Internet DRAFT - draft-huitema-ipv6-renumber
draft-huitema-ipv6-renumber
INTERNET DRAFT C. Huitema
<draft-huitema-ipv6-renumber-00.txt> Microsoft
Expires January 12, 2002 July 12, 2001
IPv6 Site Renumbering
Status of this memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
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Abstract
There has been recently a lot of the discussion in the IPNG, NGTRANS
and DNSEXT working group about the level at which IPv6 shall support
renumbering. A specific question is whether we need special support
in the DNS to enable renumbering, as specified in [RFC2874], or if
the simpler mechanisms specified in [RFC1886] are sufficient. In
order to organize the discussion, this memo presents a set of
realistic renumbering scenarios, discusses the possible frequency at
which such scenarios can be repeated, presents some tools that can
be used to organize the renumbering, and summarizes the operational
requirements that have to be met by any renumbering solution.
1 Introduction
There has been recently a lot of the discussion in the IPNG, NGTRANS
and DNSEXT working group about the level at which IPv6 shall support
renumbering. A specific question is whether we need special support
in the DNS to enable renumbering, as specified in [RFC2874], or if
the simpler mechanisms specified in [RFC1886] are sufficient. In
order to facilitate the discussion, this memo presents a set of
realistic renumbering scenarios, and then analyzes requirements and
potential solutions.
The purpose of the exercise is to evaluate how the current "IPv6 and
DNS toolbox" can be used to facilitate renumbering. In addition to
the two possible DNS formats mentioned above, the toolbox includes
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"IPv6 Stateless Address Autoconfiguration" [RFC2462] and "Router
Renumbering for IPv6" [RFC2894]. We do not detail here the operation
of the DNS in each of the scenarios - this is left as an exercise
for the DNSEXT working group.
2 Description of the scenarios
In this version of the memo, the renumbering scenarios are broadly
sketched. For example, we say nothing of "static address filters"
used for QoS and security purposes; we may guess that these could be
updated as a side effect of router renumbering, but we would be
better off with a real specification. The purpose of the exercise,
however, is to provide five realistic renumbering scenarios.
2.1 Scenario 1, first connection
A site is currently isolated. The internal subnets have been
numbered using "site local" addresses. The site joins the IPv6
Internet. The site managers use "Router Renumbering for IPv6"
[RFC2894] to automatically inform the internal routers that they
should start advertising the new prefix. The hosts receive a router
advertisement and automatically create a global address as specified
in [RFC2462].
Most sites will do this once. In many case, the first connection of
a site to the IPv6 Internet will be through a tunneling solution,
such as "6to4". For the purpose of the exercise, we will consider a
tunneled connection as just another connection, that happens to use
a virtual link instead of a dedicated interface.
2.2 Scenario 2, disconnection
A site is currently connected to the Internet. The site managers
plan to disconnect. This occurs in two phases, first deprecating the
old prefix, then removing it. Both phases are implemented using
"Router Renumbering for IPv6" [RFC2894] and "IPv6 Stateless Address
Autoconfiguration" [RFC2462].
2.3 Scenario 3, multi-homing
A site is connected to the Internet through a single provider. The
site managers set a contract with another provider, and obtain a new
prefix. The site managers use "Router Renumbering for IPv6"
[RFC2894] to automatically inform the internal routers that they
should start advertising the new prefix. The hosts receive a router
advertisement and automatically create a second global address as
specified in "IPv6 Stateless Address Autoconfiguration" [RFC2462].
2.4 Scenario 4, removing a provider
A site is connected to the Internet through two providers. The site
managers want to terminate the contract with one of these providers.
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This occurs in two phases, first deprecating the old prefix, then
removing it. Both phases are implemented using "Router Renumbering
for IPv6" [RFC2894] and "IPv6 Stateless Address Autoconfiguration"
[RFC 2462].
2.5 Scenario 5, time-of-day preference
A site is connected to the Internet through two providers. These
providers use different tariffs. The site managers desire that one
of the providers be preferred during working hours, say from 9:00 am
to 5:00 pm, and another be preferred during the rest of the day.
They use "Router Renumbering for IPv6" [RFC2894] at critical times
(9:00 am, 5:00 pm) to deprecate one of the global prefixes and
promote the other. The hosts receive router advertisements and heed
them as specified in "IPv6 Stateless Address Autoconfiguration"
[RFC2462].
There are few sub cases here:
- time of day preference along with actual renumbering of hosts
- time of day preference only reflected in DNS (no renumbering)
- time of day preference for subset of services
- load balancing by advertising subset of links
The second case is the one that probably is going to be used most as
that has the lowest impact and eliminates the DNS TTL issue that a
host can remove address before the last cached DNS entry has
expired.
3 Renumbering requirements
The discussion of the renumbering scenarios in the IPNG and NGTRANS
working group unearthed a number of operational requirements that
must be met by any renumbering solution. These requirements include
continuous addressability, DNS security, network stability, and also
a minimum frequency. In addition, we list here a non-requirement,
the automatic support of the fusion between several sites.
3.1 Continuous addressability
Since DNS records may linger in various caches for the duration of
their TTL, IPv6 addresses should remain valid for at least as long
as the TTL of the DNS record. In fact, we observe that it is also
desirable to maintain usability of an "old" prefix for some time
after it has ceased being advertised in the DNS, in order to allow
existing connections to terminate.
