draft-ietf-v6ops-addcon-03.txt   draft-ietf-v6ops-addcon-04.txt 
Network Working Group G. Van de Velde Network Working Group G. Van de Velde
Internet-Draft C. Popoviciu Internet-Draft C. Popoviciu
Expires: September 4, 2007 Cisco Systems Expires: December 22, 2007 Cisco Systems
T. Chown T. Chown
University of Southampton University of Southampton
O. Bonness O. Bonness
C. Hahn C. Hahn
T-Systems Enterprise Services GmbH T-Systems Enterprise Services GmbH
March 3, 2007 June 20, 2007
IPv6 Unicast Address Assignment Considerations IPv6 Unicast Address Assignment Considerations
<draft-ietf-v6ops-addcon-03.txt> <draft-ietf-v6ops-addcon-04.txt>
Status of this Memo Status of this Memo
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This Internet-Draft will expire on September 4, 2007. This Internet-Draft will expire on December 22, 2007.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
Abstract Abstract
One fundamental aspect of any IP communications infrastructure is its One fundamental aspect of any IP communications infrastructure is its
addressing plan. With its new address architecture and allocation addressing plan. With its new address architecture and allocation
policies, the introduction of IPv6 into a network means that network policies, the introduction of IPv6 into a network means that network
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Network Level Addressing Design Considerations . . . . . . . . 5 2. Network Level Addressing Design Considerations . . . . . . . . 5
2.1. Global Unique Addresses . . . . . . . . . . . . . . . . . 5 2.1. Global Unique Addresses . . . . . . . . . . . . . . . . . 5
2.2. Unique Local IPv6 Addresses . . . . . . . . . . . . . . . 6 2.2. Unique Local IPv6 Addresses . . . . . . . . . . . . . . . 6
2.3. 6Bone Address Space . . . . . . . . . . . . . . . . . . . 7 2.3. 6Bone Address Space . . . . . . . . . . . . . . . . . . . 7
2.4. Network Level Design Considerations . . . . . . . . . . . 7 2.4. Network Level Design Considerations . . . . . . . . . . . 7
2.4.1. Sizing the Network Allocation . . . . . . . . . . . . 8 2.4.1. Sizing the Network Allocation . . . . . . . . . . . . 8
2.4.2. Address Space Conservation . . . . . . . . . . . . . . 8 2.4.2. Address Space Conservation . . . . . . . . . . . . . . 9
3. Subnet Prefix Considerations . . . . . . . . . . . . . . . . . 8 3. Subnet Prefix Considerations . . . . . . . . . . . . . . . . . 9
3.1. Considerations for subnet prefixes shorter then /64 . . . 9 3.1. Considerations for subnet prefixes shorter then /64 . . . 9
3.2. Considerations for /64 prefixes . . . . . . . . . . . . . 9 3.2. Considerations for /64 prefixes . . . . . . . . . . . . . 10
3.3. Considerations for subnet prefixes longer then /64 . . . . 9 3.3. Considerations for subnet prefixes longer then /64 . . . . 10
3.3.1. Anycast addresses . . . . . . . . . . . . . . . . . . 10 3.3.1. Anycast addresses . . . . . . . . . . . . . . . . . . 10
3.3.2. Addresses used by Embedded-RP (RFC3956) . . . . . . . 11 3.3.2. Addresses used by Embedded-RP (RFC3956) . . . . . . . 12
3.3.3. ISATAP addresses . . . . . . . . . . . . . . . . . . . 12 3.3.3. ISATAP addresses . . . . . . . . . . . . . . . . . . . 12
3.3.4. /126 addresses . . . . . . . . . . . . . . . . . . . . 12 3.3.4. /126 addresses . . . . . . . . . . . . . . . . . . . . 13
3.3.5. /127 addresses . . . . . . . . . . . . . . . . . . . . 12 3.3.5. /127 addresses . . . . . . . . . . . . . . . . . . . . 13
3.3.6. /128 addresses . . . . . . . . . . . . . . . . . . . . 12 3.3.6. /128 addresses . . . . . . . . . . . . . . . . . . . . 13
4. Allocation of the IID of an IPv6 Address . . . . . . . . . . . 13 4. Allocation of the IID of an IPv6 Address . . . . . . . . . . . 13
4.1. Automatic EUI-64 Format Option . . . . . . . . . . . . . . 13 4.1. Automatic EUI-64 Format Option . . . . . . . . . . . . . . 14
4.2. Using Privacy Extensions . . . . . . . . . . . . . . . . . 13 4.2. Using Privacy Extensions . . . . . . . . . . . . . . . . . 14
4.3. Cryptographically Generated IPv6 Addresses . . . . . . . . 14 4.3. Manual/Dynamic Assignment Option . . . . . . . . . . . . . 14
4.4. Manual/Dynamic Assignment Option . . . . . . . . . . . . . 14 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
5. Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . 15 6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
5.1. Enterprise Considerations . . . . . . . . . . . . . . . . 15 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
5.1.1. Obtaining general IPv6 network prefixes . . . . . . . 15 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1.2. Forming an address (subnet) allocation plan . . . . . 16 8.1. Normative References . . . . . . . . . . . . . . . . . . . 15
5.1.3. Other considerations . . . . . . . . . . . . . . . . . 17 8.2. Informative References . . . . . . . . . . . . . . . . . . 15
5.1.4. Node configuration considerations . . . . . . . . . . 17 Appendix A. Case Studies . . . . . . . . . . . . . . . . . . . . 17
5.2. Service Provider Considerations . . . . . . . . . . . . . 18 A.1. Enterprise Considerations . . . . . . . . . . . . . . . . 18
5.2.1. Investigation of objective Requirements for an A.1.1. Obtaining general IPv6 network prefixes . . . . . . . 18
IPv6 addressing schema of a Service Provider . . . . 18 A.1.2. Forming an address (subnet) allocation plan . . . . . 19
5.2.2. Exemplary IPv6 address allocation plan for a A.1.3. Other considerations . . . . . . . . . . . . . . . . . 19
Service Provider . . . . . . . . . . . . . . . . . . . 21 A.1.4. Node configuration considerations . . . . . . . . . . 20
5.2.3. Additional Remarks . . . . . . . . . . . . . . . . . . 25 A.2. Service Provider Considerations . . . . . . . . . . . . . 21
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 A.2.1. Investigation of objective Requirements for an
7. Security Considerations . . . . . . . . . . . . . . . . . . . 28 IPv6 addressing schema of a Service Provider . . . . 21
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28 A.2.2. Exemplary IPv6 address allocation plan for a
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Service Provider . . . . . . . . . . . . . . . . . . . 24
9.1. Normative References . . . . . . . . . . . . . . . . . . . 28 A.2.3. Additional Remarks . . . . . . . . . . . . . . . . . . 28
9.2. Informative References . . . . . . . . . . . . . . . . . . 28 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30
Intellectual Property and Copyright Statements . . . . . . . . . . 33 Intellectual Property and Copyright Statements . . . . . . . . . . 33
1. Introduction 1. Introduction
The Internet Protocol Version 6 (IPv6) Addressing Architecture [26] The Internet Protocol Version 6 (IPv6) Addressing Architecture [26]
defines three main types of addresses: unicast, anycast and defines three main types of addresses: unicast, anycast and
multicast. This document focuses on unicast addresses, for which multicast. This document focuses on unicast addresses, for which
there are currently two principal allocated types: Global Unique there are currently two principal allocated types: Global Unique
Addresses [14] ('globals') and Unique Local IPv6 Addresses [24] Addresses [14] ('globals') and Unique Local IPv6 Addresses [24]
(ULAs). In addition until recently there has been 'experimental' (ULAs). In addition until recently there has been 'experimental'
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reduces the requirement to size subnets to device counts for the reduces the requirement to size subnets to device counts for the
purposes of (IPv4) address conservation purposes of (IPv4) address conservation
o Even though there is no broadcast for the IPv6 protocol, there is o Even though there is no broadcast for the IPv6 protocol, there is
still need to consider the number of devices in a given subnet due still need to consider the number of devices in a given subnet due
to traffic storm and level of traffic generated by hosts to traffic storm and level of traffic generated by hosts
o The implications of the vastly increased subnet size on the threat o The implications of the vastly increased subnet size on the threat
of address-based host scanning and other scanning techniques, as of address-based host scanning and other scanning techniques, as
discussed in [30]. discussed in [30].
We do not discuss here how a site or ISP should proceed with We do not discuss here how a site or ISP should proceed with
acquiring its globally routable IPv6 address prefix. However, one acquiring its globally routable IPv6 address prefix. In each case
should note that IPv6 networks currently receive their global unicast the prefix received is provider assigned (PA) or provider independent
address allocation from their 'upstream' provider, which may be (PI).
another ISP, a Local Internet Registry (LIR) or a Regional Internet
Registry (RIR). In each case the prefix received is provider
assigned (PA). Until very recently there has been no provider
independent (PI) address space for IPv6 generally available. However
ARIN is now providing PI address space allocations, subject to
customers meeting certain requirements.
We do not discuss PI policy here. The observations and We do not discuss PI policy here. The observations and
recommendations of this text are largely independent of the PA or PI recommendations of this text are largely independent of the PA or PI
nature of the address block being used. At this time we assume that nature of the address block being used. At this time we assume that
most commonly an IPv6 network which changes provider will need to most commonly an IPv6 network which changes provider will need to
undergo a renumbering process, as described in [23]. A separate undergo a renumbering process, as described in [23]. A separate
document [32] makes recommendations to ease the IPv6 renumbering document [32] makes recommendations to ease the IPv6 renumbering
process. process.
This document does not discuss implementation aspects related to the This document does not discuss implementation aspects related to the
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addresses. Most implementations know about Site-local addresses even addresses. Most implementations know about Site-local addresses even
though they are deprecated, and do not know about ULAs - even though though they are deprecated, and do not know about ULAs - even though
they represent current specification. As result transitioning they represent current specification. As result transitioning
between these types of addresses may cause difficulties. between these types of addresses may cause difficulties.
2. Network Level Addressing Design Considerations 2. Network Level Addressing Design Considerations
This section discusses the kind of IPv6 addresses used at the network This section discusses the kind of IPv6 addresses used at the network
level for the IPv6 infrastructure. The kind of addresses that can be level for the IPv6 infrastructure. The kind of addresses that can be
considered are Global Unique Addresses and ULAs. We also comment considered are Global Unique Addresses and ULAs. We also comment
here on the recently deprecated 6bone address space. here on the deprecated 6bone address space.
