Internet Engineering Task Force (IETF) K. Chittimaneni Request for Comments: 7381 Dropbox, Inc. Category: Informational T. Chown ISSN: 2070-1721 University of Southampton L. Howard Time Warner Cable V. Kuarsingh Dyn, Inc. Y. Pouffary Hewlett Packard E. Vyncke Cisco Systems October 2014 Enterprise IPv6 Deployment Guidelines Abstract Enterprise network administrators worldwide are in various stages of preparing for or deploying IPv6 into their networks. The administrators face different challenges than operators of Internet access providers and have reasons for different priorities. The overall problem for many administrators will be to offer Internet- facing services over IPv6 while continuing to support IPv4, and while introducing IPv6 access within the enterprise IT network. The overall transition will take most networks from an IPv4-only environment to a dual-stack network environment and eventually an IPv6-only operating mode. This document helps provide a framework for enterprise network architects or administrators who may be faced with many of these challenges as they consider their IPv6 support strategies. Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7381.
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Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Enterprise Assumptions . . . . . . . . . . . . . . . . . 5 1.2. IPv4-Only Considerations . . . . . . . . . . . . . . . . 5 1.3. Reasons for a Phased Approach . . . . . . . . . . . . . . 6 2. Preparation and Assessment Phase . . . . . . . . . . . . . . 7 2.1. Program Planning . . . . . . . . . . . . . . . . . . . . 7 2.2. Inventory Phase . . . . . . . . . . . . . . . . . . . . . 8 2.2.1. Network Infrastructure Readiness Assessment . . . . . 8 2.2.2. Application Readiness Assessment . . . . . . . . . . 9 2.2.3. Importance of Readiness Validation and Testing . . . 9 2.3. Training . . . . . . . . . . . . . . . . . . . . . . . . 10 2.4. Security Policy . . . . . . . . . . . . . . . . . . . . . 10 2.4.1. IPv6 Is No More Secure Than IPv4 . . . . . . . . . . 10 2.4.2. Similarities between IPv6 and IPv4 Security . . . . . 11 2.4.3. Specific Security Issues for IPv6 . . . . . . . . . . 11 2.5. Routing . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.6. Address Plan . . . . . . . . . . . . . . . . . . . . . . 14 2.7. Tools Assessment . . . . . . . . . . . . . . . . . . . . 16 3. External Phase . . . . . . . . . . . . . . . . . . . . . . . 17 3.1. Connectivity . . . . . . . . . . . . . . . . . . . . . . 18 3.2. Security . . . . . . . . . . . . . . . . . . . . . . . . 19 3.3. Monitoring . . . . . . . . . . . . . . . . . . . . . . . 20 3.4. Servers and Applications . . . . . . . . . . . . . . . . 20 3.5. Network Prefix Translation for IPv6 . . . . . . . . . . . 21 4. Internal Phase . . . . . . . . . . . . . . . . . . . . . . . 21 4.1. Security . . . . . . . . . . . . . . . . . . . . . . . . 22 4.2. Network Infrastructure . . . . . . . . . . . . . . . . . 22 4.3. End-User Devices . . . . . . . . . . . . . . . . . . . . 23 4.4. Corporate Systems . . . . . . . . . . . . . . . . . . . . 24 5. IPv6 Only . . . . . . . . . . . . . . . . . . . . . . . . . . 24 6. Considerations for Specific Enterprises . . . . . . . . . . . 26 6.1. Content Delivery Networks . . . . . . . . . . . . . . . . 26 6.2. Data Center Virtualization . . . . . . . . . . . . . . . 26 6.3. University Campus Networks . . . . . . . . . . . . . . . 26 7. Security Considerations . . . . . . . . . . . . . . . . . . . 28 8. Informative References . . . . . . . . . . . . . . . . . . . 