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Network Working Group                                          P. SarkarRequest for Comments: 4173                                           IBMCategory: Standards Track                                    D. Missimer                                                 Hewlett-Packard Company                                                          C. Sapuntzakis                                                     Stanford University                                                          September 2005Bootstrapping Clients usingthe Internet Small Computer System Interface (iSCSI) ProtocolStatus of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2005).Abstract   Internet Small Computer System Interface (iSCSI) is a proposed   transport protocol for Small Computer Systems Interface (SCSI) that   operates on top of TCP.  This memo describes a standard mechanism for   enabling clients to bootstrap themselves using the iSCSI protocol.   The goal of this standard is to enable iSCSI boot clients to obtain   the information to open an iSCSI session with the iSCSI boot server.1.  Introduction   The Small Computer Systems Interface (SCSI) is a popular family of   protocols for communicating with I/O devices, especially storage   devices.  SCSI can be characterized as a request/response messaging   protocol with a standard architecture and componentized command sets   for different device classes.   iSCSI is a proposed transport protocol for SCSI that operates on top   of TCP.  The role of iSCSI is necessitated by the evolution of the   system interconnect from a shared bus to a switched network.  IP   networks meet the architectural and performance requirements of   transporting SCSI, paving the way for the iSCSI protocol.Sarkar, et al.              Standards Track                     [Page 1]

RFC 4173                  iSCSI Bootstrapping             September 2005   Many diskless clients sometimes bootstrap off remote SCSI devices.   Such diskless entities are lightweight, space efficient, and power-   conserving and are increasingly popular in various environments.   This memo describes a standard mechanism for enabling clients to   bootstrap themselves using the iSCSI protocol.  The goal of this   standard is to enable iSCSI boot clients to obtain the information to   open an iSCSI session with the iSCSI boot server.  It is possible   that all the information is not available at the very outset, so the   memo describes steps to obtain the information required to bootstrap   clients off an iSCSI boot server.1.1.  Keywords   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inRFC 2119 [Bradner97].2.  Requirements   1. There must be no restriction of network topology between the iSCSI      boot client and the boot server other than that in effect for      establishing the iSCSI session.  Consequently, it is possible for      an iSCSI boot client to boot from an iSCSI boot server behind      gateways or firewalls as long as it is possible to establish an      iSCSI session between the client and the server.   2. The following represent the minimum information required for an      iSCSI boot client to contact an iSCSI boot server: (a) the      client's IP address (IPv6 or IPv4); (b) the server's iSCSI Target      Name; and (c) mandatory iSCSI initiator capability.   The above assume that the default LUN for the boot process is 0 and   that the default port for the iSCSI boot server is the well-known   iSCSI port [Satran02].  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.Sarkar, et al.              Standards Track                     [Page 2]

RFC 4173                  iSCSI Bootstrapping             September 2005   5. Additional protocol software (for example, BOOTP or DHCP) may be      necessary if the minimum information required for an iSCSI session      is not provided.3.  Related Work   The Reverse Address Resolution Protocol (RARP) [Finlayson84] through   the extensions defined in the Dynamic RARP (DRARP) [Brownell96]   explicitly addresses the problem of network address discovery, and   includes an automatic IP address assignment mechanism.  The Trivial   File Transfer Protocol (TFTP) [Sollins81] provides for transport of a   boot image from a boot server.  BOOTP [Croft85,Reynolds93,Wimer93]   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 [Droms97,   Droms93] and DHCPv6 [Droms02] are standards by which hosts are to be   dynamically configured in an IP network.  The Service Location   Protocol (SLP) provides for location of higher-level services   [Guttman99].4.  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,   many established protocols allow such a service in order to enable   clients to load software images.  For example, BOOTP and DHCP servers   have the capability to provide the locations of servers that can   serve software images on requests from boot clients.   Note 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.5.  DHCP Stage   In order to use an iSCSI boot server, the following pieces of   information are required for an ISCSI boot client.   - The IP address of the iSCSI boot client (IPv4 or IPv6)   - The IP transport endpoint for the iSCSI Target 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.  TCP is currently     the only transport approved for iSCSI.Sarkar, et al.              Standards Track                     [Page 3]

