Internet Draft Mark Bakke
<draft-ietf-ips-iscsi-slp-00> Cisco
Expires October 2001
Joe Czap
IBM
Jim Hafner
IBM
Howard Hall
Pirus
Jack Harwood
EMC
John Hufferd
IBM
Yaron Klein
Sanrad
Lawrence Lamers
San Valley Systems
Todd Sperry
Adaptec
Joshua Tseng
Nishan
Kaladhar Voruganti
IBM
April 2001
Finding iSCSI Targets and Name Servers Using SLP
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
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Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
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 name services,
along with the SLP service type templates that describe the services
they provide.
1. Acknowledgements
This draft was produced as a companion document for the iSCSI Naming
and Discovery team, including Joe Czap, Jim Hafner, John Hufferd, and
Kaladhar Voruganti (IBM), Howard Hall (Pirus), Jack Hardwood (EMC),
Yaron Klein (Sanrad), Lawrence Lamers (San Valley), Todd Sperry
(Adaptec), and Joshua Tseng (Nishan). Thanks also to Julian Satran
(IBM) for suggesting the use of SLP for iSCSI discovery, and to Matt
Peterson (Caldera) and James Kempf (Sun) for reviewing the document
from an SLP perspective.
2. Introduction
iSCSI [iSCSI] 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 sends SCSI commands; the server end of the connection
is called a target, and receives and executes the commands.
There are several methods an iSCSI initiator can use to find the
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targets to which it should connect. The discovery of iSCSI targets
can be configured on the initiator in several ways:
- Each target and its address can be statically configured on the
initiator.
- Each address providing targets can be configured on the initiator;
the initiator can query the address for a list of targets.
- A storage name server address can be configured on the initiator;
the initiator can use the storage name servers's protocol it
provides to obtain a list of targets.
These methods are further defined in "iSCSI Naming and Discovery
Requirements" [NDT].
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) [SLP] is an IETF
standards track protocol that provides 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 name servers.
3. Notation Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
4. Terminology
Here are some definitions that may aid readers that are unfamiliar
with either SLP, SCSI, or iSCSI. Some of these definitions have been
reproduced from [RFC2608] and "Finding an RSIP Server with SLP"
[RSIP].
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
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capabilites.
Directory Agent (DA) A process which 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 which serves as a
unique identifier for iSCSI initiators and
targets. Its format and usage is further
defined in [NDT].
iSCSI Client A logical entity, typically a host, which
includes at least one iSCSI Initiator.
iSCSI Server A logical entity, typically a storage
controller or gateway, which includes at least
one iSCSI Target.
Storage Name Server An addressible entity that provides one of
several discovery and management services that
benefit an iSCSI environment. Storage Name
Server is used as a generic term, and is not
necessarily equivalent to that used within
Fibre Channel.
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5. Using SLP for iSCSI Service Discovery
At least 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. An
iSCSI initiator may either discover these targets directly, using
SLP, or may opt to discover them through a storage name service. One
name service protocol currently under development is iSNS [ISNS]. In
the first case, only SLP is needed. In the second, SLP may be used
to discover a name server, which can be used to provide additional
capabilities beyond simple target discovery.
This section first describes the use of SLP for discovery of targets
by iSCSI initiators, and then describes the use of SLP to discover
storage name servers.
This document assumes that SLPv2 will be used when discovering iSCSI-
related services; no attempt is made to include support for SLPv1.
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5.1. Discovering iSCSI Targets using SLP
The following diagram shows the relationship between 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, and 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 intiator(s) to discover other targets.
+---------------------------------+
| iSCSI Client |
| |
| +-----------+ |
| | iSCSI | |
| | initiator | |
| +-----------+ |
| |
+--------------------------+------+
| iSCSI Driver | UA |
+--------------------------+------+
| TCP/UDP/IP |
+----------------+----------------+
| Interface 1 | Interface 2 |
+----------------+----------------+
| |
+------------+ | | +------------+
| SLP DA | | | | SLP DA |
| |----+ IP Networks +----| |
| (optional) | | | | (optional) |
+------------+ | | +------------+
| |
+-----------------+-----------------|
| Interface 1 | Interface 2 |
| 10.1.30.21 | 10.1.40.3 |
+-----------------+-----------------+
| TCP/UDP/IP |
+---------------------------+-------+
| iSCSI Driver | SA |
+---------------------------+-------|
| |
| +--------+ +--------+ +---------+ |
| | iSCSI | | iSCSI | | iSCSI | |
| | target | | target | | target | |
| | "one" | | "two" | | "iscsi" | |
| +--------+ +--------+ +---------+ |
| |
| iSCSI Server |
+-----------------------------------+
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In the above drawing, the iSCSI server has three iSCSI targets that
the client could discover. The first two, targets "one" and "two",
are actual targets that can support SCSI commands. The third,
"iscsi", is the canonical target. An initiator can log in to the
canonical target, and use an iSCSI command called "SendTargets" to
obtain a list of the other targets within this iSCSI server.
