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RFC 4174

The IPv4 Dynamic Host Configuration Protocol (DHCP) Option for the Internet Storage Name Service

Pages: 13
Proposed Standard
Updated by:  7146

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Network Working Group                                           C. Monia
Request for Comments: 4174                                    Consultant
Category: Standards Track                                       J. Tseng
                                                     Riverbed Technology
                                                              K. Gibbons
                                                      McDATA Corporation
                                                          September 2005


      The IPv4 Dynamic Host Configuration Protocol (DHCP) Option
                for the Internet Storage Name Service

Status 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

This document describes the Dynamic Host Configuration Protocol (DHCP) option to allow Internet Storage Name Service (iSNS) clients to discover the location of the iSNS server automatically through the use of DHCP for IPv4. iSNS provides discovery and management capabilities for Internet SCSI (iSCSI) and Internet Fibre Channel Protocol (iFCP) storage devices in an enterprise-scale IP storage network. iSNS provides intelligent storage management services comparable to those found in Fibre Channel networks, allowing a commodity IP network to function in a similar capacity to that of a storage area network.

Table of Contents

1. Introduction ................................................. 2 1.1. Conventions Used in This Document ...................... 2 2. iSNS Option for DHCP ......................................... 3 2.1. iSNS Functions Field ................................... 5 2.2. Discovery Domain Access Field .......................... 6 2.3. Administrative Flags Field ............................. 7 2.4. iSNS Server Security Bitmap ............................ 8 3. Security Considerations ...................................... 9 4. IANA Considerations .......................................... 11
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   5.  Normative References ......................................... 11
   6.  Informative References ....................................... 11

1. Introduction

The Dynamic Host Configuration Protocol for IPv4 provides a framework for passing configuration information to hosts. Its usefulness extends to hosts and devices using the iSCSI and iFCP protocols to connect to block level storage assets over a TCP/IP network. The iSNS Protocol provides a framework for automated discovery, management, and configuration of iSCSI and iFCP devices on a TCP/IP network. It provides functionality similar to that found on Fibre Channel networks, except that iSNS works within the context of an IP network. iSNS thereby provides the requisite storage intelligence to IP networks that are standard on existing Fibre Channel networks. Existing DHCP options cannot be used to find iSNS servers for the following reasons: a) iSNS functionality is distinctly different from other protocols using DHCP options. Specifically, iSNS provides a significant superset of capabilities compared to typical name resolution protocols such as DNS. It is designed to support client devices that allow themselves to be configured and managed from a central iSNS server. b) iSNS requires a DHCP option format that provides more than the location of the iSNS server. The DHCP option has to specify the subset of iSNS services that may be actively used by the iSNS client. The DHCP option number for iSNS is used by iSCSI and iFCP devices to discover the location and role of the iSNS server. The DHCP option number assigned for iSNS by IANA is 83.

1.1. Conventions Used in This Document

iSNS refers to the Internet Storage Name Service framework, which consists of the storage network model and associated services. 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 in [RFC2119]. All frame formats are in big-endian network byte order. RESERVED fields SHOULD be set to zero.
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   This document uses the following terms:

      "iSNS Client" - iSNS clients are processes resident in iSCSI and
      iFCP devices that initiate transactions with the iSNS server using
      the iSNS Protocol.

      "iSNS Server" - The iSNS server responds to iSNS protocol query
      and registration messages and initiates asynchronous notification
      messages.  The iSNS server stores information registered by iSNS
      clients.

      "iSCSI (Internet SCSI)" - iSCSI is an encapsulation of SCSI for a
      new generation of storage devices interconnected with TCP/IP.

      "iFCP (Internet Fibre Channel Protocol)" - iFCP is a gateway-to-
      gateway protocol designed to interconnect existing Fibre Channel
      devices using TCP/IP.  iFCP maps the Fibre Channel transport and
      fabric services to TCP/IP.

2. iSNS Option for DHCP

This option specifies the location of the primary and backup iSNS servers and the iSNS services available to an iSNS client. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code = 83 | Length | iSNS Functions | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DD Access | Administrative FLAGS | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | iSNS Server Security Bitmap | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | a1 | a2 | a3 | a4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | b1 | b2 | b3 | b4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . . . . | | Additional Secondary iSNS Servers | | . . . . | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1. iSNS Server Option
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   The iSNS Option specifies a list of IP addresses used by iSNS
   servers.  The option contains the following parameters:

      Length: The number of bytes that follow the Length field.

      iSNS Functions: A bitmapped field defining the functions supported
            by the iSNS servers.  The format of this field is described
            in section 2.1.

