IPv6 Operations L. Colitti Internet-Draft V. Cerf Intended status: Best Current Practice Google Expires: January 7, 2016 S. Cheshire Apple July 6, 2015 Host address availability recommendations draft-colitti-v6ops-host-addr-availability-00 Abstract This document recommends that networks provide general-purpose end hosts with multiple global addresses, and describes options for doing so. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on January 7, 2016. Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Colitti, et al. Expires January 7, 2016 [Page 1] Internet-Draft Host address availability recommendations July 2015 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 2. Common IPv6 deployment model . . . . . . . . . . . . . . . . 2 3. Benefits of multiple addresses . . . . . . . . . . . . . . . 3 4. Problems with assigning a limited number of addresses per host . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Overcoming limits using Network Address Translation . . . . . 4 6. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 5 7. Options for obtaining more than one address . . . . . . . . . 5 8. Operational considerations . . . . . . . . . . . . . . . . . 6 8.1. Stateful addressing and host tracking . . . . . . . . . . 6 8.2. Address space management . . . . . . . . . . . . . . . . 7 8.3. Addressing link layer scalability issues via IP routing . 7 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 11. Security Considerations . . . . . . . . . . . . . . . . . . . 8 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 12.1. Normative References . . . . . . . . . . . . . . . . . . 8 12.2. Informative References . . . . . . . . . . . . . . . . . 8 12.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Appendix A. Additional Stuff . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction This document recommends that networks provide general-purpose end hosts with multiple global addresses, and describes options for doing so. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 2. Common IPv6 deployment model IPv6 is designed to support multiple addresses, including multiple global addresses, per interface ([RFC4291] section 2.1, [RFC6433] section 5.9.4). Today, many general-purpose IPv6 hosts are configured with three or more addresses per interface: a link-local address, a stable address (e.g., using EUI-64 or [RFC7217]), one or more privacy addresses [RFC4941], and possibly one or more addresses assigned using DHCPv6 [RFC7217]. Colitti, et al. Expires January 7, 2016 [Page 2] Internet-Draft Host address availability recommendations July 2015 In most general-purpose IPv6 networks, including all 3GPP networks (see [RFC6459] section 5.2) and Ethernet and Wi-Fi networks using SLAAC [RFC4862], IPv6 hosts have the ability to configure additional IPv6 addresses from the on-link prefix without explicit requests to the network. 3. Benefits of multiple addresses Today, there are many host functions that require more than one IP address to be available to the host: o Privacy addressing to prevent tracking by off-network hosts (e.g., [RFC4941]) o Multiple processors inside the same device. For example, in many mobile devices both the application processor and baseband processor need to communicate with the network, particularly for recent technologies like ePDG. o Extending network (e.g., tethering) o Running virtual machines on hosts o Translation-based transition technologies such as 464xlat that provide IPv4 over IPv6. These require the availability of a dedicated IPv6 address in order to determine whether inbound packets are translated or native. o ILA ("Identifier-locator addressing"): https://tools.ietf.org/ html/draft-herbert-nvo3-ila o Future applications (e.g., per-application IPv6 addresses). Example of how the availability of multiple addresses per host has already allowed substantial deployment of new applications without explicit requests to the network are: o 464xlat [RFC6877]. 464xlat is usually deployed within a particular network operator's network, but there are deployment models where the PLAT is provided as a service by a different network [e.g., http://www.jpix.ad.jp/en/service/ipv6v4.html] o /64 sharing [RFC7278]. This was a way to provide IPv6 tethering without needing to wait for network operators to deploy DHCPv6 PD, which is only available in 3GPP release 10. Colitti, et al. Expires January 7, 2016 [Page 3] Internet-Draft Host address availability recommendations July 2015 4. Problems with assigning a limited number of addresses per host Assigning a limited number of addresses per host implies that functions that require multiple addresses will either be unavailable (e.g., if the network provides only one IPv6 address per host, or if the host has reached the limit of the number of addresses available), or that the functions will only be available after an explicit request to the network is granted. The necessity of explicit requests has the following drawbacks: o Increased latency, because a provisioning operation must complete before the functionality is available. o Uncertainty, because it is not known in advance if a particular operation function will be available. o Complexity, because implementations need to deal with failures and somehow present them to the user. Failures may manifest as timeouts, which may be slow and frustrating to users. o Increased load on the network's provisioning servers. Some operators may desire to configure their networks to limit the number of IPv6 addresses per host. Reasons might include hardware limitations (e.g., TCAM or neighbour cache table size constraints), operational consistency with IPv4 (e.g., an IP address management system that only supports one address per host), or business models (e.g., a desire to charge the network's users on a per-device basis). 