wdiff draft-ietf-ipngwg-unicast-aggr-01.txt draft-ietf-ipngwg-unicast-aggr-02.txt

INTERNET-DRAFT R. Hinden, Ipsilon Networks
June 12,
July 16, 1997 M. O'Dell, UUNET
S. Deering, Cisco

An IPv6 Aggregatable Global Unicast Address Format

<draft-ietf-ipngwg-unicast-aggr-01.txt>

<draft-ietf-ipngwg-unicast-aggr-02.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
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This internet draft expires on December 13, 1997. January 17, 1998.

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
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.

IPv6 unicast addresses are designed assuming that the internet 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.

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 exchange-based
aggregation. The combination will allow efficient routing
aggregation for both sites that connect directly to providers and for
sites that connect to exchanges. Sites will have the choice to
connect to either type of aggregation entity.

While this address format is designed to support exchange-based
aggregation (in addition to current provider-based aggregation) it is
not dependent on exchanges for it's overall route aggregation
properties. It will provide efficient route aggregation with only
provider-based aggregation.

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
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.C )
\___/ \___/ \___/ \___/ \___/
| / \
_|_ _/_ \ ___
/ \ / \ +-/ \
( S.E S.D ) ( S.F S.E ) ( S.G S.F )
\___/ \___/ \___/

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 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. Note that the
mechanisms used for this type of provider selection and portability
are not discussed in the document.

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* NLA ID | SLA* SLA ID | Interface ID |
| | ID | | | |
+---+-----+-----------+--------+--------------------------------+

<--Public Topology---> Site
<-------->
Topology
<------Interface Identifier----->

Where

FP Format Prefix (001)
TLA ID Top-Level Aggregator
NLA* Aggregation Identifier
NLA ID Next-Level Aggregator(s)
SLA* Aggregation Identifier
SLA ID Site-Level Aggregator(s) Aggregation Identifier
INTERFACE ID Interface Identifier

The following sections specify each part of the IPv6 Aggregatable
Global Unicast address format.

3.2 Top-Level Aggregator Aggregation ID

Top-Level Aggregators (TLA) Aggregation Identifiers (TLA ID) are the top level in the
routing hierarchy. Default-free routers must have a routing table
entry for every active TLA. TLA ID and will probably have additional
entries providing routing information for the TLA ID in which they
are located. They may have additional entries, entries in order to optimize
routing for their specific topology, but the routing topology at all
levels must be designed to minimize the number of additional entries
fed into the default free routing tables.

This addressing format supports 8,192 (2^^13) TLA's. (2^13) TLA ID's. Additional
TLA ID's 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].
ID's.

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 give them another block.
The blocks do not have to be contiguous. The IANA may also assign
TLAs to organizations directly.

Organizations assigned TLAs are required to meet the following
requirements:

- 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 on
fair, reasonable, and non-discriminatory terms, to other
providers. TLAs must not be assigned to organizations that are
only providing leaf service even if multihomed.

- Must provide registry services on fair, reasonable, and non-
discriminatory terms, 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
on fair, reasonable, and non-discriminatory terms. Organizations
are not allowed to filter out any specific TLA's (except
temporarily rules for diagnostic purposes or emergency repair purposed).

- Periodically (interval set by registry) provide to registry
utilization statistics of the TLA it has custody of. The
organization must also show evidence of carrying TLA routing and
transit traffic. This can be in the form of traffic statistics,
traceroutes, routing table dumps, or similar means.

Organizations which ID assignment are given custody of a TLA and fail to continue
to meet these may have the TLA custody revoked. defined in [TLAASN].

3.3 Next-Level Aggregator(s) Aggregation Identifier

Next-Level Aggregator(s) Aggregation Identifier's are used by TLA's organizations
assigned a TLA ID to create an addressing hierarchy and to identify
sites. The TLA organization can assign the top part of the NLA ID 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 ID | SLA* SLA ID | Interface ID |
+-----+--------------------+--------+-----------------+

Each organization assigned a TLA ID receives 32 bits of NLA* NLA ID space.
This NLA* NLA ID space allows each
TLA organization to provide service to about
approximately as many organizations as the current IPv4 internet Internet can
support total nodes.

