Network Working Group G. Van de Velde Internet-Draft C. Popoviciu Expires: December 3, 2006 Cisco Systems T. Chown University of Southampton
June 1, 2006O. Bonness C. Hahn T-Systems Enterprise Services GmbH IPv6 Unicast Address Assignment Considerations <draft-ietf-v6ops-addcon-00.txt><draft-ietf-v6ops-addcon-01.txt> Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 3, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract One fundamental aspect of any IP communications infrastructure is its addressing plan. With its new address architecture and allocation policies, the introduction of IPv6 into a network means that network designers and operators need to reconsider their existing approaches to network addressing. Lack of guidelinessguidelines on handling this aspect of network design could slow down the integration of IPv6. This draft aims to provide the information and recommendations relevant to planning the addressing aspects of IPv6 deployments. The draft also provides IPv6 addressing case studies for both an enterprise and an ISP network. In this first version of the draft we aim to provoke discussion on this important topic; more detailed case study texts will follow. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 34 2. Network Level Addressing Design Considerations . . . . . . . . 45 2.1. Global Unique Addresses . . . . . . . . . . . . . . . . . 45 2.2. Unique Local IPv6 Addresses . . . . . . . . . . . . . . . 45 2.3. 6Bone Address Space . . . . . . . . . . . . . . . . . . . 56 2.4. Network Level Design Considerations . . . . . . . . . . . 67 2.4.1. Sizing the Network Allocation . . . . . . . . . . . . 78 2.4.2. Address Space Conservation . . . . . . . . . . . . . . 78 3. Subnet Prefix Considerations . . . . . . . . . . . . . . . . . 78 3.1. Considerations for subnet prefixes shorter then /64 . . . 78 3.2. Considerations for /64 prefixes . . . . . . . . . . . . . 89 3.3. Considerations for subnet prefixes longer then /64 . . . . 89 3.3.1. Anycast addresses . . . . . . . . . . . . . . . . . . 89 3.3.2. Addresses used by Embedded-RP (RFC3956) . . . . . . . 1011 3.3.3. ISATAP addresses . . . . . . . . . . . . . . . . . . . 1011 3.3.4. /126 addresses . . . . . . . . . . . . . . . . . . . . 1112 3.3.5. /127 addresses . . . . . . . . . . . . . . . . . . . . 1112 3.3.6. /128 addresses . . . . . . . . . . . . . . . . . . . . 1112 4. Allocation of the IID of an IPv6 Address . . . . . . . . . . . 1112 4.1. Automatic EUI-64 Format Option . . . . . . . . . . . . . . 1213 4.2. Using Privacy Extensions . . . . . . . . . . . . . . . . . 1213 4.3. Cryptographically Generated IPv6 Addresses . . . . . . . . 1213 4.4. Manual/Dynamic Assignment Option . . . . . . . . . . . . . 1314 5. Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . 1314 5.1. Enterprise Considerations . . . . . . . . . . . . . . . . 1314 5.1.1. Obtaining general IPv6 network prefixes . . . . . . . 1314 5.1.2. Forming an address (subnet) allocation plan . . . . . 1415 5.1.3. Other considerations . . . . . . . . . . . . . . . . . 1516 5.1.4. Node configuration considerations . . . . . . . . . . 1516 5.1.5. Observations . . . . . . . . . . . . . . . . . . . . . 1617 5.2. Service Provider Considerations . . . . . . . . . . . . . 1617 5.2.1. Investigation of objective Requirements for an IPv6 addressing schema of a Service Provider . . . . . 17 5.2.2. IPv6 address allocation plan for a Service Provider . 19 5.2.3. Additional Remarks . . . . . . . . . . . . . . . . . . 23 6. SecurityIANA Considerations . . . . . . . . . . . . . . . . . . . 16. . 24 7. Security Considerations . . . . . . . . . . . . . . . . . . . 24 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 8.25 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 8.1.25 9.1. Normative References . . . . . . . . . . . . . . . . . . . 16 8.2.25 9.2. Informative References . . . . . . . . . . . . . . . . . . 1625 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 1928 Intellectual Property and Copyright Statements . . . . . . . . . . 2030 1. Introduction The Internet Protocol Version 6 (IPv6) Addressing Architecture  defines three main types of addresses: unicast, anycast and multicast. This document focuses on unicast addresses, for which there are currently three principal allocated types: Global Unique Addresses  ('globals'), Unique Local IPv6 Addresses  (ULAs) and 6bone address space . The document covers aspects that should be considered during IPv6 deployment for the design and planning of an addressing scheme for an IPv6 network. The network's IPv6 addressing plan may be for an IPv6- only network, or for a dual-stack infrastructure where some or all devices have addresses in both protocols. These considerations will help an IPv6 network designer to efficiently and prudently assign the IPv6 address space that has been allocated to its organization. The address assignment considerations are analyzed separately for the two major components of the IPv6 unicast addresses, namely 'Network Level Addressing' (the allocation of subnets) and the 'Subnet Prefix' (address usage within a subnet). Thus the document includes a discussion of aspects of address assignment to nodes and interfaces in an IPv6 network. Finally the document will provide two examples of asuccessfully deployed address planplans in a service provider (ISP) and an enterprise network. Parts of this document highlight the differences that an experienced IPv4 network designer should consider when planning an IPv6 deployment, for example: o IPv6 devices will more likely be multi-addressed in comparison with their IPv4 counterparts. o The practically unlimited size of an IPv6 subnet (2^64 bits) reduces the requirement to size subnets to device counts for the purposes of (IPv4) address conservation. o EventhoughEven though there is no broadcast for the IPv6 protocol, there is still need to consider the number of devices in a given subnet due to traffic storm and level of traffic generated by hosts. o The implications of the reduced threat of address-based host scanning, as discussed in . We do not discuss here how a site or ISP should proceed with acquiring its globally routable IPv6 address prefix. However, one should note that IPv6 networks receive their global unicast address allocation from their 'upstream' provider, which may be another ISP, a Local Internet Registry (LIR) or a Regional Internet Registry (RIR). In each case the prefix received is provider assigned (PA); there is currently no provider independent (PI) address space for IPv6. Thus an IPv6 network which changes provider will need to undergo a renumbering process, as described in . A separate document  makes recommendations to ease the IPv6 renumbering process. This document neither discusses implementionimplementation aspects between ULA addresses and Site-local addresses. Most implementations know about Site-local addresses even though they are deprecated, and do not know about ULAs - even though they are according current specification. As result transitioning between these types of addresses may cause difficulties. 