Network Working Group D. Wysochanski
Request for Comments: 4850 Network Appliance, Inc.
Updates: 3720 April 2007
Category: Standards Track
Declarative Public Extension Key for
Internet Small Computer Systems Interface (iSCSI) Node Architecture
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 (C) The IETF Trust (2007).
The Internet Small Computer Systems Interface (iSCSI) protocol,
described in RFC 3720, allows for extension items to the protocol in
the form of Private or Public Extension Keys. This document
describes a Public Extension Key for the purpose of enhancing iSCSI
supportability. The key accomplishes this objective by allowing
iSCSI nodes to communicate architecture details during the iSCSI
login sequence. The receiving node can then use this information for
enhanced logging and support. This document updates RFC 3720 to
allow iSCSI extension items to be defined by standards track RFCs and
experimental RFCs in addition to informational RFCs.
This document describes a declarative Public Extension Key, as
defined by Section 12.22 of RFC 3720 , that may be used to
communicate additional iSCSI node information to the peer node in a
session. The information carried in the described key has been found
to be valuable in real iSCSI customer environments as initiator and
target vendors collaborate to resolve technical issues and better
understand the interaction of iSCSI implementations.
The key has been modeled after the HTTP "Server" and "User-Agent"
header fields as specified in Sections 14.38 and 14.43 of RFC 2616
, with the text-value(s) of the key roughly equivalent to Product
Tokens in Section 3.8 of RFC 2616 . Note, however, that the text-
value(s) in the key's list-of-values MUST conform to the Text Format
as specified in Section 5.1 of RFC 3720 .
The key is sent during operational parameter negotiation of an iSCSI
session's login phase. The intended use of this key is to provide
enhanced logging and support capabilities, and to enable collection
of iSCSI implementation and usage information.
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 RFC 2119 .
The definition of the key is as follows, conforming to Sections 11
and 12 of RFC 3720 , with example list-of-values conforming to
Section 5.1 of RFC 3720 .
The key is defined with a use of "LO", making it a Leading Only key,
and does not modify Sections 11 or 12 of RFC 3720 . Thus, the key
MUST only be sent on the leading connection, MUST NOT be changed
after the leading connection login, and MUST only be sent after the
security negotiation login stage has completed (during operational
negotiation login stage). The key may be sent during normal or
Use: LO, Declarative
Senders: Initiator and Target
The initiator or target declares the details of its iSCSI node
architecture to the remote endpoint. These details may include, but
are not limited to, iSCSI vendor software, firmware, or hardware
versions, the OS version, or hardware architecture.
The length of the key value (total length of the list-of-values) MUST
NOT be greater than 255 bytes.
X#NodeArchitecture MUST NOT be redeclared.
Functional behavior of the iSCSI node (this includes the iSCSI
protocol logic -- the SCSI, iSCSI, and TCP/IP protocols) MUST NOT
depend on the presence, absence, or content of the key. The key MUST
NOT be used by iSCSI nodes for interoperability, or exclusion of
other nodes. To ensure proper use, key values SHOULD be set by the
node itself, and there SHOULD NOT be provisions for the key values to
contain user-defined text.
Nodes implementing this key MUST choose one of the following
o only transmit the key,
o only log the key values received from other nodes, or
o both transmit and log the key values.
Each node choosing to implement transmission of the key values MUST
be prepared to handle the response of RFC 3720  compliant nodes
that do not understand the key (RFC 3720  states that compliant
nodes MUST respond with X#NodeArchitecture=NotUnderstood).
Nodes that implement transmission and/or logging of the key values
may also implement administrative mechanisms that disable and/or
change the logging and key transmission detail (see Security
Considerations). Thus, a valid behavior for this key may be that a
node is completely silent (the node does not transmit any key value,
and simply discards any key values it receives without issuing a
4. Security Considerations
This extension key transmits specific implementation details about
the node that sends it; such details may be considered sensitive in
some environments. For example, if a certain software or firmware
version is known to contain security weaknesses, announcing the
presence of that version via this key may not be desirable. The
countermeasures for this security concern are:
o sending less detailed information in the key values,
o not sending the extension key, or
o using IPsec to provide confidentiality for the iSCSI connection on
which the key is sent (see RFC 3720  and RFC 3723 ).
To support the first and second countermeasures, all implementations
of this extension key MUST provide an administrative mechanism to
disable sending the key. In addition, all implementations SHOULD
provide an administrative mechanism to configure a verbosity level of
the key value, thereby controlling the amount of information sent.
