- 1 -
Network Working Group Y. Rekhter
INTERNET DRAFT T.J. Watson Research Center, IBM Corp.
P. Lothberg
STUPI.AB
Editors
February 1995
An IPv6 Global Unicast Address Format
<draft-ietf-ipngwg-unicast-addr-fmt-01.txt>
Status of this Memo
This document is an Internet Draft. 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. Internet Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use Internet
Drafts as reference material or to cite them other than as a
``working draft'' or ``work in progress.''
Please check the 1id-abstracts.txt listing contained in the
internet-drafts Shadow Directories on nic.ddn.mil, nnsc.nsf.net,
nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au to learn the
current status of any Internet Draft.
1 Introduction
This document defines an IPv6 global unicast address format for use
in the Internet. The address format defined in this document is
consistent with the IPv6 address allocation architecture [1], and is
intended to facilitate scalable Internet routing.
The format defined in this document doesn't preclude the use of other
address formats.
2 Overview of the IPv6 Address
This section recapitulates essential information from the IPv6
protocol specifications [2] concerning the basic structure of the
IPv6 addresses.
Expiration Date July 1995 [Page 1]
- 2 -
The IPv6 protocol [2] defines an IPv6 address as a 16 octets object.
The high-order bits of an IPv6 address are used to indicate a
particular type of the address. The variable-length prefix field
comprising these bits is called the Format Prefix (FP). This
document defines an address format for the 010 (binary) Format
Prefix. The same address format can be used for other FPs, as long as
these FPs identify IPv6 unicast addresses.
3 IPv6 Global Unicast Address Format for Use in the Internet
This document defines an address format for the IPv6 unicast address
assignment. It is expected that the defined format would be widely
used for systems connected (at IP) to the Internet.
The address format defined in this document conforms to the
architecture for IPv6 address allocation [1]. Specifically, the
format is designed to support aggregation of network layer
reachability information at multiple levels of routing hierarchy, as
described in [1].
For addresses of the format described in this document the address
administration is organized into a three level hierarchy -- registry,
provider, and subscriber. The address format defined here allows
flexible address allocation at each level of the address
administration hierarchy in such a way as to support a wide spectrum
of demands for address allocation.
This document assumes that the Internet routing system doesn't make
any assumptions about specific structure and semantics of an IPv6
address, except for the structure and semantics of the Format Prefix
part of the address, and the use of the "longest prefix match"
algorithm (on arbitrary bit boundaries) for making a forwarding
decision.
The address format defined in this document is intended to facilitate
scalable Internet-wide routing that doesn't impose any constraints on
connectivity among the providers, as well as among the providers and
subscribers.
The address format defined in this document does not preclude the use
of other address formats in the Internet.
3.1 Global IPv6 Unicast Addresses Structure
For the purpose of address allocation, the address format defined in
this document consists of the following parts: Format Prefix,
Registry Identifier, Registry-Specific Component, Provider-Specific
Expiration Date July 1995 [Page 2]
- 3 -
Component, and Subscriber-Specific Component.
+-------------------------------+
| Format Prefix |
+-------------------------------+
| Registry Identifier Component |
+-------------------------------+
| Registry-Specific Component |
+-------------------------------+
| Provider-Specific Component |
+-------------------------------+
| Subscriber-Specific Component |
+-------------------------------+
The following sections suggest some of the alternatives in forming
each part of the address. The suggestions are only a small number of
the technically possible addressing formats and simultaneously
demonstrate different alternatives at different levels in the
hierarchy. RFC1219 provides useful information for allocating values
within individual components. Ultimately it is the joint
responsibility of the registry, the provider and the subscriber to
agree on their local addressing structure.
3.2 Registry Identifiers Component (Registry ID)
With the growth of the Internet and its increasing globalization,
much thought has been given to the evolution of the Network Layer
address space allocation and assignment process. RFC 1466,
"Guidelines for Management of IP Address Space", proposes a plan that
defines distributed allocation and assignment of the IPv4 address
space.
As the Internet transitions to IPv6, the plan for distributed
allocation and assignment of the IPv4 address space established in
RFC1466 forms a base for the distributed allocation and assignment of
the IPv6 address space.
The Internet Registry (IR) acts as the principal registry for the
Expiration Date July 1995 [Page 3]
- 4 -
IPv6 address space; however, the IR may allocate blocks of IPv6
addresses and the assignment of those addresses to qualified Regional
Registries. The IR will serve as the default registry in cases where
no delegated registration authority has been identified. It is
expected that the IANA will act as the IR.
The Registry Identifier (Registry ID) Component of the IPv6 address
format defined in this document is intended to facilitate a broad
geographic address allocation and facilitate the operations of the
distributed Regional Registries.
The Registry ID Component immediately follows the FP part of an IPv6
address.
At present there are three Regional Registries: INTERNIC, RIPE NCC,
and APNIC. In addition, address allocation could be done directly by
the Internet Registry. Corresponding to this division of address
allocation, this document defines the following Registry IDs (and
associated with them address blocks):
- 0xF8 (5 bits long) - multi-regional (IR)
- 0xE8 (5 bits long) - RIPE NCC
- 0xD0 (5 bits long) - INTERNIC
- 0x90 (5 bits long) - APNIC
All other values of the Registry ID Component are reserved by the
IANA.