5. Overcoming limits using Network Address Translation These limits can mostly be overcome by end hosts by using NAT, and indeed in IPv4 most of these functions are provided by using NAT on the host. Thus, the limits could be overcome in IPv6 as well by implementing NAT66 on the host. Unfortunately NAT has well-known drawbacks. For example, it causes application complexity due to the need to implement NAT traversal. It hinders development of new applications. On mobile devices, it reduces battery life due to the necessity of frequent keepalives (particularly for UDP, applications that need to work on most of the Internet are forced to send keepalives at least every 30 seconds [QUIC IETF slides]). While IPv4 NAT is inevitable due to the limited amount of IPv4 space available, that argument does not apply to IPv6. Guidance from the IAB is that deployment of IPv6 NAT is not desirable [RFC5902]. Colitti, et al. Expires January 7, 2016 [Page 4] Internet-Draft Host address availability recommendations July 2015 If networks that provide limited amount of addresses become widely deployed, then the desire to overcome the problems listed in section without disabling any features may result in operating system manufacturers implementing IPv6 NAT. This is not a desirable outcome. It is not desirable for users because they may experience application brittleness. It is likely not desirable for network operators either, as they may suffer higher support costs, and even when the decision to assign only one IPv6 address per device is dictated by the network's business model, there may be little in the way of incremental revenue, because devices can share their IPv6 address with other devices. Finally, it is not desirable for operating system manufacturers and application developers, who will have to build more complexity, lengthening development time and/or reducing the time spent on other features. Indeed, it could be argued that the main reason for deploying IPv6, instead of continuing to scale the Internet using only IPv4 and large-scale NAT44, is because doing so can provide all the hosts on the planet with end-to-end connectivity that is limited not by technical factors but only by security policies. 6. Recommendations In order to avoid the problems described above, and preserve the Internet's ability to support new applications that use more than one IPv6 address, it is recommended that IPv6 network deployments provide multiple IPv6 addresses to general purpose hosts. 7. Options for obtaining more than one address Multiple IPv6 addresses can be obtained in the following ways: o Using Stateless Address Autoconfiguration [RFC4862]. SLAAC allows hosts to create global IPv6 addresses on demand by simply forming new addresses from the global prefix assigned to the link. o Using stateful DHCPv6 address assignment [RFC3315]. Most DHCPv6 clients only ask for one address, but the protocol allows requesting multiple addresses, and the server could choose to assign the client multiple addresses. It is also possible for a client to request additional addresses using a different DUID. The DHCPv6 server will decide whether to grant or reject the request based on information about the client, including its DUID, MAC address, and so on. o DHCPv6 prefix delegation [RFC3633]. DHCPv6 PD allows the client to request and be delegated a prefix, from which it can Colitti, et al. Expires January 7, 2016 [Page 5] Internet-Draft Host address availability recommendations July 2015 autonomously form other addresses. If the prefix is a /64, it can also reshare that prefix with any downstream clients via [RFC7278] /64 sharing. +-------------------------+----------+---------+----------+---------+ | | SLAAC | DHCPv6 | DHCPv6 | DHCPv4 | | | | IA_NA | PD | | +-------------------------+----------+---------+----------+---------+ | Autonomously form | Yes (/64 | No | Yes (/64 | Yes | | addresses | share) | | share) | (NAT44) | | "Unlimited" addressing | Yes | Yes | No | No | | Stateful, request-based | No | Yes | Yes | Yes | | Request-based | No | Yes | Yes | Yes | | Immune to layer 3 on- | No | Yes | Yes | Yes | | link resource | | | | | | exhaustion attacks | | | | | +-------------------------+----------+---------+----------+---------+ Table 1: Comparison of multiple address assigment options 8. Operational considerations 8.1. Stateful addressing and host tracking Some network operators - often operators networks that provide services to third parties such as university campus networks - have made the argument that the only feasible IPv6 deployment mechanism is DHCPv6, due to the need to be able to track at all