Network Working Group M. Bakke

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

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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].

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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.

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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.

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+---------------------------------+
| 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

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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:

1. If an SLP DA is found, the SA contacts the DA and registers the
service advertisement. Whether or not one or more SLPv2 DAs are
discovered, the SA maintains the advertisement itself and answers
multicast UA queries directly.

2. When the iSCSI initiator requires contact information for an
iSCSI target, the UA either contacts the DA by using unicast or
the SA by using multicast. If a UA is configured with the
address of the SA, it may avoid multicast and may contact an SA

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by using unicast. 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.

As information contained in the iSCSI target template may exceed
common network datagram sizes, the SLP implementation for both UAs
and SAs supporting this template MUST implement SLP over TCP.

4.1.1. Finding Targets Based on Initiator Credentials

To be allowed access to an iSCSI target, an initiator must be
authenticated. The initiator may be required by the target to
produce one or more of the following credentials:

- An iSCSI Initiator Name

- An IP address

- A CHAP, SRP, or Kerberos credential

- Any combination of the above

Most iSCSI targets allow access to only one or two initiators. In
the ideal discovery scenario, an initiator would send an SLP request
and receive responses ONLY for targets to which the initiator is
guaranteed a successful login. To achieve this goal, the iSCSI
target template contains the following attributes, each of which
allows a list of values:

1. auth-name: This attribute contains the list of initiator names
allowed to access this target, or the value "any", indicating
that no specific initiator name is required.

2. auth-addr: This attribute contains the list of host names
and/or IP addresses that will be allowed access to this target,
or the value "any", indicating that no specific address or
host name is required. If a large number of addresses is to
be allowed (perhaps a subnet), this attribute may contain the
value "any".

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3. auth-cred: This attribute contains a list of "method/identifier"
credentials that will be allowed access to the target, provided
they can produce the correct password or other verifier during
the login process. If no specific credentials are required, the
value "any" is used.

The list of valid method strings for auth-cred are defined in
[RFC3720], section 11.1, "AuthMethod". The identifier used after the
"/" is defined by the specific AuthMethod, also in [RFC3720].
Examples showing initiator searches based on auth-xxxx attributes are
shown in the target-specific template section below.

Also note that the auth-xxxx attributes are considered security
policy information. If these attributes are distributed, IPsec MUST
be implemented as specified in the Security Implementation section
below.

4.1.2. Supporting Access by Multiple Identities to the Same Target

If a target is to allow access to multiple host identities, more than
one combination of auth-xxxx attributes will have to be allowed. In
some of these cases, it is not possible to express the entire set of
valid combinations of auth-xxxx attributes within a single registered
service URL. For example, if a target can be addressed by

auth-name=myhost1 AND auth-cred=CHAP/user1 (identity1)

OR

auth-name-myhost2 AND auth-cred=CHAP/user2 (identity2)

the above cannot be specified in a single registered service URL,
since (auth-name=myhost1, auth-name=myhost2, auth-cred=CHAP/user1,
auth-cred=CHAP/user2) would allow either auth-name to be used with
either auth-cred. This necessitates the ability to register a target
and address under more than one service URL; one for (identity1) and
one for (identity2).

Because service URLs must be unique, (identity1) and (identity2) must
each be registered under a unique service URL. For systems that
support the configuration of multiple identities to access a target,
the service URL must contain an additional, opaque string defining
the identity. This appears after the iSCSI name in the URL string
and is separated by a "/". Each registered (target-address, target-
name, initiator-identity) tuple can then register a set of auth-xxxx
attributes.

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4.1.3. Using SLP in a Non-multicast Environment

In some networks, the use of multicast for discovery purposes is
either unavailable or not allowed. These include public or service-
provider networks that are placed between an iSCSI client and a
server. These are probably most common between two iSCSI gateways,
one at a storage service provider site, and one at a customer site.

In these networks, an initiator may allow the addresses of one or
more SAs to be configured instead of or in addition to its DA
configuration. The initiator would then make unicast SLP service
requests directly to these SAs, without the use of multicast to
discover them first.

This functionality is well within the scope of the current SLP
protocol. The main consequence for implementors is that an initiator
configured to make direct unicast requests to an SA will have to add
this to the SLP API, if it is following the service location API
defined in [RFC2614].

4.2. Discovering Storage Management Services with SLP

Storage management servers can be built to manage and control access
to targets in a variety of ways. They can 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 both
clients and servers, in addition to the target discovery already
being performed.

