IPS Prasenjit Sarkar
Internet Draft IBM
Document: draft-ietf-ips-iscsi-boot-01.txt Duncan Missimer
Category: Standards Track HP
Constantin Sapuntzakis
Cisco
12 January 2001
A Standard for BootStrapping Clients using the iSCSI Protocol
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [11].
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or made obsolete by other documents at
any time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress." The list
of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft
Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
The Small Computer Systems Interface (SCSI) is a popular family of
protocols for communicating with I/O devices, especially storage
devices. iSCSI is a proposed transport protocol for SCSI that
operates on top of TCP[12]. This memo describes a standard mechanism
to enable clients to bootstrap themselves using the iSCSI protocol.
The goal of this standard is to enable clients to obtain the
information to open an iSCSI session with the iSCSI bootstrpping
server, assuming this information is not available.
1. Requirements
1. There must be no restriction of network topology between the iSCSI
boot client and the boot server. Consequently, it is possible for an
iSCSI boot client to boot from an iSCSI boot server behind
gateways/firewalls/etc as long as it is possible to establish an
iSCSI session between the client and the server.
2. The following represents the minimum information required for an
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iSCSI boot client to contact an iSCSI boot server: (a) the client's
IP address (IPv6 or IPv4); (b) the server's iSCSI Service Delivery
Port Name; and (c) mandatory iSCSI initiator capability.
The above assumes that the default LUN for the boot process is 0 and
the default port for the iSCSI boot server is the well-known iSCSI
port. However, both may be overridden at the time of configuration.
Additional information may be required at each stage of the boot
process.
3. It is possible for the iSCSI boot client to have none of the above
information or capability on starting.
4. The client should be able to complete boot without user
intervention (for boots that occur during an unattended power-up).
However, there should be a mechanism for the user to input values so
as to bypass stages of the boot protocol.
5. Additional protocol software (for example, DHCP) may be necessary
if the minimum information required for an iSCSI session is not
provided.
2. Related Work
The Reverse Address Resolution Protocol (RARP)[7](through the
extensions defined in the Dynamic RARP (DRARP))[4] explicitly
addresses the problem of network address discovery, and includes an
automatic IP address assignment mechanism. The Trivial File Transfer
Protocol (TFTP)[9] provides for transport of a boot image from a boot
server. BOOTP[5,8,10] is a transport mechanism for a collection of
configuration information. BOOTP is also extensible, and official
extensions have been defined for several configuration parameters.
DHCPv4[3,6] and DHCPv6[13] are standards for hosts to be dynamically
configured in an IP network. The Service Location Protocol RLP
provides for location of higher level services[1,15].
3. Software stage
Some iSCSI boot clients may lack the resources to boot up with the
mandatory iSCSI initiator capability. Such boot clients may choose to
obtain iSCSI initiator software from a boot server. Currently, there
are many established protocols that allow such a service to enable
clients to load software images. For example, BOOTP and DHCP servers
have the capability to provide software images on requests from boot
clients. A particular implementation of this approach is the PXE
protocol[17], which uses DHCP extensions and MTFTP to allow boot
clients to load software images.
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It is to be noted that this document does not recommend any of the
above protocols, and the final decision of which boot protocol is to
be used to load iSCSI initiator software is left to the discretion of
the implementor.
4. DHCP stage
In order to use an iSCSI boot server, the following pieces of
information are required.
- The IP address of the iSCSI boot client (IPv4 or IPv6)
- The IP transport endpoint for the iSCSI service delivery port for
the iSCSI boot server. If the transport is TCP, for example, this
has to resolve to an IP address and a TCP port number.
- The eight-byte LUN structure identifying the device within the
iSCSI boot server.
At boot time, all or none of this information may be stored in the
firmware of the iSCSI boot client. This section describes techniques
for obtaining the required information.
An iSCSI boot client which does not know its IP address at power-on
may acquire its IP address via DHCP. An iSCSI boot client which is
capable of using both DHCPv6 and DHCPv4 should first attempt to use
DHCPv6 to obtain its IP address, falling back on DHCPv4 in the event
of failure.
Unless otherwise specified here, DHCP fields such as the client ID
and gateway information are used identically with applications other
than iSCSI.
A DHCP server (v4 or v6) may instruct an iSCSI client how to reach
its boot device. This is done using a variable length DHCP option
field known as the ISCSI Boot Service option. The option identifier
is to be allocated by the IESG during the approval process[19].
The field consists of an UTF-8[20] string and has the following
composition:
<servername> ":" <port> ":" <LUN> ":" <targetname>
The fields "port", "LUN" and "targetname" are optional and should be
left blank if there are no values corresponding to the fields.
The "servername" is the name of iSCSI server and contains either a
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valid domain name, a literal IPv4 address, or a bracketed literal
IPv6 address. If the servername field contains a literal IPv4
address, the IPv4 address is in standard dotted decimal notation. If
the servername field contains an IPv6 address, the address is
represented in bracketed literal IPv6 address format.
If the "servername" is a domain name, then the reply from the host
configuration server may contain the Domain Name Server Option[2].
The "port" is the decimal representation of the port on which the
iSCSI boot server is listening. If not specified, the port defaults
to the well-known iSCSI port.
The "LUN" field is a 16 byte hexadecimal representation of the 8-byte
LU number in hex. Digits above 9 may be either lower or upper case,
and all 16 nibbles must be present. If the LUN field is blank, then
LUN 0 is assumed.
Note that SCSI targets are allowed to present different LU numberings
for different SCSI initiators, so that to our knowledge nothing
precludes a SCSI target from exporting several different devices to
several different SCSI initiators as their respective LU 0s.