2. Network Level Addressing Design Considerations This section discusses the kind of IPv6 addresses used at the network level for the IPv6 infrastructure. The kind of addresses that can be considered are Global Unique Addresses, ULAs and 6bone address space. 2.1. Global Unique Addresses The most commonly used unicast addresses will be Global Unique Addresses ('globals'). No significant considerations are neccesarynecessary if the organization has an address space assignment and a single prefix is deployed through a single upstream provider. However, a multihomed site may deploy addresses from two or more Service Provider assigned IPv6 address ranges. Here, the network Administrator must have awareness on where and how these ranges are used on the multihomed infrastructure environment. The nature of the usage of multiple prefixes may depend on the reason for multihoming (e.g. resilience failover, load balancing, policy-based routing, or multihoming during an IPv6 renumbering event). IPv6 introduces improved support for multi-addressed hosts through the IPv6 default address selection methods described in RFC3484 . A multihomed host may thus have two addresses, one per prefix (provider), and select source and destination addresses to use as described in that RFC. 2.2. Unique Local IPv6 Addresses ULAs have replaced the originally conceived Site Local addresses in the IPv6 addressing architecture, for reasons described in . ULAs improve on site locals by offering a high probability of the global uniqueness of the prefix used, which can be beneficial in the case of (deliberate or accidental) leakage, or where networks are merged. ULAs are akin to the private address space  assigned for IPv4 networks. The ULA address range allows a network administrator to deploy IPv6 addresses on their network without asking for a globally unique 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 globally routable IPv6 address space . ULAs provide the means to deploy a fixed addressing scheme that is not affected by a change in service provider and the corresponding PA global addresses. Internal operation of the network is thus unaffected during renumbering events. Nevertheless, this type of address must be used with caution. A site using ULAs may or may not also deploy globals. In an isolated network ULAs may be deployed on their own. In a connected network, that also deploys global addresses, both may be deployed, such that hosts become multiaddressed (one global and one ULA address) and the IPv6 default address selection algorithm will pick the appropriate source and destination addresses to use, e.g. ULAs will be selected where both the source and destination hosts have ULA addresses. Because a ULA and a global site prefix are both /48 length, an administrator can choose to use the same subnetting (and host addressing) plan for both prefixes. As an example of the problems ULAs may cause, when using IPv6 multicast within the network, the IPv6 default address selection 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 stream to the IPv6 Internet for two reasons. For one, these addresses are not globally routable so RPF checks for such traffic will fail outside the internal network. The other reason is that the traffic will likely not cross the network boundary due to multicast domain control and perimeter security policies. In principal ULAs allow easier network mergers than RFC1918 addresses do for IPv4 because ULA prefixes have a high probability of uniqueness, if the prefix is chosen as described in the RFC. The usage of ULAs should be carefully considered even when not attached to the IPv6 Internet due to the potential for added complexity when connecting to the Internet at some point in the future. 2.3. 6Bone Address Space The 6Bone address space was used before the RIRs started to distribute 'production' IPv6 prefixes. The 6Bone prefixes have a common first 16 bits in the IPv6 Prefix of 3FFE::/16. This address range is deprecated as of 6th June 2006  and should be avoided on any new IPv6 network deployments. Sites using 6bone address space should renumber to production address space using procedures as defined in . 2.4. Network Level Design Considerations IPv6 provides network administrators with a significantly larger address space, enabling them to be very creative in how they can define logical and practical address plans. The subnetingsubnetting of assigned prefixes can be done based on various logical schemes that involve factors such as: o Geographical Boundaries - by assigning a common prefix to all subnets within a geographical area. o Organizational Boundaries - by assigning a common prefix to an entire organization or group within a corporate infrastructure. o Service Type - by reserving certain prefixes for predefined services such as: VoIP, Content Distribution, wireless services, Internet Access, etc. Such logical addressing plans have the potential to simplify network operations and service offerings, and to simplify network management and troubleshooting. A very large network would also have no need to consider using private address space for its infrastructure devices, simplifying network management. The network designer must however keep in mind several factors when developing these new addressing schemes: o Prefix Aggregation - The larger IPv6 addresses can lead to larger routing tables unless network designers are actively pursuing aggregation. While prefix aggregation will be enforced by the service provider, it is beneficial for the individual organizations to observe the same principles in their network design process. o Network growth - The allocation mechanism for flexible growth of a network prefix, documented in RFC3531  can be used to allow the network infrastructure to grow and be numbered in a way that is likely to preserve aggregation (the plan leaves 'holes' for growth). 