      Discovery Domain Access: A bit field indicating the types of iSNS
            clients that are allowed to modify Discovery Domains.  The
            field contents are described in section 2.2.

      Administrative Flags field: Contains the administrative settings
            for the iSNS servers discovered through the DHCP query.  The
            contents of this field are described in section 2.3.

      iSNS Server Security Bitmap: Contains the iSNS server security
            settings specified in section 2.4.

      a1...a4: Depending on the setting of the Heartbeat bit in the
            Administrative Flags field (see section 2.3), this field
            contains either the IP address from which the iSNS heartbeat
            originates (see [iSNS]) or the IP address of the primary
            iSNS server.

      b1...b4: Depending on the setting of Heartbeat bit in the
            Administrative Flags field (see section 2.3), this field
            contains either the IP address of the primary iSNS server or
            that of a secondary iSNS server.

      Additional Secondary iSNS Servers: Each set of four octets
            specifies the IP address of a secondary iSNS server.

   The Code field through IP address field a1...a4 MUST be present in
   every response to the iSNS query; therefore the Length field has a
   minimum value of 14.

   If the Heartbeat bit is set in the Administrative Flags field (see
   section 2.3), then b1...b4 MUST also be present.  In this case, the
   minimum value of the Length field is 18.

   The inclusion of Additional Secondary iSNS Servers in the response
   MUST be indicated by increasing the Length field accordingly.
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2.1. iSNS Functions Field

The iSNS Functions Field defines the iSNS server's operational role (i.e., how the iSNS server is to be used). The iSNS server's role can be as basic as providing simple discovery information, or as significant as providing IKE/IPSec security policies and certificates for the use of iSCSI and iFCP devices. The format of the iSNS Functions field is shown in Figure 2. 0 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RESERVED |S|A|E| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2. iSNS Functions Field Bit Field Significance --------- ------------ 15 Function Fields Enabled 14 DD-Based Authorization 13 Security Policy Distribution The following are iSNS Functions Field definitions: Function Fields Specifies the validity of the remaining Enabled: iSNS Function fields. If it is set to one, then the contents of all other iSNS Function fields are valid. If it is set to zero, then the contents of all other iSNS Function fields MUST be ignored. DD-based Indicates whether devices in a common Authorization: Discovery Domain (DD) are implicitly authorized to access one another. Although Discovery Domains control the scope of device discovery, they do not necessarily indicate whether a domain member is authorized to access discovered devices. If this bit is set to one, then devices in a common Discovery Domain are automatically allowed access to each other (if successfully authenticated). If this bit is set to zero, then access authorization is not implied by domain membership and must be explicitly performed by each device. In either case, devices not in a common discovery domain are not allowed to access each other.
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      Security Policy  Indicates whether the iSNS client is to
      Distribution:    download and use the security policy
                       configuration stored in the iSNS server.  If it
                       is set to one, then the policy is stored in the
                       iSNS server and must be used by the iSNS client
                       for its own security policy.  If it is set to
                       zero, then the iSNS client must obtain its
                       security policy configuration by other means.

2.2. Discovery Domain Access Field

The format of the DD Access bit field is shown in Figure 3. 0 1 1 1 1 1 1 0 ... 9 0 1 2 3 4 5 +---+---+---+---+---+---+---+---+---+ | RESERVED | if| tf| is| ts| C | E | +---+---+---+---+---+---+---+---+---+ Figure 3. Discovery Domain Access Field Bit Field Significance --------- ------------ 15 Enabled 14 Control Node 13 iSCSI Target 12 iSCSI Initiator 11 iFCP Target Port 10 iFCP Initiator Port The following are Discovery Domain Access Field definitions: Enabled: Specifies the validity of the remaining DD Access bit field. If it is set to one, then the contents of the remainder of the DD Access field are valid. If it is set to zero, then the contents of the remainder of this field MUST be ignored. Control Node: Specifies whether the iSNS server allows Discovery Domains to be added, modified, or deleted by means of Control Nodes. If it is set to one, then Control Nodes are allowed to modify the Discovery Domain configuration. If it is set to zero, then Control Nodes are not allowed to modify Discovery Domain configurations.
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      iSCSI Target,      Determine whether the respective
      iSCSI Initiator,   registered iSNS client (determined
      iFCP Target Port,  by iSCSI Node Type or iFCP Port Role)
      iFCP Initiator     is allowed to add, delete, or modify
      Port:              Discovery Domains.  If they are set to one,
                         then modification by the specified client type
                         is allowed.  If they are set to zero, then
                         modification by the specified client type is
                         not allowed.