Use of the Multi-regional Registry ID permits flexibility in address
assignments which are outside of the geographical regions already
allocated. It is expected that the IR would be responsible for
managing address space registration under the Multi-regional Registry
ID.
It is expected that the IR, and any designated Regional Registries,
allocate addresses in conformance with this overall scheme. Where
there are qualifying Regional Registries established, primary
responsibility for allocation from within that block will be
delegated to that registry.
A Regional Registry may have more than one block of addresses
allocated to it (as a result the Registry would have multiple
Registry IDs associated with it).
Expiration Date July 1995 [Page 4]
- 5 -
3.3 Registry-Specific Component (RSC)
This document assumes that within each Regional Registry there will
be a relatively large number of providers that would request
relatively small blocks of addresses, medium number of providers that
would request medium blocks of addresses, and relatively small number
of providers that would request relatively large blocks of addresses.
To accommodate a potentially wide range of demands for address space
allocation by individual providers a registry should allow the RSC to
be of variable length. The length of the RSC associated with the
address block a registry allocates to a provider determines the size
of the address block granted to that provider by the registry.
The value of the RSC associated with an address block a registry
allocates to a particular provider uniquely identifies this provider
within the registry. Since RSC is of variable length, the uniqueness
implies that no two RSC values assigned within a given registry
should be equal to each other or should exhibit a substring (subset)
relationship.
We suggest that within a registry the range of RSC length be limited
between 1 and 3 octets. Combined with FP and Registry ID, that leaves
12 to 14 octets for the Provider Specific and Subscriber Specific
components.
We further suggest that at the minimum a registry would allow address
allocation with RSC of the following length:
RSC Length Fraction of Registry's Address Space
(in bits) (per provider)
---------- ------------------------------------
24 1/(2^24)
16 1/(2^16)
8 1/(2^8)
This document assumes that some subscribers may decide to acquire
their addresses space directly out of a registry, thus making their
addresses independent of the provider(s) they directly attached to.
To accommodate such subscribers we suggest within each registry to
reserve the portion of the address space that begins with 0xFF for
address allocation to subscribers that elect to use provider-
independent addressing (as described in Section 3.6).
Expiration Date July 1995 [Page 5]
- 6 -
3.4 Provider-Specific Component (PSC)
This document assumes that within each provider there will be a
relatively large number of subscribers that would request relatively
small blocks of addresses, medium number of subscribers that would
request medium blocks of addresses, relatively small number of
subscribers that would request relatively large blocks of addresses
and very few subscribers that would require very large block of
addresses.
To accommodate a potentially wide range of demands for address space
allocation by individual subscribers a provider should allow the PSC
to be of variable length. The length of the PSC associated with the
address block a provider allocates to a subscriber determines the
size of the address block granted to that subscriber by the provider.
The value of the PSC associated with an address block a provider
allocates to a particular subscriber uniquely identifies this
subscriber within the provider. Since the PSC is of variable length,
the uniqueness implies no two PSC values assigned within a given
provider should be equal to each other or should exhibit a substring
(subset) relationship.
We suggest that within a provider the range of PSC length be limited
between 1 and 4 octets.
We further suggest that at the minimum a provider would allow address
allocation with PSC of the following length:
PSC Length Fraction of Provider's Address Space
(in bits) (per subscriber)
---------- ------------------------------------
32 1/(2^32)
24 1/(2^24)
16 1/(2^16)
8 1/(2^8)
A (direct) provider may decide to group its subscribers into regions.
This grouping may be useful when the (direct) provider is attached to
another (indirect) provider at multiple points, as it allows the
direct provider to exert a certain degree of control over the
coupling between the attachment points and flow of the traffic
destined to a particular subscriber (see Section 5.3.1 of [1]). To
accommodate such a grouping we suggest that the (direct) provider
should allocate some small number of high-order bits (e.g. between 2
and 4 bits) of PSC as a Region Identifier. The purpose of a Region
Expiration Date July 1995 [Page 6]
- 7 -
Identifier is to identify a group of subscribers that are within a
close topological proximity to each other (from the provider's point
of view), and thus could be reachable through a particular attachment
point between the (direct) provider and other (indirect) provider(s).
Regardless of whether the Region Identifier is present, we suggest
that the total length of the PSC varies from 1 to 4 octets. Combined
with FP, Registry ID, and PSC that leaves 8 to 13 octets for the
Subscriber Specific Component.
3.5 Subscriber-Specific Component (SSC)
This document leaves the organization of SSC up to individual
subscribers. However, this document assumes that for all but
relatively small subscribers, there will be sufficient number of bits
within the SSC to allow address assignment in such a way as to
provide hierarchical routing (at least two levels) within a
subscriber.
Regardless of how other components are organized, this document
suggests that for the subscribers that use IPv6 autoconfiguration
capabilities the minimum number of octets allocated to the SSC should
be 7. This would allow to embed IEEE 802 MAC addresses as the low
order 6 octets of an IPv6 address (stored in IEEE 802 canonical bit
order). Observe, that if allocation of all the other components
follows recommendations presented in this document, the SSC component
would have at least 8 octets.