The TLAs

Organizations assigned TLA ID's may also support NLAs NLA ID's in their
own Site ID space. This allows the TLAs organization assigned a TLA ID to
provide service to organizations providing public transit service and
to organizations who do not. The organizations
providing not provide public transit service become NLA's themselves. service. These NLAs
organizations receiving an NLA ID may also choose to use their Site
ID space to support other NLAs. NLA ID's. This is shown as follows:

| n | 32-n bits | 16 | 64 bits |
+-----+--------------------+--------+-----------------+
|NLA1 | Site ID | SLA* SLA ID | Interface ID |
+-----+--------------------+--------+-----------------+

| m | 32-n-m | 16 | 64 bits |
+-----+--------------+--------+-----------------+
|NLA2 | Site ID | SLA* SLA ID | Interface ID |
+-----+--------------+--------+-----------------+

| o |32-n-m-o| 16 | 64 bits |
+-----+--------+--------+-----------------+
|NLA3 | Site | SLA* ID| SLA ID | Interface ID |
+-----+--------+--------+-----------------+

The NLA delegation works in the same manner as CIDR delegation in
IPv4 [CIDR]. TLAs are required to assume registry duties rules for the
NLAs. Each level of NLA is required to assume registry duties for
the next level NLA. ID assignment are defined in [TLAASN].

The design of the bit layout of the NLA ID space for a specific TLA
ID is left to the organization responsible for that TLA. TLA ID. Likewise
the design of the bit layout of the next level NLA ID is the
responsibility of the previous level NLA. NLA ID. It is recommended that
organizations assigning NLA address space use "slow start" allocation
procedures as is currently done with IPV4 IPv4 CIDR blocks.

The design of an NLA ID allocation plan is a tradeoff between routing
aggregation efficiency and flexibility. Creating hierarchies allows
for greater amount of aggregation and results in smaller routing
tables. Flat NLA ID assignment provides for easier allocation and
attachment flexibility flexibility, but results in larger routing tables.

3.4 Site-Level Aggregator(s) Aggregation Identifier

The SLA* SLA ID 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* SLA ID field support 65,535
individual subnets.

Organizations may choose to either route their SLA* SLA ID "flat" (e.g.,
not create any logical relationship between the SLA identifiers which that
results in larger routing tables), or to create a two or more level
hierarchy (which (that results in smaller routing tables) in the SLA* SLA ID
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 structuring an SLA* SLA ID field is the
responsibility of the individual organization.

The number of subnets supported in this address format should be
sufficient for all but the largest of organizations. Organizations
which need additional subnets can arrange with the organization they
are obtaining internet 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 or be based on the 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]. These identifiers may have global scope when a
global token (e.g., IEEE 48bit MAC) is available or may have local
scope where a global token is not available (e.g., serial links,
tunnel end-points, etc.). The "u" bit (universal/local bit in IEEE
EUI-64 terminology) in the EUI-64 identifier must be set correctly,
as defined in [ARCH], to indicate global or local scope.

The procedures for creating EUI-64 based Interface Identifiers 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.

4.0 Acknowledgments

The authors would like to express our thanks to Thomas Narten, Bob
Fink, Matt Crawford, Allison Mankin, Jim Bound, Christian Huitema,
Scott Bradner, Brian Carpenter, and John Stewart. Stewart 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 <draft-ietf-ipngwg-addr-arch-v2-02.txt>,
July 1997.

[AUTH] Atkinson, R., "IP Authentication Header", RFC1826, August
1995.

[AUTO] Thompson, S., Narten T., "IPv6 Stateless Address
Autoconfiguration", RFC1971, August 1996.

[CIDR] Fuller, V., T. Li, K. Varadhan, J. Yu, "Supernetting: an
Address Assignment and Aggregation Strategy", RFC1338.

[ETHER] Crawford, M., "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. C., R. Hinden, "Internet Exchanges", document
under preparation.

[FDDI] Crawford, M., "Transmission of IPv6 Packets over FDDI
Networks", Internet Draft, <draft-ietf-ipngwg-trans-fddi-
net-00.txt>, March 1997.

[IPV6] Deering, S., Hinden, R., Editors, "Internet Protocol,
Version 6 (IPv6) Specification", RFC1883, December 1995.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC2119, BCP14, March 1997.

[TLAASN] Hinden, R., "TLA and NLA Assignment Rules", Internet Draft,
<draft-ietf-ipngwg-tla-assignment-00.txt>, July 1997.

6.0 Security Considerations

Documents of this type

IPv6 addressing documents do not directly have any direct impact the security of the on Internet
infrastructure or its applications. security. Authentication of IPv6 packets is defined
in [AUTH].

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