                         (A node may implement multiple node types.)

2.3. Administrative Flags Field

The format of the Administrative Flags bit field is shown in Figure 4. 0 1 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RESERVED |D|M|H|E| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4. Administrative Flags Bit Field Significance --------- ------------ 15 Enabled 14 Heartbeat 13 Management SCNs 12 Default Discovery Domain The following are Administrative Flags Field definitions: Enabled: Specifies the validity of the remainder of the Administrative Flags field. If it is set to one, then the contents of the remaining Administrative Flags are valid. If it is set to zero, then the remaining contents MUST be ignored, indicating that iSNS administrative settings are obtained through means other than DHCP. Heartbeat: Indicates whether the first IP address is the multicast address to which the iSNS heartbeat message is sent. If it is set to one, then a1-a4 contains the heartbeat multicast address and b1-b4 contains the IP address of the
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                         primary iSNS server, followed by the IP
                         address(es) of any backup servers (see Figure
                         1).  If it is set to zero, then a1-a4 contain
                         the IP address of the primary iSNS server,
                         followed by the IP address(es) of any backup
                         servers.

      Management SCNs:   Indicates whether control nodes are authorized
                         to register for receiving Management State
                         Change Notifications (SCNs).  Management SCNs
                         are a special class of State Change
                         Notification whose scope is the entire iSNS
                         database.  If this bit is set to one, then
                         control nodes are authorized to register for
                         receiving Management SCNs.  If it is set to
                         zero, then control nodes are not authorized to
                         receive Management SCNs (although they may
                         receive normal SCNs).

      Default Discovery  Indicates whether a newly registered
      Domain:            device that is not explicitly placed into a
                         Discovery Domain (DD) and Discovery Domain Set
                         (DDS) should be automatically placed into a
                         default DD and DDS.  If it is set to one, then
                         a default DD shall contain all devices in the
                         iSNS database that have not been explicitly
                         placed into a DD by an iSNS client.  If it is
                         set to zero, then devices not explicitly placed
                         into a DD are not members of any DD.

2.4. iSNS Server Security Bitmap

The format of the iSNS server security Bitmap field is shown in Figure 5. If valid, this field communicates to the DHCP client the security settings that are required to communicate with the indicated iSNS server. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RESERVED |T|X|P|A|M|S|E| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5. iSNS Server Security Bitmap
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           Bit Field     Significance
           ---------     ----------------
                31      Enabled
                30      IKE/IPSec
                29      Main Mode
                28      Aggressive Mode
                27      PFS
                26      Transport Mode
                25      Tunnel Mode

   The following are iSNS Server Security Bitmap definitions:

      Enabled:           Specifies the validity of the remainder of the
                         iSNS server security bitmap.  If it is set to
                         one, then the contents of the remainder of the
                         field are valid.  If it is set to zero, then
                         the contents of the rest of the field are
                         undefined and MUST be ignored.

      IKE/IPSec:         1 = IKE/IPSec enabled; 0 = IKE/IPSec disabled.

      Main Mode:         1 = Main Mode enabled; 0 = Main Mode disabled.

      Aggressive Mode:   1 = Aggressive Mode enabled;
                         0 = Aggressive Mode disabled.

      PFS:               1 = PFS enabled; 0 = PFS disabled.

      Transport Mode:    1 = Transport Mode preferred; 0 = No
                         preference.

      Tunnel Mode:       1 = Tunnel Mode preferred; 0 = No preference.

   If IKE/IPSec is disabled, this indicates that the Internet Key
   Exchange (IKE) Protocol is not available to configure IPSec keys for
   iSNS sessions to this iSNS server.  It does not necessarily preclude
   other key exchange methods (e.g., manual keying) from establishing an
   IPSec security association for the iSNS session.

   If IKE/IPsec is enabled, then for each of the bit pairs <Main Mode,
   Aggressive Mode> and <Transport Mode, Tunnel Mode>, one of the two
   bits MUST be set to 1, and the other MUST be set to 0.