3.6 Provider-independent Address Format
This section describes one possible address format for subscribers
that elect to use provider-independent addresses. The format of these
addresses is similar to the one described in the previous sections,
but it doesn't include the PSC.
This document assumes that within each registry there will be a
medium number of subscribers that would request medium block of
provider-independent addresses and relatively small number of
subscribers that would request relatively large block of provider-
independent addresses.
Each registry is expected to reserve an address block that begins
with 0xFF (8 bits) for allocation to subscribers that elect
provider-independent addresses. Following this is a variable length
Subscriber Identifier (S-ID) field. The length of the S-ID field
Expiration Date July 1995 [Page 7]
- 8 -
associated with the address block a registry allocates to a
subscriber determines the size of the address block granted to that
subscriber by the registry.
The value of the S-ID associated with an address block a registry
allocates to a particular subscriber uniquely identifies this
subscriber within the registry. Since S-ID is of variable length, the
uniqueness implies that no two S-ID values assigned within a given
registry should be equal to each other or should exhibit a substring
(subset) relationship.
We suggest that within a registry the range of S-ID length be limited
from 12 to 24 bits. We further suggest that at the minimum a registry
should allow address allocation with S-ID of the length of 12 and 24
bits. This would leaves from 12 to 13.5 octets for allocation within
individual sites (for the SSC).
One possible use of provider-independent addresses is for multihomed
sites (as described in Section 5.4.1 of [1]).
Allocation and use of provider-independent addresses requires careful
judgement. It is crucial to understand that use of such addresses for
the purpose of Internet-wide connectivity has negative impact on the
overall routing system, as the only possible routing information
abstraction above the subscriber level could occur at the continental
level (see Section 5.7 of [1]).
4 National Registry
As a variation of the proposed format, a Regional Registry may
allocate blocks of address space to several National Registries. A
National Registry then becomes the entity that allocates address
space to individual organizations (e.g. providers) within the country
served by the Registry.
To support address allocation by National Registries this document
allows to include the National Registry Id Component as part of the
address format (see below). The Component is immediately follows the
Registry Identifier Component and precedes the Registry-Specific
Component.
+-------------------------------+
| Format Prefix |
+-------------------------------+
| Registry Identifier Component |
+-------------------------------+
| National Registry ID Component|
Expiration Date July 1995 [Page 8]
- 9 -
+-------------------------------+
| Registry-Specific Component |
+-------------------------------+
| Provider-Specific Component |
+-------------------------------+
| Subscriber-Specific Component |
+-------------------------------+
This document assumes that within each regional registry there will
be a relatively small number of national registries. However, within
each national registry there will be a relatively large number of
providers that would request relatively small blocks of addresses,
medium number of providers that would request medium blocks of
addresses, and relatively small number of providers that would
request relatively large blocks of addresses.
To accommodate a potentially wide range of demands for address space
allocation by individual national registries a regional registry
should allow the National Registry ID to be of variable length. The
length of the National Registry ID associated with the address block
a regional registry allocates to a national registry determines the
size of the address block granted to that provider by the registry.
The value of the National Registry ID associated with an address
block a regional registry allocates to a particular national registry
uniquely identifies this national registry. Since the National
Registry ID is of variable length, the uniqueness implies that no two
National Registry ID values assigned within a given regional registry
should be equal to each other or should exhibit a substring (subset)
relationship.
We suggest that within a regional registry the range of the National
Registry ID length be limited between 1 and 2 octets. We further
suggest that within a national registry the range of the RSC length
be limited between 1 and 2 octets. Combined with FP, Regional
Registry ID, and National Registry ID, that leaves 12 to 14 octets
for the Provider Specific and Subscriber Specific components.
We further suggest that at the minimum a national registry would
allow address allocation with RSC of the following length:
RSC Length Fraction of Registry's Address Space
(in bits) (per provider)
---------- ------------------------------------
16 1/(2^16)
8 1/(2^8)
Expiration Date July 1995 [Page 9]
- 10 -
5 Conclusions
[TBD]
6 Acknowledgements
We would like to express our thanks to Jim Bound (DEC), Brian
Carpenter (CERN), Steve Deering (XEROX), Geoff Huston (AANET), and
Tony Li (cisco) for their review and constructive comments.
7 References
[1] Rekhter, Y., Li, T., "An Architecture for IPv6 Unicast Address
Allocation", Internet Draft
[2] Hinden, B., "IP Next Generation Addressing Architecture",
Internet Draft
8 Security Considerations
Security issues are not discussed in this memo.
9 Authors' Addresses
Yakov Rekhter
T.J. Watson Research Center, IBM Corporation
P.O. Box 704
Yorktown Heights, NY 10598
Phone: (914) 784-7361
email: yakov@watson.ibm.com
Peter Lothberg
STUPI.AB
Box 9129
S-102 72 Stockholm
Sweden
Phone:+46 8 6699720
email:roll@Stupi.SE
Expiration Date August 1995 [Page 10]