2.1. Global Unique Addresses 2.1. Global Unique Addresses
The most commonly used unicast addresses will be Global Unique The most commonly used unicast addresses will be Global Unique
Addresses ('globals'). No significant considerations are necessary Addresses ('globals'). No significant considerations are necessary
if the organization has an address space assignment and a single if the organization has an address space assignment and a single
prefix is deployed through a single upstream provider. prefix is deployed through a single upstream provider.
However, a multihomed site may deploy addresses from two or more However, a multihomed site may deploy addresses from two or more
Service Provider assigned IPv6 address ranges. Here, the network Service Provider assigned IPv6 address ranges. Here, the network
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used alongside global addresses, with ULAs used internally and used alongside global addresses, with ULAs used internally and
globals used externally. Thus use of ULAs does not imply use of NAT globals used externally. Thus use of ULAs does not imply use of NAT
for IPv6. for IPv6.
The ULA address range allows network administrators to deploy IPv6 The ULA address range allows network administrators to deploy IPv6
addresses on their network without asking for a globally unique addresses on their network without asking for a globally unique
registered IPv6 address range. A ULA prefix is 48 bits, i.e. a /48, registered IPv6 address range. A ULA prefix is 48 bits, i.e. a /48,
the same as the currently recommended allocation for a site from the the same as the currently recommended allocation for a site from the
globally routable IPv6 address space [9]. globally routable IPv6 address space [9].
A site willing to use ULA address space can have either (a) multiple
/48 prefixes (e.g. a /44) and wishes to use ULAs, or (b) has one /48
and wishes to use ULAs or (c) a site has a less-than-/48 prefix (e.g.
a /56 or /64) and wishes to use ULAs. In all above cases the ULA
addresses can be randomly chosen according the principles specified
in [19]. Using a random chosen ULA address will be conform in case
(a) provide suboptimal aggregation capability, while in case (c)
there will be overconsumption of address space.
ULAs provide the means to deploy a fixed addressing scheme that is ULAs provide the means to deploy a fixed addressing scheme that is
not affected by a change in service provider and the corresponding PA not affected by a change in service provider and the corresponding PA
global addresses. Internal operation of the network is thus global addresses. Internal operation of the network is thus
unaffected during renumbering events. Nevertheless, this type of unaffected during renumbering events. Nevertheless, this type of
address must be used with caution. address must be used with caution.
A site using ULAs may or may not also deploy globals. In an isolated A site using ULAs may or may not also deploy global addresses. In an
network ULAs may be deployed on their own. In a connected network, isolated network ULAs may be deployed on their own. In a connected
that also deploys global addresses, both may be deployed, such that network, that also deploys global addresses, both may be deployed,
hosts become multiaddressed (one global and one ULA address) and the such that hosts become multiaddressed (one global and one ULA
IPv6 default address selection algorithm will pick the appropriate address) and the IPv6 default address selection algorithm will pick
source and destination addresses to use, e.g. ULAs will be selected the appropriate source and destination addresses to use, e.g. ULAs
where both the source and destination hosts have ULA addresses. will be selected where both the source and destination hosts have ULA
Because a ULA and a global site prefix are both /48 length, an addresses. Because a ULA and a global site prefix are both /48
administrator can choose to use the same subnetting (and host length, an administrator can choose to use the same subnetting (and
addressing) plan for both prefixes. host addressing) plan for both prefixes.
As an example of the problems ULAs may cause, when using IPv6 As an example of the problems ULAs may cause, when using IPv6
multicast within the network, the IPv6 default address selection multicast within the network, the IPv6 default address selection
algorithm prefers the ULA address as the source address for the IPv6 algorithm prefers the ULA address as the source address for the IPv6
multicast streams. This is NOT a valid option when sending an IPv6 multicast streams. This is NOT a valid option when sending an IPv6
multicast stream to the IPv6 Internet for two reasons. For one, multicast stream to the IPv6 Internet for two reasons. For one,
these addresses are not globally routable so RPF checks for such these addresses are not globally routable so RPF checks for such
traffic will fail outside the internal network. The other reason is traffic will fail outside the internal network. The other reason is
that the traffic will likely not cross the network boundary due to that the traffic will likely not cross the network boundary due to
multicast domain control and perimeter security policies. multicast domain control and perimeter security policies.
In principle ULAs allow easier network mergers than RFC1918 addresses In principle ULAs allow easier network mergers than RFC1918 addresses
do for IPv4 because ULA prefixes have a high probability of do for IPv4 because ULA prefixes have a high probability of
uniqueness, if the prefix is chosen as described in the RFC. uniqueness, if the prefix is chosen as described in the RFC.
The usage of ULAs should be carefully considered even when not The usage of ULAs should be carefully considered even when not
attached to the IPv6 Internet due to the potential for added attached to the IPv6 Internet as some IPv6 specifications were
complexity when connecting to the Internet at some point in the created before the existence of ULA addresses.
future.
2.3. 6Bone Address Space 2.3. 6Bone Address Space
The 6Bone address space was used before the RIRs started to The 6Bone address space was used before the RIRs started to
distribute 'production' IPv6 prefixes. The 6Bone prefixes have a distribute 'production' IPv6 prefixes. The 6Bone prefixes have a
common first 16 bits in the IPv6 Prefix of 3FFE::/16. This address common first 16 bits in the IPv6 Prefix of 3FFE::/16. This address
range is deprecated as of 6th June 2006 [17] and should be avoided on range is deprecated as of 6th June 2006 [17] and must not be used on
any new IPv6 network deployments. Sites using 6bone address space any new IPv6 network deployments. Sites using 6bone address space
should renumber to production address space using procedures as should renumber to production address space using procedures as
defined in [23]. defined in [23].
2.4. Network Level Design Considerations 2.4. Network Level Design Considerations
IPv6 provides network administrators with a significantly larger IPv6 provides network administrators with a significantly larger
address space, enabling them to be very creative in how they can address space, enabling them to be very creative in how they can
define logical and practical address plans. The subnetting of define logical and practical address plans. The subnetting of
assigned prefixes can be done based on various logical schemes that assigned prefixes can be done based on various logical schemes that
involve factors such as: involve factors such as:
o Geographical Boundaries - by assigning a common prefix to all o Using existing systems
* translate the existing subnet number into IPv6 subnet id
* translate the VLAN id into IPv6 subnet id
o Rethink
* allocate according to your need
o Aggregation
* Geographical Boundaries - by assigning a common prefix to all
subnets within a geographical area subnets within a geographical area
o Organizational Boundaries - by assigning a common prefix to an * Organizational Boundaries - by assigning a common prefix to an
entire organization or group within a corporate infrastructure entire organization or group within a corporate infrastructure
o Service Type - by reserving certain prefixes for predefined * Service Type - by reserving certain prefixes for predefined
services such as: VoIP, Content Distribution, wireless services, services such as: VoIP, Content Distribution, wireless
Internet Access, etc services, Internet Access, Security areas etc. This type of
addressing may create dependencies on IP addresses that can
make renumbering harder if the nodes or interfaces supporting
those services on the network are sparse within the topology.
Such logical addressing plans have the potential to simplify network Such logical addressing plans have the potential to simplify network
operations and service offerings, and to simplify network management operations and service offerings, and to simplify network management
and troubleshooting. A very large network would also have no need to and troubleshooting. A very large network would also have no need to
consider using private address space for its infrastructure devices, consider using private address space for its infrastructure devices,
simplifying network management. simplifying network management.
The network designer must however keep in mind several factors when The network designer must however keep in mind several factors when
developing these new addressing schemes: developing these new addressing schemes for networks with and without
global connectivity:
o Prefix Aggregation - The larger IPv6 addresses can lead to larger o Prefix Aggregation - The larger IPv6 addresses can lead to larger
routing tables unless network designers are actively pursuing routing tables unless network designers are actively pursuing
aggregation. While prefix aggregation will be enforced by the aggregation. While prefix aggregation will be enforced by the
service provider, it is beneficial for the individual service provider, it is beneficial for the individual
organizations to observe the same principles in their network organizations to observe the same principles in their network
design process design process
o Network growth - The allocation mechanism for flexible growth of a o Network growth - The allocation mechanism for flexible growth of a
network prefix, documented in RFC3531 [13] can be used to allow network prefix, documented in RFC3531 [13] can be used to allow
the network infrastructure to grow and be numbered in a way that the network infrastructure to grow and be numbered in a way that
is likely to preserve aggregation (the plan leaves 'holes' for is likely to preserve aggregation (the plan leaves 'holes' for
growth) growth)
o ULA usage in large networks - Networks which have a large number o ULA usage in large networks - Networks which have a large number
of 'sites' that each deploy a ULA prefix which will by default be of 'sites' that each deploy a ULA prefix which will by default be
a 'random' /48 under fc00::/7 will have no aggregation of those a 'random' /48 under fc00::/7 will have no aggregation of those
prefixes. Thus the end result may be cumbersome because the prefixes. Thus the end result may be cumbersome because the
network will have large amounts of non-aggregated ULA prefixes. network will have large amounts of non-aggregated ULA prefixes.
However, there is no rule to disallow large networks to use a However, there is no rule to disallow large networks to use a
single ULA for all 'sites', as a ULA still provides 16 bits for single ULA for all 'sites', as a ULA still provides 16 bits for
subnetting to be used internally subnetting to be used internally
o It is possible that as registry policies evolve, a small site may
experience an increase in prefix length when renumbering, e.g.
from /48 to /56. For this reason, the best practice is number
subnets compactly rather than sparsely, and to use low-order bits
as much as possible when numbering subnets. In other words, even
if a /48 is allocated, act as though only a /56 is available.
Clearly, this advice does not apply to large sites and enterprises
that have an intrinsic need for a /48 prefix.
2.4.1. Sizing the Network Allocation 2.4.1. Sizing the Network Allocation
We do not discuss here how a network designer sizes their application We do not discuss here how a network designer sizes their application
for address space. By default a site will receive a /48 prefix [9] , for address space. By default a site will receive a /48 prefix [9] ,
however different RIR service regions policies may suggest however different RIR service regions policies may suggest
alternative default assignments or let the ISPs to decide on what alternative default assignments or let the ISPs to decide on what
they believe is more appropriate for their specific case [28]. The they believe is more appropriate for their specific case [28]. The
default provider allocation via the RIRs is currently a /32 [31]. default provider allocation via the RIRs is currently a /32 [31].
