Network Working Group M. Bakke

Network Working Group M. Bakke
Request for Comments: 3721 Cisco
Category: Informational J. Hafner
J. Hufferd
K. Voruganti
IBM
M. Krueger
Hewlett-Packard
April 2004

Internet Small Computer Systems Interface (iSCSI)
Naming and Discovery

Status of this Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

This document provides examples of the Internet Small Computer
Systems Interface (iSCSI; or SCSI over TCP) name construction and
discussion of discovery of iSCSI resources (targets) by iSCSI
initiators. This document complements the iSCSI protocol document.
Flexibility is the key guiding principle behind this document. That
is, an effort has been made to satisfy the needs of both small
isolated environments, as well as large environments requiring
secure/scalable solutions.

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Table of Contents

1. iSCSI Names and Addresses. . . . . . . . . . . . . . . . . . . 3
1.1. Constructing iSCSI names using the iqn. format . . . . . 5
1.2. Constructing iSCSI names using the eui. format . . . . . 8
2. iSCSI Alias. . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1. Purpose of an Alias. . . . . . . . . . . . . . . . . . . 8
2.2. Target Alias . . . . . . . . . . . . . . . . . . . . . . 9
2.3. Initiator Alias. . . . . . . . . . . . . . . . . . . . . 10
3. iSCSI Discovery. . . . . . . . . . . . . . . . . . . . . . . . 12
4. Security Considerations. . . . . . . . . . . . . . . . . . . . 13
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1. Normative References . . . . . . . . . . . . . . . . . . 13
5.2. Informative References . . . . . . . . . . . . . . . . . 14
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
Appendix A: iSCSI Naming Notes. . . . . . . . . . . . . . . . . . 15
Appendix B: Interaction with Proxies and Firewalls. . . . . . . . 16
B.1. Port Redirector . . . . . . . . . . . . . . . . 16
B.2. SOCKS server. . . . . . . . . . . . . . . . . . 17
B.3. SCSI gateway. . . . . . . . . . . . . . . . . . 17
B.4. iSCSI Proxy . . . . . . . . . . . . . . . . . . 18
B.5. Stateful Inspection Firewall. . . . . . . . . . 18
Appendix C: iSCSI Names and Security Identifiers. . . . . . . . . 19
Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . . . 21
Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 22

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1. iSCSI Names and Addresses

The main addressable, discoverable entity in iSCSI is an iSCSI Node.
An iSCSI node can be either an initiator, a target, or both. The
rules for constructing an iSCSI name are specified in [RFC3720].

This document provides examples of name construction that might be
used by a naming authority.

Both targets and initiators require names for the purpose of
identification, so that iSCSI storage resources can be managed
regardless of location (address). An iSCSI name is the unique
identifier for an iSCSI node, and is also the SCSI device name [SAM2]
of an iSCSI device. The iSCSI name is the principal object used in
authentication of targets to initiators and initiators to targets.
This name is also used to identify and manage iSCSI storage
resources.

Furthermore, iSCSI names are associated with iSCSI nodes instead of
with network adapter cards to ensure the free movement of network
HBAs between hosts without loss of SCSI state information
(reservations, mode page settings etc) and authorization
configuration.

An iSCSI node also has one or more addresses. An iSCSI address
specifies a single path to an iSCSI node and consists of the iSCSI
name, plus a transport (TCP) address which uses the following format:

<domain-name>[:<port>]

Where <domain-name> is one of:

- IPv4 address, in dotted decimal notation. Assumed if the name
contains exactly four numbers, separated by dots (.), where each
number is in the range 0..255.

- IPv6 address, in colon-separated hexadecimal notation, as
specified in [RFC3513] and enclosed in "[" and "]" characters, as
specified in [RFC2732].

- Fully Qualified Domain Name (host name). Assumed if the <domain-
name> is neither an IPv4 nor an IPv6 address.

For iSCSI targets, the <port> in the address is optional; if
specified, it is the TCP port on which the target is listening for
connections. If the <port> is not specified, the default port 3260,
assigned by IANA, will be assumed. For iSCSI initiators, the <port>
is omitted.