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 a 'random' /48 under fc00::/7 will have no aggregation of those prefixes. Thus the end result may be cumbersome because the network will have large amounts of non-aggregated ULA prefixes. 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 subnetting to be used internally. 2.4.1. Sizing the Network Allocation We do not discuss here how a network designer sizes their application for address space. By default a site will receive a /48 prefix . The default provider allocation via the RIRs is currently a /32 . These allocations are indicators for a first allocation for a network. Different sizes may be obtained based on the anticipated address usage . There are examples of allocations as large as /19 having been made from RIRs to providers at the time of writing. 2.4.2. Address Space Conservation Despite the large IPv6 address space which enables easier subneting,subnetting, it still is important to ensure an efficient use of this resource. Some addressing schemes, while facilitating aggregation and management, could lead to significant numbers of addresses being unused. Address conservation requirements are less stringent in IPv6 but they should still be observed. The proposed HD  value for IPv6 is 0.94 compared to the current value of 0.96 for IPv4. Note that for IPv6 HD is calculated for sites,sites (i.e. on a basis of /48), instead of based on addresses like with IPv4. 3. Subnet Prefix Considerations This section analyzes the considerations applied to define the subnet prefix of the IPv6 addresses. The boundaries of the subnet prefix allocation are specified in RFC4291 . In this document we analyze their practical implications. Based on RFC4291  it is 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 bits. Each of these three options areis discussed in this document. 3.1. Considerations for subnet prefixes shorter then /64 An allocation of a prefix shorter then 64 bits to a node or interface is bad practice. The shortest subnet prefix that could theoretically be assigned to an interface or node is limited by the size of the network prefix allocated to the organization. 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 that interface compared to a prescribed length of 64 bits. This however is unnecessary considering that 2^64 provides plenty of node addresses for a well designed IPv6 network. Layer two technologies 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 configuration, by a stateful Host Configuration Protocol  or by a stateful prefix delegation mechanism . 3.2. Considerations for /64 prefixes Based on RFC3177 , 64 bits is the prescribed subnet prefix length to allocate to interfaces and nodes. When using a /64 subnet length, the address assignment for these addresses can be made either by manual configuration, by a stateful Host Configuration Protocol   or by stateless autoconfiguration . Note that RFC3177 strongly prescribes 64 bit subnets for general usage, and that stateless autoconfiguration option is only defined for 64 bit subnets. 3.3. Considerations for subnet prefixes longer then /64 Address space conservation is the main motivation for using a subnet prefix length longer than 64 bits. The address assignment can be made either by manual configuration or by a stateful Host Configuration Protocol . When assigning a subnet prefix of more then 80 bits, according to RFC4291  "u" and "g" bits (respectively the 81st and 82nd bit) need to be taken into consideration and should be set correctly. In currently implemented IPv6 protocol stacks, the relevance of the "u" (universal/local) bit and "g" (the individual/group) bit are marginal and typically will not show an issue when configured wrongly, however future implementations may turn out differently. When using subnet lengths longer then 64 bits, it is important to avoid selecting addresses that may have a predefined use and could confuse IPv6 protocol stacks. The alternate usage may not be a simple unicast address in all cases. The following points should be consideratedconsidered when selecting a subnet length longer then 64 bits subnet prefix length.bits. 3.3.1. Anycast addresses 126.96.36.199. Subnet Router Anycast Address RFC4291  provides a definition for the required Subnet Router Anycast Address as follows: | n bits | 128-n bits | +------------------------------------------------+----------------++--------------------------------------------+----------------+ | subnet prefix | 00000000000000 | +------------------------------------------------+----------------++--------------------------------------------+----------------+ It is recommended to avoid allocating this IPv6 address to a device which is not a router. noNo additional dependancydependencies for the subnet prefix with the exception ofwhile the EUI-64 and an IID dependency. Thesedependencies will be discussed later in this document. 188.8.131.52. Reserved IPv6 Subnet Anycast Addresses RFC2526  stated that within each subnet, the highest 128 interface identifier values are reserved for assignment as subnet anycast addresses. The construction of a reserved subnet anycast address depends on the type of IPv6 addresses used within the subnet, as indicated by the format prefix in the addresses. The first type of Subnet Router Anycast addresses have been defined as follows for EUI-64 format: | 64 bits | 57 bits | 7 bits | +---------------------------------+------------------+------------++------------------------------+------------------+------------+ | subnet prefix | 1111110111...111 | anycast ID | +---------------------------------+------------------+------------++------------------------------+------------------+------------+ The anycast address structure implies that it is important to avoid creating a subnet prefix where the bits 65 to 121 are defined as "1111110111...111" (57 bits in total) so that confusion can be avoided. For other IPv6 address types (that is, with format prefixes other than those listed above), the interface identifier is not in EUI-64 format and may be other than 64 bits in length; these reserved subnet anycast addresses for such address types are constructed as follows: | n bits | 121-n bits | 7 bits | +---------------------------------+------------------+------------++------------------------------+------------------+------------+ | subnet prefix | 1111111...111111 | anycast ID | +---------------------------------+------------------+------------++------------------------------+------------------+------------+ | interface identifier field | In the case discussed above there is no additional dependancydependency for the subnet prefix with the exception of the EUI-64 and an IID dependency. These will be discussed later in this document. 