Network Working Group B. Liu Internet Draft Huawei Technologies Co., Ltd Intended status: Informational July 15, 2013 Expires: January 16, 2014 Running Multiple IPv6 Prefixes draft-liu-v6ops-running-multiple-prefixes-00.txt 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 16, 2014. Copyright Notice Copyright (c) 2012 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. Bing Liu Expires January 16, 2014 [Page 1] Internet-Draft Running Multiple Prefixes July 2013 Abstract This document introduces that multiple prefixes in one network/host might be common in IPv6, and describes several multiple prefixes use cases. Then some operational considerations and current gaps to support multiple prefixes operations are described. Table of Contents 1. Introduction ................................................. 3 2. Multiple Prefixes Use cases .................................. 3 2.1. Multihoming ............................................. 3 2.2. ULA+PA .................................................. 4 2.3. Make-before-break renumbering ........................... 4 2.4. Semantic Prefixes ....................................... 4 3. Basic operational considerations ............................. 5 3.1. Multiple prefix provisioning ............................ 5 3.2. Multiple addresses in one interface ..................... 5 3.3. Address selection ....................................... 6 3.4. DNS relevant ............................................ 6 4. Current Gaps ................................................. 6 5. Security Considerations ...................................... 7 6. IANA Considerations .......................................... 7 7. Acknowledgments .............................................. 7 8. References ................................................... 7 8.1. Normative References .................................... 7 8.2. Informative References .................................. 8 Liu, et al. Expires January 16, 2014 [Page 2] Internet-Draft Running Multiple Prefixes July 2013 1. Introduction IP protocols have been widely spread. More and more services are relying on IP infrastructure. And IP network architecture/functions are becoming more and more sophisticated accordingly. One aspect is the requirement of multiple prefixes. There are some probable motivations of multiple prefixes, as the following: - Multiple network provisioning, including multihoming and semantic prefixes (as described in section 2.4) etc; - Multiple logic planes, VPN/OAM .etc. In IPv6, multiple prefixes feature is naturally well-supported. Standard IPv6 stack supports multiple-addresses-per-interface as default; there is a standard address selection algorithms (RFC6724) defined for multiple prefixes purpose. Although most of the recent IPv4 stacks also support multiple-addresses-per-interfce, IPv6 makes it as mandatory and provides way of automatically managing the addresses. It is one of the most important advantages from IPv4 to IPv6. This document discusses several aspects of running multiple prefixes, which include some multiple prefixes use cases; some operational considerations of running multiple prefixes in a network; and some current gaps of supporting running multiple prefixes. 2. Multiple Prefixes Use cases 2.1. Multihoming When a network is multihomed, the multiple upstream networks would assign prefixes respectively. If a network for some reason neither acquires a PI (Provider Independent) space nor deploys IPv6 NAT, then the multihoming would resulting in hosts with multiple PA (Provider Aggregated) IPv6 addresses with different prefixes. This approach in IPv4 has rarely been used, since the IPv4 doesn't support multiple addresses/prefixes well. But it is quite practical in IPv6. This approach allows the SMEs (Small & Medium Enterprises) to do multihoming without burden from running PI address space or running IPv6 NAT. Furthermore, multiple PA spaces don't have the potential global routing system scalable issue as the PI does [RFC4894]. Liu, et al. Expires January 16, 2014 [Page 3] Internet-Draft Running Multiple Prefixes July 2013 However, multihoming with multiple PA spaces has some operational issues which mainly include address selection, next-hop selection, and DNS selection (see section 5 in [I.D-ietf-v6ops-ipv6-multihoming-without-ipv6nat]). Besides, there is another exit-router selection issue, which seems has not been addresses by any practical solution yet (see some detailed discussion in section 4). 