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Examples of addresses:

192.0.2.2
192.0.2.23:5003
[FEDC:BA98:7654:3210:FEDC:BA98:7654:3210]
[1080:0:0:0:8:800:200C:417A]
[3ffe:2a00:100:7031::1]
[1080::8:800:200C:417A]
[1080::8:800:200C:417A]:3260
[::192.0.2.5]
mydisks.example.com
moredisks.example.com:5003

The concepts of names and addresses have been carefully separated in
iSCSI:

- An iSCSI Name is a location-independent, permanent identifier for
an iSCSI node. An iSCSI node has one iSCSI name, which stays
constant for the life of the node. The terms "initiator name" and
"target name" also refer to an iSCSI name.

- An iSCSI Address specifies not only the iSCSI name of an iSCSI
node, but also a location of that node. The address consists of a
host name or IP address, a TCP port number (for the target), and
the iSCSI Name of the node. An iSCSI node can have any number of
addresses, which can change at any time, particularly if they are
assigned via DHCP.

A similar analogy exists for people. A person in the USA might be:

Robert Smith
SSN+DateOfBirth: 333-44-5555 14-MAR-1960
Phone: +1 (763) 555.1212
Home Address: 555 Big Road, Minneapolis, MN 55444
Work Address: 222 Freeway Blvd, St. Paul, MN 55333

In this case, Robert's globally unique name is really his Social
Security Number plus Date of Birth. His common name, "Robert Smith",
is not guaranteed to be unique. Robert has three locations at which
he may be reached; two Physical addresses, and a phone number.

In this example, Robert's SSN+DOB is like the iSCSI Name (date of
birth is required to disambiguate SSNs that have been reused), his
phone number and addresses are analogous to an iSCSI node's TCP
addresses, and "Robert Smith" would be a human-friendly label for
this person.

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To assist in providing a more human-readable user interface for
devices that contain iSCSI targets and initiators, a target or
initiator may also provide an alias. This alias is a simple UTF-8
string, is not globally unique, and is never interpreted or used to
identify an initiator or device within the iSCSI protocol. Its use
is described further in section 2.

1.1. Constructing iSCSI names using the iqn. format

The iSCSI naming scheme was constructed to give an organizational
naming authority the flexibility to further subdivide the
responsibility for name creation to subordinate naming authorities.
The iSCSI qualified name format is defined in [RFC3720] and contains
(in order):

- The string "iqn."

- A date code specifying the year and month in which the
organization registered the domain or sub-domain name used as the
naming authority string.

- The organizational naming authority string, which consists of a
valid, reversed domain or subdomain name.

- Optionally, a ':', followed by a string of the assigning
organization's choosing, which must make each assigned iSCSI name
unique.

The following is an example of an iSCSI qualified name from an
equipment vendor:

Organizational Subgroup Naming Authority
Naming and/or string Defined by
Type Date Auth Org. or Local Naming Authority
+--++-----+ +---------+ +--------------------------------+
| || | | | | |

iqn.2001-04.com.example:diskarrays-sn-a8675309

Where:

"iqn" specifies the use of the iSCSI qualified name as the
authority.

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"2001-04" is the year and month on which the naming authority
acquired the domain name used in this iSCSI name. This is used to
ensure that when domain names are sold or transferred to another
organization, iSCSI names generated by these organizations will be
unique.

"com.example" is a reversed DNS name, and defines the
organizational naming authority. The owner of the DNS name
"example.com" has the sole right of use of this name as this part
of an iSCSI name, as well as the responsibility to keep the
remainder of the iSCSI name unique. In this case, example.com
happens to manufacture disk arrays.

"diskarrays" was picked arbitrarily by example.com to identify the
disk arrays they manufacture. Another product that ACME makes
might use a different name, and have its own namespace independent
of the disk array group. The owner of "example.com" is
responsible for keeping this structure unique.

"sn" was picked by the disk array group of ACME to show that what
follows is a serial number. They could have just assumed that all
iSCSI Names are based on serial numbers, but they thought that
perhaps later products might be better identified by something
else. Adding "sn" was a future-proof measure.

"a8675309" is the serial number of the disk array, uniquely
identifying it from all other arrays.