RFC 4173                  iSCSI Bootstrapping             September 2005   - The eight-byte LUN structure identifying the Logical Unit within     the iSCSI boot server.   At boot time, all or none of this information may be stored in the   iSCSI boot client.  This section describes techniques for obtaining   the required information via the DHCP stage.  Otherwise, if the iSCSI   boot client has all the information, the boot client may proceed   directly to the Boot stage.   An iSCSI boot client that does not know its IP address at power-on   may acquire it via BOOTP or DHCP (v4 or v6), or via IPv6 address   autoconfiguration.  Please note that DHCP settings (such as the RA   settings in DHCPv6) may prohibit the use of DHCP in distributing   iSCSI boot information; in this case, the DHCP stage cannot be used.   Unless specified otherwise here, BOOTP or DHCP fields such as the   client ID and gateway information are used in an identical way as   applications other than iSCSI.   A BOOTP or DHCP server (v4 or v6) MAY instruct an iSCSI client how to   reach its boot device.  This is done using the variable-length option   named Root Path [Alexander93,Reynolds93].  The use of the option   field is reserved for iSCSI boot use by prefacing the string with   "iscsi:".  The Root Path option is not currently defined for DHCPv6;   if the option is defined for DHCPv6 in the future, the use of the   option as defined for iSCSI boot will apply.   The option field consists of an UTF-8 [Yergeau98] string.  The string   has the following composition:   "iscsi:"<servername>":"<protocol>":"<port>":"<LUN>":"<targetname>   The fields "servername", "port", "protocol", and "LUN" are OPTIONAL   and should be left blank if there are no corresponding values.  The   "targetname" field is not optional and MUST be provided.   The "servername" is the name of iSCSI server and contains either a   valid domain name, a literal IPv4 address, or a literal IPv6 address.   The servername must follow the specifications outlined inSection3.2.2 of the URI Specification [Lee98] [Hinden99].  The characters   allowed must also conform toSection 2.2 of the same specification.   Servername compression MUST NOT be used in this field.   The "protocol" field is the decimal representation of the IANA-   approved string for the transport protocol to be used for iSCSI.  If   the protocol field is left bank, the default value is assumed to beSarkar, et al.              Standards Track                     [Page 4]

RFC 4173                  iSCSI Bootstrapping             September 2005   "6" for TCP.  The transport protocol MUST have been approved for use   in iSCSI; currently, the only approved protocol is TCP.   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 [Satran02].   The "LUN" field is a hexadecimal representation of the LU number.  If   the LUN field is blank, then LUN 0 is assumed.  If the LUN field is   not blank, the representation MUST be divided into four groups of   four hexadecimal digits, separated by "-".  Digits above 9 may be   either lower or upper case.  An example of such a representation   would be 4752-3A4F-6b7e-2F99.  For the sake of brevity, at most three   leading zero ("0") digits MAY be omitted in any group of hexadecimal   digits.  Thus, the "LUN" representation 6734-9-156f-127 is equivalent   to 6734-0009-156f-0127.  Furthermore, trailing groups containing only   the "0" digit MAY be omitted along with the preceding "-".  So, the   "LUN" representation 4186-9 is equivalent to 4186-0009-0000-0000.   Other concise representations of the LUN field MUST NOT be used.   Note that SCSI targets are allowed to present different LU numberings   for different SCSI initiators, so to our knowledge nothing precludes   a SCSI target from exporting several different LUs to several   different SCSI initiators as their respective LUN 0s.   The "targetname" field is an iSCSI Name that is defined by the iSCSI   standard [Satran02] to uniquely identify an iSCSI target.  The   approved characters in the targetname field are stated in the iSCSI   String Profile document[Bakke04].   If the "servername" field is provided by BOOTP or DHCP, then that   field is used in conjunction with other associated fields to contact   the boot server in the Boot stage (Section 7).  However, if the   "servername" field is not provided, then the "targetname" field is   then used in the Discovery Service stage in conjunction with other   associated fields (Section 6).6.  Discovery Service Stage   This stage is required if the BOOTP or DHCP server (v4 or v6) is   unaware of any iSCSI boot servers or if the BOOTP or DHCP server is   unable to provide the minimum information required to connect to the   iSCSI boot server, other than the targetname.   The Discovery Service may be based on the SLP protocol [Guttman99,   Bakke02] and is an instantiation of the SLP Service or Directory   Agent.  Alternatively, the Discovery Service may be based on the iSNS   protocol [Tseng03] and is an instantiation of the iSNS Server.Sarkar, et al.              Standards Track                     [Page 5]