3. Security Considerations

For protecting the iSNS option, the DHCP Authentication security option as specified in [RFC3118] may present a problem due to the limited implementation and deployment of the DHCP authentication
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   option.  The IPsec security mechanisms for iSNS itself are specified
   in [iSNS] to provide confidentiality when sensitive information is
   distributed via iSNS.  See the Security Considerations section of
   [iSNS] for details and specific requirements for implementation of
   IPsec.

   In addition, [iSNS] describes an authentication block that provides
   message integrity for multicast or broadcast iSNS messages (i.e., for
   heartbeat/discovery messages only).  See [RFC3723] for further
   discussion of security for these protocols.

   If no sensitive information, as described in [iSNS], is being
   distributed via iSNS, and an Entity is discovered via iSNS,
   authentication and authorization are handled by the IP Storage
   protocols whose endpoints are discovered via iSNS; specifically, iFCP
   [iFCP] and iSCSI [RFC3720].  It is the responsibility of the
   providers of these services to ensure that an inappropriately
   advertised or discovered service does not compromise their security.

   When no DHCP security is used, there is a risk of distribution of
   false discovery information (e.g., via the iSNS DHCP option
   identifying a false iSNS server that distributes the false discovery
   information).  The primary countermeasure for this risk is
   authentication by the IP storage protocols discovered through iSNS.
   When this risk is a significant concern, IPsec SAs SHOULD be used (as
   specified in RFC 3723).  For example, if an attacker uses DHCP and
   iSNS to distribute discovery information that falsely identifies an
   iSCSI endpoint, that endpoint will lack the credentials necessary to
   complete IKE authentication successfully, and therefore will be
   prevented from falsely sending or receiving iSCSI traffic.  When this
   risk of false discovery information is a significant concern and
   IPsec is implemented for iSNS, IPsec SAs SHOULD also be used for iSNS
   traffic to prevent use of a false iSNS server; this is more robust
   than relying only on the IP Storage protocols to detect false
   discovery information.

   When IPsec is implemented for iSNS, there is a risk of a denial-of-
   service attack based on repeated use of false discovery information
   that will cause initiation of IKE negotiation.  The countermeasures
   for this are administrative configuration of each iSNS Entity to
   limit the peers it is willing to communicate with (i.e., by IP
   address range and/or DNS domain), and maintenance of a negative
   authentication cache to avoid repeatedly contacting an iSNS Entity
   that fails to authenticate.  These three measures (i.e., IP address
   range limits, DNS domain limits, negative authentication cache) MUST
   be implemented for iSNS entities when this DHCP option is used.  An
   analogous argument applies to the IP storage protocols that can be
   discovered via iSNS as discussed in RFC 3723.
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   In addition, use of the techniques described in [RFC2827] and
   [RFC3833] may also be relevant to reduce denial-of-service attacks.

4. IANA Considerations

In accordance with the policy defined in [DHCP], IANA has assigned a value of 83 for this option. There are no other IANA-assigned values defined by this specification.

5. Normative References

[DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [iSNS] Tseng, J., Gibbons, K., Travostino, F., Du Laney, C., and J. Souza, "Internet Storage Name Service (iSNS)", RFC 4171, September 2005. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages", RFC 3118, June 2001. [RFC3720] Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka, M., and E. Zeidner, "Internet Small Computer Systems Interface (iSCSI)", RFC 3720, April 2004. [RFC3723] Aboba, B., Tseng, J., Walker, J., Rangan, V., and F. Travostino, "Securing Block Storage Protocols over IP", RFC 3723, April 2004.

6. Informative References

[iFCP] Monia, C., Mullendore, R., Travostino, F., Jeong, W., and M. Edwards, "iFCP - A Protocol for Internet Fibre Channel Storage Networking", RFC 4172, September 2005. [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, May 2000. [RFC3833] Atkins, D. and R. Austein, "Threat Analysis of the Domain Name System (DNS)", RFC 3833, August 2004.
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Authors' Addresses

Kevin Gibbons McDATA Corporation 4555 Great America Parkway Santa Clara, CA 95054-1208 Phone: (408) 567-5765 EMail: kevin.gibbons@mcdata.com Charles Monia 7553 Morevern Circle San Jose, CA 95135 EMail: charles_monia@yahoo.com Josh Tseng Riverbed Technology 501 2nd Street, Suite 410 San Francisco, CA 94107 Phone: (650)274-2109 EMail: joshtseng@yahoo.com
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