INTERNET-DRAFT R. Hinden, Ipsilon Networks
May 16, 1997 M. O'Dell, UUNET
S. Deering, Cisco
An IPv6 Aggregatable Global Unicast Address Format
<draft-ietf-ipngwg-unicast-aggr-00.txt>
Status of this Memo
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This internet draft expires on November 17, 1997.
1.0 Introduction
This document defines an IPv6 aggregatable global unicast address
format for use in the Internet. The address format defined in this
document is consistent with the IPv6 Protocol [IPV6] and the "IPv6
Addressing Architecture" [ARCH]. It is designed to facilitate
scalable Internet routing.
This documented replaces RFC 2073, "An IPv6 Provider-Based Unicast
Address Format". RFC 2073 will become historic.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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document are to be interpreted as described in [RFC 2119].
2.0 Overview of the IPv6 Address
IPv6 addresses are 128-bit identifiers for interfaces and sets of
interfaces. There are three types of addresses: Unicast, Anycast,
and Multicast. This document defines a specific type of Unicast
address.
In this document, fields in addresses are given specific names, for
example "subnet". When this name is used with the term "ID" (for
"identifier") after the name (e.g., "subnet ID"), it refers to the
contents of the named field. When it is used with the term "prefix"
(e.g. "subnet prefix") it refers to all of the addressing bits to
the left of and including this field.
The specific type of an IPv6 address is indicated by the leading bits
in the address. The variable-length field comprising these leading
bits is called the Format Prefix (FP).
This document defines an address format for the 001 (binary) Format
Prefix for Aggregatable Global Unicast addresses. The same address
format could be used for other Format Prefixes, as long as these
Format Prefixes also identify IPv6 unicast addresses. Only the "001"
Format Prefix is defined here.
3.0 IPv6 Aggregatable Global Unicast Address Format
This document defines an address format for the IPv6 aggregatable
global unicast address assignment. The authors believe that this
address format will be widely used for IPv6 nodes connected to the
Internet. This address format is designed to support both the
current provider-based aggregation and a new type of aggregation
called exchanges. The combination will allow efficient routing
aggregation for both sites that connect directly to providers and
sites that connect to exchanges. Sites will have the choice to
connect to either type of aggregation entity.
Aggregatable addresses are organized into a three level hierarchy:
- Public Topology
- Site Topology
- Interface Identifier
Public topology is the collection of providers and exchanges who
provide public Internet transit services. Site topology is local to
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a specific site or organization which does not provide public transit
service to nodes outside of the site. Interface identifiers identify
interfaces on links.
______________ ______________
--+/ \+--------------+/ \+----------
( P1 ) +----+ ( P3 ) +----+
+\______________/ | |----+\______________/+--| |--
| +--| X1 | +| X2 |
| ______________ / | |-+ ______________ / | |--
+/ \+ +-+--+ \ / \+ +----+
( P2 ) / \ +( P4 )
--+\______________/ / \ \______________/
| / \ | |
| / | | |
| / | | |
_|_ _/_ _|_ _|_ _|_
/ \ / \ / \ / \ / \
( S.A ) ( S.B ) ( P5 ) ( P6 )( S.D )
\___/ \___/ \___/ \___/ \___/
| / \
_|_ _/_ \ ___
/ \ / \ +-/ \
( S.E ) ( S.F ) ( S.G )
\___/ \___/ \___/
As shown in the figure above, the aggregatable address format is
designed to support long-haul providers (shown as P1, P2, P3, and
P4), exchanges [EXCH] (shown as X1 and X2), multiple levels of
providers (shown at P5 and P6), and subscribers (shown as S.x)
Exchanges (unlike current NAPs, FIXes, etc.) will allocate IPv6
addresses. Organizations who connect to these exchanges will also
subscribe (directly, indirectly via the exchange, etc.) for long-
haul service from one or more long-haul providers. Doing so, they
will achieve addressing independence from long-haul transit
providers. They will be able to change long-haul providers without
having to renumber their organization. They can also be multihomed
via the exchange to more than one long-haul provider without having
to have address prefixes from each long-haul provider.
IPv6 unicast addresses are designed assuming that the internet
routing system makes forwarding decisions based on a "longest prefix
match" algorithm on arbitrary bit boundaries and does not have any
knowledge of the internal structure of IPv6 addresses. The structure
in IPv6 addresses is for assignment and allocation. The only
exception to this is the distinction made between unicast and
multicast addresses.