These allocations are indicators for a first allocation for a These allocations are indicators for a first allocation for a
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Despite the large IPv6 address space which enables easier subnetting, Despite the large IPv6 address space which enables easier subnetting,
it still is important to ensure an efficient use of this resource. it still is important to ensure an efficient use of this resource.
Some addressing schemes, while facilitating aggregation and Some addressing schemes, while facilitating aggregation and
management, could lead to significant numbers of addresses being management, could lead to significant numbers of addresses being
unused. Address conservation requirements are less stringent in IPv6 unused. Address conservation requirements are less stringent in IPv6
but they should still be observed. but they should still be observed.
The proposed HD [10] value for IPv6 is 0.94 compared to the current The proposed HD [10] value for IPv6 is 0.94 compared to the current
value of 0.96 for IPv4. Note that for IPv6 HD is calculated for value of 0.96 for IPv4. Note that for IPv6 HD is calculated for
sites (i.e. on a basis of /48), instead of based on addresses like sites (e.g. on a basis of /48), instead of based on addresses like
with IPv4. with IPv4.
3. Subnet Prefix Considerations 3. Subnet Prefix Considerations
This section analyzes the considerations applied to define the subnet This section analyzes the considerations applied to define the subnet
prefix of the IPv6 addresses. The boundaries of the subnet prefix prefix of the IPv6 addresses. The boundaries of the subnet prefix
allocation are specified in RFC4291 [26]. In this document we allocation are specified in RFC4291 [26]. In this document we
analyze their practical implications. Based on RFC4291 [26] it is analyze their practical implications. Based on RFC4291 [26] it is
legal for any IPv6 unicast address starting with binary address '000' legal for any IPv6 unicast address starting with binary address '000'
to have a subnet prefix larger than, smaller than or of equal to 64 to have a subnet prefix larger than, smaller than or of equal to 64
bits. Each of these three options is discussed in this document. bits. Each of these three options is discussed in this document.
3.1. Considerations for subnet prefixes shorter then /64 3.1. Considerations for subnet prefixes shorter then /64
An allocation of a prefix shorter then 64 bits to a node or interface An allocation of a prefix shorter then 64 bits to a node or interface
is considered bad practice. The shortest subnet prefix that could is considered bad practice. One exception to this statement is when
theoretically be assigned to an interface or node is limited by the using 6to4 technology where a /16 prefix is utilised for the pseudo-
size of the network prefix allocated to the organization. One interface [8]. The shortest subnet prefix that could theoretically
exception to this recommendation is when using 6to4 technology where be assigned to an interface or node is limited by the size of the
a /16 prefix is utilised for the pseudo-interface [8]. network prefix allocated to the organization.
A possible reason for choosing the subnet prefix for an interface A possible reason for choosing the subnet prefix for an interface
shorter then /64 is that it would allow more nodes to be attached to shorter then /64 is that it would allow more nodes to be attached to
that interface compared to a prescribed length of 64 bits. This that interface compared to a prescribed length of 64 bits. This
however is unnecessary considering that 2^64 provides plenty of node however is unnecessary for most networks considering that 2^64
addresses for a well designed IPv6 network. Layer two technologies provides plenty of node addresses.
are unlikely to support such large numbers of nodes within a single
link (e.g. Ethernet limited to 48-bits of hosts)
The subnet prefix assignments can be made either by manual The subnet prefix assignments can be made either by manual
configuration, by a stateful Host Configuration Protocol [11] or by a configuration, by a stateful Host Configuration Protocol [11], by a
stateful prefix delegation mechanism [16]. stateful prefix delegation mechanism [16] or implied by stateless
autoconfiguration from prefix RAs.
3.2. Considerations for /64 prefixes 3.2. Considerations for /64 prefixes
Based on RFC3177 [9], 64 bits is the prescribed subnet prefix length Based on RFC3177 [9], 64 bits is the prescribed subnet prefix length
to allocate to interfaces and nodes. to allocate to interfaces and nodes.
When using a /64 subnet length, the address assignment for these When using a /64 subnet length, the address assignment for these
addresses can be made either by manual configuration, by a stateful addresses can be made either by manual configuration, by a stateful
Host Configuration Protocol [11] [18] or by stateless Host Configuration Protocol [11] [18] or by stateless
autoconfiguration [2]. autoconfiguration [2].
Note that RFC3177 strongly prescribes 64 bit subnets for general Note that RFC3177 strongly prescribes 64 bit subnets for general
usage, and that stateless autoconfiguration option is only defined usage, and that stateless autoconfiguration option is only defined
for 64 bit subnets. for 64 bit subnets. However, implementations could use proprietary
mechanism for stateless autoconfiguration for different then 64 bit
prefix length.
3.3. Considerations for subnet prefixes longer then /64 3.3. Considerations for subnet prefixes longer then /64
Address space conservation is the main motivation for using a subnet Address space conservation is the main motivation for using a subnet
prefix length longer than 64 bits. prefix length longer than 64 bits, however this kind of address
conservation is of futile benefit compared with the additional
considerations one must make when creating and maintain an IPv6
address plan.
The address assignment can be made either by manual configuration or The address assignment can be made either by manual configuration or
by a stateful Host Configuration Protocol [11]. by a stateful Host Configuration Protocol [11].
When assigning a subnet prefix of more then 80 bits, according to When assigning a subnet prefix of more then 80 bits, according to
RFC4291 [26] "u" and "g" bits (respectively the 81st and 82nd bit) RFC4291 [26] "u" and "g" bits (respectively the 81st and 82nd bit)
need to be taken into consideration and should be set correctly. In need to be taken into consideration and should be set correctly. In
currently implemented IPv6 protocol stacks, the relevance of the "u" currently implemented IPv6 protocol stacks, the relevance of the "u"
(universal/local) bit and "g" (the individual/group) bit are marginal (universal/local) bit and "g" (the individual/group) bit are marginal
and typically will not show an issue when configured wrongly, however and typically will not show an issue when configured wrongly, however
skipping to change at page 10, line 29 skipping to change at page 11, line 10
3.3.1.1. Subnet Router Anycast Address 3.3.1.1. Subnet Router Anycast Address
RFC4291 [26] provides a definition for the required Subnet Router RFC4291 [26] provides a definition for the required Subnet Router
Anycast Address as follows: Anycast Address as follows:
| n bits | 128-n bits | | n bits | 128-n bits |
+--------------------------------------------+----------------+ +--------------------------------------------+----------------+
| subnet prefix | 00000000000000 | | subnet prefix | 00000000000000 |
+--------------------------------------------+----------------+ +--------------------------------------------+----------------+
It is recommended to avoid allocating this IPv6 address to a device It is recommended to avoid allocating this IPv6 address to an device
which is not a router. No additional dependencies for the subnet which expects to have a normal unicast address. No additional
prefix while the EUI-64 and an IID dependencies will be discussed dependencies for the subnet prefix while the EUI-64 and IID
later in this document. dependencies will be discussed later in this document.
3.3.1.2. Reserved IPv6 Subnet Anycast Addresses 3.3.1.2. Reserved IPv6 Subnet Anycast Addresses
RFC2526 [4] stated that within each subnet, the highest 128 interface RFC2526 [4] stated that within each subnet, the highest 128 interface
identifier values are reserved for assignment as subnet anycast identifier values are reserved for assignment as subnet anycast
addresses. addresses.
The construction of a reserved subnet anycast address depends on the The construction of a reserved subnet anycast address depends on the
type of IPv6 addresses used within the subnet, as indicated by the type of IPv6 addresses used within the subnet, as indicated by the
format prefix in the addresses. format prefix in the addresses.
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This format implies that when selecting subnet prefixes longer then This format implies that when selecting subnet prefixes longer then
64, and the bits beyond the 64th one are non-zero, the subnet can not 64, and the bits beyond the 64th one are non-zero, the subnet can not
use embedded-RP. use embedded-RP.
In addition it is discouraged to assign a matching embedded-RP IPv6 In addition it is discouraged to assign a matching embedded-RP IPv6
address to a device that is not a real Multicast Rendezvous Point, address to a device that is not a real Multicast Rendezvous Point,
eventhough it would not generate major problems. eventhough it would not generate major problems.
3.3.3. ISATAP addresses 3.3.3. ISATAP addresses
ISATAP [25] is an automatic tunneling protocol used to provide IPv6 ISATAP [25] is an experimental automatic tunneling protocol used to
connectivity over an IPv4 campus or enterprise environment. In order provide IPv6 connectivity over an IPv4 campus or enterprise
to leverage the underlying IPv4 infrastructure, the IPv6 addresses environment. In order to leverage the underlying IPv4
are constructed in a special format. infrastructure, the IPv6 addresses are constructed in a special
format.
An IPv6 ISATAP address has the IPv4 address embedded, based on a An IPv6 ISATAP address has the IPv4 address embedded, based on a
predefined structure policy that identifies them as an ISATAP predefined structure policy that identifies them as an ISATAP
address. address.
[IPv6 Prefix (64 bits)][0000:5EFE][IPv4 address] [IPv6 Prefix (64 bits)][0000:5EFE][IPv4 address]
When using subnet prefix length longer then 64 bits it is good
engineering practice that the portion of the IPv6 prefix from bit 65
to the end of the host-id does not match with the well-known ISATAP
[0000:5EFE] address when assigning an IPv6 address to a non-ISATAP
interface.
When using subnet prefix length longer then 64 bits it is recommended In its actual definition there is no multicast support on ISATAP.
that that the portion of the IPv6 prefix from bit 65 to the end of
the subnet prefix does not match with the well-known ISATAP [0000:
5EFE] address portion.
In its actual definition there is no multicast support on ISATAP
3.3.4. /126 addresses 3.3.4. /126 addresses
The 126 bit subnet prefixes are typically used for point-to-point The 126 bit subnet prefixes are typically used for point-to-point
links similar to a the IPv4 address conservative /30 allocation for links similar to a the IPv4 address conservative /30 allocation for
point-to-point links. The usage of this subnet address length does point-to-point links. The usage of this subnet address length does
not lead to any additional considerations other than the ones not lead to any additional considerations other than the ones
discussed earlier in this section, particularly those related to the discussed earlier in this section, particularly those related to the
"u" and "g" bits. "u" and "g" bits.
skipping to change at page 13, line 41 skipping to change at page 14, line 21
from that moment onward assign the remaining 64 IID bits in a from that moment onward assign the remaining 64 IID bits in a
stateless manner. All the considerations for selecting a valid IID stateless manner. All the considerations for selecting a valid IID
have been incorporated in the EUI-64 methodology. have been incorporated in the EUI-64 methodology.
