INTERNET-DRAFT R. Hinden, Nokia
May 7, 2003
Globally Unique IPv6 Local Unicast Addresses
<draft-hinden-ipv6-global-local-addr-00.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."
To view the list Internet-Draft Shadow Directories, see
http://www.ietf.org/shadow.html.
This internet draft expires on November 7, 2003.
Abstract
This document defines an unicast address format that is globally
unique and is intended for local communications, usually inside of a
site. They are not expected to be routable on the global Internet
given current routing technology.
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1.0 Introduction
This document defines an IPv6 unicast address format that is globally
unique and is intended for local communications [IPV6]. They are not
expected to be routable on the global Internet given current routing
technology. They are routable inside of a more limited area such as
a site. They may also be routed between a limited set of sites.
Globally unique IPv6 local addresses have the following
characteristics:
- Globally unique prefix.
- Well known prefix to allow for easy filtering at site
boundaries.
- Allows sites to be combined with out creating any address
conflicts or require renumbering of interfaces using these
prefixes.
- Internet Service Provider independent and can be used for
communications inside of a site without having any permanent or
intermittent Internet connectivity.
- If accidentally leaked outside of a site via routing or DNS,
there is no conflict with any other addresses.
- No requirement for applications to treat these address
differently from any other kind of global unicast addresses.
This document defines the format of Globally Unique IPv6 Local
addresses, how to allocate them, and usage considerations including
routing, site border routers, DNS, application support, VPN usage,
and guidelines for how to use for local communication inside a site.
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].
2.0 Acknowledgments
The underlying idea of creating globally unique IPv6 local addresses
describe in this document been proposed a number of times by a
variety of people. The author of this draft does not claim exclusive
credit. Credit goes to Brian Carpenter, Christian Huitema, Aidan
Williams, Andrew White, Michel Py, Charlie Perkins, and many others.
The author would also like to thank Brain Carpenter, Charlie Perkins,
Harald Alvestrand, Keith Moore, Margaret Wasserman, and Michel Py for
their comments and suggestions on this draft.
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3.0 Globally Unique IPv6 Local Unicast Address Format
The globally unique IPv6 local addresses are created using a
centrally allocated global ID. They have the following format:
| n |
| bits | m bits | 16 bits | 64 bits |
+--------+------------+-----------+-----------------------------+
| prefix | global ID | subnet ID | interface ID |
+--------+------------+-----------+-----------------------------+
Where:
prefix prefix to identify Globally Unique IPv6 Local
unicast addresses.
global ID global identifier used to create a globally
unique prefix. See section 3.1 for additional
information.
subnet ID 16-bit subnet ID is an identifier of a subnet
within the site.
interface ID 64-bit IID as defined in [ADDARCH].
There are a range of choices available when choosing the size of the
prefix and Global ID field length. There is a direct tradeoff
between having a Global ID field large enough to support foreseeable
future growth and not using too much of the IPv6 address space
needlessly. A reasonable way of evaluating a specific field length
is to compare it to a projected 2050 world population of 9.3 billion
[POPUL]. A range of prefix choices is shown in the following table:
Prefix Global ID Number Prefixes Prefixes % of IPv6
Length per Person Address Space
/11 37 137,438,953,472 15 0.049%
/10 38 274,877,906,944 30 0.098%
/9 39 549,755,813,888 59 0.195%
/8 40 1,099,511,627,776 118 0.391%
/7 41 2,199,023,255,552 236 0.781%
/6 42 4,398,046,511,104 473 1.563%
A very high utilization ratio of these allocations can be assumed
because no internal structure is required in the field nor is there
any reason to be able to aggregate the prefixes.
The author believes that a /7 prefix resulting in a 41 bit Global ID
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is a good choice. It provides for a large number of assignments
(i.e., 2.2 trillion) and at the same time uses less than .8% of the
total IPv6 address space. It is unlikely that this space will be
exhausted. If more than this was needed, then additional IPv6
address space could be allocated for this purpose.
For the rest of this document the FC00::/7 prefix and a 41-bit Global
ID is used.
3.1 Global ID
The Global ID values of zero and all ones are reserved for future use
and must not be assigned.
The allocation of global IDs should be pseudo-random. They should
not be assigned sequentially or by locality. This to ensure that
there is not any relationship between allocations and to help clarify
that these prefixes are not intended to be routed globally.
Specifically, these prefixes are designed to not aggregate.
Global IDs should be assigned centrally by a single allocation
authority because they are pseudo-random and without any structure.
This is easiest to accomplish if there is a single source of the
assignments.
3.1.1 Global ID Allocation Requirements
Global ID allocations should be
- Available to anyone in an unbiased manner.