For example, a lower verbosity might enable transmission of node
architecture component names only, but no version numbers.
The choice of which countermeasure is most appropriate depends on the
environment. However, sending less detailed information in the key
values may be an acceptable countermeasure in many environments,
since it provides a compromise between sending too much information
and the other more complete countermeasures of not sending the key at
all or using IPsec.
In addition to security considerations involving transmission of the
key contents, any logging method(s) used for the key values MUST keep
the information secure from intruders. For all implementations, the
requirements to address this security concern are:
o Display of the log MUST only be possible with administrative
rights to the node.
o Options to disable logging to disk and to keep logs for a fixed
duration SHOULD be provided.
Finally, it is important to note that different nodes may have
different levels of risk, and these differences may affect the
implementation. The components of risk include assets, threats, and
vulnerabilities. Consider the following example iSCSI nodes, which
demonstrate differences in assets and vulnerabilities of the nodes,
and as a result, differences in implementation:
o One iSCSI target based on a special-purpose operating system.
Since the iSCSI target controls access to the data storage
containing company assets, the asset level is seen as very high.
Also, because of the special-purpose operating system, in which
vulnerabilities are less well-known, the vulnerability level is
viewed as low.
o Multiple iSCSI initiators in a blade farm, each running a general-
purpose operating system. The asset level of each node is viewed
as low, since blades are replaceable and low cost. However, the
vulnerability level is viewed as high, since there are many well-
known vulnerabilities to the general-purpose operating system.
For the above target, an appropriate implementation might be logging
of received key values, but no transmission of the key. For the
initiators, an appropriate implementation might be transmission of
the key, but no logging of received key values.
5. IANA Considerations
The standards action of this document updates RFC 3720 to allow any
iSCSI extension item, specifically X# extension text keys, Y# digest
algorithms, and Z# authentication methods, to be defined by a
standards track, experimental, or informational RFC. This document
is a standards track RFC that defines an X# extension text key.
IANA registered this key as follows:
o Key Name: X#NodeArchitecture
o Description: Node architecture details
o Reference: [RFC4850]
The update to RFC 3720 to allow additional types of RFCs for iSCSI
Extension items has the same effect as if the following changes were
made to the text of RFC 3720 (RFC text cannot be changed after
1) In Section 11.1, the requirement that Z# Authentication methods
"MUST be described by an informational RFC." is changed to "MUST
be described by a standards track RFC, an experimental RFC, or an
2) In Section 12.1, the requirement that Y# Digest algorithms "MUST
be described by an informational RFC." is changed to "MUST be
described by a standards track RFC, an experimental RFC, or an
3) In Section 12.22, the requirement that X# text keys "MUST be
described by an informational RFC." is changed to "MUST be
described by a standards track RFC, an experimental RFC, or an
4) In Section 13.3, the description of allowed RFC types for
extension items is changed from "The RFC may be informational
rather than Standards-Track," to "The RFC MUST be standards track,
experimental, or informational,"
5) In Section 13.5.2, the phrase "standards track" is changed to
"standards track or experimental" in the last sentence of the
first paragraph, so that the sentence reads: "If the specification
is a standards track or experimental document, the usual IETF
procedures for such documents are followed."
The registries for iSCSI extension items should be managed as if
these changes had been made to the text of RFC 3720.
6.1. Normative References
 Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
 Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka, M., and E.
Zeidner, "Internet Small Computer Systems Interface (iSCSI)",
RFC 3720, April 2004.
6.2. Informative References
 Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
 Aboba, B., Tseng, J., Walker, J., Rangan, V., and F. Travostino,
"Securing Block Storage Protocols over IP", RFC 3723, April
Appendix A. Acknowledgments
The IP Storage (ips) Working Group in the Transport Area of IETF has
been responsible for defining the iSCSI protocol (apart from a host
of other relevant IP Storage protocols). The author acknowledges the
contributions of the entire working group.
The following individuals directly contributed to identifying issues
and/or suggesting resolutions to the issues found in this document:
David Black, Mallikarjun Chadalapaka, Paul Koning, Julian Satran,
John Hufferd, Claire Kraft, Ranga Sankar, Joseph Pittman, Greg Berg,
John Forte, Jim Yuill, William Studenmund, and Ken Sandars. This
document benefited from all these contributions.
Finally, the author recognizes Network Appliance, Inc. for
sponsorship and support during the development of this work.
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