4.2. Using Privacy Extensions 4.2. Using Privacy Extensions
The main purpose of IIDs generated based on RFC3041 [6] is to provide The main purpose of IIDs generated based on RFC3041 [6] is to provide
privacy to the entity using this address. While there are no privacy to the entity using this address. While there are no
particular constraints in the usage of these addresses as defined in particular constraints in the usage of these addresses as defined in
[6] there are some implications to be aware of when using privacy [6] there are some implications to be aware of when using privacy
addresses as documented in section 4 of RFC3041 [6]: addresses as documented in section 4 of RFC3041 [6]
o The privacy extension algorithm may complicate flexibility in
future transport protocols
o These addresses may add complexity to the operational management
and troubleshooting of the infrastructure (i.e. which address
belongs to which real host)
o A reverse DNS lookup check may be broken when using privacy
extensions
4.3. Cryptographically Generated IPv6 Addresses
Cryptographically Generated Addresses (CGAs) are based upon RFC3972
[22] and provide a method for binding a public signature key to an
IPv6 address in the Secure Neighbor Discovery (SEND) protocol [21].
The basic idea is to generate the interface identifier (i.e. the
rightmost 64 bits) of the IPv6 address by computing a cryptographic
hash of the public key. The resulting IPv6 address is called a
cryptographically generated address (CGA). The corresponding private
key can then be used to sign messages sent from that address.
Implications to be aware of when using CGA addresses are found in
section 7 of RFC3972 [22]:
o When using CGA addresses the values of the "u" and "g" bits are
ignored however it does not add any security or implementation
implications
o There is no mechanism for proving that an address is not a CGA
o When it is discovered that a node has been compromised, a new
signature key and a new CGA should be generated
Due to the fact that CGA generated addresses are almost
indistinguishable from a privacy address and has similar properties
for many purposes, the same considerations as with privacy addresses
are also valid for CGA generated addresses.
4.4. Manual/Dynamic Assignment Option 4.3. Manual/Dynamic Assignment Option
This section discusses those IID allocations that are not implemented This section discusses those IID allocations that are not implemented
through stateless address configuration (Section 4.1). They are through stateless address configuration (Section 4.1). They are
applicable regardless of the prefix length used on the link. It is applicable regardless of the prefix length used on the link. It is
out of scope for this section to discuss the various assignment out of scope for this section to discuss the various assignment
methods (e.g. manual configuration, DHCPv6, etc). methods (e.g. manual configuration, DHCPv6, etc).
In this situation the actual allocation is done by human intervention In this situation the actual allocation is done by human intervention
and consideration needs to be given to the complete IPv6 address so and consideration needs to be given to the complete IPv6 address so
that it does not result in overlaps with any of the well known IPv6 that it does not result in overlaps with any of the well known IPv6
skipping to change at page 15, line 6 skipping to change at page 14, line 47
o Addresses used by Embedded-RP o Addresses used by Embedded-RP
o ISATAP Addresses o ISATAP Addresses
When using an address assigned by human intervention it is When using an address assigned by human intervention it is
recommended to choose IPv6 addresses which are not obvious to guess recommended to choose IPv6 addresses which are not obvious to guess
and/or avoid any IPv6 addresses that embed IPv4 addresses used in the and/or avoid any IPv6 addresses that embed IPv4 addresses used in the
current infrastructure. Following these two recommendations will current infrastructure. Following these two recommendations will
make it more difficult for malicious third parties to guess targets make it more difficult for malicious third parties to guess targets
for attack, and thus reduce security threats to a certain extent. for attack, and thus reduce security threats to a certain extent.
5. Case Studies 5. IANA Considerations
5.1. Enterprise Considerations There are no extra IANA consideration for this document.
6. Security Considerations
This IPv6 addressing document does not have any direct impact on
Internet infrastructure security.
7. Acknowledgements
Constructive feedback and contributions have been received from Marla
Azinger, Stig Venaas, Pekka Savola, John Spence, Patrick Grossetete,
Carlos Garcia Braschi, Brian Carpenter, Mark Smith, Janos Mohacsi,
Jim Bound, Fred Templin and Ginny Listman.
8. References
8.1. Normative References
8.2. Informative References
[1] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E.
Lear, "Address Allocation for Private Internets", BCP 5,
RFC 1918, February 1996.
[2] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[3] Hinden, R., Fink, R., and J. Postel, "IPv6 Testing Address
Allocation", RFC 2471, December 1998.
[4] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast
Addresses", RFC 2526, March 1999.
[5] Retana, A., White, R., Fuller, V., and D. McPherson, "Using 31-
Bit Prefixes on IPv4 Point-to-Point Links", RFC 3021,
December 2000.
[6] Narten, T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001.
[7] Durand, A., Fasano, P., Guardini, I., and D. Lento, "IPv6
Tunnel Broker", RFC 3053, January 2001.
[8] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via
IPv4 Clouds", RFC 3056, February 2001.
[9] IAB and IESG, "IAB/IESG Recommendations on IPv6 Address
Allocations to Sites", RFC 3177, September 2001.
[10] Durand, A. and C. Huitema, "The H-Density Ratio for Address
Assignment Efficiency An Update on the H ratio", RFC 3194,
November 2001.
[11] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003.
[12] Draves, R., "Default Address Selection for Internet Protocol
version 6 (IPv6)", RFC 3484, February 2003.
[13] Blanchet, M., "A Flexible Method for Managing the Assignment of
Bits of an IPv6 Address Block", RFC 3531, April 2003.
[14] Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global Unicast
Address Format", RFC 3587, August 2003.
[15] Savola, P., "Use of /127 Prefix Length Between Routers
Considered Harmful", RFC 3627, September 2003.
[16] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host
Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[17] Fink, R. and R. Hinden, "6bone (IPv6 Testing Address
Allocation) Phaseout", RFC 3701, March 2004.
[18] Droms, R., "Stateless Dynamic Host Configuration Protocol
(DHCP) Service for IPv6", RFC 3736, April 2004.
[19] Huitema, C. and B. Carpenter, "Deprecating Site Local
Addresses", RFC 3879, September 2004.
[20] Savola, P. and B. Haberman, "Embedding the Rendezvous Point
(RP) Address in an IPv6 Multicast Address", RFC 3956,
November 2004.
[21] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[22] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[23] Baker, F., Lear, E., and R. Droms, "Procedures for Renumbering
an IPv6 Network without a Flag Day", RFC 4192, September 2005.
[24] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[25] Templin, F., Gleeson, T., Talwar, M., and D. Thaler, "Intra-
Site Automatic Tunnel Addressing Protocol (ISATAP)", RFC 4214,
October 2005.
[26] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[27] Chown, T., Venaas, S., and C. Strauf, "Dynamic Host
Configuration Protocol (DHCP): IPv4 and IPv6 Dual-Stack
Issues", RFC 4477, May 2006.
[28] ARIN, "http://www.arin.net/policy/nrpm.html#six54".
[29] De Clerq, J., Ooms, D., Prevost, S., and F. Le Faucheur,
"Connecting IPv6 Islands over IPv4 MPLS using IPv6 Provider
Edge Routers (6PE) (draft-ooms-v6ops-bgp-tunnel-06.txt)",
June 2006.
[30] Chown, T., "IPv6 Implications for TCP/UDP Port Scanning
(draft-ietf-v6ops-scanning-implications-00.txt)", June 2006.
[31] APNIC, ARIN, RIPE NCC, "IPv6 Address Allocation and Assignment
Policy (www.ripe.net/ripe/docs/ipv6policy.html)", January 2003.
[32] Chown, T., Thompson, M., Ford, A., and S. Venaas, "Things to
think about when Renumbering an IPv6 network
(draft-chown-v6ops-renumber-thinkabout-05.txt)", March 2007.
[33] "List of Internet-Drafts relevant to the Multi6-WG
(http://ops.ietf.org/multi6/draft-list.html )".
[34] Lear, E., "Things MULTI6 Developers should think about
(draft-ietf-multi6-things-to-think-about-01)", January 2005.
[35] Nordmark, E. and T. Li, "Threats relating to IPv6 multihoming
solutions (draft-ietf-multi6-multihoming-threats-03)",
January 2005.
Appendix A. Case Studies
This appendix contains two case studies for IPv6 addressing schemas
that have been based on the statements and considerations of this
draft. These case studies illustrate how this draft has been used in
two specific network scenarios. The case studies may serve as basic
considerations for an administrator who designs the IPv6 addressing
schema for an enterprise or ISP network, but are not intended to
serve as general design proposal for every kind of IPv6 network.
A.1. Enterprise Considerations
In this section we consider a case study of a campus network that is In this section we consider a case study of a campus network that is
deploying IPv6 in parallel with existing IPv4 protocols in a dual- deploying IPv6 in parallel with existing IPv4 protocols in a dual-
stack environment. The specific example is the University of stack environment. The specific example is the University of
Southampton (UK), focusing on a large department within that network. Southampton (UK), focusing on a large department within that network.
The deployment currently spans around 1,000 hosts and over 1,500 The deployment currently spans around 1,000 hosts and over 1,500
users. users.
5.1.1. Obtaining general IPv6 network prefixes A.1.1. Obtaining general IPv6 network prefixes
In the case of a campus network, the site will typically take its In the case of a campus network, the site will typically take its
connectivity from its National Research and Education Network (NREN). connectivity from its National Research and Education Network (NREN).
Southampton connects to JANET, the UK academic network, via its local Southampton connects to JANET, the UK academic network, via its local
regional network LeNSE. JANET currently has a /32 allocation from regional network LeNSE. JANET currently has a /32 allocation from
RIPE of 2001:630::/32. The current recommended practice is for sites RIPE of 2001:630::/32. The current recommended practice is for sites
to receive a /48 allocation, and on this basis Southampton has to receive a /48 allocation, and on this basis Southampton has
received such a prefix for its own use, specifically 2001:630: received such a prefix for its own use, specifically 2001:630:
d0::/48. The regional network also uses its own allocation from the d0::/48. The regional network also uses its own allocation from the
NREN provider. NREN provider.