2.2. ULA+PA Unique Local Addresses (ULAs) are defined in [RFC4193] as provider- independent prefixes. Since there is a 40 bits pseudo random field in the ULA prefix, there is no practical risk of collision (please refer to section 3.2.3 in [RFC4193] for more detail). The main purpose of using ULA along with GUA (Global Unique Address) is to provide a logically local routing plane separated from the globally routing plane. The benefit is to ensure stable and specific local communication regardless of the uplink (who provides the GUA connectivity, e.g. an ISP) failure or change. This benefit is especially meaningful for the home network or private OAM function in an enterprise. In some special cases such as renumbering, enterprise administrators may want to avoid the need to renumber their internal-only, private nodes when they have to renumber the PA addresses of the whole network because of changing ISPs, ISPs restructure their address allocations, or whatever reasons. In these situations, ULA is an effective tool for the internal-only nodes. 2.3. Make-before-break renumbering [RFC4192] describes a procedure that can be used to renumber a network from one prefix to another smoothly through a "make-before- break" transition. In the transition period, both the old and new prefixes are available; it is a very good use of multiple prefixes that could avoid the session outage issue in most of the situations when renumbering a network. 2.4. Semantic Prefixes [I-D.jiang-semantic-prefix] describes a framework to embed some parameters into the IPv6 prefix segment. The parameters might contain user types, service types, applications, security requirements, traffic identity types, quality requirements and other criteria may Liu, et al. Expires January 16, 2014 [Page 4] Internet-Draft Running Multiple Prefixes July 2013 also be relevant parameters which a network operator may wish to use to treat packets differently and efficiently. With this approach, for example, the ISPs could provision one subscriber multiple addresses/prefixes to access different services. 3. Basic operational considerations There might be some argument/worry that in practice running multiple prefixes would makes terrible operational complexity. It is apprehensible that most of the administrators are not be accustomed to this model, since it is quite different with that in IPv4. But considering running multiple prefixes in IPv6 might be very common, administrators need to adapt this new operational model regardless of personal preference. Following sub-sections summarize several important operational considerations that try to eliminate the FUD of the administrators. 3.1. Multiple prefix provisioning - Multiple provisioning domains: considering current DHCP architecture does not fit multiple provisioning domains well, the administrators should avoid that multiple provisioning domains all directly configuring the host through DHCP, since it might cause confusion for the host. - Multiple provisioning mechanisms: if administrators applied DHCP/SLAAC co-exist in one network, then they need to learn that there might be some issues, which are reported in [I-D.liu-bonica-dhcpv6-slaac-problems]. 3.2. Multiple addresses in one interface IPv4 stacks support multiple IP address per interface in the terms of "secondary" addresses. This is very useful in practice, especially for routers. So in IPv6, it became a mandatory feature. Every IPv6 interface has a link-local IP address as default. The interfaces connected outside might also have a PA address or ULA address. In some operation systems (e.g. Windows 7), there's a temporary address for privacy purpose as default. So when the interface is connected, there might be three addresses as minimum. So for the host, current implementations support this feature very well; normally this wouldn't be a problem for host multiple addresses configuration. Liu, et al. Expires January 16, 2014 [Page 5] Internet-Draft Running Multiple Prefixes July 2013 However, some current IPAM/NMS applications might have not ready for this multiple addresses mappings. This could be an issue for complete management. 3.3. Address selection Address selecition is an error prone issue in running multiple prefixes. [RFC5220] reported various potential problems with address selection in deployment. Some of them have been handled in the updated standard address selection mechanism [RFC6724]. (Editor's Note: to be filled.) 