3.3.2. Addresses used by Embedded-RP (RFC3956) Embedded-RP  reflects the concept of integrating the Rendezvous Point (RP) IPv6 address into the IPv6 multicast group address. Due to this embedding and the fact that the length of the IPv6 address AND the IPv6 multicast address are 128 bits, it is not possible to have the complete IPv6 address of the multicast RP embedded as such. This resulted in a restriction of 15 possible RP-addresses per prefix that can be used with embedded-RP. The space assigned for the embedded-RP is based on the 4 low order bits, while the remainder of the Interface ID is set to all '0'. [IPv6-prefix (64 bits)][60 bits all '0'][RIID] Where: [RIID] = 4 bit. Consequently this leads to the awarenessThis format implies that when whenselecting subnet prefixes longer then 64, whereand the bits beyond the 64th bitone are none-zero embedded-RPnone-zero, the subnet can not be used for that subnet.use embedded-RP. In addition it is discouraged to assign a matching embedded-RP IPv6 address to a device that is not a real Multicast RendezVousRendezvous Point. 3.3.3. ISATAP addresses ISATAP  is an automatic tunneling protocol used to provide IPv6 connectivity over an IPv4 campus or enterprise environment. In order to leverage the underlying IPv4 infrastructure, the IPv6 addresses are constructed in a special format. An IPv6 ISATAP  address has the IPv4 address embedded, based on a predefined structure policy that identifies them as an ISATAP  address. [IPv6 Prefix (64 bits)][0000:5EFE][IPv4 address] When using subnet prefix length longer then 64 bits it is recommended that that the portion of the IPv6 prefix from bit 65 to the end of the subnet prefix does not match with the welknownwell-known ISATAP [0000:5EFE][0000: 5EFE] address portion. In its actual definition there is no multicast support on ISATAP 3.3.4. /126 addresses The 126 bit subnet prefixes are typically used for point-to-point links similar to the RFC3021  recommendations for IPv4. The usage of this subnet address length does not lead to any additional considerations other than the ones discussed earlier in this section, particularly those related to the "u" and "g" bits. 3.3.5. /127 addresses The usage of the /127 addresses is not valid and should be strongly discouraged as documented in RFC3627 . 3.3.6. /128 addresses The 128 bit address prefix may be used in those situations where we know that one, and only one address is sufficient. Example usage would be the offlinkoff-link loopback address of a network device. When choosing a 128 bit prefix, it is recommended to take the "u" and "g" bits into consideration and to make sure that there is no overlap with either the following well knownwell-known addresses: o Subnet Router Anycast Address o Reserved Subnet Anycast Address o Addresses used by Embedded-RP o ISATAP Addresses 4. Allocation of the IID of an IPv6 Address In order to have a complete IPv6 address, an interface must be associated a prefix and an Interface Identifier (IID). Section 3 of this document analyzed the prefix selection considerations. This section discusses the elements that should be considered when assigning the IID portion of the IPv6 address. There are various ways to allocate an IPv6 address to a device or interface. The option with the least amount of caveats for the network administrator is that of EUI-64  based addresses. For the manual or dynamic options, the overlap with well known IPv6 addresses should be avoided. 4.1. Automatic EUI-64 Format Option When using this method the network administrator has to allocate a valid 64 bit subnet prefix. The EUI-64  allocation procedure can from that moment onwards assign the remaining 64 IID bits in a stateless manner. All the considerations for selecting a valid IID have been incorporated in the EUI-64 methodology. 4.2. Using Privacy Extensions The main purpose of IIDs generated based on RFC3041  is to provide privacy to the entity using this address. While there isare no particular restraintsconstraints in the usage of these addresses as defined in  there are some implications to be aware of when using privacy addresses as documented in section 4 of RFC3041 : o The privacy extension algoritmalgorithm 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  and provide a method for binding a public signature key to an IPv6 address in the Secure Neighbor Discovery (SEND) protocol . 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 : 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 This section discusses those IID allocations that are not implemented through stateless address configuration (Section 4.1). They are applicable regardless of the prefix length used on the link. It is out of scope for this section to discuss the various assignment methods (e.g. manual configuration, DHCPv6, etc). In this situation the actual allocation is done by human intervention 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 addresses: o Subnet Router Anycast Address o Reserved Subnet Anycast Address o Addresses used by Embedded-RP o ISATAP Addresses When using an address assigned by human intervention it is recommended to choose IPv6 addresses which are not abviousobvious to guess and/or avoid any IPv6 addresses that embed IPv4 addresses used in the current infrastructure. Following these two recommendations will make it more difficult for malicious third parties to guess targets for attack, and thus reduce security threats to a certain extent. 5. Case Studies tbc. 5.1. Enterprise Considerations 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- stack environment. The specific example is the University of Southampton (UK). The case study is a 'work in progress' as the deployment is an evolving one, currently covering around 1,500 hosts. 