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has advantages for multicast group address allocation. In IPv4 a has advantages for multicast group address allocation. In IPv4 a
site needs to use techniques like GLOP to pick a globally unique site needs to use techniques like GLOP to pick a globally unique
multicast group to use. This is problematic if the site does not use multicast group to use. This is problematic if the site does not use
BGP and have an ASN. In IPv6 unicast-prefix-based IPv6 multicast BGP and have an ASN. In IPv6 unicast-prefix-based IPv6 multicast
addresses empower a site to pick a globally unique group address addresses empower a site to pick a globally unique group address
based on its unicast own site or link prefix. Embedded RP is also in based on its unicast own site or link prefix. Embedded RP is also in
use, is seen as a potential advantage for IPv6 and multicast, and has use, is seen as a potential advantage for IPv6 and multicast, and has
been tested successfully across providers between sites (including been tested successfully across providers between sites (including
paths to/from the US and UK). paths to/from the US and UK).
5.1.2. Forming an address (subnet) allocation plan A.1.2. Forming an address (subnet) allocation plan
The campus has a /16 prefix for IPv4 use; in principle 256 subnets of The campus has a /16 prefix for IPv4 use; in principle 256 subnets of
256 addresses. In reality the subnetting is muddier, because of 256 addresses. In reality the subnetting is muddier, because of
concerns of IPv4 address conservation; subnets are sized to the hosts concerns of IPv4 address conservation; subnets are sized to the hosts
within them, e.g. a /26 IPv4 prefix is used if a subnet has 35 hosts within them, e.g. a /26 IPv4 prefix is used if a subnet has 35 hosts
in it. While this is efficient, it increases management burden when in it. While this is efficient, it increases management burden when
physical deployments change, and IPv4 subnets require resizing (up or physical deployments change, and IPv4 subnets require resizing (up or
down), even with DHCP in use. down), even with DHCP in use.
The /48 IPv6 prefix is considerably larger than the IPv4 allocation The /48 IPv6 prefix is considerably larger than the IPv4 allocation
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congruent addressing, our firewall policies are also aligned for IPv4 congruent addressing, our firewall policies are also aligned for IPv4
and IPv6 traffic at our site border. and IPv6 traffic at our site border.
The subnet allocation plan required a division of the address space The subnet allocation plan required a division of the address space
per school or department. Here a /56 was allocated to the school per school or department. Here a /56 was allocated to the school
level of the university; there are around 30 schools currently. A level of the university; there are around 30 schools currently. A
/56 of IPv6 address space equates to 256 /64 size subnet allocations. /56 of IPv6 address space equates to 256 /64 size subnet allocations.
Further /56 allocations were made for central IT infrastructure, for Further /56 allocations were made for central IT infrastructure, for
the network infrastructure and the server side systems. the network infrastructure and the server side systems.
5.1.3. Other considerations A.1.3. Other considerations
The network uses a Demilitarized Zone (DMZ) topology for some level The network uses a Demilitarized Zone (DMZ) topology for some level
of protection of 'public' systems. Again, this topology is congruent of protection of 'public' systems. Again, this topology is congruent
with the IPv4 network. with the IPv4 network.
There are no specific transition methods deployed internally to the There are no specific transition methods deployed internally to the
campus; everything is using the conventional dual-stack approach. campus; everything is using the conventional dual-stack approach.
There is no use of ISATAP [25] for example. There is no use of ISATAP [25] for example.
For the Mobile IPv6 early trials, we have allocated one prefix for For the Mobile IPv6 early trials, we have allocated one prefix for
Home Agent (HA) use. We have not yet considered in detail how Mobile Home Agent (HA) use. We have not yet considered in detail how Mobile
IPv6 usage may grow, and whether more or even every subnet will IPv6 usage may grow, and whether more or even every subnet will
require HA support. require HA support.
The university operates a tunnel broker [7] service on behalf of The university operates a tunnel broker [7] service on behalf of
UKERNA for JANET sites. This uses separate address space from JANET, UKERNA for JANET sites. This uses separate address space from JANET,
not our university site allocation. not our university site allocation.
5.1.4. Node configuration considerations A.1.4. Node configuration considerations
We currently use stateless autoconfiguration on most subnets for IPv6 We currently use stateless autoconfiguration on most subnets for IPv6
hosts. There is no DHCPv6 service deployed yet, beyond tests of hosts. There is no DHCPv6 service deployed yet, beyond tests of
early code releases. We plan to deploy DHCPv6 for address assignment early code releases. We plan to deploy DHCPv6 for address assignment
when robust client and server code is available (at the time of when robust client and server code is available (at the time of
writing the potential for this looks good, e.g. via the ISC writing the potential for this looks good, e.g. via the ISC
implementation). We also are seeking a common integrated DHCP/DNS implementation). We also are seeking a common integrated DHCP/DNS
management platform, even if the servers themselves are not co- management platform, even if the servers themselves are not co-
located, including integrated DHCPv4 and DHCPv6 server configuration, located, including integrated DHCPv4 and DHCPv6 server configuration,
as discussed in [27]. Currently we add client statelessly as discussed in [27]. Currently we add client statelessly
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physical hosts are using which addresses. We note that RFC3041 is physical hosts are using which addresses. We note that RFC3041 is
only an issue for outbound connections, and that there is potential only an issue for outbound connections, and that there is potential
to assign privacy addresses via DHCPv6. to assign privacy addresses via DHCPv6.
We manually configure server addresses to avoid address changes on a We manually configure server addresses to avoid address changes on a
change of network adaptor. With IPv6 you can choose to pick ::53 for change of network adaptor. With IPv6 you can choose to pick ::53 for
a DNS server, or can pick 'random' addresses for obfuscation, though a DNS server, or can pick 'random' addresses for obfuscation, though
that's not an issue for publicly advertised addresses (dns, mx, web, that's not an issue for publicly advertised addresses (dns, mx, web,
etc). etc).
5.2. Service Provider Considerations A.2. Service Provider Considerations
In this section an IPv6 addressing schema is sketched that could In this section an IPv6 addressing schema is sketched that could
serve as an example for an Internet Service Provider. serve as an example for an Internet Service Provider.
Sub-section 5.2.1 starts with some thoughts regarding objective Sub-section A.2.1 starts with some thoughts regarding objective
requirements of such an addressing schema and derives a few general requirements of such an addressing schema and derives a few general
thumb rules that have to be kept in mind when designing an ISP IPv6 thumb rules that have to be kept in mind when designing an ISP IPv6
addressing plan. addressing plan.
Sub-section 5.2.2 illustrates these findings of 5.2.1 with an Sub-section A.2.2 illustrates these findings of A.2.1 with an
exemplary IPv6 addressing schema for an MPLS-based ISP offering exemplary IPv6 addressing schema for an MPLS-based ISP offering
Internet Services as well as Network Access services to several Internet Services as well as Network Access services to several
millions of customers. millions of customers.
5.2.1. Investigation of objective Requirements for an IPv6 addressing A.2.1. Investigation of objective Requirements for an IPv6 addressing
schema of a Service Provider schema of a Service Provider
The first step of the IPv6 addressing plan design for a Service The first step of the IPv6 addressing plan design for a Service
provider should identify all technical, operational, political and provider should identify all technical, operational, political and
business requirements that have to be satisfied by the services business requirements that have to be satisfied by the services
supported by this addressing schema. supported by this addressing schema.
According to the different technical constraints and business models According to the different technical constraints and business models
as well as the different weights of these requirements (from the as well as the different weights of these requirements (from the
point of view of the corresponding Service Provider) it is very point of view of the corresponding Service Provider) it is very
likely that different addressing schemas will be developed and likely that different addressing schemas will be developed and
deployed by different ISPs. Nevertheless the addressing schema of deployed by different ISPs. Nevertheless the addressing schema of
sub-section 5.2.2 is one possible example. sub-section A.2.2 is one possible example.
For this document it is assumed that our exemplary ISP has to fulfill For this document it is assumed that our exemplary ISP has to fulfill
several roles for its customers as there are: several roles for its customers as there are:
o Local Internet Registry o Local Internet Registry
o Network Access Provider o Network Access Provider
o Internet Service Provider o Internet Service Provider
5.2.1.1. Requirements for an IPv6 addressing schema from the LIR A.2.1.1. Requirements for an IPv6 addressing schema from the LIR
perspective of the Service Provider perspective of the Service Provider
In their role as LIR the Service Providers have to care about the In their role as LIR the Service Providers have to care about the
policy constraints of the RIRs and the standards of the IETF policy constraints of the RIRs and the standards of the IETF
regarding IPv6 addressing. In this context, the following basic regarding IPv6 addressing. In this context, the following basic
requirements and recommendations have to be considered and should be requirements and recommendations have to be considered and should be
satisfied by the IPv6 address allocation plan of a Service Provider: satisfied by the IPv6 address allocation plan of a Service Provider:
o As recommended in RFC 3177 [9] and in several RIR policies o As recommended in RFC 3177 [9] and in several RIR policies
"Common" customers sites (normally private customers) should "Common" customers sites (normally private customers) should
receive a /48 prefix from the aggregate of the Service Provider. receive a /48 prefix from the aggregate of the Service Provider.
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ratio that is proposed for IPv6. This requirement corresponds to ratio that is proposed for IPv6. This requirement corresponds to
the demand for an efficient usage of the IPv6 address aggregate by the demand for an efficient usage of the IPv6 address aggregate by
the Service Provider. (Note: The currently valid IPv6 HD-ratio of the Service Provider. (Note: The currently valid IPv6 HD-ratio of
0.94 means an effective usage of about 31% of a /20 prefix of the 0.94 means an effective usage of about 31% of a /20 prefix of the
Service Provider on the basis of /48 assignments.) Service Provider on the basis of /48 assignments.)
o All assignments to customers have to be documented and stored into o All assignments to customers have to be documented and stored into
a database that can also be queried by the RIR. a database that can also be queried by the RIR.
o The LIR has to make available means for supporting the reverse DNS o The LIR has to make available means for supporting the reverse DNS
mapping of the customer prefixes. mapping of the customer prefixes.