- Permanent with no periodic fees.
- One time non-refundable allocation fee in the order of 10 Euros
per allocation.
- The ownership of each individual allocation should be private,
but should be escrowed.
The allocation authority should permit allocations to be obtained
without having any sort of internet connectivity. For example in
addition to web based registration they should support some methods
like telephone, postal mail, fax, telex, etc. They should also
accept a variety of payment methods and currencies.
The reason for the one time 10 Euro charge for each prefix is to
provide a barrier to any hoarding of the these allocations but at the
same time keep the cost low enough to not create a barrier to anyone
needing one. The charge is non-refundable in order to keep overhead
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low.
The ownership of the allocations is not needed to be public since the
resulting addresses are intended to be used for local communication.
It is escrowed to insure there are no duplicate allocations and in
case it is needed in the future.
An example of a allocation authority is a non-profit organization
such as the Public Internet Registry (PIR) that the Internet Society
has created to manage the .org domain. They already know how to
collect small sums efficiently and there are safeguards in place for
the appropriate use of any excess revenue generated.
Note, there are many possible ways of of creating an allocation
authority. It is important to keep in mind when reviewing
alternatives that the goal is to pick one that can do the job. It
doesn't have to be perfect, only good enough to do the job at hand.
The author believes that the PIR would satisfy this requirement.
3.3 Routing
Globally IPv6 Local address are designed to be routed inside of a
site in the same manner as other types of unicast addresses. They
can be carried in any IPv6 routing protocol without any change.
It is expected that they would share the same subnet IDs if provider
based global unicast addresses were being used concurrently [GLOBAL].
Any routing protocol that is used between sites is required to filter
out any incoming or outgoing globally unique IPv6 local routes. The
exception to this is if specific /48 globally unique IPv6 local
routes have been configured to allow for inter-site communication.
If BGP is being used at the site border with an ISP, by default
filters MUST be installed in the BGP configuration to keep any site-
local prefixes from being advertised outside of the site or for site-
local prefixes to be learned from another site. The exception to
this is if there are specific /48 routes created for one or more
globally unique IPv6 local prefixes.
3.4 Renumbering and Site Merging
The use of globally unique IPv6 local addresses in a site results in
making communication using these addresses independent of renumbering
a site's provider based global addresses.
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When merging multiple sites none of the addresses created with these
prefixes need to be renumbered because all of the addresses are
unique. Routes for each specific prefix would have to be configured
to allow routing to work correctly between the formerly separate
sites.
3.5 Site Border Router and Firewall Filtering
While no serious harm will be done if packets with these addresses
are sent outside of a site via a default route, it is recommended
that they be filtered to keep any packets with globally unique IPv6
local destination addresses from leaking outside of the site and to
keep any site prefixes from being advertised outside of their site.
Site border routers SHOULD install a black hole route for the
Globally Unique IPv6 Local prefix FC00::/7. This will insure that
packets with Globally Unique IPv6 Local destination addresses will
not be forwarded outside of the site via a default route.
Site border routers and firewalls SHOULD NOT forward any packets with
globally unique IPv6 local source or destination addresses outside of
the site unless they have been explicitly configured with routing
information about other globally unique IPv6 local prefixes. The
default behavior of these devices SHOULD be to filter them.
3.6 DNS Issues
Globally Unique IPv6 Local addresses SHOULD NOT be installed in the
global DNS. They may be installed in a naming system local to the
site or kept separate from the global DNS using techniques such as
"two-faced" DNS.
If globally unique IPv6 local address are configured in the global
DNS, no harm is done because they are unique and will not create any
confusion. The may not be reachable, but this is a property that is
common to all types of global IPv6 unicast addresses.
For future study names with globally unique IPv6 local addresses may
be resolved inside of the site using dynamic naming systems such as
Multicast DNS.
3.7 Application and Higher Level Protocol Issues
Application and other higher level protocols can treat Globally
Unique IPv6 Local addresses in the same manner as other types of
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global unicast addresses. No special handling is required. This
type of addresses may not be reachable, but that is no different from
other types of IPv6 global unicast addresses. Applications need to
be able to handle multiple addresses that may or may not be reachable
any point in time.
3.8 Use of Globally Unique IPv6 Local Addresses for Local Communications
IPv6 globally unique IPv6 local addresses, like global scope unicast
addresses, are only assigned to nodes if their use has been enabled
(via IPv6 address autoconfiguration [ADDAUTO], DHCPv6 [DHCP6], or
manually) and configured in the DNS. They are not created
automatically the way that IPv6 link-local addresses are and will not
appear or be used unless they are purposely configured.