3.4. DNS relevant Normally, one SP only allows only its users to look at DNS records of the service. So in multiple network provisioning scenarios, each DNS query from a host must be forwarded to a suitable DNS server. Hosts normally are not able to select a DNS server for each DNS query target. [RFC6731] is developed for this purpose; it defined DHCPv4/v6 options to deliver the DNS selection policies for hosts. However, since it hasn't published for long, there have not been many implementations supporting it. 4. Current Gaps o Some IPAM/NMS tools might not be able to handle one interface and multiple addresses mappings. o ULA+IPv4 selection There is a special case that needs to be noticed, which is described in section 2.2.2 of [RFC5220]. When an enterprise has IPv4 Internet connectivity but does not yet have IPv6 Internet connectivity, and the enterprise wants to provide site-local IPv6 connectivity, a ULA is the best choice for site-local IPv6 connectivity. Each employee host will have both an IPv4 global or private address and a ULA. Here, when this host tries to connect to an outside node that has registered both A and AAAA records in the DNS, the host will choose AAAA as the destination address and the ULA for the source address according to the IPv6 preference of the default address selection policy. This will clearly result in a connection failure. Liu, et al. Expires January 16, 2014 [Page 6] Internet-Draft Running Multiple Prefixes July 2013 Although with Happy Eyeballs [RFC6555] this connection failure problem could be solved, but unwanted timeouts would obviously lower the user experience. One possible approach of eliminating the timeouts is configuring IPv4 preference on the hosts, and not including DNS A records but only AAAA records for the internal nodes in the internal DNS server, then outside nodes have both A and AAAA records could be connected through IPv4 as default and internal nodes could be always connected through IPv6. But since IPv6 preference is default, changing the default in all nodes is not easy. o Multiple PA exit-router selection In multiple PA multihoming networks, if the ISPs enable ingress filtering at the edge, then the administrators need to deal with the the exit router selection issues. Currently there is no well-used solution, so the administrator might need to communicate with the ISP for not filtering the prefixes. 5. Security Considerations TBD. 6. IANA Considerations This draft does not request any IANA actions. 7. Acknowledgments Many useful comments and contributions were made by Sheng Jiang. This document was prepared using 2-Word-v2.0.template.dot. 8. References 8.1. Normative References [RFC3315] R. Droms, Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,September 2007. [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, September 2007. Liu, et al. Expires January 16, 2014 [Page 7] Internet-Draft Running Multiple Prefixes July 2013 8.2. Informative References [RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for Renumbering an IPv6 Network without a Flag Day", RFC 4192, September 2005. [RFC4984] Meyer, D., Ed., Zhang, L., Ed., and K. Fall, Ed., "Report from the IAB Workshop on Routing and Addressing", RFC 4984, September 2007. [RFC5220] Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama, "Problem Statement for Default Address Selection in Multi- Prefix Environments: Operational Issues of RFC 3484 Default Rules", RFC 5220, July 2008. [RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with Dual-Stack Hosts", RFC 6555, April 2012. [RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown, "Default Address Selection for Internet Protocol Version 6 (IPv6)", RFC 6724, September 2012. [RFC6731] Savolainen, T., Kato, J., and T. Lemon, "Improved Recursive DNS Server Selection for Multi-Interfaced Nodes", RFC 6731, December 2012. [I-D.ietf-6man-addr-select-opt] Matsumoto, A.M., Fujisaki T.F., and T. Chown, "Distributing Address Selection Policy using DHCPv6", Working in Progress, April 2013. [I-D.liu-bonica-dhcpv6-slaac-problem] Liu, B., and R. Bonica, "DHCPv6/SLAAC Address Configuration Interaction Problem Statement", Working in Progress, February 2013. [I.D-ietf-v6ops-ipv6-multihoming-without-ipv6nat] Troan, O., Ed. Miles, D., Matsushima, S., Okimoto T., and D. Wing, "IPv6 Multihoming without Network Address Translation", Working in Progress, March 2013. Liu, et al. Expires January 16, 2014 [Page 8] Internet-Draft Running Multiple Prefixes July 2013 Authors' Addresses Bing Liu Huawei Technologies Co., Ltd Q14, Huawei Campus No.156 Beiqing Rd. Hai-Dian District, Beijing 100095 P.R. China Email: leo.liubing@huawei.com