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Network Working Group Request for Comments: 4076 Category: Informational |
T. Chown University of Southampton S. Venaas UNINETT A. Vijayabhaskar Cisco Systems (India) Private Limited May 2005 |
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
Copyright © The Internet Society (2005).
IPv6 hosts using Stateless Address Autoconfiguration are able to
configure their IPv6 address and default router settings
automatically. However, further settings are not available. If
these hosts wish to configure their DNS, NTP, or other specific
settings automatically, the stateless variant of the Dynamic Host
Configuration Protocol for IPv6 (DHCPv6) could be used. This
combination of Stateless Address Autoconfiguration and stateless
DHCPv6 could be used quite commonly in IPv6 networks. However, hosts
using this 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, a change 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.
1. Introduction
2. Problem Statement
3. Renumbering Scenarios
3.1. Site Renumbering
3.2. Changes to a DHCPv6-assigned Setting
4. Renumbering Requirements
5. Considerations in Choosing a Solution
6. Solution Space
7. Summary
8. Security Considerations
9. Acknowledgements
10. References
10.1. Normative References
10.2. Informative References
IPv6 hosts using Stateless Address Autoconfiguration [2] are able to
configure their IPv6 address and default router settings
automatically. Although 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 configured
automatically.
The full version of the Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [3] 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 configure their DNS, NTP, or other specific settings automatically, the stateless variant [4] of DHCPv6 could be used. This variant is more lightweight. It does not do address assignment; instead, it only provides additional configuration parameters, such as DNS resolver addresses. It does not maintain dynamic state about the information assigned to clients, and therefore there is no need to maintain dynamic per-client state on the server.
This combination of Stateless Address Autoconfiguration and stateless DHCPv6 could be used quite commonly in IPv6 networks.
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 messages to individual clients to trigger them to initiate 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. Note that in DHCPv6, Reconfigure messages must be unicast; multicast is not allowed.
Thus, events including the following cannot be handled:
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.
Note that the scope of the problem could extend beyond Stateless DHCPv6, since only IP address options have a lifetime; i.e., there is no mechanism even in the full DHCPv6 that "expires" old information or otherwise forces a client to recheck that new/updated information is available. However, with full DHCPv6, a node may learn of updates to non-address options when renewing its address lease.
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.
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. Therefore, a site changing its ISP must renumber its network. Any such site renumbering will require hosts to reconfigure both their own address and default router settings and their stateless DHCPv6-assigned settings.
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 and is moved to a new network (prefix), or if an existing server is decommissioned or known to be unavailable.
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 whereby the hosts are 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 planned or unplanned, from the perspective of the network administrator. There is already work underway toward understanding the planned renumbering [5] scenario for IPv6 networks. However, there is currently no mechanism in stateless DHCPv6 for handling planned renumbering events.
A number of considerations could be listed for a desirable solution:
Solutions should be designed and presented in a separate document. An initial brief set of candidate solutions might include the following:
There will also be conditions under which a client should send an Information-request, such as reconnection to a link. Recommendations for these cases are outside the scope of this document, but we expect ongoing work in the DNA WG (as scoped in Goals of Detecting Network Attachment (DNA) in IPv6 [6]) to yield recommendations.
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 learned through stateless DHCPv6. A short list of candidate solutions is presented, which the authors hope will be expanded upon in subsequent documents.
There are no security considerations in this problem statement per se. However, whatever mechanism is designed or chosen to address this problem should avoid introducing new security concerns for (stateless) DHCPv6.
The issues of maintaining appropriate security through a renumbering
event are outside the scope of this document (if specific servers
within the network are being added or removed, firewall
configurations and ACLs, for example, will need to reflect this).
However, this is an important area for further work.
The authors would like to thank Ralph Droms, Bernie Volz, and other individuals on the DHC mail list for their comments on this document, as well as colleagues on the 6NET project. We also thank the review comments, particularly those from Thomas Narten.
[1] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998.
[2] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[3] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003.
[4] Droms, R., "Stateless Dynamic Host Configuration Protocol (DHCP) Service for IPv6", RFC 3736, April 2004.
[5] Baker, F., Lear, E. and R. Droms, "Procedures for Renumbering an IPv6 Network without a Flag Day", Work in Progress, July 2004.
[6] Choi, J., "Goals of Detecting Network Attachment (DNA) in IPv6", Work in Progress, October 2004.
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 Kalusivalingam
Cisco Systems (India) Private Limited
9, Brunton Road
Bangalore 560025
India
EMail: vibhaska@cisco.com
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