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RFC 3721 - Internet Small Computer Systems Interface (iSCSI) Nam

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Network Working Group                                           M. Bakke
Request for Comments: 3721                                         Cisco
Category: Informational                                        J. Hafner
                                                              J. Hufferd
                                                            K. Voruganti
                                                              M. Krueger
                                                              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.


   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.

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

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

   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

   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:


   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.

   Examples of addresses:

   The concepts of names and addresses have been carefully separated in

   -  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.

   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

   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" specifies the use of the iSCSI qualified name as the

      "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

      "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
   +--++-----+ +-----------------+ +-----------+
   |  ||     | |                 | |           |


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


   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

   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"
    +-+ +-----+ +------------+ +--------+ +-----------+
    | | |     | |            | |        | |           |

   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

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

   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

   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

   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)
      |  ||              |

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

   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

   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.

   |  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

   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

   |  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

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.

   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

   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.

   |  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:

   |  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

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

   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

      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

   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,

   [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.

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

   [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.

Appendix A: iSCSI Naming Notes

   Some iSCSI Name Examples for Targets

   -  Assign to a target based on controller serial number


   -  Assign to a target based on serial number


   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

   Some iSCSI Name Examples for Initiators

   -  Assign to the OS image by fully qualified host name


   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


   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


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."

   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.

   -  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

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

   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

   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.

   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

   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.

Authors' Addresses

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

   EMail: kaladhar@us.ibm.com

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

   Phone: +1 763 398-1054
   EMail: mbakke@cisco.com

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

   Phone: +1 408 927-1892
   EMail: hafner@almaden.ibm.com

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

   Phone: +1 408 256-0403
   EMail: hufferd@us.ibm.com

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

   Phone: +1 916 785-2656
   EMail: marjorie_krueger@hp.com

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