28 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 34 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction An enterprise network is defined in [RFC4057] as a network that has multiple internal links, one or more router connections to one or more providers, and is actively managed by a network operations entity (the "administrator", whether a single person or a department of administrators). Administrators generally support an internal network, consisting of users' workstations; personal computers; mobile devices; other computing devices and related peripherals; a server network, consisting of accounting and business application servers; and an external network, consisting of Internet-accessible services such as web servers, email servers, VPN systems, and customer applications. This document is intended as guidance for enterprise network architects and administrators in planning their IPv6 deployments. The business reasons for spending time, effort, and money on IPv6 will be unique to each enterprise. The most common drivers are due to the fact that when Internet service providers, including mobile wireless carriers, run out of IPv4 addresses, they will provide native IPv6 and non-native IPv4. The non-native IPv4 service may be NAT64, NAT444, Dual-Stack Lite (DS-Lite), Mapping of Address and Port using Translation (MAP-T), Mapping of Address and Port using Encapsulation (MAP-E), or other transition technologies. Compared to tunneled or translated service, native traffic typically performs better and more reliably than non-native. For example, for client networks trying to reach enterprise networks, the IPv6 experience will be better than the transitional IPv4 if the enterprise deploys IPv6 in its public-facing services. The native IPv6 network path should also be simpler to manage and, if necessary, troubleshoot. Further, enterprises doing business in growing parts of the world may find IPv6 growing faster there, where again potential new customers, employees, and partners are using IPv6. It is thus in the enterprise's interest to deploy native IPv6 at the very least in its public-facing services but ultimately across the majority or all of its scope. The text in this document provides specific guidance for enterprise networks and complements other related work in the IETF, including [IPv6-DESIGN] and [RFC5375].
1.1. Enterprise Assumptions For the purpose of this document, we assume the following: o The administrator is considering deploying IPv6 (but see Section 1.2 below). o The administrator has existing IPv4 networks and devices that will continue to operate and be supported. o The administrator will want to minimize the level of disruption to the users and services by minimizing the number of technologies and functions that are needed to mediate any given application. In other words, provide native IP wherever possible. Based on these assumptions, an administrator will want to use technologies that minimize the number of flows being tunneled, translated, or intercepted at any given time. The administrator will choose transition technologies or strategies that both allow most traffic to be native and manage non-native traffic. This will allow the administrator to minimize the cost of IPv6 transition technologies by containing the number and scale of transition systems. Tunnels used for IPv6/IPv4 transition are expected as near-/mid-term mechanisms, while IPv6 tunneling will be used for many long-term operational purposes such as security, routing control, mobility, multihoming, traffic engineering, etc. We refer to the former class of tunnels as "transition tunnels". 1.2. IPv4-Only Considerations As described in [RFC6302], administrators should take certain steps even if they are not considering IPv6. Specifically, Internet-facing servers should log the source port number, timestamp (from a reliable source), and the transport protocol. This will allow investigation of malefactors behind address-sharing technologies such as NAT444, MAP, or DS Lite. Such logs should be protected for integrity, safeguarded for privacy, and periodically purged within applicable regulations for log retention. Other IPv6 considerations may impact ostensibly IPv4-only networks, e.g., [RFC6104] describes the rogue IPv6 Router Advertisement (RA) problem, which may cause problems in IPv4-only networks where IPv6 is enabled in end systems on that network. Further discussion of the security implications of IPv6 in IPv4-only networks can be found in [RFC7123].