Another example shows how the ':' separator helps owners of sub-
domains to keep their name spaces unique:

Naming Defined by
Type Date Authority Naming Authority
+--++-----+ +-----------------+ +-----------+
| || | | | | |

iqn.2001-04.com.example.storage:tape.sys1.xyz

Naming Defined by
Type Date Authority Naming Authority
+--++-----+ +----------------------+ +-----------+
| || | | | | |

iqn.2001-04.com.example.storage.tape:sys1.xyz

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Note that, except for the ':' separator, both names are identical.
The first was assigned by the owner of the subdomain
"storage.example.com"; the second was assigned by the owner of
"tape.storage.example.com". These are both legal names, and are
unique.

The following is an example of a name that might be constructed by a
research organization:

Naming Defined by Defined by
Type Date Authority cs dept User "oaks"
+-+ +-----+ +------------+ +--------+ +-----------+
| | | | | | | | | |
iqn.2000-02.edu.example.cs:users.oaks:proto.target4

In the above example, Professor Oaks of Example University is
building research prototypes of iSCSI targets. EU's computer science
department allows each user to use his or her user name as a naming
authority for this type of work, by attaching "users.<username>"
after the ':', and another ':', followed by a string of the user's
choosing (the user is responsible for making this part unique).
Professor Oaks chose to use "proto.target4" for this particular
target.

The following is an example of an iSCSI name string from a storage
service provider:

Organization String
Naming Defined by Org.
Type Date Authority Naming Authority
+-+ +-----+ +-------------+ +----------------------+
| | | | | | | |
iqn.1995-11.com.example.ssp:customers.4567.disks.107

In this case, a storage service provider (ssp.example.com) has
decided to re-name the targets from the manufacturer, to provide the
flexibility to move the customer's data to a different storage
subsystem should the need arise.

The Storage Service Provider (SSP) has configured the iSCSI Name on
this particular target for one of its customers, and has determined
that it made the most sense to track these targets by their Customer
ID number and a disk number. This target was created for use by
customer #4567, and is the 107th target configured for this customer.

Note that when reversing these domain names, the first component
(after the "iqn.") will always be a top-level domain name, which
includes "com", "edu", "gov", "org", "net", "mil", or one of the

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two-letter country codes. The use of anything else as the first
component of these names is not allowed. In particular, companies
generating these names must not eliminate their "com." from the
string.

Again, these iSCSI names are NOT addresses. Even though they make
use of DNS domain names, they are used only to specify the naming
authority. An iSCSI name contains no implications of the iSCSI
target or initiator's location. The use of the domain name is only a
method of re-using an already ubiquitous name space.

1.2. Constructing iSCSI names using the eui. format

The iSCSI eui. naming format allows a naming authority to use IEEE
EUI-64 identifiers in constructing iSCSI names. The details of
constructing EUI-64 identifiers are specified by the IEEE
Registration Authority (see [EUI64]).

Example iSCSI name:

Type EUI-64 identifier (ASCII-encoded hexadecimal)
+--++--------------+
| || |
eui.02004567A425678D

2. iSCSI Alias

The iSCSI alias is a UTF-8 text string that may be used as an
additional descriptive name for an initiator and target. This may
not be used to identify a target or initiator during login, and does
not have to follow the uniqueness or other requirements of the iSCSI
name. The alias strings are communicated between the initiator and
target at login, and can be displayed by a user interface on either
end, helping the user tell at a glance whether the initiators and/or
targets at the other end appear to be correct. The alias must NOT be
used to identify, address, or authenticate initiators and targets.

The alias is a variable length string, between 0 and 255 characters,
and is terminated with at least one NULL (0x00) character, as defined
in [RFC3720]. No other structure is imposed upon this string.

2.1. Purpose of an Alias

Initiators and targets are uniquely identified by an iSCSI Name.
These identifiers may be assigned by a hardware or software
manufacturer, a service provider, or even the customer. Although
these identifiers are nominally human-readable, they are likely to be
assigned from a point of view different from that of the other side

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of the connection. For instance, a target name for a disk array may
be built from the array's serial number, and some sort of internal
target ID. Although this would still be human-readable and
transcribable, it offers little assurance to someone at a user
interface who would like to see "at-a-glance" whether this target is
really the correct one.

