Network Working Group D. Provan
Request for Comments: 2241 Novell, Inc.
Category: Standards Track November 1997
DHCP Options for Novell Directory Services
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 (1997). All Rights Reserved.
Abstract
This document defines three new DHCP options for delivering
configuration information to clients of the Novell Directory
Services. The first option carries a list of NDS servers. The second
option carries the name of the client's NDS tree. The third carries
the initial NDS context. These three options provide an NDS client
with enough information to connect to an NDS tree without manual
configuration of the client.
Novell Directory Services is a distributed, replicated, hierarchical
database of objects representing network resources such as nodes,
services, users, and applications. An NDS client must be able to
locate an NDS server in order to authenticate itself to the network
and gain access to the database. In addition, the node's user is
better served if the NDS client's attention is focused on the area of
the NDS database likely to be of the most interest to the user. This
specification describes DHCP options [1] that carry NDS information
to TCP/IP clients of NDS. The first option, the NDS Servers Option,
carries a list of NDS servers. The other two options, the NDS Tree
Name Option and the NDS Context Option, provide the client with a
default context within the NDS database.
Provan Standards Track [Page 1]
RFC 2241 DHCP Options November 1997
The NDS Tree Name Option and the NDS Context Option carry 16-bit
Unicode text encoded into an octet stream using UTF-8 [4]. A complete
DHCP implementation can represent of the entire Unicode character set
supported by NDS. At the same time, 7-bit ASCII text is unchanged by
the UTF-8 transformation. In environments where the NDS tree name and
context are restricted to the range of 7-bit ASCII characters, ASCII-
only DHCP clients and servers can support these options by using the
ASCII text as the UTF-8 encoded data.
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. [2]
This option specifies one or more NDS servers for the client to
contact for access to the NDS database. Servers SHOULD be listed in
order of preference.
The code for this option is 85. The minimum length of this option is
4 octets, and the length MUST be a multiple of 4.
Code Len Address 1 Address 2
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+--
| 85 | n | a1 | a2 | a3 | a4 | a1 | a2 | a3 | a4 | ...
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+--
This option specifies the name of the NDS tree the client will be
contacting. NDS tree names are 16-bit Unicode strings. For
transmission in the NDS Tree Name Option, an NDS tree name is
transformed into octets using UTF-8. The string should NOT be zero
terminated.
The code for this option is 86. The maximum possible length for this
option is 255 bytes.
Code Len NDS Tree Name
+----+----+----+----+----+----+--
| 86 | n | c1 | c2 | c3 | c4 | ...
+----+----+----+----+----+----+--
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RFC 2241 DHCP Options November 1997
This option specifies the initial NDS context the client should use.
NDS contexts are 16-bit Unicode strings. For transmission in the NDS
Context Option, an NDS context is transformed into octets using UTF-
8. The string should NOT be zero terminated.
A single DHCP option can only contain 255 octets. Since an NDS
context name can be longer than that, this option can appear more
than once in the DHCP packet. The contents of all NDS Context options
in the packet should be concatenated as suggested in the DHCP
specification [3, page 24] to get the complete NDS context. A single
encoded character could be split between two NDS Context Options.
The code for this option is 87. The maximum length for each instance
of this option is 255, but, as just described, the option may appear
more than once if the desired NDS context takes up more than 255
octets. Implementations are discouraged from enforcing any specific
maximum to the final concatenated NDS context.
Code Len Initial NDS Context
+----+----+----+----+----+----+--
| 87 | n | c1 | c2 | c3 | c4 | ...
+----+----+----+----+----+----+--
[1] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC-2132, March 1997.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC-2119, March 1997.
[3] Droms, R., "Dynamic Host Configuration Protocol", RFC-2131,
March 1997.
[4] Yergeau, F., "UTF-8, a transformation format of Unicode and
ISO 10646", RFC-2044, October 1996
DHCP currently provides no authentication or security mechanisms.
Potential exposures to attack are discussed in section 7 of the DHCP
protocol specification [3]. In particular, these DHCP options allow
an unauthorized DHCP server to misdirect an NDS client to a
nonexistent NDS server or even a spoof NDS server. These threats are
similar to what NDS faces during normal operations in its native IPX
environment.
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RFC 2241 DHCP Options November 1997
Copyright (C) The Internet Society (1997). All Rights Reserved.
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Provan Standards Track [Page 5]