5.2.1.2. IPv6 addressing schema requirements from the ISP perspective A.2.1.2. IPv6 addressing schema requirements from the ISP perspective
of the Service Provider of the Service Provider
From ISP perspective the following basic requirements could be From ISP perspective the following basic requirements could be
identified: identified:
o The IPv6 address allocation schema must be able to realize a o The IPv6 address allocation schema must be able to realize a
maximal aggregation of all IPv6 address delegations to customers maximal aggregation of all IPv6 address delegations to customers
into the address aggregate of the Service Provider. Only this into the address aggregate of the Service Provider. Only this
provider aggregate will be routed and injected into the global provider aggregate will be routed and injected into the global
routing table (DFZ). This strong aggregation keeps the routing routing table (DFZ). This strong aggregation keeps the routing
tables of the DFZ small and eases filtering and access control tables of the DFZ small and eases filtering and access control
very much. very much.
o The IPv6 addressing schema of the SP should contain maximal o The IPv6 addressing schema of the SP should contain optimal
flexibility since the infrastructure of the SP will change over flexibility since the infrastructure of the SP will change over
the time with new customers, transport technologies and business the time with new customers, transport technologies and business
cases. The requirement of maximal flexibility is contrary to the cases. The requirement of optimal flexibility is contrary to the
requirements of strong IPv6 address aggregation and efficient requirements of strong IPv6 address aggregation and efficient
address usage, but at this point each SP has to decide which of address usage, but at this point each SP has to decide which of
these requirements to prioritize. these requirements to prioritize.
o Keeping the multilevel network hierarchy of an ISP in mind, due to o Keeping the multilevel network hierarchy of an ISP in mind, due to
addressing efficiency reasons not all hierarchy levels can and addressing efficiency reasons not all hierarchy levels can and
should be mapped into the IPv6 addressing schema of an ISP. should be mapped into the IPv6 addressing schema of an ISP.
Sometimes it is much better to implement "flat" addressing for the Sometimes it is much better to implement a more "flat" addressing
ISP network than to loose big chunks of the IPv6 address aggregate for the ISP network than to loose big chunks of the IPv6 address
in addressing each level of network hierarchy. Besides that a aggregate in addressing each level of network hierarchy. (Note:
decoupling of provider network addressing and customer addressing In special cases it is even recommendable for really "small" ISPs
is recommended. (Note: A strong aggregation e.g. on POP, to design and implement a totally flat IPv6 addressing schema
aggregation router or Label Edge Router (LER) level limits the without any level of hierarchy.)
numbers of customer routes that are visible within the ISP network o Besides that a decoupling of provider network addressing and
but brings also down the efficiency of the IPv6 addressing schema. customer addressing is recommended. (Note: A strong aggregation
That's why each ISP has to decide how many internal aggregation e.g. on POP, aggregation router or Label Edge Router (LER) level
levels it wants to deploy.) limits the numbers of customer routes that are visible within the
ISP network but brings also down the efficiency of the IPv6
addressing schema. That's why each ISP has to decide how many
internal aggregation levels it wants to deploy.)
5.2.1.3. IPv6 addressing schema requirements from the Network Access A.2.1.3. IPv6 addressing schema requirements from the Network Access
provider perspective of the Service Provider provider perspective of the Service Provider
As already done for the LIR and the ISP roles of the SP it is also As already done for the LIR and the ISP roles of the SP it is also
necessary to identify requirements that come from its Network Access necessary to identify requirements that come from its Network Access
Provider role. Some of the basic requirements are: Provider role. Some of the basic requirements are:
o The IPv6 addressing schema of the SP must be flexible enough to o The IPv6 addressing schema of the SP must be chosen in a way that
adapt changes that are injected from the customer side. This it can handle new requirements that are triggered from customer
covers changes to addressing architecture or routing topology that side. This can be for instance the growing needs of the customers
are triggered from for instance the growing needs of the customers regarding IPv6 addresses as well as customer driven modifications
regarding IPv6 addresses as well as changes that come from within the access network topology (e.g. when the customer moves
topological modifications (e.g. when the customer moves from one from one point of network attachment (POP) to another). (See
point of network attachment (POP) to another). section A.2.3.4 "Changing Point of Network Attachment".)
o For each IPv6 address assignment to customers a "buffer zone" must o For each IPv6 address assignment to customers a "buffer zone"
be reserved that allows the customer to grow in its addressing should be reserved that allows the customer to grow in its
range without renumbering or assignment of additional prefixes. addressing range without renumbering or assignment of additional
prefixes.
o The IPv6 addressing schema of the SP must deal with multiple- o The IPv6 addressing schema of the SP must deal with multiple-
attachments of a single customer to the SP network infrastructure attachments of a single customer to the SP network infrastructure
(i.e. multi-homed network access with the same SP). (i.e. multi-homed network access with the same SP).
These few requirements are only part of all the requirements a These few requirements are only part of all the requirements a
Service Provider has to investigate and keep in mind during the Service Provider has to investigate and keep in mind during the
definition phase of its addressing architecture. Each SP will most definition phase of its addressing architecture. Each SP will most
likely add more constraints to this list. likely add more constraints to this list.
5.2.1.4. A few thumb rules for designing an IPv6 ISP addressing A.2.1.4. A few thumb rules for designing an IPv6 ISP addressing
architecture architecture
As outcome of the above enumeration of requirements regarding an ISP As outcome of the above enumeration of requirements regarding an ISP
IPv6 addressing plan the following design "thumb rules" have been IPv6 addressing plan the following design "thumb rules" have been
derived: derived:
o No "One size fits all" Each ISP must develop its own IPv6 address o No "One size fits all". Each ISP must develop its own IPv6
allocation schema depending on its concrete business needs. It is address allocation schema depending on its concrete business
not practicable to design one addressing plan that fits for all needs. It is not practicable to design one addressing plan that
kinds of ISPs (Small / big, Routed / MPLS-based, access / transit, fits for all kinds of ISPs (Small / big, Routed / MPLS-based,
LIR / No-LIR, etc.). access / transit, LIR / No-LIR, etc.).
o The levels of IPv6 address aggregation within the ISP addressing o The levels of IPv6 address aggregation within the ISP addressing
schema should strongly correspond to the implemented network schema should strongly correspond to the implemented network
structure and their number should be minimized because of structure and their number should be minimized because of
efficiency reasons. It is assumed that the SPs own infrastructure efficiency reasons. It is assumed that the SPs own infrastructure
will be addressed in a fairly flat way whereas the part of the will be addressed in a fairly flat way whereas the part of the
customer addressing architecture should contain several levels of customer addressing architecture should contain several levels of
aggregation. aggregation.
o Keep the number of IPv6 customer routes inside your network as o Keep the number of IPv6 customer routes inside your network as
small as necessary. A totally flat customer IPv6 addressing small as necessary. A totally flat customer IPv6 addressing
architecture without any intermediate aggregation level will lead architecture without any intermediate aggregation level will lead
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o The ISP IPv6 addressing schema should provide maximal flexibility. o The ISP IPv6 addressing schema should provide maximal flexibility.
This has to be realized for supporting different sizes of customer This has to be realized for supporting different sizes of customer
IPv6 address aggregates ("big" customers vs. "small" customers) as IPv6 address aggregates ("big" customers vs. "small" customers) as
well as to allow future growing rates (e.g. of customer well as to allow future growing rates (e.g. of customer
aggregates) and possible topological or infrastructural changes. aggregates) and possible topological or infrastructural changes.
o A limited number of aggregation levels and sizes of customer o A limited number of aggregation levels and sizes of customer
aggregates will ease the management of the addressing schema. aggregates will ease the management of the addressing schema.
This has to be weighed against the previous "thumb rule" - This has to be weighed against the previous "thumb rule" -
flexibility. flexibility.
5.2.2. Exemplary IPv6 address allocation plan for a Service Provider A.2.2. Exemplary IPv6 address allocation plan for a Service Provider
In this example, the Service Provider is assumed to operate an MPLS In this example, the Service Provider is assumed to operate an MPLS
based backbone and implements 6PE [29] to provide IPv6 backbone based backbone and implements 6PE [29] to provide IPv6 backbone
transport between the different locations (POPs) of a fully dual- transport between the different locations (POPs) of a fully dual-
stacked network access and aggregation area. stacked network access and aggregation area.
Besides that it is assumed that the Service Provider: Besides that it is assumed that the Service Provider:
o has received a /20 from its RIR o has received a /20 from its RIR
o operates its own LIR o operates its own LIR
o has to address its own IPv6 infrastructure o has to address its own IPv6 infrastructure
o delegates prefixes from this aggregate to its customers o delegates prefixes from this aggregate to its customers
This addressing schema should illustrate how the /20 IPv6 prefix of This addressing schema should illustrate how the /20 IPv6 prefix of
the SP can be used to address the SP-own infrastructure and to the SP can be used to address the SP-own infrastructure and to
delegate IPv6 prefixes to its customers following the above mentioned delegate IPv6 prefixes to its customers following the above mentioned
requirements and thumb rules as far as possible. requirements and thumb rules as far as possible.
The below figure summarizes the device types in an SP network and the The below figure summarizes the device types in a SP network and the
typical network design of a MPLS-based service provider. The network typical network design of a MPLS-based service provider. The network
hierarchy of the SP has to be taken into account for the design of an hierarchy of the SP has to be taken into account for the design of an
IPv6 addressing schema and defines its basic shape and the various IPv6 addressing schema and defines its basic shape and the various
levels of aggregation. levels of aggregation.
+------------------------------------------------------------------+ +------------------------------------------------------------------+
| LSRs of the MPLS Backbone of the SP | | LSRs of the MPLS Backbone of the SP |
+------------------------------------------------------------------+ +------------------------------------------------------------------+
| | | | | | | | | |
| | | | | | | | | |
skipping to change at page 22, line 47 skipping to change at page 25, line 46
Basic design decisions for the exemplary Service Provider IPv6 Basic design decisions for the exemplary Service Provider IPv6
address plan regarding customer prefixes take into consideration: address plan regarding customer prefixes take into consideration:
o The prefixes assigned to all customers behind the same LER (e.g. o The prefixes assigned to all customers behind the same LER (e.g.
LER or LER-BB) are aggregated under one LER prefix. This ensures LER or LER-BB) are aggregated under one LER prefix. This ensures
that the number of labels that have to be used for 6PE is limited that the number of labels that have to be used for 6PE is limited
and hence provides a strong MPLS label conservation. and hence provides a strong MPLS label conservation.
o The /20 prefix of the SP is separated into 3 different pools that o The /20 prefix of the SP is separated into 3 different pools that
are used to allocate IPv6 prefixes to the customers of the SP: are used to allocate IPv6 prefixes to the customers of the SP:
* A pool (e.g. /24) for satisfying the addressing needs of really * A pool (e.g. /24) for satisfying the addressing needs of really
"big" customers (as defined in 5.2.2.1 sub-section A.) that "big" customers (as defined in A.2.2.1 sub-section A.) that
need IPv6 prefixes larger than /48 (e.g. /32). These customers need IPv6 prefixes larger than /48 (e.g. /32). These customers
are assumed to be connected to several POPs of the access are assumed to be connected to several POPs of the access
network, so that this customer prefix will be visible in each network, so that this customer prefix will be visible in each
of these POPs. of these POPs.