The use of an alias helps solve that problem. An alias is simply a
descriptive name that can be assigned to an initiator or target, that
is independent of the name, and does not have to be unique. Since it
is not unique, the alias must be used in a purely informational way.
It may not be used to specify a target at login, or used during
authentication.

Both targets and initiators may have aliases.

2.2. Target Alias

To show the utility of an alias, here is an example using an alias
for an iSCSI target.

Imagine sitting at a desktop station that is using some iSCSI devices
over a network. The user requires another iSCSI disk, and calls the
storage services person (internal or external), giving any
authentication information that the storage device will require for
the host. The services person allocates a new target for the host,
and sends the Target Name for the new target, and probably an
address, back to the user. The user then adds this Target Name to
the configuration file on the host, and discovers the new device.

Without an alias, a user managing an iSCSI host would click on some
sort of management "show targets" button to show the targets to which
the host is currently connected.

+--Connected-To-These-Targets----------------------
|
| Target Name
|
| iqn.1995-04.com.example:sn.5551212.target.450
| iqn.1995-04.com.example:sn.5551212.target.489
| iqn.1995-04.com.example:sn.8675309
| iqn.2001-04.com.example.storage:tape.sys1.xyz
| iqn.2001-04.com.example.storage.tape:sys1.xyz
|
+--------------------------------------------------

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In the above example, the user sees a collection of iSCSI Names, but
with no real description of what they are for. They will, of course,
map to a system-dependent device file or drive letter, but it's not
easy looking at numbers quickly to see if everything is there.

If a storage administrator configures an alias for each target name,
the alias can provide a more descriptive name. This alias may be
sent back to the initiator as part of the login response, or found in
the iSCSI MIB. It then might be used in a display such as the
following:

+--Connected-To-These-Targets----------------------
|
| Alias Target Name
|
| Oracle 1 iqn.1995-04.com.example:sn.5551212.target.450
| Local Disk iqn.1995-04.com.example:sn.5551212.target.489
| Exchange 2 iqn.1995-04.com.example:sn.8675309
|
+--------------------------------------------------

This would give the user a better idea of what's really there.

In general, flexible, configured aliases will probably be supported
by larger storage subsystems and configurable gateways. Simpler
devices will likely not keep configuration data around for things
such as an alias. The TargetAlias string could be either left
unsupported (not given to the initiator during login) or could be
returned as whatever the "next best thing" that the target has that
might better describe it. Since it does not have to be unique, it
could even return SCSI inquiry string data.

Note that if a simple initiator does not wish to keep or display
alias information, it can be simply ignored if seen in the login
response.

2.3. Initiator Alias

An initiator alias can be used in the same manner as a target alias.
An initiator may send the alias in a login request, when it sends its
iSCSI Initiator Name. The alias is not used for authentication, but
may be kept with the session information for display through a
management Graphical User Interface (GUI) or command-line interface
(for a more complex subsystem or gateway), or through the iSCSI MIB.

Note that a simple target can just ignore the Initiator Alias if it
has no management interface on which to display it.

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Usually just the hostname would be sufficient for an initiator alias,
but a custom alias could be configured for the sake of the service
provider if needed. Even better would be a description of what the
machine was used for, such as "Exchange Server 1", or "User Web
Server".

Here's an example of a management interface showing a list of
sessions on an iSCSI target network entity. For this display, the
targets are using an internal target number, which is a fictional
field that has purely internal significance.

+--Connected-To-These-Initiators-------------------
|
| Target Initiator Name
|
| 450 iqn.1995-04.com.example.sw:cd.12345678-OEM-456
| 451 iqn.1995-04.com.example.os:hostid.A598B45C
| 309 iqn.1995-04.com.example.sw:cd.87654321-OEM-259
|
+--------------------------------------------------

And with the initiator alias displayed:

+--Connected-To-These-Initiators-------------------
|
| Target Alias Initiator Name
|
| 450 Web Server 4 iqn.1995-04.com.example.sw:cd.12...
| 451 scsigw.example.com iqn.1995-04.com.example.os:hosti...
| 309 Exchange Server iqn.1995-04.com.example.sw:cd.87...
|
+--------------------------------------------------

This gives the storage administrator a better idea of who is
connected to their targets. Of course, one could always do a reverse
DNS lookup of the incoming IP address to determine a host name, but
simpler devices really don't do well with that particular feature due
to blocking problems, and it won't always work if there is a firewall
or iSCSI gateway involved.