RFC 4173                  iSCSI Bootstrapping             September 2005   The iSCSI boot client may have obtained the targetname of the iSCSI   boot server in the DHCP stage (Section 5).  In that case, the iSCSI   boot client queries the SLP Discovery Service using query string 1 of   the iSCSI Target Concrete Service Type Template, as specified inSection 6.2 of the iSCSI SLP interaction document [Bakke02], to   resolve the targetname to an IP address and port number.   Alternatively, the iSCSI boot client may query the iSNS Discovery   Service with a Device Attribute Query with the targetname as the   query parameter [Tseng03].  Once this is obtained, the iSCSI boot   client proceeds to the Boot stage (Section 7).   It is possible that the port number obtained from the Discovery   Service may conflict with the one obtained from the DHCP stage.  In   such a case, the implementor has the option to try both port numbers   in the Boot stage.   If the iSCSI boot client does not have any targetname information,   the iSCSI boot client may then query the SLP Discovery Service with   query string 4 of the iSCSI Target Concrete Service Type Template, as   specified inSection 6.2 of the iSCSI SLP interaction document   [Bakke02].  In response to this query, the SLP Discovery Service   provides the boot client with a list of iSCSI boot servers the boot   client is allowed to access.  Alternatively, the iSCSI boot client   can query the iSNS Discovery Service to verify if the targets in   particular Discovery Domain are bootable [Tseng03].   If the list of iSCSI boot servers is empty, subsequent actions are   left to the discretion of the implementor.  Otherwise, the iSCSI boot   client may contact any iSCSI boot server in the list.  Moreover, the   order in which iSCSI boot servers are contacted is also left to the   discretion of the implementor.7.  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 that are 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 by the   booted software in the iSCSI boot client.Sarkar, et al.              Standards Track                     [Page 6]

RFC 4173                  iSCSI Bootstrapping             September 20058.  Security Considerations   The security discussion is centered around securing the communication   involved in the iSCSI boot process.   However, the issue of applying credentials to a boot image loaded   through the iSCSI boot mechanism is outside the scope of this   document.  One key difference between the iSCSI boot mechanism and   BOOTP-based image loading is the fact that the identity of a boot   image may not be known when the Boot stage starts.  The identity of   certain boot images and their locations are known only after the   contents of a boot disk exposed by the iSCSI boot service are   examined.  Furthermore, images themselves may recursively load other   images based on both hardware configurations and user input.   Consequently, a practical way to verify loaded boot images is to make   sure that each image loading software verifies the image to be loaded   using a mechanism of their choice.   The considerations involved in designing a security architecture for   the iSCSI boot process include configuration, deployment, and   provisioning issues apart from typical security considerations.   Enabling iSCSI boot creates a critical operational dependence on an   external system with obvious security implications, and thus   administrator awareness of this enablement is extremely important.   Therefore, iSCSI boot SHOULD NOT be enabled or put high in the boot   order without an explicit administrative action.   In all phases of the boot process, a client must ensure that a server   is authorized to send it certain information.  This means that the   authenticated identity of a server must have an authorization   indication.  A list of authorized servers can be pre-configured into   a client, or the list can be downloaded in an authenticated form from   a prior stage in the boot process.   The software stage SHOULD NOT be involved in a secure iSCSI boot   process, as this would add the additional complexity of trying to   secure the process of loading the software necessary to run the later   stages of iSCSI boot.  Authentication and integrity protection of   downloaded boot software has proven to be difficult and complex due   to administrative issues and limitations of the BIOS environment.  It   is therefore assumed that all the necessary software is resident on   the iSCSI boot client.   If the DHCP stage is implemented using the DHCP protocol, the iSCSI   boot client SHOULD implement the DHCP authentication ([Droms01],   [Droms02] for IPv6).  In this case, an administration interface   SHOULD be provided for the configuration of the DHCP authentication   credentials, both when the network interface is on the motherboardSarkar, et al.              Standards Track                     [Page 7]