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3.1 Aggregatable Global Unicast Address Structure
The aggregatable global unicast address format is as follows:
| 3 | 13 | 32 | 16 | 64 bits |
+---+-----+-----------+--------+--------------------------------+
|FP | TLA | NLA* | SLA* | Interface ID |
+---+-----+-----------+--------+--------------------------------+
<--Public Topology---> Site
<-------->
Topology
<------Interface Identifier----->
Where
FP Format Prefix (001)
TLA Top-Level Aggregator
NLA* Next-Level Aggregator(s)
SLA* Site-Local Aggregator(s)
INTERFACE ID Interface Identifier
The following sections specify each part of the IPv6 Aggregatable
Global Unicast address format.
3.2 Top-Level Aggregator
Top-Level Aggregators (TLA) are the top level in the routing
hierarchy. Default-free routers will, at a minimum, have a routing
table entry for every active TLA.
This addressing format supports 8,192 (2^^13) TLA's. Additional TLA
may be added by using this format for additional format prefixes.
The addition of another FP will add another 8,192 TLA's.
3.2.1 Assignment of TLAs
TLAs are assigned to organizations providing public transit topology.
They are specifically not assigned to organizations only providing
leaf or private transit topology. TLA assignment does not imply
ownership. It does imply stewardship over valuable internet
property.
The IAB and IESG have authorized the Internet Assigned Numbers
Authority (IANA) as the appropriate entity to have the responsibility
for the management of the IPv6 address space as defined in [ALLOC].
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The IANA will assign small blocks of TLAs to IPv6 registries. The
registries will assign the TLAs to organizations meeting the
requirements for TLAs. When the registries have assigned all of
their TLAs they can request that the IANA to give them another block.
The blocks do not have to be contiguous. The IANA may also assign
TLAs to organizations directly.
TLA assignment requirements are as follows:
- Must have a plan to offer public native IPv6 service within 6
months from assignment. Plan must include plan for NLA
allocation.
- Plan or track record providing public internet transit service to
other providers. TLAs should not be assigned to organization that
are only providing leaf service even if multihomed.
- Must provide registry services for the NLA address space it is
responsible for under its TLA. This must include both sites and
next level providers.
- Must provide transit routing and forwarding to all assigned TLAs.
Organization is not allowed to filter out any specific TLA's
(except temporarily for diagnostic purposes).
- Periodically (interval set by registry) provide to registry
utilization statistics of the TLA it has custody of. The
organization must also provide traffic statistics on amounts of
traffic for transit TLA traffic.
Organizations which are given custody of a TLA and fail to continue
to meet these (or other future requirements defined by the IANA) may
have the TLA custody revoked.
3.3 Next-Level Aggregator(s)
Next-Level Aggregator(s) are used by TLA's to create an addressing
hierarchy and to identify sites. The TLA can assign the top part of
the NLA in a manner to create an addressing hierarchy appropriate to
its network. It can use the remainder of the bits in the field to
identify sites it wishes to serve. This is shown as follows:
| n | 32-n bits | 16 | 64 bits |
+-----+--------------------+--------+-----------------+
|NLA1 | Site | SLA* | Interface ID |
+-----+--------------------+--------+-----------------+
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Each TLA receives 32 bits of NLA* space. This NLA* space allows each
TLA to provide service to about as many organizations as the current
IPv4 internet can support total nodes.
The TLAs may also support NLAs in their own Site ID space. This
allows the TLAs to provide service to organizations providing public
transit service and organizations who do not. The organizations
providing public transit service become NLA's themselves. These NLAs
may also choose to use their Site ID space to support other NLAs.
This is shown as follows:
| n | 32-n bits | 16 | 64 bits |
+-----+--------------------+--------+-----------------+
|NLA1 | Site | SLA* | Interface ID |
+-----+--------------------+--------+-----------------+
| m | 32-n-m | 16 | 64 bits |
+-----+--------------+--------+-----------------+
|NLA2 | Site | SLA* | Interface ID |
+-----+--------------+--------+-----------------+
| o |32-n-m-o| 16 | 64 bits |
+-----+--------+--------+-----------------+
|NLA3 | Site | SLA* | Interface ID |
+-----+--------+--------+-----------------+
The NLA delegation works the the same manner as CIDR delegation in
IPv4 [CIDR]. TLAs are required to assume registry duties for the
NLAs. Each level of NLA is required to assume registry duties for
the next level NLA.
The design of the bit layout of the NLA space for a specific TLA is
left to the organization responsible for that TLA. Likewise the
design of the bit layout of the next level NLA is the responsibility
of the previous level NLA. It is recommended that organizations
assigning NLA address space use "slow start" allocation procedures as
is currently done with IPV4 CIDR blocks.