5.1.1. Obtaining general IPv6 network prefixes In the case of a campus network, the site will typically take its connectivity from its National Research and Education Network (NREN). Southampton connects to JANET, the UK academic network. JANET currently has a /32 allocation from RIPE of 2001:630::/32. The current recommended practice is for sites to receive a /48 allocation, and on this basis Southampton has received such a prefix for its own use, specifically 2001:630:d0::/48. No ULA addressing is used on site. The campus does not expect to change service provider, and thus does not plan to use ULAs for the (perceived) benefit of easing network renumbering. Indeed, the campus has renumbered following the aforementioned renumbering procedure  on two occassions,occasions, and this has proven adequate (with provisos documented in . We also do not see any need to deploy ULAs for in or out of band network management; there are enough IPv6 prefixes available in the site allocation for the infrastructure. No 6bone addressing is used on site. This was phased out some time ago. We note that as of 6th June 2006 transit ISPs will likely filter any attempted use of such prefixes. Southampton does participate in global and organisationorganization scope IPv6 multicast networks. Multicast address allocations are not discussed here as they are not in scope for the document. Embedded RP is in use, and has been tested successfully across providers between sites. 5.1.2. Forming an address (subnet) allocation plan The campus has a /16 prefix for IPv4 use; in principle 256 subnets of 256 addresses. In reality the subnetting is muddier, because of 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 in it. While this is efficient, it increases management burden when physical deployments change, and IPv4 subnets require resizing (up or down), even with DHCP in use. The /48 IPv6 prefix is considerably larger than the IPv4 allocation already in place at the site. It is loosely equivalent to a 'Class A' IPv4 prefix in that it has 2^16 (over 65,000) subnets, but has an effectively unlimited subnet address size (2^64) compared to 256 in the IPv4 equivalent. The increased subnet size means that /64 IPv6 prefixes can be used on all subnets, without any requirement to resize them at a later date. The increased subnet volume allows subnets to be allocated more generously to schools and departments in the campus. While address conservation is still important, it is no longer an impediment on network management. Rather, address (subnet) allocation is more about planning for future expansion. In a dual-stack network, we chose to deploy our IP subnets congruently for IPv4 and IPv6. This is because the systems are still in the same administrative domains and the same geography. We do not expect to have IPv6-only subnets in production use for a while yet, outside testbedstest beds and our early Mobile IPv6 trials. The firewall would ideally be a single dual-stack device with consistent policies (by host rather than IP version), however this is currently implemented as a firewall per IP protocol due to vendor limitations (Nokia/Checkpoint for IPv4, BSD pf tool for IPv6). The subnet allocation plan required a division of the address space per school or department. Here a /56 was allocated to the school level of the university; there are around 30 schools currently. Further allocations were made for central IT infrastructure, for the network infrastructure and the server side systems. 5.1.3. Other considerations The network uses a Demilitarized Zone (DMZ) topology for some level of protection of 'public' systems. Again, this topology is congruent with the IPv4 network. There are no specific transition methods deployed internally to the campus; everything is using the conventional dual-stack approach. There is no use of tools such as ISATAP for example. For the Mobile IPv6 early trails, we have allocated one prefix for Home Agent (HA) use. We have not yet considered how Mobile IPv6 usage may grow, and whether more or even every subnet will require HA support. The university operates a tunnel broker service on behalf of UKERNA. This uses separate address space from JANET, not the main university allocation. 5.1.4. Node configuration considerations We currently use stateless autoconfiguration on most subnets for IPv6 hosts. There is no DHCPv6 service deployed yet, beyond tests of early code releases. We do seek a common integrated DHCP/DNS management platform, even if the servers themselves are not colocated.co- located. Currently we add client statelessly autoconfigured addresses to the DNS manually. Our administrators would prefer the use of DHCP because they believe it gives them some management control. Regarding the  implications, we note that all our hosts are dual- stack, and thus are potentially exposed over both protocols anyway. We publish all addresses in DNS, and do not operate a two faced DNS. We have internal usage of RFC3041 privacy addresses currently, but may wish to administratibelyadministratively disable this (perhaps via DHCP), but we need to determine the feasibility of this on all systems, e.g. for WLAN guests or other user-maintained systems. Network management should be simpler without RFC3041 in opeation.operation. Note RFC3041 is only an issue for outbound connections. We manually configure server addresses to avoid address changes on a change of network adaptor. With IPv6 you can choose to pick ::53 for a DNS server, or can pick 'random' addresses for obfuscation, though that's not an issue for publicly advertised addresses (dns, mx, web, etc). 5.1.5. Observations The site is not (yet) using prefix delegation tools for IPv6. 5.2. Service Provider Considerations case studies are requested and in development. they should be added for the -01 draft. 6. Security Considerations ThisIn this section an IPv6 addressing documents does not have any direct impact onschema is sketched that could serve as an example by a Service Provider offering Internet infrastructure security. 7. Acknowledgements Constructive feedbackServices as well as Network Access services to millions of customers. In this example, the Service Provider is assumed to operate an MPLS based backbone and contributions haveimplements 6PE to provide IPv6 backbone transport between the different locations (POPs) of a fully dual-stacked network access and aggregation area. Besides that it is assumed that the Service Provider o has received a /20 from its RIR o operates its own LIR o has to address its own IPv6 infrastructure o delegates prefixes from this aggregate to its customers. Hence this addressing schema covers the numbering of the Service Provider IPv6 network devices as well the customer aggregates chosen out of the /20 prefix of the SP. 5.2.1. Investigation of objective Requirements for an IPv6 addressing schema of a Service Provider The first step of the IPv6 addressing plan design for a Service provider should be the identification of all technical, operational, political and business requirements that have to be satisfied by the services supported by this addressing schema. According to the different technical constraints and business models as well as the different weights of these requirements (from the point of view of the corresponding Service Provider) it is very likely that different addressing schemas will be developed and deployed by different ISPs. Nevertheless the addressing schema of this section is one possible example. 