Again, these are purely informational and optional and require a
management application.

Aliases are extremely easy to implement. Targets just send a
TargetAlias whenever they send a TargetName. Initiators just send an
InitiatorAlias whenever they send an InitiatorName. If an alias is
received that does not fit, or seems invalid in any way, it is
ignored.

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3. iSCSI Discovery

The goal of iSCSI discovery is to allow an initiator to find the
targets to which it has access, and at least one address at which
each target may be accessed. This should generally be done using as
little configuration as possible. This section defines the discovery
mechanism only; no attempt is made to specify central management of
iSCSI devices within this document. Moreover, the iSCSI discovery
mechanisms listed here only deal with target discovery and one still
needs to use the SCSI protocol for LUN discovery.

In order for an iSCSI initiator to establish an iSCSI session with an
iSCSI target, the initiator needs the IP address, TCP port number and
iSCSI target name information. The goal of iSCSI discovery
mechanisms are to provide low overhead support for small iSCSI
setups, and scalable discovery solutions for large enterprise setups.
Thus, there are several methods that may be used to find targets
ranging from configuring a list of targets and addresses on each
initiator and doing no discovery at all, to configuring nothing on
each initiator, and allowing the initiator to discover targets
dynamically. The various discovery mechanisms differ in their
assumptions about what information is already available to the
initiators and what information needs to be still discovered.

iSCSI supports the following discovery mechanisms:

a. Static Configuration: This mechanism assumes that the IP address,
TCP port and the iSCSI target name information are already
available to the initiator. The initiators need to perform no
discovery in this approach. The initiator uses the IP address and
the TCP port information to establish a TCP connection, and it
uses the iSCSI target name information to establish an iSCSI
session. This discovery option is convenient for small iSCSI
setups.

b. SendTargets: This mechanism assumes that the target's IP address
and TCP port information are already available to the initiator.
The initiator then uses this information to establish a discovery
session to the Network Entity. The initiator then subsequently
issues the SendTargets text command to query information about the
iSCSI targets available at the particular Network Entity (IP
address). SendTargets command details can be found in the iSCSI
document [RFC3720]. This discovery option is convenient for iSCSI
gateways and routers.

c. Zero-Configuration: This mechanism assumes that the initiator does
not have any information about the target. In this option, the
initiator can either multicast discovery messages directly to the

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targets or it can send discovery messages to storage name servers.
Currently, there are many general purpose discovery frameworks
available such as Salutation [John], Jini [John], UPnP [John], SLP
[RFC2608] and iSNS [iSNS]. However, with respect to iSCSI, SLP
can clearly perform the needed discovery functions [iSCSI-SLP],
while iSNS [iSNS] can be used to provide related management
functions including notification, access management,
configuration, and discovery management. iSCSI equipment that
need discovery functions beyond SendTargets should at least
implement SLP, and then consider iSNS when extended discovery
management capabilities are required such as in larger storage
networks. It should be noted that since iSNS will support SLP,
iSNS can be used to help manage the discovery information returned
by SLP.

4. Security Considerations

Most security issues relating to iSCSI naming are discussed in the
main iSCSI document [RFC3720] and the iSCSI security document
[RFC3723].

In addition, Appendix B discusses naming and discovery issues when
gateways, proxies, and firewalls are used to solve security or
discovery issues in some situations where iSCSI is deployed.

iSCSI allows several different authentication methods to be used.
For many of these methods, an authentication identifier is used,
which may be different from the iSCSI node name of the entity being
authenticated. This is discussed in more detail in Appendix C.

5. References

5.1. Normative References

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

[EUI64] EUI - "Guidelines for 64-bit Global Identifier (EUI-64)
Registration Authority,
http://standards.ieee.org/regauth/oui/tutorials/
EUI64.html

[SAM2] R. Weber et al, INCITS T10 Project 1157-D revision 24,
"SCSI Architectural Model - 2 (SAM-2)", Section 4.7.6
"SCSI device name", September 2002.