* A pool (e.g. /24) for the LERs with direct customer connections * A pool (e.g. /24) for the LERs with direct customer connections
(e.g. dedicated line access) and without an additional (e.g. dedicated line access) and without an additional
aggregation area between the customer and the LER. (These LERs aggregation area between the customer and the LER. (These LERs
are mostly connected to a limited number of customers because are mostly connected to a limited number of customers because
of the limited number of interfaces/ports.) of the limited number of interfaces/ports.)
* A larger pool (e.g. 14*/24) for LERs (e.g. LER-BB) that serve * A larger pool (e.g. 14*/24) for LERs (e.g. LER-BB) that serve
a high number of customers that are normally connected via some a high number of customers that are normally connected via some
kind of aggregation network (e.g. DSL customers behind a BB- kind of aggregation network (e.g. DSL customers behind a BB-
RAR or Dial-In customers behind a RAR). RAR or Dial-In customers behind a RAR).
* The IPv6 address delegation within each Pool (end customer * The IPv6 address delegation within each Pool (end customer
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kind of aggregation network (e.g. DSL customers behind a BB- kind of aggregation network (e.g. DSL customers behind a BB-
RAR or Dial-In customers behind a RAR). RAR or Dial-In customers behind a RAR).
* The IPv6 address delegation within each Pool (end customer * The IPv6 address delegation within each Pool (end customer
delegation or also the aggregates that are dedicated to the delegation or also the aggregates that are dedicated to the
LERs itself) should be chosen with an additional buffer zone of LERs itself) should be chosen with an additional buffer zone of
100% - 300% for future growth. I.e. 1 or 2 additional prefix 100% - 300% for future growth. I.e. 1 or 2 additional prefix
bits should be reserved according to the expected future growth bits should be reserved according to the expected future growth
rate of the corresponding customer / the corresponding network rate of the corresponding customer / the corresponding network
device aggregate. device aggregate.
5.2.2.1. Defining an IPv6 address allocation plan for customers of the A.2.2.1. Defining an IPv6 address allocation plan for customers of the
Service Provider Service Provider
5.2.2.1.1. 'Big' customers A.2.2.1.1. 'Big' customers
SP's "big" customers receive their prefix from the /24 IPv6 address SP's "big" customers receive their prefix from the /24 IPv6 address
aggregate that has been reserved for their "big" customers. A aggregate that has been reserved for their "big" customers. A
customer is considered as "big" customer if it has a very complex customer is considered as "big" customer if it has a very complex
network infrastructure and/or huge IPv6 address needs (e.g. because network infrastructure and/or huge IPv6 address needs (e.g. because
of very large customer numbers) and/or several uplinks to different of very large customer numbers) and/or several uplinks to different
POPs of the SP network. POPs of the SP network.
The assigned IPv6 address prefixes can have a prefix length in the The assigned IPv6 address prefixes can have a prefix length in the
range 32-48 and for each assignment a 100 or 300% future growing zone range 32-48 and for each assignment a 100 or 300% future growing zone
is marked as "reserved" for this customer. This means for instance is marked as "reserved" for this customer. This means for instance
that with a delegation of a /34 to a customer the corresponding /32 that with a delegation of a /34 to a customer the corresponding /32
prefix (which contains this /34) is reserved for the customers future prefix (which contains this /34) is reserved for the customers future
usage. usage.
The prefixes for the "big" customers can be chosen from the The prefixes for the "big" customers can be chosen from the
corresponding "big customer" pool by either using an equidistant corresponding "big customer" pool by either using an equidistant
algorithm or using mechanisms similar to the Sparse Allocation algorithm or using mechanisms similar to the Sparse Allocation
Algorithm (SAA) [31]. Algorithm (SAA) [31].
5.2.2.1.2. 'Common' customers A.2.2.1.2. 'Common' customers
All customers that are not "big" customers are considered as "common" All customers that are not "big" customers are considered as "common"
customers. They represent the majority of customers hence they customers. They represent the majority of customers hence they
receive a /48 out of the IPv6 customer address pool of the LER where receive a /48 out of the IPv6 customer address pool of the LER where
they are directly connected or aggregated. they are directly connected or aggregated.
Again a 100 - 300% future growing IPv6 address range is reserved for Again a 100 - 300% future growing IPv6 address range is reserved for
each customer, so that a "common" customer receives a /48 allocation each customer, so that a "common" customer receives a /48 allocation
but has a /47 or /46 reserved. but has a /47 or /46 reserved.
(Note: If it is obvious that the likelyhood of needing a /47 or /46
in the future is very small for a "common" customer, than no growing
buffer should be reserved for it and only a /48 will be assigned
without any growing buffer.)
In the network access scenarios where the customer is directly In the network access scenarios where the customer is directly
connected to the LER the customer prefix is directly taken out of the connected to the LER the customer prefix is directly taken out of the
customer IPv6 address aggregate (e.g. /38) of the corresponding LER. customer IPv6 address aggregate (e.g. /38) of the corresponding LER.
In all other cases (e.g. the customer is attached to a RAR that is In all other cases (e.g. the customer is attached to a RAR that is
themselves aggregated to an AG or to a LER) at least 2 different themselves aggregated to an AG or to a LER) at least 2 different
approaches are possible. approaches are possible.
1) Mapping of Aggregation Network Hierarchy into Customer IPv6 1) Mapping of Aggregation Network Hierarchy into Customer IPv6
Addressing Schema. The aggregation network hierarchy could be mapped Addressing Schema. The aggregation network hierarchy could be mapped
skipping to change at page 24, line 50 skipping to change at page 28, line 4
allocate all the customer prefixes directly out of the customer IPv6 allocate all the customer prefixes directly out of the customer IPv6
address pool of the LER where the customers are attached and address pool of the LER where the customers are attached and
aggregated and to ignore the intermediate aggregation network aggregated and to ignore the intermediate aggregation network
infrastructure. This approach leads of course to a higher amount of infrastructure. This approach leads of course to a higher amount of
customer routes at LER and aggregation network level but takes a customer routes at LER and aggregation network level but takes a
great amount of complexity out of the addressing schema. great amount of complexity out of the addressing schema.
Nevertheless the aggregation of the customer prefixes to one prefix Nevertheless the aggregation of the customer prefixes to one prefix
at LER level is realized as required above. at LER level is realized as required above.
(Note: The handling of (e.g. technically triggered) changes within (Note: The handling of (e.g. technically triggered) changes within
the ISP access network is shortly discussed in section 5.2.3.5.) the ISP access network is shortly discussed in section A.2.3.5.)
If the actual observed growing rates show that the reserved growing If the actual observed growing rates show that the reserved growing
zones are not needed than these growing areas can be freed and used zones are not needed than these growing areas can be freed and used
for assignments for prefix pools to other devices at the same level for assignments for prefix pools to other devices at the same level
of the network hierarchy. of the network hierarchy.
5.2.2.2. Defining an IPv6 address allocation plan for the Service A.2.2.2. Defining an IPv6 address allocation plan for the Service
Provider Network Infrastructure Provider Network Infrastructure
For the IPv6 addressing of SPs own network infrastructure a /32 (or For the IPv6 addressing of SPs own network infrastructure a /32 (or
/40) from the "big" customers address pool can be chosen. /40) from the "big" customers address pool can be chosen.
This SP infrastructure prefix is used to code the network This SP infrastructure prefix is used to code the network
infrastructure of the SP by assigning a /48 to every POP/location and infrastructure of the SP by assigning a /48 to every POP/location and
using for instance a /56 for coding the corresponding router within using for instance a /56 for coding the corresponding router within
this POP. Each SP internal link behind a router interface could be this POP. Each SP internal link behind a router interface could be
coded using a /64 prefix. (Note: While it is suggested to choose a coded using a /64 prefix. (Note: While it is suggested to choose a
skipping to change at page 25, line 45 skipping to change at page 28, line 47
(Note: The /32 prefix that has been chosen for addressing SPs own (Note: The /32 prefix that has been chosen for addressing SPs own
IPv6 network infrastructure gives enough place to code additional IPv6 network infrastructure gives enough place to code additional
functionalities like security levels or private and test functionalities like security levels or private and test
infrastructure although such approaches haven't been considered in infrastructure although such approaches haven't been considered in
more detail for the above described SP until now.) more detail for the above described SP until now.)
Point-to-point links to customers (e.g. PPP links, dedicated line Point-to-point links to customers (e.g. PPP links, dedicated line
etc.) may be addressed using /126 prefixes out of the first /64 of etc.) may be addressed using /126 prefixes out of the first /64 of
the access routers that could be reserved for this reason. the access routers that could be reserved for this reason.
5.2.3. Additional Remarks A.2.3. Additional Remarks
5.2.3.1. ULA A.2.3.1. ULA
From the actual view point of SP there is no compelling reason why From the actual view point of SP there is no compelling reason why
ULAs should be used from a SP. Look at section 2.2. ULAs should be used from a SP. Look at section 2.2.
ULAs could be used inside the SP network in order to have an ULAs could be used inside the SP network in order to have an
additional "site-local scoped" IPv6 address for SPs own additional "site-local scoped" IPv6 address for SPs own
infrastructure for instance for network management reasons and maybe infrastructure for instance for network management reasons and maybe
also in order to have an addressing schema that couldn't be reached also in order to have an addressing schema that couldn't be reached
from outside the SP network. from outside the SP network.
In the case when ULAs are used it is possible to map the proposed In the case when ULAs are used it is possible to map the proposed
internal IPv6 addressing of SPs own network infrastructure as internal IPv6 addressing of SPs own network infrastructure as
described in 5.2.2.2 above directly to the ULA addressing schema by described in A.2.2.2 above directly to the ULA addressing schema by
substituting the /48 POP prefix with a /48 ULA site prefix. substituting the /48 POP prefix with a /48 ULA site prefix.
5.2.3.2. Multicast A.2.3.2. Multicast
IPv6 Multicast-related addressing issues are out of the scope of this IPv6 Multicast-related addressing issues are out of the scope of this
document. document.