184.108.40.206. Requirements for an IPv6 addressing schema from the LIR perspective of the Service Provider In their role as LIR the Service Providers have to care about the policy constraints of the RIRs and the standards of the IETF regarding IPv6 addressing. In this context, the following basic requirements and recommendations have to be taken into account and should be satisfied by the IPv6 address allocation plan of a Service Provider: o As recommended in RFC 3177  and in several RIR policies "Common" customers sites (normally private customers) should receive a /48 prefix from the aggregate of the Service Provider. (Note: The addressing plan must be flexible enough and take into account the possible change of the minimum allocation size for end users currently under definition by the RIRs.) o "Big customers" (like big enterprises, governmental agencies etc.) may receive shorter prefixes according to their needs when this need could be documented and justified to the RIR. o The IPv6 address allocation schema has to be able to meet the HD- ratio of 0.94 as it is defined for IPv6. This requirement corresponds to the demand for an efficient usage of the IPv6 address aggregate by the Service Provider. (Note: A HD-ratio of 0.94 means an effective usage of about 31% of the /20 of the Service Provider on the basis of /48 assignments.) o All assignments to customers have to be documented and stored into a database that can also be queried by the RIR. o The LIR has to make available means for supporting the reverse DNS mapping of the customer prefixes. 220.127.116.11. IPv6 addressing schema requirements from the ISP perspective of the Service Provider From ISP perspective the following basic requirements could be identified: o The IPv6 address allocation schema must be able to realize a maximal aggregation of all IPv6 address delegations to customers into the /20 of the Service Provider. Only this /20 will be routed and injected from the Service Provider into the global routing table (DFZ). This strong aggregation keeps the routing tables of the DFZ small and eases filtering and access control very much. (Note: A strong aggregation e.g. on POP or LER basis limits as well the numbers of customer routes that are visible within the ISP network.) o The IPv6 addressing schema of the SP should contain maximal flexibility since the infrastructure of the SP will change over the time with new customers, transport technologies and business cases. The requirement of maximal flexibility is contrary to the requirements of strong IPv6 address aggregation and efficient address usage, but at this point each SP has to decide which of these requirements to prioritize. o Keeping the multilevel network hierarchy of an ISP in mind, due to addressing efficiency reasons not all hierarchy levels can and should be mapped into the IPv6 addressing schema of an ISP. Sometimes it is much better to implement "flat" addressing for the ISP network than to loose big chunks of the IPv6 address aggregate in addressing each level of network hierarchy. Besides that a decoupling of provider network addressing and customer addressing is recommended. 18.104.22.168. IPv6 addressing schema requirements from the Network Access provider perspective of the Service Provider 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 Provider role. Some of the basic requirements are: o The IPv6 addressing schema of the SP must be flexible enough to adapt changes that are injected from the customer side. This covers changes that are based on the raising IPv6 address needs of the customer as well as changes that come from topological modifications (e.g. when the customer moves from one point of network attachment (POP) to another). o For each IPv6 address assignment to customers a "buffer zone" must be reserved that allows the customer to grow in its addressing range without renumbering or assignment of additional prefixes. o The IPv6 addressing schema of the SP must deal with multiple- attachments of a single customer to the SP network infrastructure (i.e. multi-homed network access with the same SP). These few requirements are only part of all the requirements a Service Provider has to investigate and keep in mind during the definition phase of its addressing architecture. Each SP will most likely add more constraints to this list. 5.2.2. IPv6 address allocation plan for a Service Provider This section illustrates how the /20 IPv6 prefix of the SP can be used to address the SP-own infrastructure and to delegate IPv6 prefixes to its customers following the above mentioned requirements as far as possible. The below figure summarizes the device types in an SP network and the typical network design. The network hierarchy of the SP has to be taken into account for the design of an IPv6 addressing schema and defines its basic shape. +------------------------------------------------------------------+ | LSRs of the MPLS Backbone of the SP | +------------------------------------------------------------------+ | | | | | | | | | | +-----+ +-----+ +--------+ +--------+ +--------+ | LER | | LER | | LER-BB | | LER-BB | | LER-BB | +-----+ +-----+ +--------+ +--------+ +--------+ | | | | | | / | | | | | | | | | / | | | | | | | +------+ +------+ +------+ | | | | | | |BB-RAR| |BB-RAR| | AG | | | | | | | +------+ +------+ +------+ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +-----+ +-----+ +-----+ +-----+ | | | | | | | | | RAR | | RAR | | RAR | | RAR | | | | | | | | | +-----+ +-----+ +-----+ +-----+ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +-------------------------------------------------------------------+ | Customer networks | +-------------------------------------------------------------------+ Figure: Exemplary Service Provider Network LSR ... Label Switch Router LER ... Label Edge Router LER-BB ... Broadband Label Edge Router RAR ... Remote Access Router BB-RAR ... Broadband Remote Access Router AG ... Aggregation Router Basic design decisions for the SP IPv6 address plan regarding customer prefixes take into consideration: o The prefixes assigned to all customers behind the same LER (e.g. LER or LER-BB) are aggregated under one prefix. This ensures that the number of labels that have to be used for 6PE is limited and hence provides a strong MPLS label conservation. 