1.3. Reasons for a Phased Approach Given the challenges of transitioning user workstations, corporate systems, and Internet-facing servers, a phased approach allows incremental deployment of IPv6, based on the administrator's own determination of priorities. This document outlines suggested phases: a Preparation and Assessment Phase, an Internal Phase, and an External Phase. The Preparation Phase is highly recommended to all administrators, as it will save errors and complexity in later phases. Each administrator must decide whether to begin with an External Phase (enabling IPv6 for Internet-facing systems, as recommended in [RFC5211]) or an Internal Phase (enabling IPv6 for internal interconnections first). Each scenario is likely to be different to some extent, but we can highlight some considerations: o In many cases, customers outside the network will have IPv6 before the internal enterprise network. For these customers, IPv6 may well perform better, especially for certain applications, than translated or tunneled IPv4, so the administrator may want to prioritize the External Phase such that those customers have the simplest and most robust connectivity to the enterprise, or at least its external-facing elements. o Employees who access internal systems by VPN may find that their ISPs provide translated IPv4, which does not support the required VPN protocols. In these cases, the administrator may want to prioritize the External Phase and any other remotely accessible internal systems. It is worth noting that a number of emerging VPN solutions provide dual-stack connectivity; thus, a VPN service may be useful for employees in IPv4-only access networks to access IPv6 resources in the enterprise network (much like many public tunnel broker services, but specifically for the enterprise). Some security considerations are described in [RFC7359]. o Internet-facing servers cannot be managed over IPv6 unless the management systems are IPv6 capable. These might be Network Management Systems (NMS), monitoring systems, or just remote management desktops. Thus, in some cases, the Internet-facing systems are dependent on IPv6-capable internal networks. However, dual-stack Internet-facing systems can still be managed over IPv4. o Virtual Machines (VMs) may enable a faster rollout once initial system deployment is complete. Management of VMs over IPv6 is still dependent on the management software supporting IPv6.
o IPv6 is enabled by default on all modern operating systems, so it may be more urgent to manage and have visibility on the internal traffic. It is important to manage IPv6 for security purposes, even in an ostensibly IPv4-only network, as described in [RFC7123]. o In many cases, the corporate accounting, payroll, human resource, and other internal systems may only need to be reachable from the internal network, so they may be a lower priority. As enterprises require their vendors to support IPv6, more internal applications will support IPv6 by default, and it can be expected that eventually new applications will only support IPv6. The inventory, as described in Section 2.2, will help determine the systems' readiness, as well as the readiness of the supporting network elements and security, which will be a consideration in prioritization of these corporate systems. o Some large organizations (even when using private IPv4 addresses [RFC1918]) are facing IPv4 address exhaustion because of the internal network growth (for example, the vast number of VMs) or because of the acquisition of other companies that often raise private IPv4 address overlapping issues. o IPv6 restores end-to-end transparency even for internal applications (of course security policies must still be enforced). When two organizations or networks merge [RFC6879], the unique addressing of IPv6 can make the merger much easier and faster. A merger may, therefore, prioritize IPv6 for the affected systems. These considerations are in conflict; each administrator must prioritize according to their company's conditions. It is worth noting that the reasons given in "A Large Corporate User's View of IPng", described in [RFC1687], for reluctance to deploy have largely been satisfied or overcome in the intervening years. 2. Preparation and Assessment Phase 2.1. Program Planning Since enabling IPv6 is a change to the most fundamental Internet Protocol, and since there are so many interdependencies, having a professional project manager organize the work is highly recommended. In addition, an executive sponsor should be involved in determining the goals of enabling IPv6 (which will establish the order of the phases) and should receive regular updates. It may be necessary to complete the Preparation Phase before determining whether to prioritize the Internal or External Phase,
since needs and readiness assessments are part of that phase. For a large enterprise, it may take several iterations to really understand the level of effort required. Depending on the required schedule, it may be useful to roll IPv6 projects into other architectural upgrades -- this can be an excellent way to improve the network and reduce costs. However, by increasing the scope of projects, the schedule is often affected. For instance, a major systems upgrade may take a year to complete, where just patching existing systems may take only a few months. The deployment of IPv6 will not generally stop all other technology work. Once IPv6 has been identified as an important initiative, all projects, both new and in progress, will need to be reviewed to ensure IPv6 support. It is normal for assessments to continue in some areas while execution of the project begins in other areas. This is fine, as long as recommendations in other parts of this document are considered, especially regarding security (for instance, one should not deploy IPv6 on a system before security has been evaluated). 2.2. Inventory Phase To comprehend the scope of the Inventory Phase, we recommend dividing the problem space in two: network infrastructure readiness and applications readiness. 2.2.1. Network Infrastructure Readiness Assessment The goal of this assessment is to identify the level of IPv6 readiness of network equipment. This will identify the effort required to move to an infrastructure that supports IPv6 with the same functional service capabilities as the existing IPv4 network. This may also require a feature comparison and gap analysis between IPv4 and IPv6 functionality on the network equipment and software. IPv6 support will require testing; features often work differently in vendors' labs than production networks. Some devices and software will require IPv4 support for IPv6 to work. The inventory will show which network devices are already capable, which devices can be made IPv6 ready with a code/firmware upgrade, and which devices will need to be replaced. The data collection consists of a network discovery to gain an understanding of the topology and inventory network infrastructure equipment and code versions with information gathered from static files and IP address management, DNS, and DHCP tools.
