From 0f97800873ba38f4364ca4f4abe8e0f9d5a74ff2 Mon Sep 17 00:00:00 2001 From: Job Snijders Date: Tue, 18 Jul 2017 14:12:00 +0200 Subject: [PATCH] Reformatting to 'one sentence per line' This diff does not introduce any textual changes. --- draft-nbourbaki-6man-classless-ipv6.xml | 388 +++++++++++------------- 1 file changed, 172 insertions(+), 216 deletions(-) diff --git a/draft-nbourbaki-6man-classless-ipv6.xml b/draft-nbourbaki-6man-classless-ipv6.xml index bdd7f03..22db1ef 100644 --- a/draft-nbourbaki-6man-classless-ipv6.xml +++ b/draft-nbourbaki-6man-classless-ipv6.xml @@ -13,37 +13,38 @@ - - IPv6 is Classless + - - The Intertubes -
- - 42 Rue du Jour - Sophia-Antipolis - - ::1 - FR - - bourbaki@bogus.com -
- + IPv6 is Classless - + + The Intertubes +
+ + 42 Rue du Jour + Sophia-Antipolis + + ::1 + FR + + bourbaki@bogus.com +
+ - Internet - 6man + - + Internet + 6man - 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 the fixed position of - that boundary for interface addressing. + - + + 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 the fixed position of that boundary for interface addressing. + + + - + - + -
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- 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 the fixed - position of that boundary for interface addressing. + + 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 the fixed position of that boundary for interface addressing. + - 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. + + 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. + + This document also clarifies that IPv6 routing subnets may be of any length up to 128. + -
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- 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 assignment remain compelling. + + 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 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 , an - IPv6 Prefix Length Recommendation for Forwarding, and the IETF - recommendation for the generation of stable Interface Identifiers - . + + It is also assumed that the reader understands IPv6 , the IP Version 6 Addressing Architecture , the proposed changes to RFC4291 and RFC2464 , an IPv6 Prefix Length Recommendation for Forwarding, and the IETF recommendation for the generation of stable Interface Identifiers . + - is also worth - reading to clarify uses of varying prefix lengths on a single - link. + + is also worth reading to clarify uses of varying prefix lengths on a single link. + - -
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- 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. - - + + 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: - As IPv6 usage has evolved and grown over in recent years, it has - become evident that it faces several scaling and coordination - problems. These problems are analogous to allocation and coordination - problems that motivated IPv4 CIDR allocation and later abundant IPv4 - PAT, they include: - - - Address allocation models for specific counts of fixed length subnets - to downstream networks or devices from /48 down to /64 are based on - design assumptions of how subnets are or should be allocated and - populated within ipv4 networks. - - - Hierarchical allocation of fixed-length subnets requires coordination - between lower / intermediate / upper network elementss. It has - implict assumption that policies and size allocation allowed the top - of the hierarchy will accomodate present and future use cases with - fixed lenth subnet allocation. - - - Coordination with upstream networks across administrative domains for - the allocation of fixed length subnets reveals topology and intent that - may be private in scope. Policies for hierarchical allcation are applied - top-down and amount to permission to build a particular topology (for - example mobile device tethering, virtual machine instantiation, containers - and so on). - - - -
+ + + 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. + + + -
- - 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 . + + As IPv6 usage has evolved and grown over in recent years, it has become evident that it faces several scaling and coordination problems. + These problems are analogous to allocation and coordination problems that motivated IPv4 CIDR allocation and later abundant IPv4 PAT, they include: - 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. + -
+ + Address allocation models for specific counts of fixed length subnets to downstream networks or devices from /48 down to /64 are based on design assumptions of how subnets are or should be allocated and populated within ipv4 networks. + + + Hierarchical allocation of fixed-length subnets requires coordination between lower / intermediate / upper network elementss. + It has implict assumption that policies and size allocation allowed the top of the hierarchy will accomodate present and future use cases with fixed lenth subnet allocation. + + + Coordination with upstream networks across administrative domains for the allocation of fixed length subnets reveals topology and intent that may be private in scope. + Policies for hierarchical allcation are applied top-down and amount to permission to build a particular topology (for example mobile device tethering, virtual machine instantiation, containers and so on). + + + + + + +