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: * A pool (e.g. /24) for satisfying the addressing needs of real "big" customers (as defined in 22.214.171.124 sub-section A.) that need IPv6 prefixes larger than /48 (e.g. /32). These customers are assumed to be connected to several POPs of the access network, so that this customer prefix will be visible in each of these POPs. * A pool (e.g. /24) for the LERs with direct customer connections (e.g. dedicated line access) and without an additional aggregation area between the customer and the LER. (These LERs are mostly connected to a limited number of customers because of the limited number of interfaces/ports.) * 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 kind of aggregation network (e.g. DSL customers behind a BB- RAR or Dial-In customers behind a RAR). * The IPv6 address delegation within each Pool (end customer delegation or also the aggregates that are dedicated to the LERs itself) should be chosen with an additional buffer zone of 300% for future growth. 126.96.36.199. Defining an IPv6 address allocation plan for customers of the Service Provider 188.8.131.52.1. 'Big' customers SP's "big" customers receive their prefix from the /24 IPv6 address aggregate that has been reserved for their "big" customers. A customer is considered as "big" customer if it has a very complex network infrastructure and/or huge IPv6 address needs (e.g. because of very large customer numbers) and/or several uplinks to different POPs of the SP network. The assigned IPv6 address prefixes can have a prefix length in the range 32-48 and for each assignment a 300% future growing zone is marked as "reserved" for this customer. This means that for instance with a delegation of a /34 to a customer the /32 that contains this /34 is reserved for the customer for future usage. The prefixes for the "big" customers can be chosen from the corresponding LER customer pool by either using an equidistant algorithm or using mechanisms simililar to the Sparse Alocation Algorithm (SAA) . 184.108.40.206.2. 'Common' customers All customers that are not "big" customers are considered as "common" customers. They represent the majority of customers hence they receive a /48 out of the IPv6 customer address pool of the LER where they are directly connected or aggregated. Again a 300% future growing IPv6 address range is reserved for each customer, so that a "common" customer receives a /48 allocation but has a /46 reserved. In the network access scenarios where the customer is directly connected to the LER the customer prefix is directly taken out of the 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 themselves aggregated to an AG or to a LER) at least 2 different approaches are possible. 1.) Mapping of Aggregation Network Hierarchy into Customer IPv6 Addressing Schema. The aggregation network hierarchy could be mapped into the design of the customer prefix pools of each network level in order to achieve a maximal aggregation at the LER level as well as at the intermediate levels. (Example: Customer - /48, RAR - /38, AG - /32, LER-BB - /30). At each network level an adequate growing zone should be reserved. (Note: This approach requires of course some "fine tuning" of the addressing schema based on a very good knowledge of the Service Provider network topology including actual growing ranges and rates.) When the IPv6 customer address pool of a LER (or another device of the aggregation network - AG or RAR) is exhausted, the related LER (or AG or RAR) prefix is shortened by 1 or 2 bits (e.g. from /38 to /37 or /36) so that the originally reserved growing zone can be used for further IPv6 address allocations to customers. In the case where the growing zone is exhausted as well a new prefix range from the corresponding pool of the next higher hierarchy level can be requested. 2.) "Flat" Customer IPv6 Addressing Schema. The other option is to allocate all the customer prefixes directly out of the customer IPv6 address pool of the LER where the customers are attached and aggregated and ignore the intermediate aggregation network infrastructure. This approach leads of course to a higher amount of customer routes at LER and aggregation network level but takes a great amount of complexity out of the addressing schema. Nevertheless the aggregation of the customer prefixes to one prefix at LER level is realized as required above. If the actual observed growing rates show that the reserved growing 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 of the network hierarchy. 220.127.116.11. Defining an IPv6 address allocation plan for the Service Provider Network Infrastructure For the IPv6 addressing of SPs own network infrastructure a /32 (or /40) from the "big" customers address pool can be chosen. This SP infrastructure prefix is used to code the network infrastructure of the SP by assigning a /48 to every POP/location and using for instance a /56 for coding the corresponding router within this POP. Each SP internal link behind a router interface could be coded using a /64 prefix. (Note: While it is suggested to chose a /48 for addressing the POP/location of the SP network it is left to each SP to decide what prefix length to assign to the routers and links within this POP.) The IIDs of the router interfaces may be generated by using EUI-64 or through plain manual configuration e.g. for coding additional network or operational information into the IID. It is assumed that a 300% growing zones for each level of network hierarchy and additional prefixes may be assigned to POPs and/or routers if needed. Loopback interfaces of routers may be chosen from the first /64 of the /56 router prefix (in the example above). (Note: The /32 prefix that has been chosen for addressing SPs own IPv6 network infrastructure gives enough place to code additional functionalities like security levels or private and test infrastructure although such approaches haven't been considered in more detail for the above described SP until now.) 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 the access routers that could be reserved for this reason. 