Since IPv6 might already be present in the environment, through default configurations or VPNs, an infrastructure assessment (at minimum) is essential to evaluate potential security risks. 2.2.2. Application Readiness Assessment Just like network equipment, application software needs to support IPv6. This includes OS, firmware, middleware, and applications (including internally developed applications). Vendors will typically handle IPv6 enablement of off-the-shelf products, but often enterprises need to request this support from vendors. For internally developed applications, it is the responsibility of the enterprise to enable them for IPv6. Analyzing how a given application communicates over the network will dictate the steps required to support IPv6. Applications should avoid instructions specific to a given IP address family. Any applications that use APIs, such as the C language, that expose the IP version specifically, need to be modified to also work with IPv6. There are two ways to IPv6-enable applications. The first approach is to have separate logic for IPv4 and IPv6, thus leaving the IPv4 code path mainly untouched. This approach causes the least disruption to the existing IPv4 logic flow, but introduces more complexity, since the application now has to deal with two logic loops with complex race conditions and error recovery mechanisms between these two logic loops. The second approach is to create a combined IPv4/IPv6 logic, which ensures operation regardless of the IP version used on the network. Knowing whether a given implementation will use IPv4 or IPv6 in a given deployment is a matter of some art; see Source Address Selection [RFC6724] and Happy Eyeballs [RFC6555]. It is generally recommended that the application developer use industry IPv6-porting tools to locate the code that needs to be updated. Some discussion of IPv6 application porting issues can be found in [RFC4038]. 2.2.3. Importance of Readiness Validation and Testing Lastly, IPv6 introduces a completely new way of addressing endpoints, which can have ramifications at the network layer all the way up to the applications. So to minimize disruption during the transition phase, we recommend complete functionality, scalability, and security testing to understand how IPv6 impacts the services and networking infrastructure.
2.3. Training Many organizations falter in IPv6 deployment because of a perceived training gap. Training is important for those who work with addresses regularly, as with anyone whose work is changing. Better knowledge of the reasons IPv6 is being deployed will help inform the assessment of who needs training and what training they need. 2.4. Security Policy It is obvious that IPv6 networks should be deployed in a secure way. The industry has learned a lot about network security with IPv4, so network operators should leverage this knowledge and expertise when deploying IPv6. IPv6 is not so different than IPv4: it is a connectionless network protocol using the same lower-layer service and delivering the same service to the upper layer. Therefore, the security issues and mitigation techniques are mostly identical with the same exceptions that are described further. 2.4.1. IPv6 Is No More Secure Than IPv4 Some people believe that IPv6 is inherently more secure than IPv4 because it is new. Nothing can be more wrong. Indeed, being a new protocol means that bugs in the implementations have yet to be discovered and fixed and that few people have the operational security expertise needed to operate securely an IPv6 network. This lack of operational expertise is the biggest threat when deploying IPv6: the importance of training is to be stressed again. One security myth is that, thanks to its huge address space, a network cannot be scanned by enumerating all IPv6 addresses in a /64 LAN; hence, a malevolent person cannot find a victim. [RFC5157] describes some alternate techniques to find potential targets on a network, for example, enumerating all DNS names in a zone. Additional advice in this area is also given in [HOST-SCANNING]. Another security myth is that IPv6 is more secure because it mandates the use of IPsec everywhere. While the original IPv6 specifications may have implied this, [RFC6434] clearly states that IPsec support is not mandatory. Moreover, if all the intra-enterprise traffic is encrypted, both malefactors and security tools that rely on payload inspection (Intrusion Prevention System (IPS), firewall, Access Control List (ACL), IP Flow Information Export (IPFIX) ([RFC7011] and [RFC7012]), etc.) will be affected. Therefore, IPsec is as useful in IPv6 as in IPv4 (for example, to establish a VPN overlay over a non- trusted network or to reserve for some specific applications).