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+ + + 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 . + + + + 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. + + +
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- For historical reasons, when a prefix is needed on a link, - barring other considerations, a /64 is recommended . + + For historical reasons, when a prefix is needed on a link, barring other considerations, a /64 is recommended . + - The length of the Interface Identifier in Stateless Address - Autoconfiguration is a parameter; its - length SHOULD be sufficient for effective randomization for privacy - reasons. For example, a /48 might be sufficient. But operationally - we recommend, barring strong considerations to the contrary, using - 64-bits for SLAAC in order not to discover bugs where 64 was - hard-coded, and to favor portability of devices and operating - systems. + + The length of the Interface Identifier in Stateless Address Autoconfiguration is a parameter; its length SHOULD be sufficient for effective randomization for privacy reasons. + For example, a /48 might be sufficient. + But operationally we recommend, barring strong considerations to the contrary, using 64-bits for SLAAC in order not to discover bugs where 64 was hard-coded, and to favor portability of devices and operating systems. + - Nonetheless, there is no reason in theory why an IPv6 node - should not operate with different interface identfier lengths on - different physical interfaces. Thus, a correct implementation of - SLAAC must in fact allow for any prefix length, with the value being - a parameter per interface. For instance, the Interface Identifier - length in the recommended (see ) algorithm - for selecting stable interface identifiers - is a parameter, rather than a hardcoded value. + + Nonetheless, there is no reason in theory why an IPv6 node should not operate with different interface identfier lengths on different physical interfaces. + Thus, a correct implementation of SLAAC must in fact allow for any prefix length, with the value being a parameter per interface. + For instance, the Interface Identifier length in the recommended (see ) algorithm for selecting stable interface identifiers is a parameter, rather than a hardcoded value. + -
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- Assuming that nodes employ unpredictable interface identifiers - , the subnet size may have an impact on some - security and privacy properties of a network. Namely, the smaller - the subnet size, the more feasible it becomes to perform IPv6 - address scans . - For some specific subnets, such as point to point links, this may be - less of an issue. + - On the other hand, we assume that a number of IPv6 - implementations fail to enforce limits on the size of some of the - data structures they employ for communicating with neighboring - nodes, such as the Neighbor Cache. In such cases, the use of - smaller subnets forces an operational limit on such data structures, - thus helping mitigate some pathological behaviors (such as Neighbor - Cache Exhaustion attacks). + Assuming that nodes employ unpredictable interface identifiers , the subnet size may have an impact on some security and privacy properties of a network. + Namely, the smaller the subnet size, the more feasible it becomes to perform IPv6 address scans . + For some specific subnets, such as point to point links, this may be less of an issue. + - + + On the other hand, we assume that a number of IPv6 implementations fail to enforce limits on the size of some of the data structures they employ for communicating with neighboring nodes, such as the Neighbor Cache. + In such cases, the use of smaller subnets forces an operational limit on such data structures, thus helping mitigate some pathological behaviors (such as Neighbor Cache Exhaustion attacks). + + +
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+ + This document has no IANA Considerations. + +
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+ + The authors of this document are as follows: - This document has no IANA Considerations. + + Randy Bush, Internet Initiative Japan + Brian Carpenter, University of Auckland + Fernando Gont, SI6 Networks / UTN-FRH + Nick Hilliard, INEX + Joel Jaeggli, Fastly + Geoff Huston, APNIC + Chris Morrow, Google, Inc. + Job Snijders, NTT Communications + + - +
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- The authors of this document are as follows: - - Randy Bush, Internet Initiative Japan - Brian Carpenter, University of Auckland - Fernando Gont, SI6 Networks / UTN-FRH - Nick Hilliard, INEX - Joel Jaeggli, Fastly - Geoff Huston, APNIC - Chris Morrow, Google, Inc. - Job Snijders, NTT Communications - - + + + + + + + -
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