
standards track protocol providing several features that will
simplify locating iSCSI services. This document describes how SLP
can be used in iSCSI environments to discover targets, addresses
providing targets, and storage management servers.
2. Notation Conventions
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in [RFC2119].
Bakke & Hufferd Standards Track [Page 2]
RFC 4018 iSCSI and SLPv2 April 2005
3. Terminology
Here are some definitions that may aid readers who are unfamiliar
with SLP, SCSI, or iSCSI. Some of these definitions have been
reproduced from [RFC2608] and "Finding an RSIP Server with SLP"
[RFC3105].
User Agent (UA) A process working on the client's behalf
to establish contact with some service.
The UA retrieves service information from
the Service Agents or Directory Agents.
Service Agent (SA) A process working on behalf of one or more
services to advertise the services and
their capabilities.
Directory Agent (DA) A process that collects service
advertisements. There can only be one DA
present per given host.
Scope A named set of services, typically making
up a logical administrative group.
Service Advertisement A URL, attributes, and a lifetime
(indicating how long the advertisement is
valid) providing service access
information and capabilities description
for a particular service.
Initiator A logical entity, typically within a host,
that sends SCSI commands to targets to be
executed. An initiator is usually present
in the form of a device driver.
Target A logical entity, typically within a
storage controller or gateway that
receives SCSI commands from an initiator
and executes them. A target includes one
or more Logical Units (LUs); each LU is a
SCSI device, such as a disk or tape drive.
iSCSI Name A UTF-8 character string that serves as a
unique identifier for iSCSI initiators and
targets. Its format and usage is further
defined in [RFC3721].
iSCSI Client A logical entity, typically a host that
includes at least one iSCSI Initiator.
Bakke & Hufferd Standards Track [Page 3]
RFC 4018 iSCSI and SLPv2 April 2005
iSCSI Server A logical entity, typically a storage
controller or gateway that includes at
least one iSCSI Target.
Storage Management Server An addressable entity that provides
management services that benefit an iSCSI
environment. "Storage management server"
is used as a generic term and does not
indicate a specific protocol or service.
4. Using SLP for iSCSI Service Discovery
Two entities are involved in iSCSI discovery. The end result is that
an iSCSI initiator (e.g., a host) discovers iSCSI targets, usually
provided by storage controllers or gateways.
iSCSI targets are registered with SLP as a set of service URLs, one
for each address on which the target may be accessed. Initiators
discover these targets by using SLP service requests. Targets that
do not directly support SLP or that are under the control of a
management service may be registered by a proxy service agent as part
of the software providing this service.
iSCSI entities may also use SLP to discover higher-level management
services when these are needed.
This section first describes the use of SLP for discovery of targets
by iSCSI initiators, it then describes the use of SLP to discover
storage management servers.
This document assumes that SLPv2 will be used for discovering iSCSI-
related services; no attempt is made to include support for SLPv1.
4.1. Discovering iSCSI Targets with SLP
The following diagram shows the relationship among iSCSI clients,
servers, initiators, and targets. An iSCSI client includes at least
one iSCSI initiator, and an SLP user agent (UA). An iSCSI server
includes at least one iSCSI target an SLP service agent (SA). Some
entities, such as extended copy engines, include both initiators and
targets. These include both an SA, for its targets to be discovered,
and a UA, for its initiator(s) to discover other targets.
Bakke & Hufferd Standards Track [Page 4]
RFC 4018 iSCSI and SLPv2 April 2005
+---------------------------------+
| iSCSI Client |
| +-----------+ |
| | iSCSI | |
| | initiator | |
| | "myhost" | |
| +-----------+ |
| |
+--------------------------+------+
| iSCSI Driver | UA |
+--------------------------+------+
| TCP/UDP/IP |
+----------------+----------------+
| Interface 1 | Interface 2 |
+----------------+----------------+
| |
+------------+ | | +------------+
| SLP DA | | | | SLP DA |
| (optional) |----+ IP Networks +----| (optional) |
+------------+ | | +------------+
| |
+-----------------+-----------------|
| Interface 1 | Interface 2 |
| 192.0.2.131 | 192.0.2.3 |
+-----------------+-----------------+
| TCP/UDP/IP |
+---------------------------+-------+
| iSCSI Driver | SA |
+---------------------------+-------|
| |
| +--------+ +--------+ +---------+ |
| | iSCSI | | iSCSI | | iSCSI | |
| | target | | target | | target | |
| | "one" | | "two" | | "three" | |
| +--------+ +--------+ +---------+ |
| iSCSI Server |
+-----------------------------------+
In the above drawing, the iSCSI server has three iSCSI targets that
the client could discover, named "one", "two" and "three". The iSCSI
client has an iSCSI initiator with the name "myhost". The iSCSI
client may use the initiator name in its SLP Service Requests as a
filter to discover only targets that are configured to accept iSCSI
connections from "myhost".
Each iSCSI target and initiator has a unique name, called an iSCSI
Name. This identifier is the same regardless of the network path
(through adapter cards, networks, and interfaces on the storage
Bakke & Hufferd Standards Track [Page 5]
RFC 4018 iSCSI and SLPv2 April 2005
device) over which the target is discovered and accessed. For this
example, the iSCSI names "one", "two", and "three" are used for the
targets; the initiator uses the name "myhost". An actual iSCSI name
would incorporate more structure, including a naming authority, and
is not described here.
Each of the iSCSI targets in the drawing can appear at two addresses,
since two network interfaces are present. Each target would have two
service URLs, unless a single service URL included a DNS host name
mapping to both addresses.
An iSCSI target URL consists of its fully qualified host name or IP
address, the TCP port on which it is listening, and its iSCSI name.
An iSCSI server must register each of its individual targets at each
of its network addresses.
The iSCSI server constructs a service advertisement of the type
"service:iscsi:target" for each of the service URLs it wishes to
register. The advertisement contains a lifetime, along with other
attributes that are defined in the service template.
If the server in the above drawing is listening at TCP port 3260 for
both network addresses, the service URLs registered would be
- 192.0.2.131:3260/one
- 192.0.2.131:3260/two
- 192.0.2.131:3260/three
- 192.0.2.3:3260/one
- 192.0.2.3:3260/two
- 192.0.2.3:3260/three
The remainder of the discovery procedure is identical to that used by
any client/server pair implementing SLP:
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