The last security myth is that amplification attacks (such as [SMURF]) do not exist in IPv6 because there is no more broadcast. Alas, this is not true as ICMP error (in some cases) or information messages can be generated by routers and hosts when forwarding or receiving a multicast message (see Section 2.4 of [RFC4443]). Therefore, the generation and the forwarding rate of ICMPv6 messages must be limited as in IPv4. It should be noted that in a dual-stack network, the security implementation for both IPv4 and IPv6 needs to be considered, in addition to security considerations related to the interaction of (and transition between) the two, while they coexist. 2.4.2. Similarities between IPv6 and IPv4 Security As mentioned earlier, IPv6 is quite similar to IPv4; therefore, several attacks apply for both protocol families, including: o Application layer attacks: such as cross-site scripting or SQL injection o Rogue device: such as a rogue Wi-Fi access point o Flooding and all traffic-based denial of services (including the use of control plane policing for IPv6 traffic: see [RFC6192]) A specific case of congruence is IPv6 Unique Local Addresses (ULAs) [RFC4193] and IPv4 private addressing [RFC1918], which do not provide any security by 'magic'. In both cases, the edge router must apply strict filters to block those private addresses from entering and, just as importantly, leaving the network. This filtering can be done by the enterprise or by the ISP, but the cautious administrator will prefer to do it in the enterprise. IPv6 addresses can be spoofed as easily as IPv4 addresses, and there are packets with bogon IPv6 addresses (see [CYMRU]). Anti-bogon filtering must be done in the data and routing planes. It can be done by the enterprise or by the ISP, or both, but again the cautious administrator will prefer to do it in the enterprise. 2.4.3. Specific Security Issues for IPv6 Even if IPv6 is similar to IPv4, there are some differences that create some IPv6-only vulnerabilities or issues. We give examples of such differences in this section. Privacy extension addresses [RFC4941] are usually used to protect individual privacy by periodically changing the interface identifier
part of the IPv6 address to avoid tracking a host by its otherwise always identical and unique 64-bit Extended Unique Identifier (EUI-64) based on Media Access Control (MAC). While this presents a real advantage on the Internet, moderated by the fact that the prefix part remains the same, it complicates the task of following an audit trail when a security officer or network operator wants to trace back a log entry to a host in their network because when the tracing is done, the searched IPv6 address could have disappeared from the network. Therefore, the use of privacy extension addresses usually requires additional monitoring and logging of the binding of the IPv6 address to a data-link layer address (see also the monitoring section in [IPv6-SECURITY], Section 2.5). Some early enterprise deployments have taken the approach of using tools that harvest IP/MAC address mappings from switch and router devices to provide address accountability; this approach has been shown to work, though it can involve gathering significantly more address data than in equivalent IPv4 networks. An alternative is to try to prevent the use of privacy extension addresses by enforcing the use of DHCPv6, such that hosts only get addresses assigned by a DHCPv6 server. This can be done by configuring routers to set the M bit in RAs, combined with all advertised prefixes being included without the A bit set (to prevent the use of stateless autoconfiguration). Of course, this technique requires that all hosts support stateful DHCPv6. It is important to note that not all operating systems exhibit the same behavior when processing RAs with the M bit set. The varying OS behavior is related to the lack of prescriptive definition around the A, M, and O bits within the Neighbor Discovery Protocol (NDP). [DHCPv6-SLAAC-PROBLEM] provides a much more detailed analysis on the interaction of the M bit and DHCPv6. Extension headers complicate the task of stateless packet filters such as ACLs. If ACLs are used to enforce a security policy, then the enterprise must verify whether its ACLs (but also stateful firewalls) are able to process extension headers (this means understand them enough to parse them to find the upper-layer payloads) and to block unwanted extension headers (e.g., to implement [RFC5095]). This topic is discussed further in [RFC7045]. Fragmentation is different in IPv6 because it is done only by the source host and never during a forwarding operation. This means that ICMPv6 packet-too-big messages must be allowed to pass through the network and not be filtered [RFC4890]. Fragments can also be used to evade some security mechanisms such as RA-Guard [RFC6105]. See also [RFC5722] and [RFC7113]. One of the biggest differences between IPv4 and IPv6 is the introduction of NDP [RFC4861], which includes a variety of important IPv6 protocol functions, including those provided in IPv4 by the