The "targetname" field is a string containing the name of the iSCSI
target, the details of which are specified by the iSCSI standard[12].
If the targetname is provided, the iSCSI boot client may use the
targetname as mandated by the iSCSI standard.
The above assumes that the default connection method uses TCP as
stated in the iSCSI standard. Should SCTP[18] be also approved as a
transport mechanism for iSCSI, then the draft will be amended to
provide for alternate transport protocols.
5. Discovery Service stage:
This stage is required if the DHCP server (v4 or v6) is unaware of
the identity of the iSCSI boot server.
The iSCSI boot client then may start the discovery process according
to the specifications stated in the iSCSI Naming and Discovery
document[14]. The discovery service provides the boot client with a
list of SCSI targets the client is allowed to access, along with the
access permissions for each of the target. The nature and
implemention of the discovery service is outside the scope of this
document.
The iSCSI boot client goes through the list of SCSI targets and must
select the first SCSI target with the bootable attribute as the iSCSI
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boot server. If such an attribute does not exist in any of the SCSI
targets, the boot client must select the first SCSI target in the
list of SCSI targets as the iSCSI boot server.
If the list of SCSI targets is empty, subsequent actions are left to
the discretion of the implementor.
The packets and software requirements are stated in the iSCSI Naming
and Discovery document[14].
6. Boot Stage
Once the iSCSI boot client has obtained the minimum information to
open an iSCSI session with the iSCSI boot server, the actual booting
process can start.
The actual sequence of iSCSI commands needed to complete the boot
process is left to the implementor. This was done because of varying
requirements from different vendors and equipments, making it
difficult to specify a common subset of the iSCSI standard that would
be acceptable to everybody.
The iSCSI session established for boot may be taken over the booted
software in the boostrapping client - this is left to the discretion
of the implementor.
7. Security
Securing the host configuration protocol is beyond the scope of this
document. Authentication of DHCP messages is described in [16].
The iSCSI standard support various methods of authenticated login and
encrypted and authenticated connections for security. How to
configure the security parameters of an iSCSI boot client is beyond
the scope of this document.
The security discussions in the iSCSI standard[12] are applicable to
this document.
Acknowledgments
We wish to thank John Hufferd for taking the initiative to form the
iSCSI boot team. We also wish to thank Doug Otis and David Robinson
for helpful suggestions and pointers regarding the draft document.
References
[1] Guttman, E., Perkins, C., Verizades, J., Day, M., "Service
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Location Protocol v2", RFC 2608, June 1999.
[2] Alexander, S., and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, Lachman Technology, Inc., Bucknell
University, October 1993.
[3] R. Droms, "Dynamic Host Configuration Protocol", RFC 2131,
Bucknell University, March 1997.
[4] Brownell, D, "Dynamic Reverse Address Resolution Protocol
(DRARP)", Work in Progress.
[5] Croft, B., and J. Gilmore, "Bootstrap Protocol (BOOTP)", RFC 951,
Stanford and SUN Microsystems, September 1985.
[6] Droms, D., "Interoperation between DHCP and BOOTP" RFC 1534,
Bucknell University, October 1993.
[7] Finlayson, R., Mann, T., Mogul, J., and M. Theimer, "A Reverse
Address Resolution Protocol", RFC 903, Stanford, June 1984.
[8] Reynolds, J., "BOOTP Vendor Information Extensions", RFC 1497,
USC/Information Sciences Institute, August 1993.
[9] Sollins, K., "The TFTP Protocol (Revision 2)", RFC 783, NIC,
June 1981.
[10] Wimer, W., "Clarifications and Extensions for the Bootstrap
Protocol", RFC 1532, Carnegie Mellon University, October 1993.
[11] Bradner, S., "The Internet Standards Process --
Revision 3", RFC 2026, October 1996.
[12] Satran, J., "iSCSI", Internet-Draft, November 2000.
[13] Bound, J., Canney, M., and Perkins, C., "Dynamic Host
Configuration
Protocol for IPv6", Internet-Draft, November 2000.
[14] Voruganti, K. et al., "iSCSI Naming and Discovery", Internet-
Draft,
November 2000.
[15] Veizades, J., Guttman, E., Perkins, C., Kaplan, S., "Service
Location Protocol", RFC 2165, June 1997.
[16] Droms, R., Arbaugh, W., "Authentication for DHCP Messages",
Internet-Draft, November 2000.
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[17] http://developer.intel.com/ial/WfM/wfm20/design/pxedt/index.htm
[18] Stewart, R., et al. "Stream Control Transmission Protocol", RFC
2960, October 2000.
[19] Droms, R., "Procedures and IANA Guidelines for Approval of New
DHCP Options and Message Types", RFC 2939, September 2000.
[20] Yergeau, F., "UTF-8: A Transformation Format for ISO-10646", RFC
2279, January 1998.
Author's Addresses
Prasenjit Sarkar
IBM Almaden Research Center
650 Harry Road
San Jose, CA 95120, USA
Phone: +1 408 927 1417
Email: psarkar@almaden.ibm.com
Duncan Missimer
Hewlett-Packard Company
19420 Homestead Road, M/S 43lo
Cupertino, CA 95014, USA
Phone: +1 408 447 5390
Email: duncan_missimer@hp.com
Constantine Sapuntzakis
Cisco Systems, Inc.
170 W. Tasman Drive
San Jose, CA 95134, USA
Phone: +1 650 520 0205
Email: csapuntz@cisco.com
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