3.4 Site-Level Aggregator(s)
The SLA* field is used by an individual organization to create its
own local addressing hierarchy and to identify subnets. This is
analogous to subnets in IPv4 except that each organization has a much
greater number of subnets. The 16 bit SLA* field support 65,535
individual subnets.
Organizations may choose to either route their SLA* "flat" (e.g., not
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create any logical relationship between the SLA identifiers), or to
create a two or more level hierarchy in the SLA* field. The latter
is shown as follows:
| n | 16-n | 64 bits |
+-----+------------+-------------------------------------+
|SLA1 | Subnet | Interface ID |
+-----+------------+-------------------------------------+
| m |16-n-m | 64 bits |
+----+-------+-------------------------------------+
|SLA2|Subnet | Interface ID |
+----+-------+-------------------------------------+
The approach chosen for how to the structure of an SLA* field is the
responsibility of the individual organization.
The number of subnets supported should be sufficient for all but the
largest of organizations. Organizations which need additional
subnets can arrange with the organization they are obtaining internet
service from to obtain additional site identifiers and use this to
create additional subnets.
3.5 Interface ID
Interface identifiers are used to identify interfaces on a link.
They are required to be unique on that link. They may also be unique
over a broader scope. In many cases an interface's identifier will
be the same as that interface's link-layer address.
Interface IDs used in the aggregatable global unicast address format
are required to be 64 bits long and to be constructed in IEEE EUI-64
format [EUI-64]. Interface identifiers formed using EUI-64
identifiers may have global scope when a global token is available or
may have local scope where a global token is not available (e.g.,
serial links, tunnel end-points, etc.). Where EUI-64 identifiers are
used it is required that the "u" bit (universal/local bit in IEEE
EUI-64 terminology) be set correctly.
The construction of Interface Identifiers constructed in EUI-64
format is defined in [ARCH]. The details on forming interface
identifiers is defined in the appropriate "IPv6 over <link>"
specification such as "IPv6 over Ethernet" [ETHER], "IPv6 over FDDI"
[FDDI], etc.
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4.0 Acknowledgments
The authors would like to express our thanks to Thomas Narten, Bob
Fink, Matt Crawford, Allison Mankin, Jim Bound, Christian Huitema,
and Scott Bradner for their review and constructive comments.
5.0 References
[ALLOC] IAB and IESG, "IPv6 Address Allocation Management",
RFC1881, December 1995.
[ARCH] Hinden, R., "IP Version 6 Addressing Architecture",
Internet Draft, <draft-ietf-ipngwg-addr-arch-00.txt>, May
1997.
[AUTO] Thompson, S., Narten T., "IPv6 Stateless Address
Autoconfiguration", RFC1971, August 1996.
[CIDR] V. Fuller, T. Li, K. Varadhan, J. Yu, "Supernetting: an
Address Assignment and Aggregation Strategy", RFC1338.
[ETHER] M. Crawford, "Transmission of IPv6 Packets over Ethernet
Networks", Internet Draft, <draft-ietf-ipngwg-trans-
ethernet-00.txt>, March 1997.
[EUI64] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
Registration Authority",
http://standards.ieee.org/db/oui/tutorials/EUI64.html,
March 1997.
[EXCH] Hinden, R., Huitema, C. "Internet Exchanges", document
under preparation.
[FDDI] M. Crawford, "Transmission of IPv6 Packets over FDDI
Networks", Internet Draft, <draft-ietf-ipngwg-trans-
fddi-00.txt>, March 1997.
[IPV6] S. Deering, R. Hinden, Editors, "Internet Protocol, Version
6 (IPv6) Specification", RFC1883, December 1995.
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC2119, BCP14, March 1997.
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6.0 Security Considerations
Documents of this type do not directly impact the security of the
Internet infrastructure or its applications.
7.0 Authors' Addresses
Robert M. Hinden phone: 1 408 990-2004
Ipsilon Networks, Inc. email: hinden@ipsilon.com
232 Java Drive
Sunnyvale, CA 94089
USA
Mike O'Dell phone: 1 703 206-5890
UUNET Technologies, Inc. email: mo@uunet.uu.net
3060 Williams Drive
Fairfax, VA 22030
USA
Stephen E. Deering phone: 1 408 527-8213
Cisco Systems, Inc. email: deering@cisco.com
170 West Tasman Drive
San Jose, CA 95134-1706
USA
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