The following drawing shows an iSCSI client, an iSCSI server, and a
storage management server. To simplify the drawing, the second IP
network is not shown but is assumed to exist. The storage management
server would use its own protocol (smsp) to provide capabilities to
iSCSI clients and servers; these clients and servers can both use SLP
to discover the storage management server.

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RFC 4018 iSCSI and SLPv2 April 2005

+---------------------------+
| iSCSI Client |
| |
| +-----------+ |
| | iSCSI | |
| | initiator | |
| +-----------+ |
| |
+---------------+------+----+ +------------+
| iSCSI Driver | smsp | UA | | SLP DA |
+---------------+------+----+ | |
| TCP/UDP/IP | | (optional) |
+---------------+------+----+ +------------+
| |
| IP Network |
------------------------------------------
| |
| |
+---------------+-----------+ +---------------------+
| TCP/UDP/IP | | TCP/UDP/IP |
+---------------+------+----+ +---------------------+
| iSCSI Driver | smsp | UA | | SA | smsp |
+---------------+------+----+ +---------------------+
| | | |
| +--------+ +--------+ | | storage mgmt server |
| | iSCSI | | iSCSI | | | |
| | target | | target | | +---------------------+
| | 1 | | 2 | |
| +--------+ +--------+ |
| |
| iSCSI Server |
+---------------------------+

Note the difference between the storage management 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 management server model, the iSCSI
clients and servers both implement UAs, and the management server
implements the SA.

A storage management server's URL contains the domain name or IP
address and TCP or UDP port number. No other information is
required.

The storage management server constructs a service advertisement of
the type "service:iscsi:sms" for each of the addresses at which it
appears. The advertisement contains the URL and a lifetime, along
with other attributes that are defined in the service template.

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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 management service.

Targets that support a storage management service implement a UA in
addition to the SA. A target may alternatively just implement the UA
and allow the storage management service to advertise its targets
appropriately by providing an SA and registering the appropriate
service:iscsi:target registrations on the target's behalf: The target
device would not have to advertise its own targets. This has no
impact on the initiator.

This allows the initiators' discovery of targets to be completely
interoperable regardless of which storage management service is used,
or whether one is used at all, or whether the target registrations
are provided directly by the target or by the management service.

4.3. Internationalization Considerations

SLP allows internationalized strings to be registered and retrieved.
Attributes in the template that are not marked with an 'L' (literal)
will be registered in a localized manner. An "en" (English)
localization MUST be registered, and others MAY be registered.

Attributes that include non-ASCII characters will be encoded by using
UTF-8, as discussed in [RFC3722] and [RFC3491].

5. iSCSI SLP Templates

Three templates are provided: an iSCSI target template, a management
service template, and an abstract template to encapsulate the two.

5.1. 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 section 6.

Template Text:
-------------------------template begins here-----------------------
template-type=iscsi
template-version=1.0

template-description=

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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------------------------

5.2. 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 perhaps management services) wishing to discover
targets in this way will generally use one of the following queries:

1. Find a specific target, given its iSCSI Target Name:

Service: service:iscsi:target
Scope: initiator-scope-list
Query: (iscsi-name=iqn.2001-04.com.example:sn.456)

2. Find all of the iSCSI Target Names that may allow access to a
given initiator:

Service: service:iscsi:target
Scope: initiator-scope-list
Query: (auth-name=iqn.1998-03.com.example:hostid.045A7B)

3. Find all of the iSCSI Target Names that may allow access to
any initiator:

Service: service:iscsi:target
Scope: initiator-scope-list
Query: (auth-name=any)

4. Find all of the iSCSI Target Names that may allow access to
this initiator, or that will allow access to any initiator:

Service: service:iscsi:target
Scope: initiator-scope-list
Query: &(auth-name=iqn.1998-03.com.example:hostid.045A7B)
(auth-name=any)

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5. Find all of the iSCSI Target Names that may allow access to
a given CHAP user name:

Service: service:iscsi:target
Scope: initiator-scope-list
Query: (auth-cred=chap/my-user-name)

6. Find all of the iSCSI Target Names that may allow access to a
given initiator that supports two IP addresses, a CHAP credential
and SRP credential, and an initiator name:

Service: service:iscsi:target
Scope: initiator-scope-list
Query: &(|(auth-name=iqn.com.example:host47)(auth-name=any)
|(auth-addr=192.0.2.3)(auth-addr=192.0.2.131)(auth-addr=any)
|(auth-cred=chap/foo)(auth-cred=srp/my-user-name)
(auth-cred=any))

7. Find the iSCSI Target Names from which the given initiator is
allowed to boot:

Service: service:iscsi:target
Scope: initiator-scope-list
Query: (boot-list=iqn.1998-03.com.example:hostid.045A7B)

8. In addition, a management service may wish to discover all
targets:

Service: service:iscsi:target
Scope: management-server-scope-list
Query: <empty-string>

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 section 6.