Address Resolution Protocol (ARP) [RFC0826]. NDP runs over ICMPv6 (which as stated above means that security policies must allow some ICMPv6 messages to pass, as described in RFC 4890), but has the same lack of security as, for example, ARP, in that there is no inherent message authentication. While Secure Neighbor Discovery (SEND) [RFC3971] and Cryptographically Generated Addresses (CGAs) [RFC3972] have been defined, they are not widely implemented). The threat model for RAs within the NDP suite is similar to that of DHCPv4 (and DHCPv6), in that a rogue host could be either a rogue router or a rogue DHCP server. An IPv4 network can be made more secure with the help of DHCPv4 snooping in edge switches, and likewise RA snooping can improve IPv6 network security (in IPv4-only networks as well). Thus, enterprises using such techniques for IPv4 should use the equivalent techniques for IPv6, including RA-Guard [RFC6105] and all work in progress from the Source Address Validation Improvement (SAVI) WG, e.g., [RFC6959], which is similar to the protection given by dynamic ARP monitoring in IPv4. Other DoS vulnerabilities are related to NDP cache exhaustion, and mitigation techniques can be found in ([RFC6583]). As stated previously, running a dual-stack network doubles the attack exposure as a malevolent person has now two attack vectors: IPv4 and IPv6. This simply means that all routers and hosts operating in a dual-stack environment with both protocol families enabled (even if by default) must have a congruent security policy for both protocol versions. For example, permit TCP ports 80 and 443 to all web servers and deny all other ports to the same servers must be implemented both for IPv4 and IPv6. It is thus important that the tools available to administrators readily support such behavior. 2.5. Routing An important design choice to be made is what IGP is to use inside the network. A variety of IGPs (IS-IS, OSPFv3, and Routing Information Protocol Next Generation (RIPng)) support IPv6 today, and picking one over the other is a design choice that will be dictated mostly by existing operational policies in an enterprise network. As mentioned earlier, it would be beneficial to maintain operational parity between IPv4 and IPv6; therefore, it might make sense to continue using the same protocol family that is being used for IPv4. For example, in a network using OSPFv2 for IPv4, it might make sense to use OSPFv3 for IPv6. It is important to note that although OSPFv3 is similar to OSPFv2, they are not the same. On the other hand, some organizations may chose to run different routing protocols for different IP versions. For example, one may chose to run OSPFv2 for IPv4 and IS-IS for IPv6. An important design question to consider here is whether to support one IGP or two different IGPs in the longer term. [IPv6-DESIGN] presents advice on the design choices
that arise when considering IGPs and discusses the advantages and disadvantages to different approaches in detail. 2.6. Address Plan The most common problem encountered in IPv6 networking is in applying the same principles of conservation that are so important in IPv4. IPv6 addresses do not need to be assigned conservatively. In fact, a single, larger allocation is considered more conservative than multiple non-contiguous small blocks because a single block occupies only a single entry in a routing table. The advice in [RFC5375] is still sound and is recommended to the reader. If considering ULAs, give careful thought to how well it is supported, especially in multiple address and multicast scenarios, and assess the strength of the requirement for ULA. [ULA-USAGE] provides much more detailed analysis and recommendations on the usage of ULAs. The enterprise administrator will want to evaluate whether the enterprise will request address space from a Local Internet Registry (LIR) such as an ISP; a Regional Internet Registry (RIR) such as AfriNIC, APNIC, ARIN, LACNIC, or RIPE-NCC; or a National Internet Registry (NIR) operated in some countries. The normal allocation is Provider-Aggregated (PA) address space from the enterprise's ISP, but use of PA space implies renumbering when changing providers. Instead, an enterprise may request Provider-Independent (PI) space; this may involve an additional fee, but the enterprise may then be better able to be multihomed using that prefix and will avoid a renumbering process when changing ISPs (though it should be noted that renumbering caused by outgrowing the space, merger, or other internal reason would still not be avoided with PI space). The type of address selected (PI vs. PA) should be congruent with the routing needs of the enterprise. The selection of address type will determine if an operator will need to apply new routing techniques and may limit future flexibility. There is no right answer, but the needs of the External Phase may affect what address type is selected. Each network location or site will need a prefix assignment. Depending on the type of site/location, various prefix sizes may be used. In general, historical guidance suggests that each site should get at least a /48, as documented in RFC 5375 and [RFC6177]. In addition to allowing for simple planning, this can allow a site to use its prefix for local connectivity, should the need arise, and if the local ISP supports it. When assigning addresses to end systems, the enterprise may use manually configured addresses (common on servers) or Stateless Address Autoconfiguration (SLAAC) or DHCPv6 for client systems.
Early IPv6 enterprise deployments have used SLAAC both for its simplicity and the time DHCPv6 has taken to mature. However, DHCPv6 is now very mature; thus, workstations managed by an enterprise may use stateful DHCPv6 for addressing on corporate LAN segments. DHCPv6 allows for the additional configuration options often employed by enterprise administrators, and by using stateful DHCPv6, administrators correlating system logs know which system had which address at any given time. Such an accountability model is familiar from IPv4 management, though DHCPv6 hosts are identified by a DHCP Unique Identifier (DUID) rather than a MAC address. For equivalent accountability with SLAAC (and potentially privacy addresses), a monitoring system that harvests IP/MAC mappings from switch and router equipment could be used. A common deployment consideration for any enterprise network is how to get host DNS records updated. Commonly, either the host will send DNS updates or the DHCP server will update records. If there is sufficient trust between the hosts and the DNS server, the hosts may update (and the enterprise may use SLAAC for addressing). Otherwise, the DHCPv6 server can be configured to update the DNS server. Note that an enterprise network with this more controlled environment will need to disable SLAAC on network segments and force end hosts to use DHCPv6 only. In the data center or server room, assume a /64 per VLAN. This applies even if each individual system is on a separate VLAN. In a /48 assignment, typical for a site, there are then still 65,535 /64 blocks. Some administrators reserve a /64 but configure a small subnet, such as /112, /126, or /127, to prevent rogue devices from attaching and getting numbers; an alternative is to monitor traffic for surprising addresses or Neighbor Discovery (ND) tables for new entries. Addresses are either configured manually on the server or reserved on a DHCPv6 server, which may also synchronize forward and reverse DNS (though see [RFC6866] for considerations on static addressing). SLAAC is not recommended for servers because of the need to synchronize RA timers with DNS Times to Live (TTLs) so that the DNS entry expires at the same time as the address. All user access networks should be a /64. Point-to-point links where NDP is not used may also utilize a /127 (see [RFC6164]). Plan to aggregate at every layer of network hierarchy. There is no need for variable length subnet mask (VLSM) [RFC1817] in IPv6, and addressing plans based on conservation of addresses are shortsighted. Use of prefixes longer then /64 on network segments will break common IPv6 functions such as SLAAC [RFC4862]. Where multiple VLANs or other Layer 2 domains converge, allow some room for expansion. Renumbering due to outgrowing the network plan is a nuisance, so