RFC 4173                  iSCSI Bootstrapping             September 2005   and when it is removable.  Note that DHCP authentication   ([Droms01],[Droms02] for IPv6) is focused on intra-domain   authentication, which is assumed to be enough for iSCSI boot   scenarios.  In the context of the secure iSCSI boot process, the   reply from the DHCP server in the DHCP stage SHOULD include the   serverName in IPv4 (or IPv6) format to avoid reliance on a DNS server   (for resolving names) or a Discovery Service entity (to look up   targetnames).  This reduces the number of entities involved in the   secure iSCSI boot process.   If the Discovery Service stage is implemented using SLP, the iSCSI   boot client SHOULD provide IPsec support (OPTIONAL to use) for the   SLP protocol, as defined in [Bakke02] and [Aboba03].  If the   Discovery Service stage is implemented using iSNS, the iSCSI boot   client SHOULD provide IPsec support (OPTIONAL to use) for the iSNS   protocol, as defined in [Tseng03] and [Aboba03].  When iSNS or SLP   are used to distribute security policy or configuration information,   at a minimum, per-packet data origin authentication, integrity, and   replay protection SHOULD be used to protect the discovery protocol.   For the final communication between the iSCSI boot client and the   iSCSI boot server in the Boot stage, IPsec and in-band authentication   SHOULD be implemented according to the guidelines in the main iSCSI   draft [Satran02] and [Aboba03].  Due to memory constraints, it is   expected that iSCSI boot clients will only support the pre-shared key   authentication in IKE.  Where the host IP address is assigned   dynamically, IKE main mode SHOULD NOT be used, as explained in   [Satran02] and [Aboba03].  Regardless of the way parameters in   previous stages (DHCP, SLP, iSNS) were obtained (securely or not),   the iSCSI boot session is vulnerable as any iSCSI session (see   [Satran02] and [Aboba03] for iSCSI security threats).  Therefore,   security for this session SHOULD be configured and used according to   [Satran02] and [Aboba03] guidelines.   Note that if a boot image inherits an iSCSI session from a previously   loaded boot image, it also inherits the security properties of the   iSCSI session.Acknowledgements   We wish to thank John Hufferd for taking the initiative to form the   iSCSI boot team.  We also wish to thank Doug Otis, Julian Satran,   Bernard Aboba, David Robinson, Mark Bakke, Ofer Biran, and   Mallikarjun Chadalapaka for helpful suggestions and pointers   regarding the draft document.Sarkar, et al.              Standards Track                     [Page 8]

