Dynamic Host Congiguration T. Chown
Internet-Draft University of Southampton
Expires: August 30, 2004 S. Venaas
UNINETT
A. Vijayabhaskar
Hewlett-Packard STSD-I
March 2004
Renumbering Requirements for Stateless DHCPv6
draft-ietf-dhc-stateless-dhcpv6-renumbering-01
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Abstract
IPv6 hosts using Stateless Address Autoconfiguration are able to
automatically configure their IPv6 address and default router
settings. However, further settings are not available. If such
hosts wish to automatically configure their DNS, NTP or other
specific settings the stateless variant of the Dynamic Host
Configuration Protocol for IPv6 (DHCPv6) could be used. This
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combination of Stateless Address Autoconfiguration and stateless
DHCPv6 could be used quite commonly in IPv6 networks. However, hosts
using such a combination currently have no means by which to be
informed of changes in stateless DHCPv6 option settings, e.g. the
addition of a new NTP server address, changes in DNS search paths, or
full site renumbering. This document is presented as a problem
statement from which a solution should be proposed in a subsequent
document.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
3. Renumbering Scenarios . . . . . . . . . . . . . . . . . . . . 4
3.1 Site renumbering . . . . . . . . . . . . . . . . . . . . . 4
3.2 Changes to a DHCPv6-assigned setting . . . . . . . . . . . 4
4. Renumbering Requirements . . . . . . . . . . . . . . . . . . . 4
5. Considerations in choosing a solution . . . . . . . . . . . . 5
6. Solution Space . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
10. Normative References . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . 8
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1. Introduction
IPv6 hosts using Stateless Address Autoconfiguration [1] are able to
automatically configure their IPv6 address and default router
settings. While Stateless Address Autoconfiguration for IPv6 allows
automatic configuration of these settings, it does not provide a
mechanism for additional, non IP-address settings to be automatically
configured.
The full version of the Dynamic Host Configuration Protocol for IPv6
(DHCPv6) [2] is designed to provide both stateful address assignment
to IPv6 hosts, as well as additional (non IP-address) configuration
including DNS, NTP and other specific settings. A full stateful
DHCPv6 server allocates the addresses and maintains the clients
bindings to keep track of client leases.
If hosts using Stateless Address Autoconfiguration for IPv6 wish to
automatically configure their DNS, NTP or other specific settings the
stateless variant [3] of DHCPv6 could be used. The stateless variant
of DHCPv6 is more lightweight. It does not do address assignment,
instead it only provides additional configuration parameters like DNS
resolver addresses. It does not maintain state about the information
assigned to clients; the additional parameters do not have an
explicit life-time associated with them in the same way that IP
addresses do, and hence the DHCPv6 server does not need to maintain
the state of the clients.
This combination of Stateless Address Autoconfiguration and stateless
DHCPv6 could be used quite commonly in IPv6 networks. In the absence
of an alternative method for DNS, NTP and other options to be
automatically configured, it may become the most common combination
for statelessly configuring hosts.
2. Problem Statement
A problem however lies in the ability, or lack of ability, of clients
using this combination to be informed of (or to deduce) changes in
DHCPv6 assigned settings.
While a DHCPv6 server unicasts Reconfigure message to individual
clients to trigger the clients to intiate Information-request/reply
configuration exchanges to update their configuration settings, the
stateless variant of DHCPv6 cannot use the Reconfigure mechanism
because it does not maintain a list of IP addresses (leases) to send
the unicast messages to.
Thus events including the following cannot be handled:
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o Full site renumbering
o DNS server change of address
o NTP server change of address
o Changes in DNS search paths
It would be highly desirable that a host using the combination of
Stateless Address Autoconfiguration and stateless DHCPv6 could handle
a renumbering or reconfiguration event, whether planned or unplanned
by the network administrator.
3. Renumbering Scenarios
There are two main scenarios for changes to DHCPv6-assigned settings,
that would require the client to initiate an Information-request/
reply exchange to update the configuration.
3.1 Site renumbering
One of the fundamental principles of IPv6 is that sites receive their
IPv6 address allocations from an ISP using provider assigned (PA)
address space. There is currently no provider independent (PI)
address space in IPv6. A site wishing to change ISP must thus
renumber its network. Any such site renumbering will require hosts
to reconfigure both their own address and default router settings as
well as their stateless DHCPv6-assigned settings.