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5.2. Informative References

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

[RFC2732] Hinden, R., Carpenter, B. and L. Masinter, "Format for
Literal IPv6 Addresses in URL's", RFC 2732, December
1999.

[RFC2979] Freed, N., "Behavior of and Requirements for Internet
Firewalls", RFC 2979, October 2000.

[RFC3303] Srisuresh, P., Kuthan, J., Rosenberg, J., Molitor, A. and
A. Rayhan, "Middlebox Communication Architecture and
Framework", RFC 3303, August 2002.

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

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

[iSCSI-SLP] Bakke, M., et al., "Finding iSCSI Targets and Name
Servers using SLP", Work in Progress, March 2003.

[iSNS] Tseng, J., et al., "Internet Storage Name Service
(iSNS)", Work in Progress, January 2003.

[John] R. John, "UPnP, Jini and Salutation- A look at some
popular coordination frameworks for future networked
devices", http://www.cswl.com/whiteppr/tech/upnp.html",
June 17, 1999.

6. Acknowledgements

Joe Czap (IBM), Howard Hall (Pirus), Jack Harwood (EMC), Yaron Klein
(SANRAD), Larry Lamers (Adaptec), Josh Tseng (Nishan Systems), and
Todd Sperry (Adaptec) have participated and made contributions during
development of this document.

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Appendix A: iSCSI Naming Notes

Some iSCSI Name Examples for Targets

- Assign to a target based on controller serial number

iqn.2001-04.com.example:diskarray.sn.8675309

- Assign to a target based on serial number

iqn.2001-04.com.example:diskarray.sn.8675309.oracle-db-1

Where oracle-db-1 might be a target label assigned by a user.

This would be useful for a controller that can present different
logical targets to different hosts.

Obviously, any naming authority may come up with its own scheme and
hierarchy for these names, and be just as valid.

A target iSCSI Name should never be assigned based on interface
hardware, or other hardware that can be swapped and moved to other
devices.

Some iSCSI Name Examples for Initiators

- Assign to the OS image by fully qualified host name

iqn.2001-04.com.example.os:dns.com.customer1.host-four

Note the use of two FQDNs - that of the naming authority and also
that of the host that is being named. This can cause problems, due
to limitations imposed on the size of the iSCSI Name.

- Assign to the OS image by OS install serial number

iqn.2001-04.com.example.os:newos5.12345-OEM-0067890-23456

Note that this breaks if an install CD is used more than once.
Depending on the O/S vendor's philosophy, this might be a feature.

- Assign to the Raid Array by a service provider

iqn.2001-04.com.example.myssp:users.mbakke05657

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RFC 3721 iSCSI Naming and Discovery April 2004

Appendix B: Interaction with Proxies and Firewalls

iSCSI has been designed to allow SCSI initiators and targets to
communicate over an arbitrary IP network. This means that in theory,
making some assumptions about authentication and security, the whole
internet could be used as one giant storage network.

However, there are many access and scaling problems that would come
up when this is attempted.

1. Most iSCSI targets may only be meant to be accessed by one or a
few initiators. Discovering everything would be unnecessary.

2. The initiator and target may be owned by separate entities, each
with their own directory services, authentication, and other
schemes. An iSCSI-aware proxy may be required to map between
these things.

3. Many environments use non-routable IP addresses, such as the "10."
network.

For these and other reasons, various types of firewalls [RFC2979] and
proxies will be deployed for iSCSI, similar in nature to those
already handling protocols such as HTTP and FTP.

B.1. Port Redirector

A port redirector is a stateless device that is not aware of iSCSI.
It is used to do Network Address Translation (NAT), which can map IP
addresses between routable and non-routable domains, as well as map
TCP ports. While devices providing these capabilities can often
filter based on IP addresses and TCP ports, they generally do not
provide meaningful security, and are used instead to resolve internal
network routing issues.

Since it is entirely possible that these devices are used as routers
and/or aggregators between a firewall and an iSCSI initiator or
target, iSCSI connections must be operable through them.

Effects on iSCSI:

- iSCSI-level data integrity checks must not include information
from the TCP or IP headers, as these may be changed in between the
initiator and target.