Template Text:
-------------------------template begins here-----------------------
template-type=iscsi:target
template-version=1.0

template-description=

This is a 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

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the following:

- the iSCSI target name
- iSCSI initiator identifiers (iSCSI name, credential, IP address)
- the service URL

template-url-syntax=
url-path = hostport "/" iscsi-name [ "/" identity ]
hostport = host [ ":" port ]
host = hostname / hostnumber ; DNS name or IP address
hostname = *( domainlabel "." ) toplabel
alphanum = ALPHA / DIGIT
domainlabel = alphanum / alphanum *[alphanum / "-"] alphanum
toplabel = ALPHA / ALPHA *[ alphanum / "-" ] alphanum
hostnumber = ipv4-number / ipv6-addr ; IPv4 or IPv6 address
ipv4-number = 1*3DIGIT 3("." 1*3DIGIT)
ipv6-addr = "[" ipv6-number "]"
ipv6-number = 6( h16 ":" ) ls32
/ "::" 5( h16 ":" ) ls32
/ [ h16 ] "::" 4( h16 ":" ) ls32
/ [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
/ [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
/ [ *3( h16 ":" ) h16 ] "::" h16 ":" ls32
/ [ *4( h16 ":" ) h16 ] "::" ls32
/ [ *5( h16 ":" ) h16 ] "::" h16
/ [ *6( h16 ":" ) h16 ] "::"
ls32 = ( h16 ":" h16 ) / ipv4-number
; least-significant 32 bits of ipv6 address
h16 = 1*4HEXDIG
port = 1*DIGIT
iscsi-name = iscsi-char ; iSCSI target name
identity = iscsi-char ; optional identity string
iscsi-char = ALPHA / DIGIT / escaped / ":" / "-" / "."
; Intended to allow UTF-8 encoded strings
escaped = 1*("\" HEXDIG HEXDIG)
;
; The iscsi-name part of the URL is required and must be the iSCSI
; name of the target being registered.
; A device representing multiple targets must individually
; register each target/address combination with SLP.
; The identity part of the URL is optional, and is used to
; indicate an identity that is allowed to access this target.
;
; Example (split into two lines for clarity):
; service:iscsi:target://192.0.2.3:3260/
; iqn.2001-04.com.example:sn.45678
;
; IPv6 addresses are also supported; they use the notation

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; specified above and in [RFC3513], section 2.2

iscsi-name = string
# The iSCSI Name of this target.
# This must match the iscsi-name in the url-path.

portal-group = integer
# The iSCSI portal group tag for this address. Addresses sharing
# the same iscsi-name and portal-group tag can be used within the
# same iSCSI session. Portal groups are described in [RFC3720].

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

mgmt-entity = string O
# The fully qualified domain name, or IP address in dotted-decimal
# notation, of the management interface of the entity containing
# this target.
#

alias = string O
# The alias string contains a descriptive name of the target.

auth-name = string M X
# A list of iSCSI Initiator Names that can access this target.
# Normal iSCSI names will be 80 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 default name "any", any initiator
# is allowed to access this target, provided it matches
# the other auth-xxx attributes.
#
# This attribute contains security policy information. If this
# attribute is distributed via an Attribute Reply message,
# IPsec MUST be implemented.

auth-addr = string M X
# A list of initiator IP addresses (or host names) which will
# be allowed access to this target. If this list contains the
# default name "any", any IP address is allowed access to this
# target, provided it matches the other auth-xxx attributes.