3.2 Changes to a DHCPv6-assigned setting
An administrator may need to change one or more stateless
DHCPv6-assigned settings, e.g. an NTP server, DNS server, or the DNS
search path. This may be required if a new, additional DNS server is
brought online, is moved to a new network (prefix), or an existing
server is decommissioned or known to be unavailable.
4. Renumbering Requirements
Ideally, any of the above scenarios should be handled automatically
by the hosts on the network. For this to be realised, a method is
required for the hosts to be informed that they should request new
stateless DHCPv6-assigned setting information.
The solution to the problem may depend on whether the renumbering or
configuration change is a planned or unplanned one, from the
perspective of the network administrator. There is already work
underway in understanding the planned renumbering [4] scenario for
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IPv6 networks. However, there is currently no mechanism in stateless
DHCPv6 to even handle planned renumbering events.
The unplanned renumbering event, which may be more common in smaller,
unmanaged networks, is more difficult to cater for. Ideally, any
solution for the problem should consider planned and unplanned
events.
The solution should also be secure, such that additional security
concerns are not added to the stateless DHCPv6 networking
environment.
5. Considerations in choosing a solution
There are a number of considerations that could be listed for a
desirable solution:
o It should support planned renumbering; it is desirable to support
unplanned renumbering.
o Security is important; e.g., avoiding denialof service attacks
mounted through Reconfigure messages sent from an attacker.
o It must be possible to update options even if the network is not
renumbered.
o It is desirable to maintain the "stateless" property; i.e., no
per-client state should need to be kept in the server.
6. Solution Space
Solutions should be designed and presented in a separate document.
An initial, brief set of candidate solutions might include:
o Adding a Reconfigure message mechanism that would work in the
stateless DHCPv6 environment. This could enable planned or
unplanned events, but may require a multicast mechanism to be
realised.
o Conveying a valid lifetime timer to clients for stateless
DHCPv6-assigned settings. This could primarily enable planned
events, but with a small time-out it could to some extent handle
unplanned events at the expense of the additional request traffic.
o Using some form of Router Advertisement as a hint to request new
stateless DHCPv6-assigned settings. Using only an observed new
Router Advertisement prefix as a hint to re-request settings would
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not handle changes that are purely to NTP, DNS or other options.
Other possible means of detection of network (re)attachment could
also be used as cues (e.g. see IPv6 DNA Goals [5]).
o Changing semantics of the DHCPv6 'O' flag such that toggling its
value may trigger an Information-request message.
7. Summary
This document presents a problem statement for how IPv6 hosts that
use the combination of Stateless Address Autoconfiguration and
stateless DHCPv6 may be informed of renumbering events or other
changes to the settings that they originally learnt through stateless
DHCPv6. A short list of candidate solutions is presented, which the
authors hope may be expanded upon in subsequent documents.
8. Security Considerations
There are no security considerations in this problem statemement per
se. However, whatever mechanism is designed or chosen to address
this problem should avoid the introduction of new security concerns
for (stateless) DHCPv6.
9. Acknowledgements
The authors would like to thank Ralph Droms and Bermie Volz for their
comments on this draft.
10 Normative References
[1] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[2] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M.
Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 3315, July 2003.
[3] Droms, R., "Stateless Dynamic Host Configuration Protocol (DHCP)
Service for IPv6", RFC 3736, April 2004.
[4] Baker, F., Lear, E. and R. Droms, "Procedures for Renumbering an
IPv6 Network without a Flag Day",
draft-baker-ipv6-renumber-procedure-01 (work in progress),
October 2003.
[5] Choi, J., "Detecting Network Attachment in IPv6 Goals",
draft-ietf-dna-goals-00 (work in progress), June 2004.
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Authors' Addresses
Tim Chown
University of Southampton
School of Electronics and Computer Science
Southampton, Hampshire SO17 1BJ
United Kingdom
EMail: tjc@ecs.soton.ac.uk
Stig Venaas
UNINETT
Trondheim NO 7465
Norway
EMail: venaas@uninett.no
Vijayabhaskar A K
Hewlett-Packard STSD-I
29, Cunningham Road
Bangalore 560052
India
EMail: vijayak@india.hp.com
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