An IPv6 Provider-Based Unicast Address Format
obsoleted by
- rfc-2374 — An IPv6 Aggregatable Global Unicast Address Format
Extracted elements (18)
An extremely large subscriber can be assigned its own Provider ID, granting additional bits of address space to build a local address hierarchy, as an alternative to being assigned a block of subscriber prefixes.
Some subscribers may acquire address space directly from a registry, making their addresses provider-independent. This is accommodated by allowing direct registry assignment of Provider IDs to such organizations.
The address format is designed to support aggregation of network layer reachability information at multiple levels of routing hierarchy, facilitating scalable Internet-wide routing without imposing constraints on connectivity among providers or between providers and subscribers.
The document recommends that subscribers use IPv6 stateless address autoconfiguration [AUTO] with 48-bit IEEE-802 MAC addresses as Interface IDs, leaving 16 bits for the Subnet ID. This is sufficient for all but the largest subscribers (up to 65,535 subnets).
The IPv4 address allocation plan from RFC 1466 (distributed allocation via Regional Registries) was adopted as the base model for IPv6 address allocation, including the use of IANA as principal registry and delegation to qualified Regional Registries.
The Multi-Regional Registry ID (IANA-managed) permits flexibility for address assignments outside geographical regions already allocated to specific Regional Registries.
The routing system is assumed to make no assumptions about the specific structure and semantics of an IPv6 address beyond the Format Prefix and longest-prefix-match forwarding, allowing the provider-based structure to be transparent to the forwarding plane.
A provider may allocate some high-order bits of the Subscriber ID as a Subscriber-Region ID to group subscribers in close topological proximity, allowing the provider to control traffic routing through specific attachment points to indirect providers.
Address administration is organized into a three-level hierarchy: registry, provider, and subscriber. The format supports flexible address allocation at each level to support a wide spectrum of allocation demands.
National Registries are created by Regional Registries by subdividing the Provider ID field. A National Registry then allocates address space to individual providers within the country it serves.
The Format Prefix (FP) is a variable-length field comprising the leading bits of an IPv6 address that indicates the specific address type. This document defines the '010' (binary) FP for Provider-Based Unicast addresses.
The Provider ID uniquely identifies a provider within a registry. The Subscriber ID structure and assignment strategy is specified by each provider. Together they occupy 56 bits, with the split between them left to individual registries.
The Registry ID is a 5-bit field immediately following the Format Prefix, identifying the Regional Registry responsible for address allocation. Values are assigned to IANA (Multi-Regional: 10000), RIPE NCC (01000), INTERNIC (11000), and APNIC (00100); all other values are reserved by IANA.
This document defines the Registry ID value space for IPv6 provider-based unicast addresses. Assigned values are: Multi-Regional/IANA (10000), RIPE NCC (01000), INTERNIC (11000), APNIC (00100). All other values are reserved by the IANA.
Security issues are not discussed in this memo.
National Registries add an extra hierarchy layer within the Provider ID field: '010' (3 bits) + Registry ID (5 bits) + National Registry ID (m bits) + Provider ID (variable) + Subscriber ID (variable) + Intra-Subscriber (64 bits), where the national and provider ID fields together total 56-n bits.
The IPv6 provider-based unicast address uses a 128-bit format: 3-bit Format Prefix '010', 5-bit Registry ID, n-bit Provider ID, (56-n)-bit Subscriber ID, and 64-bit Intra-Subscriber part. The total non-intra-subscriber portion is 64 bits, leaving 64 bits for local addressing.
The recommended Intra-Subscriber layout uses 16 bits for Subnet ID and 48 bits for Interface ID (e.g., IEEE-802 MAC address), within the 64-bit Intra-Subscriber field. This yields up to 65,535 subnets per subscriber prefix.