Each of the iSCSI targets has a unique name, called an iSCSI Node
Name, or simply iSCSI Name. This identifier is the same regardless
of the network path (through adapter cards, networks, interfaces on
the storage device) over which the target is discovered and accessed.
For this example, the iSCSI names "one" and "two" are used. A real
iSCSI name incorporates 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, then, would
have two URLs.
An iSCSI target URL consists of its fully qualified host name or IP
address, the TCP port on which it is listening, and its world- wide
unique identifier. If the server in this drawing is listening at TCP
port 3000 for both network addresses, the service URLs present would
be:
- 10.1.30.21:3000/one
- 10.1.30.21:3000/two
- 10.1.30.21:3000/iscsi
- 10.1.40.3:3000/one
- 10.1.40.3:3000/two
- 10.1.40.3:3000/iscsi
An iSCSI server has two options when registering targets with the
service location protocol:
- Register the canonical target "iscsi" at each of its network
addresses. The initiator can use this target to discover the
others. This would create two service URLs in the example.
- The server can register the individual targets, "one" and "two", at
each of its network addresses. This would create four service URLs
in the example.
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Although a target could do both types of registration, it would
probably not be helpful.
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 which are defined in the service template.
The remainder of the discovery procedure is identical to that used by
any client/server pair implementing SLP:
1. If an SLP DA is found, the SA contacts the DA and registers
the advertisement. If no DA is found, the SA maintains the
advertisement itself, answering multicast UA queries
directly.
2. When the iSCSI initiator requires contact information for an
iSCSI target, the UA either contacts the DA using unicast or
the SA using multicast. The UA includes a query based on
the attributes to indicate the characteristics of the
target(s) it requires.
3. Once the UA has the host name or address of the iSCSI server
as well as the port number and iSCSI Target Name, it can begin the
normal iSCSI login to the target.
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5.2. Discovering Storage Name Services using SLP
Storage Name Servers can be built to perform discovery of targets in
a variety of ways. They can also provide extended services beyond
discovery, which could include storage allocation and management.
None of these services are defined here; the intent of this document
is to allow these services to be discovered by clients.
The following drawing shows an iSCSI client, an iSCSI server, and a
storage name server. To simplify the drawing, the second IP network
is not shown, but is assumed to exist. The storage name server would
use its own protocol (snsp) to provide capabilities to iSCSI clients
and servers; these clients and servers could both use SLP to discover
the storage name server.
+---------------------------+
| iSCSI Client |
| |
| +-----------+ |
| | iSCSI | |
| | initiator | |
| +-----------+ |
| |
+---------------+------+----+ +------------+
| iSCSI Driver | snsp | UA | | SLP DA |
+---------------+------+----+ | |
| TCP/UDP/IP | | (optional) |
+---------------+------+----+ +------------+
| |
| IP Network |
------------------------------------------
| |
| |
+---------------+-----------+ +---------------------+
| TCP/UDP/IP | | TCP/UDP/IP |
+---------------+------+----+ +---------------------+
| iSCSI Driver | snsp | UA | | SA | snsp |
+---------------+------+----+ +---------------------+
| | | |
| +--------+ +--------+ | | storage name server |
| | iSCSI | | iSCSI | | | |
| | target | | target | | +---------------------+
| | 1 | | 2 | |
| +--------+ +--------+ |
| |
| iSCSI Server |
+---------------------------+
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Note the difference between the storage name server model and the
previously-defined target discovery model. When target discovery was
used, the iSCSI Server implemented an SA, to be discovered by the
initiator's UA. In the storage name server model, the iSCSI clients
and servers both implement UAs, and the name server implements the
SA. To be discovered by an initiator in this model, a target first
find the storage name server, and then register itself with the name
server using the name server's protocol.
A storage name server's URL contains the domain name or IP address
and TCP port. No other information is required.
The iSCSI server constructs a service advertisement of the type
"service:iscsi:target" for each of the addresses at which it appears.
The advertisement contains the URL, a lifetime, along with other
attributes which are defined in the service template.
The remainder of the discovery procedure is identical to that used to
discover iSCSI targets, except that both initiators and targets would
normally be "clients" of the storage name service.
5.3. Supporting Discovery of Targets and Name Services
An initiator should support, at a minimum, discovery of targets using
SLP. If an initiator also supports a storage name service, the
initiator should use SLP to discover the storage name service, and
perform target discovery through the name service. An initiator may
discover other targets directly even when using a name service, or
may discover targets via multiple name services.