times IPv6 addresses are assigned to which hosts. (Example: [1] ). One reason frequently cited for this is protection from liability for copyright infringement or other illegal activity. It is worth noting that using DHCPv6 does not by itself ensure that hosts will actually use the addresses assigned to them by the network as opposed to using any other address on the prefix. Such guarantees can only be provided by link-layer security mechanisms that enforce that particular IPv6 addresses are used by particular link-layer addresses (e.g., SAVI [RFC7039]). If those mechanisms are available, it is possible to use them to provide tracking, instead. This form of tracking is much more reliable because it operates independently of how addresses are allocated. Many large enterprise networks, including the enterprise networks of the authors, are fully dual-stack but do not use or support DHCPv6. Colitti, et al. Expires January 7, 2016 [Page 6] Internet-Draft Host address availability recommendations July 2015 8.2. Address space management In IPv4, all but the world's largest IPv4 networks can be addressed using RFC 1918 space. The total size of net 10 is roughly 2^24 (16 million) endpoints, with each endpoint receiving one IPv4 address. In IPv6, that is equivalent to assigning one /64 per host out of a /40. Under current RIR policies, a /40 is easy to obtain for an enterprise network. In other words, assigning a single IPv6 /64 per host is as feasible as assigning a single IPv4 address per host. Currently, residential users receive one IPv4 address and a /56 or /60 IPv6 prefix. While such networks do not have enough space to assign a /64 per device, today such networks almost universally use SLAAC. Unlike IPv4 where addresses came at a premium, in all these networks, there is enough IPv6 address space to supply clients with multiple IPv6 addresses. 8.3. Addressing link layer scalability issues via IP routing The number of IPv6 addresses on a link has direct impact for networking infrastructure nodes (routers, switches) and other nodes on the link. Setting aside exhaustion attacks via Layer 2 address spoofing, every (Layer 2, IP) address pair impacts networking hardware requirements in terms of memory, MLD snooping, solicited node multicast groups, etc. Many of these same impacts can be felt by neighboring hosts. Switching to a DHCPv6-PD model means there are only forwarding decisions, with only one routing entry and one ND cache entry per device on the network. 9. Acknowledgements The authors thank Dieter Siegmund and David Schinazi for their input and contributions. 10. IANA Considerations This memo includes no request to IANA. All drafts are required to have an IANA considerations section (see the update of RFC 2434 [I-D.narten-iana-considerations-rfc2434bis] for a guide). If the draft does not require IANA to do anything, the section contains an explicit statement that this is the case (as above). If there are no requirements for IANA, the section will be removed during conversion into an RFC by the RFC Editor. Colitti, et al. Expires January 7, 2016 [Page 7] Internet-Draft Host address availability recommendations July 2015 11. Security Considerations All drafts are required to have a security considerations section. See RFC 3552 [RFC3552] for a guide. 12. References 12.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 12.2. Informative References [I-D.narten-iana-considerations-rfc2434bis] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", draft-narten-iana- considerations-rfc2434bis-09 (work in progress), March 2008. [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations", BCP 72, RFC 3552, July 2003. [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, December 2003. [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, September 2007. [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 4941, September 2007. [RFC5902] Thaler, D., Zhang, L., and G. Lebovitz, "IAB Thoughts on IPv6 Network Address Translation", RFC 5902, July 2010. [RFC6433] Hoffman, P., "Requirements for a Working Group Milestones Tool", RFC 6433, November 2011. Colitti, et al. Expires January 7, 2016 [Page 8] Internet-Draft Host address availability recommendations July 2015 [RFC6459] Korhonen, J., Soininen, J., Patil, B., Savolainen, T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation Partnership Project (3GPP) Evolved Packet System (EPS)", RFC 6459, January 2012. [RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: Combination of Stateful and Stateless Translation", RFC 6877, April 2013. [RFC7217] Gont, F., "A Method for Generating Semantically Opaque Interface Identifiers with IPv6 Stateless Address Autoconfiguration (SLAAC)", RFC 7217, April 2014. [RFC7278] Byrne, C., Drown, D., and A. Vizdal, "Extending an IPv6 /64 Prefix from a Third Generation Partnership Project (3GPP) Mobile Interface to a LAN Link", RFC 7278, June 2014. 12.3. URIs [1] https://code.google.com/p/android/issues/detail?id=32621#c60 Appendix A. Additional Stuff This becomes an Appendix. Authors' Addresses Lorenzo Colitti Google Roppongi 6-10-1 Minato, Tokyo 106-6126 JP Email: lorenzo@google.com Vint Cerf Google Stuart Cheshire Apple Colitti, et al. Expires January 7, 2016 [Page 9]