In order for hosts to autoconfigure globally unique IPv6 local
addresses routers have to be configured to advertise globally unique
IPv6 local /64 prefixes in router advertisements. Likewise, a DHCPv6
server must have been configured to assign them. In order for a node
to learn the globally unique IPv6 local address of another node, the
globally unique IPv6 local address must have been installed in the
DNS. For these reasons, it is straight forward to control their
usage in a site.
To limit the use of globally unique IPv6 local addresses the
following guidelines apply:
- Nodes that are to only be reachable inside of a site, the local
DNS should be configured to only include the globally unique
IPv6 local addresses of these nodes. Nodes with only globally
unique IPv6 local addresses must not be installed in the global
DNS.
- Nodes that are to be limited to only communicate with other
nodes in the site should be set to only autoconfigure globally
unique IPv6 local addresses via [ADDAUTO] or to only receive
globally unique IPv6 local addresses via [DHCP6]. Note: For the
case where both global and globally unique IPv6 local prefixes
are being advertised on a subnet, this will require a switch in
the devices to only autoconfigure globally unique IPv6 local
addresses.
- Nodes that are to be reachable from inside of the site and from
outside of the site, the DNS should be configured to include the
global addresses of these nodes. The local DNS may be
configured to also include the globally unique IPv6 local
addresses of these nodes.
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- Nodes that can communicate with other nodes inside of the site
and outside of the site, should autoconfigure global addresses
via [ADDAUTO] or receive global address via [DHCP6]. They may
also obtain globally unique IPv6 local addresses via the same
mechanisms.
3.9 Use of Globally Unique IPv6 Local Addresses with VPNs
Globally unique IPv6 local addresses can be used for inter-site
Virtual Private Networks (VPN) if appropriate routes are set up.
Because the addresses are unique these VPNs will work reliably and
have the additional property that they will continue to work if the
individual sites are renumbered or merged.
4.0 Advantages and Disadvantages
4.1 Advantages
This approach has the following advantages:
- Provides globally unique local prefixes that can be used
independently of any provider based IPv6 unicast address
allocations. This is useful for sites not always connected to
the Internet or sites that wish to have a distinct prefix that
can be used to localize traffic inside of the site.
- Applications can treat these addresses in an identical manner as
any other type of global IPv6 unicast addresses.
- Sites can be merged without any renumbering of the globally
unique IPv6 local addresses.
- Sites can change their provider based IPv6 unicast address
without disrupting any communication using globally unique IPv6
local addresses.
- Well known prefix that allows for easy filtering at site
boundary.
- Can be used for inter-site VPNs.
- If accidently leaked outside of a site via routing or DNS, there
is no conflict with any other addresses.
4.2 Disadvantages
This approach has the following disadvantages:
- Not possible to route globally unique IPv6 local prefixes on the
global Internet with current routing technology.
- Requires the creation of a central allocation authority.
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5.0 Security Considerations
Globally unique IPv6 local addresses do not provide any inherent
security to the nodes that use them. They may be used with filters
at site boundaries to keep globally unique IPv6 local traffic inside
of the site, but this is no more or less secure than filtering any
other type of global IPv6 unicast addresses.
6.0 IANA Considerations
The IANA should allocate the FC00::/7 prefix for Globally Unique IPv6
Local addresses. The Global ID values of zero and all ones are
reserved for future use and should not be assigned.
The IANA should setup a allocation authority for Globally Unique IPv6
Local prefixes. This allocation authority should consistent with the
requirements described in section 3.1 of this document.
REFERENCES
Normative
[ADDARCH] Hinden, R., S. Deering, S., "IP Version 6 Addressing
Architecture", RFC3515, April 2003.
[GLOBAL] Hinden, R., S. Deering, E. Nordmark, "IPv6 Global Unicast
Address Format", Internet Draft, <draft-ietf-ipv6-unicast-
aggr-v2-02.txt>, February 2003.
[IPV6] Deering, S., R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC2460, December 1998.
[POPUL] Population Reference Bureau, "World Population Data Sheet
of the Population Reference Bureau 2002", August 2002.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", RFC2026, BCP00009, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC2119, BCP14, March 1997.
Non-Normative
[ADDAUTO] Thomson, S., T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC2462, December 1998.
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[DHCP6] Droms, R., et. al., "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", Internet Draft, <draft-ietf-dhc-
dhcpv6-28.txt>, November 2002.
AUTHOR'S ADDRESS
Robert M. Hinden
Nokia
313 Fairchild Drive
Mountain View, CA 94043
USA
phone: +1 650 625-2004
email: bob.hinden@nokia.com
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