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#
# This attribute contains security policy information. If this
# attribute is distributed via an Attribute Reply message,
# IPsec MUST be implemented.

auth-cred = string M X
# A list of credentials which will be allowed access to the target
# (provided they can provide the correct password or other
# authenticator). Entries in this list are of the form
# "method/identifier", where the currently defined methods are
# "chap" and "srp", both of which take usernames as their
# identifiers.
#
# This attribute contains security policy information. If this
# attribute is distributed via an Attribute Reply message,
# IPsec MUST be implemented.

boot-list = string M O
# A list of iSCSI Initiator Names that can boot from this target.
# This list works precisely like the auth-name 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.
#
# This attribute contains security policy information. If this
# attribute is distributed via an Attribute Reply message,
# IPsec MUST be implemented.

--------------------------template ends here------------------------

5.3. iSCSI Storage Management Service Templates

This template defines the service "service:iscsi:sms". An entity
supporting one or more iSCSI management service protocols may
register itself with SLP as this service type. iSCSI clients and
servers wishing to discover storage management services using SLP
will usually search for them by the protocol(s) they support:

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Service: service:iscsi:sms
Scope: initiator-scope-list
Query: (protocols=isns)

Name of submitter: Mark Bakke
Language of service template: en
Security Considerations: see section 6.

Template Text:
-------------------------template begins here-----------------------
template-type=iscsi:sms
template-version=1.0

template-description=
This is a concrete service type. The iscsi:sms service type
provides the capability for entities supporting iSCSI to discover
appropriate management services.

template-url-syntax=
url-path = ; The URL of the management service [RFC2608].

protocols = string M
# The list of protocols supported by this name service. This
# list may be expanded in the future. There is no default.
#
# "isns" - This management service supports the use of the iSNS
# protocol for access management, health monitoring, and
# discovery management services. This protocol is defined
# in [ISNS].
isns

transports = string M L
tcp
# This is a list of transport protocols that the registered
# entity supports.
tcp, udp

server-priority = integer
# The priority a client should give this server, when choosing
# between multiple servers with the same protocol type.
# When multiple servers are discovered for a given protocol type,
# this parameter indicates their relative precedence. Server
# precedence is protocol-specific; for some protocols, the primary
# server may have the highest server-priority value, while for

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# others it may have the lowest. For example, with iSNS, the primary
# server has the lowest value (value 0).

--------------------------template ends here------------------------

6. Security Considerations

The SLPv2 security model as specified in [RFC2608] does not provide
confidentiality but does provide an authentication mechanism for UAs
to ensure that service advertisements only come from trusted SAs,
with the exception that it does not provide a mechanism to
authenticate "zero-result responses". See [RFC3723] for a discussion
of the SLPv2 [RFC2608] security model.

Once a target or management server is discovered, authentication and
authorization are handled by the iSCSI protocol, or by the management
server's protocol. It is the responsibility of the providers of
these services to ensure that an inappropriately advertised or
discovered service does not compromise their security.

When no security is used for SLPv2, there is a risk of distribution
of false discovery information. The primary countermeasure for this
risk is authentication. When this risk is a significant concern,
IPsec SAs and iSCSI in-band authentication SHOULD be used for iSCSI
traffic subject to this risk to ensure that iSCSI traffic only flows
between endpoints that have participated in IKE authentication and
iSCSI in-band authentication. For example, if an attacker
distributes discovery information falsely claiming that it is an
iSCSI target, it will lack the secret information necessary to
complete IKE authentication or iSCSI in-band authentication
successfully and therefore will be prevented from falsely sending or
receiving iSCSI traffic.

A risk remains of a denial of service attack based on repeated use of
false discovery information that will cause initiation of IKE
negotiation. The countermeasures for this are administrative
configuration of each iSCSI Target to limit the peers it is willing
to communicate with (i.e., by IP address range and/or DNS domain),
and maintenance of a negative authentication cache to avoid
repeatedly contacting an iSCSI Target that fails to authenticate.
These three measures (i.e., IP address range limits, DNS domain
limits, negative authentication cache) MUST be implemented.

The auth-name, auth-addr, auth-cred, and boot-list attributes
comprise security policy information. When these are distributed,
IPsec MUST be implemented.

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6.1. Security Implementation

Security for SLPv2 in an IP storage environment is specified in
[RFC3723]. IPsec is mandatory-to-implement for IPS clients and
servers. Thus, all IP storage clients, including those invoking SLP,
can be assumed to support IPsec. SLP servers, however, cannot be
assumed to implement IPsec, since there is no such requirement in
standard SLP. In particular, SLP Directory Agents (DA) may be
running on machines other than those running the IPS protocols.