For example, the name service may be used to discover targets at a
remote location, and SLP may used to discover local targets that are
not part of the service.
Targets that support a particular storage name service can be
configured to be discovered through that name service. A target
configured in this way should not answer direct SLP discovery
requests from initiators; they should effectively disable their
service:iscsi:target SA functionality while under the control of a
name service. This prevents targets from being duplicated between
SLP and the name service. A target should also not be configured to
support more than one name service at the same time.
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5.4. Interoperating Between Initiators, Targets, and Name Services
Many initiators will support the basic discovery of targets using
SLP, but will not always support a particular storage name service in
use. A storage name server may provide the capability to support
these initiators by forming service advertisements for use through
its SA on behalf of the targets it has discovered. This would allow
an initiator to discover targets in a storage name service
environment, without having direct support for the storage name
service protocol in use.
Targets not supporting the storage name service protocol in use can
be discovered separately from the name service.
6. iSCSI SLP Templates
Three templates are provided: an iSCSI target template, a name
service template, and an abstract template to encapsulate the two.
6.1. The iSCSI Abstract Service Type Template
This template defines the abstract service "service:iscsi". It is
used as a top-level service to encapsulate all other iSCSI-related
services.
Name of submitter: Mark Bakke
Language of service template: en
Security Considerations:
See the security considerations of the concrete service types.
Template Text:
-------------------------template begins here-----------------------
template-type=iscsi
template-version=0.1
template-description=
This is an abstract service type. The purpose of the iscsi
service type is to encompass all of the services used to support
the iSCSI protocol.
template-url-syntax=
url-path= ; Depends on the concrete service type.
--------------------------template ends here------------------------
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6.2. The iSCSI Target Concrete Service Type Template
This template defines the service "service:iscsi:target". An entity
containing iSCSI targets that wishes them discovered via SLP would
register each of them, with each of their addresses, as this service
type.
Initiators and name services wishing to discover targets in this way
will generally use one of the following query strings:
1. Find a specific target, given its iSCSI Target Name:
Service: service:iscsi:target
Scope: initiator-or-name-server-scope-list
Query: (iscsi-name=fqn.com.acme.sn.456)
2. Find all of the iSCSI Target Names that may allow access to a
given
initiator:
Service: service:iscsi:target
Scope: initiator-or-name-server-scope-list
Query: (access-list=fqn.com.os.hostid.045A7B)
3. In addition, a name service may wish to discover all targets,
and assume responsibility for them. It may issue a simple query
for all of the targets:
Service: service:iscsi:target
Scope: name-server-scope-list
Query: none
4. Find the iSCSI Target Names from which the given initiator is
allowed
to boot:
Service: service:iscsi:target
Scope: name-server-scope-list
Query: (boot-list=fqn.com.os.hostid.045A7B)
More details on booting from an iSCSI target are defined in [BOOT].
Name of submitter: Mark Bakke
Language of service template: en
Security Considerations:
See later section.
Template Text:
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-------------------------template begins here-----------------------
template-type=iscsi:target
template-version=0.1
template-description=
This is concrete service type. The iscsi:target service type is used
to register individual target addresses to be discovered by others.
UAs will generally search for these by including one of the following:
- the iSCSI target name
- the iSCSI initiator name (must be in the access-list of the target)
- the service URL
template-url-syntax=
url-path = ipaddr [ : tcpport ] / iscsi-name
ipaddr = DNS host name or ip address
tcpport = decimal tcp port number
iscsi-name = iSCSI target name
; The iscsi-name part of the URL is required and may be either the iSCSI
; name of the target being registered, or the canonical name "iscsi". If an
; initiator discovers a canonical iSCSI name, it should log in to that
; target, and issue the iSCSI SendTargets command to discover additional
; targets. A device representing multiple targets may then either
; register each of them with SLP, or just register a single "iscsi"
; target, which will be used to discover the remainder of the
; targets.
