Network Working Group A.K. Vijayabhaskar
Internet-Draft Hewlett-Packard
Expires: Sep 14, 2003 14 Mar 2003
Client Preferred Prefix option for DHCPv6
draft-ietf-dhc-dhcpv6-opt-cliprefprefix-01.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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 obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 14, 2003.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes the Client Preferred Prefix option by which
the client can specify its preferred prefixes on which the addresses
need to be allocated by the server.
1. Introduction
Scenario 1: The client's link has multiple prefixes of different
scopes and the administrator policy on the server insists that the
addresses need to be allocated on site-local prefixes only. The
client will not be able to communicate with a node that belongs to a
different site, as the server allocates only site-local addresses in
IAs.
Vijayabhaskar A K Expires September 14, 2003 [Page 1]
Internet-Draft Client Preferred Prefix option for DHCPv6 Mar 2003
Scenario 2: The client's link has two prefixes: site-local and global.
The administrator policy insists that addresses need to be allocated
on both the prefixes. All the nodes on a link will not communicate
with external sites and thus all of them do not require global
addresses. However, the server allocates addresses on both the
prefixes. So, the client needs to send the release message to release
the unwanted addresses, which requires extra transactions.
Scenario 3: The node has used the stateless autoconf and learned
about prefixes. Say, the link has two prefixes 3ffe::/64 and
3fff::/64 and the link has been subnetted to two sets with these
prefixes. Now, suddenly the RAs say to use stateful autoconf. It
depends up on the dhcpv6 configuration whether the node will get both
the prefixes or not. It will be worser if the node using 3ffe::/64
has to renumber to 3fff::/64 unnecessarily, though both the prefixes
are valid in the link.
Scenario 4: In a highly secured environment where there is only a
known IPv6 prefix by specific entities provided the knowledge of that
prefix out of band not over a network. The entity will request this
prefix as a DHCPv6 client and will provide secret security parameter
to the DHCPv6 server. The server then provides a complete address for
that prefix. The entity client now can use that address for
communications with nodes that accept no other prefix on the network.
The applications for this are special operations for entities like
the Military, Law Enforcement, Fire Departments, and Doctors.
To overcome the problems described in the above Scenarios, the client
can specify its preferred prefixes to the server using Client
Preferred Prefix option.
2. Requirements
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in RFC 2119 [2]
3. Terminology
This document uses terminology specific to IPv6 and DHCPv6 as defined
in section "Terminology" of the DHCP specification.
4. Client Preferred Prefix option
Client Preferred Prefix option is used by the client to specify its
preferred prefixes to the server.
Vijayabhaskar A K Expires September 14, 2003 [Page 2]
Internet-Draft Client Preferred Prefix option for DHCPv6 Mar 2003
The format of the Client Preferred Prefix option is as shown below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_CLIENT_PREF_PREFIX | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| prefix-len | |
+-+-+-+-+-+-+-+-+-+ |
| |
| subnet prefix (n bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| prefix-len | |
+-+-+-+-+-+-+-+-+-+ |
| |
| subnet prefix (n bytes) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. client-pref-prefix-options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code: OPTION_CLIENT_PREF_PREFIX (tbd)
option-len: total length of the prefix-len and subnet prefix lists
and its encapsulated options.
prefix-len: prefix length of the subnet address.
subnet prefix: 'n' bytes of subnet prefix, where 'n' is minimum
number of bytes required to refer 'prefix-len' bits
of the prefix.
client-pref-prefix-options: options associated with Client
Preferred Prefix option.
5. Server Behavior
If the server policy doesn't support client preferred prefix option,
then it can either send reply with OptionUnsupported in the
encapsulated error code option in client preferred prefix option or
allocate addresses based on its original policy. The server behavior
SHOULD be configurable by the administrator.
If the server policy supports client preferred prefix option and if
this option contains one or more prefixes which are not valid for the
client's link, then, the server MUST send the reply with error code
NotOnLink.
Vijayabhaskar A K Expires September 14, 2003 [Page 3]
Internet-Draft Client Preferred Prefix option for DHCPv6 Mar 2003
If the server policy supports client preferred prefix option and all
the prefixes in this option are valid for the client's link, then the
server MUST allocate addresses only on the prefixes specified in
client preferred prefix option encapsulated in the IAs.
6. Client Behavior
If the client has received OptionUnsupported error, it can either
choose the next server to send request, till the server list gets
exhausted or it can start the configuration exchange as specified in
Section 18.1.1 of [1] without the client preferred prefix option.
If the server list has exhausted then, it MUST start the configuration
exchange as specified in Section 18.1.1 of [1] without the client
preferred prefix option.
If the client has received the addresses with the prefixes that were
not specified in client preferred prefix option, it can release the
unwanted addresses.
7. Appearance of these options
Client Preferred Prefix option MUST occur only in Request and Reply
messages. This option MUST occur in Reply messages only if it
encapsulates the Error code option.
Client Preferred Prefix option MUST occur only as an encapsulated
option in the IA or IA_TA option.
Client Preferred Prefix option MUST only have Error code option as the
encapsulated option.
8. Security Considerations
Since, this option can occur only in IA or IA_TA option, all the
IA-relevant security considerations are applicable to this option too.
To avoid attacks through this option, the DHCP client SHOULD use
authenticated DHCP (see section "Authentication of DHCP messages"
in the DHCPv6 specification [1]).
9. IANA Considerations
IANA is requested to assign an option code to this option from the
option-code space defined in section "DHCPv6 Options" of the DHCPv6
specification [1].
10. Normative Reference
[1] Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
Droms (ed.), "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress), November
2002.
Vijayabhaskar A K Expires September 14, 2003 [Page 4]
Internet-Draft Client Preferred Prefix option for DHCPv6 Mar 2003
11. Informative Reference
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
Author's Address
Vijayabhaskar A K
Hewlett-Packard ESD-I
29, Cunningham Road
Bangalore - 560052
India
Phone: +91-80-2053085
E-Mail: vijayak@india.hp.com
Vijayabhaskar A K Expires September 14, 2003 [Page 5]
Internet-Draft Client Preferred Prefix option for DHCPv6 Mar 2003
Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS 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.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society. Thanks to Jim Bound for his thorough review
of the document.
Vijayabhaskar A K Expires September 14, 2003 [Page 6]
