IPS Prasenjit Sarkar
Internet Draft IBM
Document: draft-ietf-ips-iscsi-boot-00.txt Duncan Missimer
Category: Standards Track HP
Constantin Sapuntzakis
Cisco
17 November 2000
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
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of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft
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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) and (b) the server's iSCSI Service Delivery
Port Name.
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 can 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 when the boot client software is started.
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 Resource Location Protocol RLP
provides for location of higher level services[1].
3. 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.
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- The eight-byte LUN structure identifying the device within the
iSCSI boot server (see section 4.12.2 of SAM-2 17 Sept 2000)
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 DHCPv4 or BOOTP server may instruct an iSCSI client how to reach
its boot device. The servers use the "file" field of the BOOTP/DHCPV4
header to instruct the iSCSI client of which boot server to connect
to and how to do so. The format of the "file" field is:
"iscsi:" <servername> ":" <port> ":" <LUN> ":" <targetname>
The "file" field begins with literal UTF-8 string "iscsi:" to
instruct the client to use iSCSI/TCP (as opposed to NFS or some other
mechanism) to boot.
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
domain name, a literal IPv4 address, or a bracketed literal IPv6
address. If the servername field contains a domain name, the domain
name must comply with the restrictions in section 3 of RFC1034 and
section 2.1 of RFC1123. 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 as
specified in RFCs 2373 and 2732.
If the "servername" is a domain name, then the reply from the host
configuration server MAY contain the Domain Name Server Option
described in section 3.8 of RFC 2132.
The "port" is the decimal representation of the port on which the
iSCSI server is listening. If not specified, the port defaults to the
well-known iSCSI port.
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The "LUN" field is 16 UTF-8 bytes representing the 8-byte LU number
in hex. Digits above 9 may be either lower or upper case, and all 16
nibbles must be present. 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 UTF-8 ([RFC2279]) 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.
In the case of a DHCPv6 server, a proposed extension for iSCSI boot
information would provide the information returned in the "file"
field by a DHCPv4 server. The interpretation of the information will
be identical in both DHCPv4 and DHCPv6. The proposed extension would
be obtained as per the rules stated in RFC 2939.
If the iSCSI working group registers an extension for iSCSI boot
information which may be used by both DHCPv4 and DHCPv6, then that
extension field shall be used by the DHCPv4 server rather than the
"file" field.
The above assumes that the default connection method uses TCP as
stated in the iSCSI standard. Should SCTP (RFC 2960) be also approved
as a transport mechanism for iSCSI, then the draft will be amended to
provide for alternate transport protocols.
Detailed message formats will be available in a future version of
this draft.
4. Discovery Server stage:
This stage is required if the DHCP server (v4 or v6) is unaware of
the identity of the iSCSI boot server. In such a situation, the DHCP
server must return the identity of an iSCSI discovery server within a
proposed extension for iSCSI Discovery Server. This extension would
be obtained following the rules stated in RFC 2939 and would apply to
both DHCPv4 and DHCPv6.
The iscsi boot client then MAY send a message to the discovery server
according to the specifications stated in the iSCSI Naming and
Discovery document[14]. The discovery server provides the boot client
a list of SCSI targets the client is allowed to access, along with
the access permissions for each of the target.
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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
boostrapping 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].
5. 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 equipment, 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.
6. Security
Securing the host configuration protocol is beyond the scope of this
document. Authentication of DHCP messages is described in draft-ietf-
dhc-authentication-14.txt.
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 (current) scope of this document.
The security discussions in the iSCSI standard[12] are applicable to
this document.
Acknowledgments
We wish to thank John Hufferd (IBM) for taking the initiative to form
the iSCSI boot team, and Julian Satran (IBM) for providing insightful
comments. We also wish to thank the unnamed others for their help
with this document.
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References
[1] Acetta, M., "Resource Location Protocol", RFC 887, CMU, December
1983.
[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 2132,
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, May 2000.
[14] Voruganti, K. et al., "iSCSI Naming and Discovery", Internet-
Draft,
November 2000.
Author's Addresses
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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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