5.2.3.3. POP Multi-homing A.2.3.3. POP Multi-homing
POP (or better LER) Multi-homing of customers with the same SP can be POP (or better LER) Multi-homing of customers with the same SP can be
realized within the proposed IPv6 addressing schema of the SP by realized within the proposed IPv6 addressing schema of the SP by
assigning multiple LER-dependent prefixes to this customer (i.e. assigning multiple LER-dependent prefixes to this customer (i.e.
considering each customer location as a single-standing customer) or considering each customer location as a single-standing customer) or
by choosing a customer prefix out of the pool of "big" customers. by choosing a customer prefix out of the pool of "big" customers.
The second solution has the disadvantage that in every LER where the The second solution has the disadvantage that in every LER where the
customer is attached this prefix will appear inside the IGP routing customer is attached this prefix will appear inside the IGP routing
table requiring an explicit MPLS label. table requiring an explicit MPLS label.
(Note: The described negative POP/LER Multi-homing effects to the (Note: The described negative POP/LER Multi-homing effects to the
addressing architecture in the SP access network are not tackled by addressing architecture in the SP access network are not tackled by
implementing the Shim6 Site Multi-homing approach since this approach implementing the Shim6 Site Multi-homing approach since this approach
targets only on a mechanism for dealing with multiple prefixes in end targets only on a mechanism for dealing with multiple prefixes in end
systems -- the SP will nevertheless have unaggregated customer systems -- the SP will nevertheless have unaggregated customer
prefixes in its internal routing tables.) prefixes in its internal routing tables.)
5.2.3.4. Changing Point of Network Attachement A.2.3.4. Changing Point of Network Attachement
In the possible case that a customer has to change its point of In the possible case that a customer has to change its point of
network attachment to another POP/LER within the ISP access network network attachment to another POP/LER within the ISP access network
two different approaches can be applied assuming that the customer two different approaches can be applied assuming that the customer
uses PA addresses out of the SP aggregate: uses PA addresses out of the SP aggregate:
1.) The customer has to renumber its network with an adequate 1.) The customer has to renumber its network with an adequate
customer prefix out of the aggregate of the corresponding LER/RAR of customer prefix out of the aggregate of the corresponding LER/RAR of
its new network attachement. To minimise the administrative burden its new network attachement. To minimise the administrative burden
for the customer the prefix should be of the same size as the former. for the customer the prefix should be of the same size as the former.
This conserves the IPv6 address aggregation within the SP network This conserves the IPv6 address aggregation within the SP network
(and the MPLS label space) but adds additional burden to the (and the MPLS label space) but adds additional burden to the
customer. Hence this approach will most likely only be chosen in the customer. Hence this approach will most likely only be chosen in the
case of 'small customers' with temporary addressing needs and/or case of "small customers" with temporary addressing needs and/or
prefix delegation with address auto-configuration. prefix delegation with address auto-configuration.
2.) The customer does not need to renumber its network and keeps its 2.) The customer does not need to renumber its network and keeps its
address aggregate. address aggregate.
This apporach leads to additional more-specific routing entries This apporach leads to additional more-specific routing entries
within the IGP routing table of the LER and will hence consume within the IGP routing table of the LER and will hence consume
additional MPLS labels - but it is totally transparent to the additional MPLS labels - but it is totally transparent to the
customer. Because this results in additional administrative effort customer. Because this results in additional administrative effort
and will stress the router resources (label space, memory) of the ISP and will stress the router resources (label space, memory) of the ISP
this solution will only be offered to the most valuable customers of this solution will only be offered to the most valuable customers of
an ISP (like e.g. "big customers" or "enterprise customers"). an ISP (like e.g. "big customers" or "enterprise customers").
Nevertheless the ISP has again to find a fair trade-off between Nevertheless the ISP has again to find a fair trade-off between
customer renumbering and sub-optimal address aggregation (i.e. the customer renumbering and sub-optimal address aggregation (i.e. the
generation of additional more-specific routing entries within the IGP generation of additional more-specific routing entries within the IGP
and the waste of MPLS Label space). and the waste of MPLS Label space).
5.2.3.5. Restructuring of SP (access) network and Renumbering A.2.3.5. Restructuring of SP (access) network and Renumbering
A technically triggered restructuring of the SP (access) network (for A technically triggered restructuring of the SP (access) network (for
instance because of split of equipment or installation of new instance because of split of equipment or installation of new
equipment) should not lead to a customer network renumbering. This equipment) should not lead to a customer network renumbering. This
challenge should be handled in advance by an intelligent network challenge should be handled in advance by an intelligent network
design and IPv6 address planing. design and IPv6 address planing.
In the worst case the customer network renumbering could be avoided In the worst case the customer network renumbering could be avoided
through the implementation of more specific customer routes. (Note: through the implementation of more specific customer routes. (Note:
Since this kind of network restructuring will mostly happen within Since this kind of network restructuring will mostly happen within
the access network (at the level) below the LER, the LER aggregation the access network (at the level) below the LER, the LER aggregation
level will not be harmed and the more-specific routes will not level will not be harmed and the more-specific routes will not
consume additional MPLS label space.) consume additional MPLS label space.)
5.2.3.6. Extensions needed for the later IPv6 migration phases A.2.3.6. Extensions needed for the later IPv6 migration phases
The proposed IPv6 addressing schema for a SP needs some slight The proposed IPv6 addressing schema for a SP needs some slight
enhancements / modifications for the later phases of IPv6 enhancements / modifications for the later phases of IPv6
integration, for instance in the case when the whole MPLS backbone integration, for instance in the case when the whole MPLS backbone
infrastructure (LDP, IGP etc.) is realized over IPv6 transport an infrastructure (LDP, IGP etc.) is realized over IPv6 transport and an
addressing of the LSRs is needed. Other changes may be necessary as IPv6 addressing of the LSRs is needed. Other changes may be
well but should not be explained at this point. necessary as well but should not be explained at this point.
6. IANA Considerations
There are no extra IANA consideration for this document.
7. Security Considerations
This IPv6 addressing document does not have any direct impact on
Internet infrastructure security.
8. Acknowledgements
Constructive feedback and contributions have been received from Marla
Azinger, Stig Venaas, Pekka Savola, John Spence, Patrick Grossetete,
Carlos Garcia Braschi, Brian Carpenter, Mark Smith and Ginny Listman.
9. References
9.1. Normative References
9.2. Informative References
[1] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E.
Lear, "Address Allocation for Private Internets", BCP 5,
RFC 1918, February 1996.
[2] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[3] Hinden, R., Fink, R., and J. Postel, "IPv6 Testing Address
Allocation", RFC 2471, December 1998.
[4] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast
Addresses", RFC 2526, March 1999.
[5] Retana, A., White, R., Fuller, V., and D. McPherson, "Using 31-
Bit Prefixes on IPv4 Point-to-Point Links", RFC 3021,
December 2000.
[6] Narten, T. and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6", RFC 3041, January 2001.
[7] Durand, A., Fasano, P., Guardini, I., and D. Lento, "IPv6
Tunnel Broker", RFC 3053, January 2001.
[8] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via
IPv4 Clouds", RFC 3056, February 2001.
[9] IAB and IESG, "IAB/IESG Recommendations on IPv6 Address
Allocations to Sites", RFC 3177, September 2001.
[10] Durand, A. and C. Huitema, "The H-Density Ratio for Address
Assignment Efficiency An Update on the H ratio", RFC 3194,
November 2001.
[11] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003.
[12] Draves, R., "Default Address Selection for Internet Protocol
version 6 (IPv6)", RFC 3484, February 2003.
[13] Blanchet, M., "A Flexible Method for Managing the Assignment of
Bits of an IPv6 Address Block", RFC 3531, April 2003.
[14] Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global Unicast
Address Format", RFC 3587, August 2003.
[15] Savola, P., "Use of /127 Prefix Length Between Routers
Considered Harmful", RFC 3627, September 2003.
[16] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host
Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[17] Fink, R. and R. Hinden, "6bone (IPv6 Testing Address
Allocation) Phaseout", RFC 3701, March 2004.
[18] Droms, R., "Stateless Dynamic Host Configuration Protocol
(DHCP) Service for IPv6", RFC 3736, April 2004.
[19] Huitema, C. and B. Carpenter, "Deprecating Site Local
Addresses", RFC 3879, September 2004.
[20] Savola, P. and B. Haberman, "Embedding the Rendezvous Point
(RP) Address in an IPv6 Multicast Address", RFC 3956,
November 2004.
[21] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[22] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[23] Baker, F., Lear, E., and R. Droms, "Procedures for Renumbering
an IPv6 Network without a Flag Day", RFC 4192, September 2005.
[24] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[25] Templin, F., Gleeson, T., Talwar, M., and D. Thaler, "Intra-
Site Automatic Tunnel Addressing Protocol (ISATAP)", RFC 4214,
October 2005.
[26] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[27] Chown, T., Venaas, S., and C. Strauf, "Dynamic Host
Configuration Protocol (DHCP): IPv4 and IPv6 Dual-Stack
Issues", RFC 4477, May 2006.
[28] ARIN, "http://www.arin.net/policy/nrpm.html#six54".
[29] De Clerq, J., Ooms, D., Prevost, S., and F. Le Faucheur,
"Connecting IPv6 Islands over IPv4 MPLS using IPv6 Provider
Edge Routers (6PE) (draft-ooms-v6ops-bgp-tunnel-06.txt)",
June 2006.
[30] Chown, T., "IPv6 Implications for TCP/UDP Port Scanning
(draft-ietf-v6ops-scanning-implications-00.txt)", June 2006.
[31] APNIC, ARIN, RIPE NCC, "IPv6 Address Allocation and Assignment
Policy (www.ripe.net/ripe/docs/ipv6policy.html)", January 2003.
[32] Chown, T., Thompson, M., Ford, A., and S. Venaas, "Things to
think about when Renumbering an IPv6 network
(draft-chown-v6ops-renumber-thinkabout-05.txt)", March 2007.
[33] "List of Internet-Drafts relevant to the Multi6-WG
(http://ops.ietf.org/multi6/draft-list.html )".
[34] Lear, E., "Things MULTI6 Developers should think about
(draft-ietf-multi6-things-to-think-about-01)", January 2005.
[35] Nordmark, E. and T. Li, "Threats relating to IPv6 multihoming
solutions (draft-ietf-multi6-multihoming-threats-03)",
January 2005.
Authors' Addresses Authors' Addresses
Gunter Van de Velde Gunter Van de Velde
Cisco Systems Cisco Systems
De Kleetlaan 6a De Kleetlaan 6a
Diegem 1831 Diegem 1831
Belgium Belgium
Phone: +32 2704 5473 Phone: +32 2704 5473
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