This is addressed in the scenarios 2 and 4 through a two phase
approach: first deprecate a prefix, then at the end of the TTL
remove it. In IPv6, if an address prefix is deprecated, the host can
continue using it for existing connections or existing associations,
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but should use only the preferred prefixes when initiating new
connections. In order to meet the TTL requirements, the hosts not
refuse new connections on deprecated prefixes.
3.2 DNS server load upon renumbering
When it comes to creating new addresses, or deprecating them, we
really have two choices. One possibility is to let the hosts use
dynamic DNS updates to create or update AAAA or A6 records on the
fly; another possibility is to have the site managers update the
AAAA or A6 records in a reference file. We have to analyse the
benefit/cost of AAAA/A6 in this context.
A particularly nasty consequence can occur if many hosts create new
addresses and attempt almost simultaneous DNS updates. This
phenomenon is discussed in [DISPRE], and a possible solution is
presented in conjunction with the use of A6 records.
3.3 The DNS security requirement
One additional concern is the interaction between renumbering, AAAA,
and DNSSEC -- specifically, the cost of re-signing a zone with new
addresses. The careful system administrator would do this after the
new prefix was known, but before the new prefix started to be used.
The effort required to re-sign scales linearly with the number of
RR's changed. Fortunately, this task is parallelizable; however,
the processors doing the work must be trusted with the zone's
private key. Folks with appropriate levels of paranoia likely won't
want to do much else with this hardware besides maintain the
zone(s).
As an unscientific test, during the DNSEXT meeting in Minneapolis
Bill Sommerfeld took the mit.edu zone (with about 82000 hosts),
synthesized AAAA records for all hosts, and signed it using the
tools included with a recent bind 9 release. His recollection was
that signing the synthesized zone took roughly 90 minutes on his
laptop -- a 333mhz Celeron, which averages to about 1000 signatures
per minute on this system, or maybe 3000 signatures per minute per
GHz of CPU. In the absence of DNAME, a roughly similar re-signing
effort is required for PTR zones: we would thus need two signatures
per address, one for AAAA, one on PTR. In these conditions, we are
down to 1500 addresses per minute per GHZ of CPU.
Renumbering a million-address network would take a bit over 11 GHz-
hours of cpu time just for the dnssec signatures alone; whether
anyone would actually want to renumber a million-nodes network is
indeed debatable.
Note that resigning needs to be complete before the RR's can be
replaced -- i.e., the time for renumbering to be complete is the
resigning time plus the TTL...
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3.4 Name servers
To avoid cyclical references or "can opener-in-can" situations for
records pointed to by NS records, name servers basically must have
address records that provide their entire address, i.e. either AAAA
record or A6 records with a null length prefix. This means that, in
any renumbering scenario, individual records will have to be
published for the site's name servers, even if A6 is used.
3.5 Non requirement: fusion of sites
During the mailing list discussions, it was decided to not consider
a very specific type of renumbering: the merging of independent
sites. This is a noticeably different case, where the internal
numbering of a site may need to be radically altered, and a new
addressing plan needs to be created.
Fortunately though, this one generally is a rare event, is usually
known and can be planned for well in advance, and the disruptions
that occur are usually occurring in all kinds of other fields as
well, not just the network, so people tend to be a little more
forgiving (eg: people are more likely to curse when the merged
payroll division doesn't manage to get anyone's salary paid on time,
than when the net is flaky for half a day due to the numbering
changes not having propagated properly).
4 Security Considerations
This memo presents renumbering scenarios. Renumbering has
implications on security, since it forces the use of new addresses
and may invalidate previous bindings between names and addresses.
Secure bindings may require the use of DNS security; the effects of
renumbering on DNS security is discussed in section 3.3.
5 IANA Considerations
This document does not call for an IANA action.
6 Copyright
The following copyright notice is copied from RFC 2026 [Bradner,
1996], Section 10.4, and describes the applicable copyright for this
document.
Copyright (C) The Internet Society XXX 0, 0000. 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
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document itself may not be modified in any way, such as by removing
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7 Intellectual Property
The following notice is copied from RFC 2026 [Bradner, 1996],
Section 10.4, and describes the position of the IETF concerning
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The IETF takes no position regarding the validity or scope of any
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8 Acknowledgements
This memo incorporates text submitted to the working group lists by
Bill Sommerfeld, Robert Elz, and Jun-ichiro itojun Hagino. Olafur
Gudmundsson was instrumental in prodding the author to submit it
before the deadline.
9 References
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[RFC2874] M. Crawford, C. Huitema, "DNS Extensions to Support IPv6
Address Aggregation and Renumbering", RFC 2874, July 2000.
[RFC1886] S. Thomson, C. Huitema, "DNS Extensions to support IP
version 6", RFC 1886, December 1995.
[RFC2462] S. Thomson, T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[RFC2894] M. Crawford, "Router Renumbering for IPv6", RFC 2894,
August 2000.
[DISPRE] M. Crawford, "Discovery of Resource Records Designating
IPv6 Address prefixes", Work in progress, November 2000.
10 Author's Addresses
Christian Huitema
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
Email: huitema@microsoft.com
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