IPsec SHOULD be implemented for SLPv2 as specified in [RFC3723]; this
includes ESP with a non-null transform to provide both authentication
and confidentiality.

When SLPv2 can be used to distribute auth-name, auth-addr, auth-cred,
and boot-list information (see section 5.2 above), IPsec MUST be
implemented, as these items are considered sensitive security policy
information. If IPsec is not implemented, auth-name, auth-addr,
auth-cred, and boot-list information MUST NOT be distributed via
SLPv2 and MUST NOT be used if discovered via SLPv2.

Because the IP storage services have their own authentication
capabilities when located, SLPv2 authentication is OPTIONAL to
implement and use (as discussed in more detail in [RFC3723]).

7. IANA Considerations

This document describes three SLP Templates. They have been reviewed
and approved by the IESG and registered in the IANA's "SVRLOC
Templates" registry. This process is described in the IANA
Considerations section of [RFC2609].

8. Summary

This document describes how SLP can be used by iSCSI initiators to
find iSCSI targets and storage management servers. Service type
templates for iSCSI targets and storage management servers are
presented.

9. Normative References

[RFC2608] Guttman, E., Perkins, C., Veizades, J., and M. Day,
"Service Location Protocol, Version 2", RFC 2608, June
1999.

[RFC2609] Guttman, E., Perkins, C., and J. Kempf, "Service
Templates and Service: Schemes", RFC 2609, June 1999.

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RFC 4018 iSCSI and SLPv2 April 2005

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
Profile for Internationalized Domain Names (IDN)", RFC
3491, March 2003.

[RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003.

[RFC3720] Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka, M.,
and E. Zeidner, "Internet Small Computer Systems
Interface (iSCSI)", RFC 3720, April 2004.

[RFC3722] Bakke, M., "String Profile for Internet Small Computer
Systems Interface (iSCSI) Names", RFC 3722, April 2004.

[RFC3723] Aboba, B., Tseng, J., Walker, J., Rangan, V., and F.
Travostino, "Securing Block Storage Protocols over IP",
RFC 3723, April 2004.

10. Informative References

[RFC2614] Kempf, J. and E. Guttman, "An API for Service Location",
RFC 2614, June 1999.

[SAM2] ANSI T10. "SCSI Architectural Model 2", March 2000.

[RFC3721] Bakke, M., Hafner, J., Hufferd, J., Voruganti, K., and M.
Krueger, "Internet Small Computer Systems Interface
(iSCSI) Naming and Discovery", RFC 3721, April 2004.

[ISNS] Tseng, J., Gibbons, K., Travostino, F., Du Laney, C. and
J. Souza, "Internet Storage Name Service", Work in
Progress, February 2004.

[BOOT] Sarkar, P., Missimer, D. and C. Sapuntzakis, "A Standard
for Bootstrapping Clients using the iSCSI Protocol", Work
in Progress, March 2004.

[RFC3105] Kempf, J. and G. Montenegro, "Finding an RSIP Server with
SLP", RFC 3105, October 2001.

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11. Acknowledgements

This document was produced by the iSCSI Naming and Discovery team,
including Joe Czap, Jim Hafner, John Hufferd, and Kaladhar Voruganti
(IBM), Howard Hall (Pirus), Jack Harwood (EMC), Yaron Klein (Sanrad),
Marjorie Krueger (HP), 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.

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RFC 4018 iSCSI and SLPv2 April 2005

Authors' Addresses

Mark Bakke
Cisco Systems, Inc.
7900 International Drive, Suite 400
Bloomington, MN
USA 55425

EMail: [email protected]

Kaladhar Voruganti
IBM Almaden Research Center
650 Harry Road
San Jose, CA 95120

EMail: [email protected]

John L. Hufferd
IBM Storage Systems Group
5600 Cottle Road
San Jose, CA 95193

Phone: +1 408 997-6136
EMail: [email protected]

Marjorie Krueger
Hewlett-Packard Corporation
8000 Foothills Blvd
Roseville, CA 95747-5668, USA

Phone: +1 916 785-2656
EMail: [email protected]

Todd Sperry
Adaptec, Inc.
691 South Milpitas Boulevard
Milpitas, Ca. 95035

Phone: +1 408 957-4980
EMail: [email protected]

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RFC 4018 iSCSI and SLPv2 April 2005

Full Copyright Statement

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contained in BCP 78, and except as set forth therein, the authors
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