allow room within it. Generally, plan to grow to about twice the current size that can be accommodated; where rapid growth is planned, allow for twice that growth. Also, if DNS (or reverse DNS) authority may be delegated to others in the enterprise, assignments need to be on nibble boundaries (that is, on a multiple of 4 bits, such as /64, /60, /56, ..., /48, /44), to ensure that delegated zones align with assigned prefixes. If using ULAs, it is important to note that AAAA and PTR records for ULAs are not recommended to be installed in the global DNS. Similarly, reverse (address-to-name) queries for ULA must not be sent to name servers outside of the organization, due to the load that such queries would create for the authoritative name servers for the ip6.arpa zone. For more details, please refer to Section 4.4 of [RFC4193]. Enterprise networks are increasingly including virtual networks where a single, physical node may host many virtualized addressable devices. It is imperative that the addressing plans assigned to these virtual networks and devices be consistent and non-overlapping with the addresses assigned to real networks and nodes. For example, a virtual network established within an isolated lab environment may, at a later time, become attached to the production enterprise network. 2.7. Tools Assessment Enterprises will often have a number of operational tools and support systems that are used to provision, monitor, manage, and diagnose the network and systems within their environment. These tools and systems will need to be assessed for compatibility with IPv6. The compatibility may be related to the addressing and connectivity of various devices as well as IPv6 awareness of the tools and processing logic. The tools within the organization fall into two general categories: those that focus on managing the network and those that are focused on managing systems and applications on the network. In either instance, the tools will run on platforms that may or may not be capable of operating in an IPv6 network. This lack in functionality may be related to operating system version or based on some hardware constraint. Those systems that are found to be incapable of utilizing an IPv6 connection, or which are dependent on an IPv4 stack, may need to be replaced or upgraded. In addition to devices working on an IPv6 network natively, or via a transition tunnel, many tools and support systems may require additional software updates to be IPv6 aware or even a hardware
upgrade (usually for additional memory, IPv6 addresses are larger and for a while, IPv4 and IPv6 addresses will coexist in the tool). This awareness may include the ability to manage IPv6 elements and/or applications in addition to the ability to store and utilize IPv6 addresses. Considerations when assessing the tools and support systems may include the fact that IPv6 addresses are significantly larger than IPv4, requiring data stores to support the increased size. Such issues are among those discussed in [RFC5952]. Many organizations may also run dual-stack networks; therefore, the tools need to not only support IPv6 operation but may also need to support the monitoring, management, and intersection with both IPv6 and IPv4 simultaneously. It is important to note that managing IPv6 is not just constrained to using large IPv6 addresses, but also that IPv6 interfaces and nodes are likely to use two or more addresses as part of normal operation. Updating management systems to deal with these additional nuances will likely consume time and considerable effort. For networking systems, like node management systems, it is not always necessary to support local IPv6 addressing and connectivity. Operations such as SNMP MIB polling can occur over IPv4 transport while seeking responses related to IPv6 information. Where this may seem advantageous to some, it should be noted that without local IPv6 connectivity, the management system may not be able to perform all expected functions -- such as reachability and service checks. Organizations should be aware that changes to older IPv4-only SNMP MIB specifications have been made by the IETF and are related to legacy operation in [RFC2096] and [RFC2011]. Updated specifications are now available in [RFC4292] and [RFC4293] that modified the older MIB framework to be IP protocol agnostic, supporting both IPv4 and IPv6. Polling systems will need to be upgraded to support these updates as well as the end stations, which are polled.