;
; Examples:
; service:iscsi:target://10.1.3.40:4000/fqn.com.acme.sn.45678
; service:iscsi:target://mystorage.mycompany.com/iscsi
iscsi-name = string
# The iSCSI Name of this target.
# This must match the iscsi-name in the url-path.
transports = string M L
tcp
# This is a list of transport protocols that the registered
# entity supports. iSCSI is currently supported over TCP,
# but it is anticipated that it could be supported over other
# transports, such as SCTP, in the future.
tcp
entity = string O
# Normally the FQDN of the management interface of the entity
# containing this target.
mgmt-ipaddr = string O
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# The IP address of the management interface appropriate for SNMP,
# web-based, or telnet management of the entity containing this
# target.
alias = string O
# The alias string contains a descriptive name of the target.
access-list = string M
# A list of iSCSI Initiator Names that can access this target.
# Normal iSCSI names will be 50 characters or less; max length is 255.
# Normally, only one or a few values will be in the list.
# Using the equivalence search on this will evaluate to "true"
# if any one of the items in this list matches the query.
# If this list contains the canonical name "iscsi", any initiator
# is allowed to access this target.
boot-list = string M O
# A list of iSCSI Initiator Names that can boot from this target.
# This list works precisely like the access-list attribute. A name appearing
# in this list must either appear in the access-list, or the
# access-list must contain the initiator name "iscsi". Otherwise, an
# initiator will be unable to find its boot target.
# If boot-list contains the name "iscsi", any host can boot from it,
# but I am not sure if this is useful to anyone.
# If this attribute is not registered, this target is not "bootable".
#
# Note that the LUN the host boots from is not specified here; a
# host will generally attempt to boot from LUN 0.
#
# It is quite possible that other attributes will need to be defined
# here for booting as well.
--------------------------template ends here------------------------
6.3. iSCSI Name Service Templates
This template defines the service "service:iscsi:name-service". An
entity supporting one or more iSCSI name service protocols may
register itself with SLP as this service type.
Initiators wishing to discover name services using SLP will usually
search for them by the protocol(s) they support:
Service: service:iscsi:name-service
Scope: initiator-scope-list
Query: (protocols=isns)
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Name of submitter: Mark Bakke
Language of service template: en
Security Considerations:
See later section.
Template Text:
-------------------------template begins here-----------------------
template-type=iscsi:name-service
template-version=0.1
template-description=
This is a concrete service type. The iscsi:name-service service type
provides the capability for entities supporting iSCSI to discover
appropriate name services.
template-url-syntax=
url-path = The URL of the name service. Defined in RFC 2608.
protocols = string M L
# The list of protocols supported by this name service. This
# list may be expanded in the future. There is no default.
#
# "isns" - The name service supports the use of the iSNS protocol
# to locate and register targets, and provide further
# information on them. This protocol is defined in [ISNS].
isns
--------------------------template ends here------------------------
7. Security Considerations
Service type templates provide information that is used to interpret
information obtained by clients through SLP. If the iSCSI templates
are modified or if false templates are distributed, iSCSI targets and
name servers may not correctly register themselves, or iSCSI clients
may not be able to interpret service information.
SLP provides an authentication mechanism for UAs to assure that
service advertisments only come from trusted SAs. [RFC2608] If trust
is an issue, particularly with respect to the information sought by
the client about IPSEC and IKE support, then SLP authentication
should be enabled in the network.
Once a target or name server is discovered, authentication and
authorization are handled by the iSCSI protocol, or by the name
server's protocol. It is the responsibility of the providers of
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these services to ensure that an inappropriately advertised or
discovered service does not compromise their security.
8. Summary
This document describes how SLP can be used by iSCSI initiators to
find iSCSI targets and name servers. Service type templates for
iSCSI targets and name servers are presented.
9. References
[RFC2608] E. Guttman, C. Perkins, J. Veizades, M. Day. Service
Location Protocol, version 2 RFC 2608, July, 1999.
[RFC2609] E. Guttman, C. Perkins, J. Kempf. Service Templates and
service: Schemes RFC 2609, July, 1999.
[RFC2119] S. Bradner. Key Words for Use in RFCs to Indicate
Requirement Levels. RFC 2119, March 1997.
[ISCSI] J. Satran, et. al. "iSCSI", draft-ietf-ips-iscsi-04.txt,
February 2001.
[SAM2] ANSI T10. "SCSI Architectural Model 2", March 2000.
[NDT] K. Voruganti, et. al. "iSCSI Naming and Discovery
Requirements", draft-ietf-ips-iscsi-name-disc-01, April
2001.
[ISNS] J. Tseng, et. al. "Internet Storage Name Service",
draft-ietf-ips-isns-00, January 2001.
[BOOT] P. Sarkar, D. Missimer, C. Sapuntzakis. "A Standard for
Bootstrapping Clients using the iSCSI Protocol",
draft-ietf-ips-iscsi-boot-02, February 2001.
[RSIP] Kempf, J., Montenegro, G., "Finding an RSIP Server with
SLP", draft-ietf-nat-rsip-slp-00, February 2000.
Author's Address:
Mark Bakke
Cisco Systems, Inc.
6450 Wedgwood Road
Maple Grove, MN
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USA 55311
Voice: +1 763-398-1000
E-Mail: mbakke@cisco.com
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