5.2.3. Additional Remarks 18.104.22.168. ULA 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 could be used inside the SP network in order to have an additional "site-local scoped" IPv6 address for SPs own infrastructure for instance for network management reasons and maybe also in order to have an addressing schema that couldn't be reached from outside the SP network. In the case when ULAs are used it is possible to map the proposed internal IPv6 addressing of SPs own network infrastructure as described in 22.214.171.124 above directly to the ULA addressing schema by substituting the /48 POP prefix with a /48 ULA site prefix. 126.96.36.199. Multicast IPv6 Multicast-related addressing issues are out of the scope of this document. 188.8.131.52. POP Multi-homing or Change of POP 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 assigning multiple LER-dependent prefixes to this customer (i.e. considering each customer location as a single-standing customer) or by choosing a customer prefix out of the pool of "big" customers. The second solution has the disadvantage that in every LER where the customer is attached this prefix will appear inside the IGP routing table requiring an explicit MPLS label. An equal effect happens when a customer changes its point of attachment to another POP/LER since in this case the customer prefix could not be aggregated into the LER prefix and needs to be advertised more specific in the IGP. (Note: The described negative POP/LER Multi-homing effects to the addressing architecture in the SP access network are not tackled by implementing the Shim6 Site Multi-homing approach since this approach targets only on a mechanism for dealing with multiple prefixes in end systems -- the SP will nevertheless have unaggregated customer prefixes in its internal routing tables.) 184.108.40.206. Extensions needed for the later IPv6 migration phases The proposed IPv6 addressing schema for a SP needs some slight enhancements / modifications for the later phases of IPv6 integration, for instance in the case when the whole MPLS backbone infrastructure (LDP, IGP etc.) is realized over IPv6 transport an addressing of the LSRs is needed. Other changes may be 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 documents does not have any direct impact on Internet infrastructure security. 8. Acknowledgements Constructive feedback and contributions have been received from Stig Venaas, Pekka Savola, John Spencer, Patrick Grossetete and Carlos Garcia Braschi. 8.9. References 220.127.116.11. Normative References 18.104.22.168. Informative References  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996.  Thomson, S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998.  Hinden, R., Fink, R., and J. Postel, "IPv6 Testing Address Allocation", RFC 2471, December 1998.  Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast Addresses", RFC 2526, March 1999.  Retana, A., White, R., Fuller, V., and D. McPherson, "Using 31- Bit Prefixes on IPv4 Point-to-Point Links", RFC 3021, December 2000.  Narten, T. and R. Draves, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001.  IAB and IESG, "IAB/IESG Recommendations on IPv6 Address Allocations to Sites", RFC 3177, September 2001.  Durand, A. and C. Huitema, "The H-Density Ratio for Address Assignment Efficiency An Update on the H ratio", RFC 3194, November 2001.  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003.  Draves, R., "Default Address Selection for Internet Protocol version 6 (IPv6)", RFC 3484, February 2003.  Blanchet, M., "A Flexible Method for Managing the Assignment of Bits of an IPv6 Address Block", RFC 3531, April 2003.  Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global Unicast Address Format", RFC 3587, August 2003.  Savola, P., "Use of /127 Prefix Length Between Routers Considered Harmful", RFC 3627, September 2003.  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, December 2003.  Fink, R. and R. Hinden, "6bone (IPv6 Testing Address Allocation) Phaseout", RFC 3701, March 2004.  Droms, R., "Stateless Dynamic Host Configuration Protocol (DHCP) Service for IPv6", RFC 3736, April 2004.  Huitema, C. and B. Carpenter, "Deprecating Site Local Addresses", RFC 3879, September 2004.  Savola, P. and B. Haberman, "Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address", RFC 3956, November 2004.  Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.  Aura, T., "Cryptographically Generated Addresses (CGA)", RFC 3972, March 2005.  Baker, F., Lear, E., and R. Droms, "Procedures for Renumbering an IPv6 Network without a Flag Day", RFC 4192, September 2005.  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast Addresses", RFC 4193, October 2005.  Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006.  Templin, F., Gleeson, T., Talwar, M., and D. Thaler, "Intra- Site Automatic Tunnel Addressing Protocol (ISATAP)", draft-ietf-ngtrans-isatap-24 (work in progress), January 2005.  Templin, F., Gleeson, T., Talwar, M., and D. Thaler, "Intra- Site Automatic Tunnel Addressing Protocol (draft-ietf-ngtrans-isatap-24.txt)", July 2005.  Chown, T., "IPv6 Implications for TCP/UDP Port Scanning (chown- v6ops- port-scanning-implications-02.txt)", October 2005.  APNIC, ARIN, RIPE NCC, "IPv6 Address Allocation and Assignment Policy (www.ripe.net/ripe/docs/ipv6policy.html)", January 2003.  Chown, T., Thompson, M., Ford, A., and S. Venaas, "Things to think about when Renumbering an IPv6 network (draft-chown-v6ops-renumber-thinkabout-03.txt)", July 2005.  Paul Wilson, Raymond Plzak, Axel Pawlik, "IPv6 Address Space Management (www.ripe.net/ripe/docs/ipv6-sparse.html)", February 2005. Authors' Addresses Gunter Van de Velde Cisco Systems De Kleetlaan 6a Diegem 1831 Belgium Phone: +32 2704 5473 Email: email@example.com Ciprian Popoviciu Cisco Systems 7025-6 Kit Creek Road Research Triangle Park, North Carolina PO Box 14987 USA Phone: +1 919 392-3723 Email: firstname.lastname@example.org Tim Chown University of Southampton Highfield Southampton, SO17 1BJ United Kingdom Phone: +44 23 8059 3257 Email: email@example.com Olaf Bonness T-Systems Enterprise Services GmbH Goslarer Ufer 35 Berlin, 10589 Germany Phone: +49 30 3497 3124 Email: Olaf.Bonness@t-systems.com Christian Hahn T-Systems Enterprise Services GmbH Goslarer Ufer 35 Berlin, 10589 Germany Phone: +49 30 3497 3164 Email: HahnC@t-systems.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. 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