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RFC 3721 iSCSI Naming and Discovery April 2004

- iSCSI messages that specify a particular initiator or target, such
as login requests and third party requests, should specify the
initiator or target in a location-independent manner. This is
accomplished using the iSCSI Name.

- When an iSCSI discovery connection is to be used through a port
redirector, a target will have to be configured to return a domain
name instead of an IP address in a SendTargets response, since the
port redirector will not be able to map the IP address(es)
returned in the iSCSI message. It is a good practice to do this
anyway.

B.2. SOCKS server

A SOCKS server can be used to map TCP connections from one network
domain to another. It is aware of the state of each TCP connection.

The SOCKS server provides authenticated firewall traversal for
applications that are not firewall-aware. Conceptually, SOCKS is a
"shim-layer" that exists between the application (i.e., iSCSI) and
TCP.

To use SOCKS, the iSCSI initiator must be modified to use the
encapsulation routines in the SOCKS library. The initiator then
opens up a TCP connection to the SOCKS server, typically on the
canonical SOCKS port 1080. A sub-negotiation then occurs, during
which the initiator is either authenticated or denied the connection
request. If authenticated, the SOCKS server then opens a TCP
connection to the iSCSI target using addressing information sent to
it by the initiator in the SOCKS shim. The SOCKS server then
forwards iSCSI commands, data, and responses between the iSCSI
initiator and target.

Use of the SOCKS server requires special modifications to the iSCSI
initiator. No modifications are required to the iSCSI target.

As a SOCKS server can map most of the addresses and information
contained within the IP and TCP headers, including sequence numbers,
its effects on iSCSI are identical to those in the port redirector.

B.3. SCSI gateway

This gateway presents logical targets (iSCSI Names) to the
initiators, and maps them to SCSI targets as it chooses. The
initiator sees this gateway as a real iSCSI target, and is unaware of
any proxy or gateway behavior. The gateway may manufacture its own
iSCSI Names, or map the iSCSI names using information provided by the
physical SCSI devices. It is the responsibility of the gateway to

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RFC 3721 iSCSI Naming and Discovery April 2004

ensure the uniqueness of any iSCSI name it manufactures. The gateway
may have to account for multiple gateways having access to a single
physical device. This type of gateway is used to present parallel
SCSI, Fibre Channel, SSA, or other devices as iSCSI devices.

Effects on iSCSI:

- Since the initiator is unaware of any addresses beyond the
gateway, the gateway's own address is for all practical purposes
the real address of a target. Only the iSCSI Name needs to be
passed. This is already done in iSCSI, so there are no further
requirements to support SCSI gateways.

B.4. iSCSI Proxy

An iSCSI proxy is a gateway that terminates the iSCSI protocol on
both sides, rather than translate between iSCSI and some other
transport. The proxy functionality is aware that both sides are
iSCSI, and can take advantage of optimizations, such as the
preservation of data integrity checks. Since an iSCSI initiator's
discovery or configuration of a set of targets makes use of address-
independent iSCSI names, iSCSI does not have the same proxy
addressing problems as HTTP, which includes address information into
its URLs. If a proxy is to provide services to an initiator on
behalf of a target, the proxy allows the initiator to discover its
address for the target, and the actual target device is discovered
only by the proxy. Neither the initiator nor the iSCSI protocol
needs to be aware of the existence of the proxy. Note that a SCSI
gateway may also provide iSCSI proxy functionality when mapping
targets between two iSCSI interfaces.

Effects on iSCSI:

- Same as a SCSI gateway. The only other effect is that iSCSI must
separate data integrity checking on iSCSI headers and iSCSI data,
to allow the data integrity check on the data to be propagated
end-to-end through the proxy.

B.5. Stateful Inspection Firewall (stealth iSCSI firewall)

The stealth model would exist as an iSCSI-aware firewall, that is
invisible to the initiator, but provides capabilities found in the
iSCSI proxy.

Effects on iSCSI:

- Since this is invisible, there are no additional requirements on
the iSCSI protocol for this one.

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RFC 3721 iSCSI Naming and Discovery April 2004

This one is more difficult in some ways to implement, simply because
it has to be part of a standard firewall product, rather than part of
an iSCSI-type product.