RFC 4173                  iSCSI Bootstrapping             September 2005Normative References   [Aboba03]      Aboba, B., Tseng, J., Walker, J., Rangan, V., and F.                  Travostino, "Securing Block Storage Protocols over                  IP",RFC 3723, April 2004.   [Alexander93]  Alexander, S. and R. Droms, "DHCP Options and BOOTP                  Vendor Extensions",RFC 2132, March 1997.   [Bakke02]      Bakke, M., Hufferd, J., Voruganti, K., Krueger, M.,                  and T. Sperry, "Finding Internet Small Computer                  Systems Interface (iSCSI) Targets and Name Servers by                  Using Service Location Protocol version 2 (SLPv2)",RFC 4018, April 2005.   [Bakke04]      Bakke, M., "String Profile for Internet Small Computer                  Systems Interface (iSCSI) Names",RFC 3722, April                  2004.   [Bradner97]    Bradner, S., "Key words for use in RFCs to Indicate                  Requirement Levels",BCP 14,RFC 2119, March 1997.   [Croft85]      Croft, W. and J. Gilmore, "Bootstrap Protocol",RFC951, September 1985.   [Droms93]      Droms, R., "Interoperation Between DHCP and BOOTP",RFC 1534, October 1993.   [Droms97]      Droms, R., "Dynamic Host Configuration Protocol",RFC2131, March 1997.   [Droms01]      Droms, R. and W. Arbaugh, "Authentication for DHCP                  Messages",RFC 3118, June 2001.   [Droms02]      Droms, R., Bound, J., Volz, B., Lemon, T., Perkins,                  C., and M. Carney, "Dynamic Host Configuration                  Protocol for IPv6 (DHCPv6)",RFC 3315, July 2003.   [Guttman99]    Guttman, E., Perkins, C., Veizades, J., and M. Day,                  "Service Location Protocol, Version 2",RFC 2608, June                  1999.   [Hinden99]     Hinden, R., Carpenter, B., and L. Masinter, "Format                  for Literal IPv6 Addresses in URL's",RFC 2732,                  December 1999.Sarkar, et al.              Standards Track                     [Page 9]

RFC 4173                  iSCSI Bootstrapping             September 2005   [Lee98]        Berners-Lee, T., Fielding, R., and L. Masinter,                  "Uniform Resource Identifiers (URI): Generic Syntax",RFC 2396, August 1998.   [Reynolds93]   Reynolds, J., "BOOTP Vendor Information Extensions",RFC 1497, August 1993.   [Satran02]     Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka,                  M., and E. Zeidner, "Internet Small Computer Systems                  Interface (iSCSI)",RFC 3720, April 2004.   [Tseng03]      Tseng, J., Gibbons, K., Travostino, F., Du Laney, C.,                  and J. Souza, "Internet Storage Name Service (iSNS)",RFC 4171, April 2005.   [Yergeau98]    Yergeau, F., "UTF-8, a transformation format of ISO                  10646", STD 63,RFC 3629, November 2003.   [Wimer93]      Wimer, W., "Clarifications and Extensions for the                  Bootstrap Protocol",RFC 1542, October 1993.Informative References   [Brownell96]   Brownell, D., "Dynamic RARP Extensions for Automatic                  Network Address Acquisition",RFC 1931, April 1996.   [Finlayson84]  Finlayson, R., Mann, T., Mogul, J., and M. Theimer,                  "Reverse Address Resolution Protocol", STD 38,RFC903, June 1984.   [Sollins81]    Sollins, K., "The TFTP Protocol (Revision 2)", STD 33,RFC 1350, July 1992.Sarkar, et al.              Standards Track                    [Page 10]

RFC 4173                  iSCSI Bootstrapping             September 2005Authors' 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   10955 Tantau Ave   Cupertino, CA 95014, USA   EMail: duncan.missimer@ieee.org   Constantine Sapuntzakis   Stanford University   353 Serra Hall #407   Stanford, CA 94305, USA   EMail: csapuntz@alum.mit.eduSarkar, et al.              Standards Track                    [Page 11]

RFC 4173                  iSCSI Bootstrapping             September 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Sarkar, et al.              Standards Track                    [Page 12]