diff --git a/draft-nbourbaki-6man-classless-ipv6.xml b/draft-nbourbaki-6man-classless-ipv6.xml index 3bb3d9b..36cd501 100644 --- a/draft-nbourbaki-6man-classless-ipv6.xml +++ b/draft-nbourbaki-6man-classless-ipv6.xml @@ -11,10 +11,10 @@ - + - IPv6 is Classless + IPv6 is Classless The Intertubes @@ -34,13 +34,11 @@ - Over the history of IPv6, various classful address models have - been proposed, with the most notable being Top-Level Aggregation - (TLA) and Next-Level Aggregation (NLA) Identifiers. They have all - proved to be mistakes. The last remnant of classful addressing is - a rigid network / interface identifier boundary at /64. - This document removes that boundary as far as routing and addressing - are concerned. + Over the history of IPv6, various classful address models have been + proposed, none of which has withstood the test of time. The last + remnant of IPv6 classful addressing is a rigid network interface + identifier boundary at /64. This document removes that boundary for + routing and interface addressing. @@ -63,44 +61,43 @@
- Over the history of IPv6, various classful address models have - been proposed, with the most notable being Top-Level Aggregation - (TLA) and Next-Level Aggregation (NLA) Identifiers; see, for - example, . They have all proved to be - mistakes. For example, TLA and NLA were obsoleted by . The last remnant of classful addressing is a - rigid network / interface identifier boundary at /64. - This document removes that boundary as far as routing and addressing - are concerned. + Over the history of the IPv6 protocol, several classful addressing + models have been proposed. The most notable example recommended Top-Level + Aggregation (TLA) and Next-Level Aggregation (NLA) Identifiers , but was obsoleted by , leaving + a single remnant of classful addressing in IPv6: a rigid network + interface identifier boundary at /64. This document removes that + boundary for interface addressing. - Some confusion has been caused by the IP Version 6 Addressing - Architecture, , and the proposed changes in - with respect to the - minimum subnet size. - - Meanwhile, link prefixes of varied lengths, /127, /126, /124, - /120, ... /64 have been successfully deployed for many years. - Having the formal specification be unclear risks potential - mis-implementation by the naïve, which could result in operational - disasters. + Recent proposed changes to the IP Version 6 Addressing Architecture + specification have caused controversy. + While link prefixes of varied lengths, e.g. /127, /126, /124, + /120, ... /64 have been successfully deployed for many years, glaring + mismatches between a formal specification and long-standing field + deployment practices are never wise, not least because of the strong + risk of mis-implementation, which can easily result in serious + operational problems. + + This document also clarifies that IPv6 routing subnets may be of any + length up to 128.
- + It is assumed that the reader understands the history of classful addressing in IPv4 and why it was abolished . Of course, the acute need to conserve address space that forced the adoption of classless addressing for IPv4 does - not apply to IPv6; but the arguments for operational flexibility in - address allocation remain compelling. + not apply to IPv6, but the arguments for operational flexibility in + address assignment remain compelling. It is also assumed that the reader understands IPv6 , the IP Version 6 Addressing Architecture , the proposed changes to RFC4291 and RFC2464 - , and the recent - recommendations for the generation of stable Interface Identifiers + , and the IETF + recommendation for the generation of stable Interface Identifiers . - - An important recent IPv6 development was that, for host computers - on local area networks, the way in which interface identifiers were - formed was no longer bound to layer 2 addresses (MACs) . Therefore their - length, previously fixed at 64 bits , is in - fact a variably-sized parameter as stated in . + For host computers on local area networks, generation of interface + identifiers is no longer necessarily bound to layer 2 addresses (MACs) + . Therefore their + length, previously fixed at 64 bits , is in fact + a variably-sized parameter as explicitly acknowledged in Section + 5.5.3(d) of which states: + + + Note that a future revision of the address architecture [RFC4291] + and a future link-type-specific document, which will still be + consistent with each other, could potentially allow for an + interface identifier of length other than the value defined in the + current documents. Thus, an implementation should not assume a + particular constant. Rather, it should expect any lengths of + interface identifiers. + + +
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- - To state it simply, IPv6 unicast subnetting is based on prefixes - of any valid length up to 128 except for links where an Internet - Standard that has nothing to do with routing may impose a - particular length. Examples are Stateless Address AutoConfiguration + IPv6 unicast interfaces may use any subnet length up to 128 except + for situations where an Internet Standard document may impose a + particular length, for example Stateless Address Autoconfiguration (SLAAC) , or Using 127-Bit IPv6 Prefixes on Inter-Router Links . - Nodes must always support routing on any valid network prefix - length, even if SLAAC or other standards are in use, because routing - could choose to differentiate at a different granularity than is - used by any such automated link local address configuration - tools. + Additionally, this document clarifies that a node or router MUST + support routing of any valid network prefix length, even if SLAAC or + other standards are in use, because routing could choose to + differentiate at a different granularity than is used by any such + automated link local address configuration tools.