Also note that this type of firewall is only effective in the
outbound direction (allowing an initiator behind the firewall to
connect to an outside target), unless the iSCSI target is located in
a DMZ (De-Militarized Zone) [RFC3303]. It does not provide adequate
security otherwise.

Appendix C: iSCSI Names and Security Identifiers

This document has described the creation and use of iSCSI Node Names.
There will be trusted environments where this is a sufficient form of
identification. In these environments the iSCSI Target may have an
Access Control List (ACL), which will contain a list of authorized
entities that are permitted to access a restricted resource (in this
case a Target Storage Controller). The iSCSI Target will then use
that ACL to permit (or not) certain iSCSI Initiators to access the
storage at the iSCSI Target Node. This form of ACL is used to
prevent trusted initiators from making a mistake and connecting to
the wrong storage controller.

It is also possible that the ACL and the iSCSI Initiator Node Name
can be used in conjunction with the SCSI layer for the appropriate
SCSI association of LUNs with the Initiator. The SCSI layer's use of
the ACL will not be discussed further in this document.

There will be situations where the iSCSI Nodes exist in untrusted
environments. That is, some iSCSI Initiator Nodes may be authorized
to access an iSCSI Target Node, however, because of the untrusted
environment, nodes on the network cannot be trusted to give the
correct iSCSI Initiator Node Names.

In untrusted environments an additional type of identification is
required to assure the target that it really knows the identity of
the requesting entity.

The authentication and authorization in the iSCSI layer is
independent of anything that IPSec might handle, underneath or around
the TCP layer. This means that the initiator node needs to pass some
type of security related identification information (e.g., userid) to
a security authentication process such as SRP, CHAP, Kerberos etc.
(These authentication processes will not be discussed in this
document.)

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RFC 3721 iSCSI Naming and Discovery April 2004

Upon the completion of the iSCSI security authentication, the
installation knows "who" sent the request for access. The
installation must then check to ensure that such a request, from the
identified entity, is permitted/authorized. This form of
Authorization is generally accomplished via an Access Control List
(ACL) as described above. Using this authorization process, the
iSCSI target will know that the entity is authorized to access the
iSCSI Target Node.

It may be possible for an installation to set a rule that the
security identification information (e.g., UserID) be equal to the
iSCSI Initiator Node Name. In that case, the ACL approach described
above should be all the authorization that is needed.

If, however, the iSCSI Initiator Node Name is not used as the
security identifier there is a need for more elaborate ACL
functionality. This means that the target requires a mechanism to
map the security identifier (e.g., UserID) information to the iSCSI
Initiator Node Name. That is, the target must be sure that the
entity requesting access is authorized to use the name, which was
specified with the Login Keyword "InitiatorName=". For example, if
security identifier 'Frank' is authorized to access the target via
iSCSI InitiatorName=xxxx, but 'Frank' tries to access the target via
iSCSI InitiatorName=yyyy, then this login should be rejected.

On the other hand, it is possible that 'Frank' is a roaming user (or
a Storage Administrator) that "owns" several different systems, and
thus, could be authorized to access the target via multiple different
iSCSI initiators. In this case, the ACL needs to have the names of
all the initiators through which 'Frank' can access the target.

There may be other more elaborate ACL approaches, which can also be
deployed to provide the installation/user with even more security
with flexibility.

The above discussion is trying to inform the reader that, not only is
there a need for access control dealing with iSCSI Initiator Node
Names, but in certain iSCSI environments there might also be a need
for other complementary security identifiers.

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RFC 3721 iSCSI Naming and Discovery April 2004

Authors' Addresses

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

EMail: [email protected]

Mark Bakke
Cisco Systems, Inc.
6450 Wedgwood Road
Maple Grove, MN 55311

Phone: +1 763 398-1054
EMail: [email protected]

Jim Hafner
IBM Almaden Research Center
650 Harry Road
San Jose, CA 95120

Phone: +1 408 927-1892
EMail: [email protected]

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

Phone: +1 408 256-0403
EMail: [email protected]

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

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

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RFC 3721 iSCSI Naming and Discovery April 2004

Full Copyright Statement

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