Internet Engineering Task Force O. Troan, Ed. Internet-Draft Cisco Intended status: Informational D. Miles Expires: January 27, 2011 Alcatel-Lucent S. Matsushima SOFTBANK TELECOM Corp. T. Okimoto NTT D. Wing Cisco July 26, 2010 IPv6 Multihoming without Network Address Translation draft-troan-multihoming-without-nat66-01 Abstract Network Address and Port Translation (NAPT) works well for conserving global addresses and addressing multihoming requirements, because an IPv4 NAPT router implements three functions: source address selection, next-hop resolution and optionally DNS resolution. For IPv6 hosts one approach could be the use of IPv6 NAT. However, NAT should be avoided, if at all possible, to permit transparent host-to- host connectivity. In this document, we analyze the use cases of multihoming. We also describe functional requirements for multihoming without the use of NAT in IPv6 for hosts and small IPv6 networks that would otherwise be unable to meet minimum IPv6 allocation criteria . 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 27, 2011. Copyright Notice Troan, et al. Expires January 27, 2011 [Page 1] Internet-Draft IPv6 Multihoming without NAT July 2010 Copyright (c) 2010 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. IPv6 multihomed network scenarios . . . . . . . . . . . . . . 5 3.1. Classification of network scenarios for multihomed host . 5 3.2. Multihomed network environment . . . . . . . . . . . . . . 7 3.3. Multihomed Problem Statement . . . . . . . . . . . . . . . 8 4. Problem statement and analysis . . . . . . . . . . . . . . . . 9 4.1. Source address selection . . . . . . . . . . . . . . . . . 10 4.2. Next-hop selection . . . . . . . . . . . . . . . . . . . . 10 4.3. DNS server selection . . . . . . . . . . . . . . . . . . . 11 5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 12 5.1. End-to-End transparency . . . . . . . . . . . . . . . . . 12 5.2. Policy enforcement . . . . . . . . . . . . . . . . . . . . 12 5.3. Scalability . . . . . . . . . . . . . . . . . . . . . . . 13 6. Implementation approach . . . . . . . . . . . . . . . . . . . 13 6.1. Source address selection . . . . . . . . . . . . . . . . . 13 6.2. Next-hop selection . . . . . . . . . . . . . . . . . . . . 13 6.3. DNS resolver selection . . . . . . . . . . . . . . . . . . 14 7. Considerations for host without multi-prefix support . . . . . 14 7.1. IPv6 NAT . . . . . . . . . . . . . . . . . . . . . . . . . 15 7.2. Co-exisitence consideration . . . . . . . . . . . . . . . 15 8. Security Considerations . . . . . . . . . . . . . . . . . . . 16 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 11.1. Normative References . . . . . . . . . . . . . . . . . . . 16 11.2. Informative References . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 Troan, et al. Expires January 27, 2011 [Page 2] Internet-Draft IPv6 Multihoming without NAT July 2010 1. Introduction IPv6 provides enough globally unique addresses to permit every conceivable host on the Internet to be uniquely addressed without the requirement for Network Address Port Translation (NAPT [RFC3022]) offering a renaissance in host-to-host transparent connectivity. Unfortunately, this may not be possible due to the necessity of NAT even in IPv6, because of multihoming. Multihoming is a blanket term to describe a host or small network that is connected to more than one upstream network. Whenever a host or small network (which does not meet minimum IPv6 allocation criteria) is connected to multiple upstream networks IPv6 addressing is assigned by each respective service provider resulting in hosts with more than one active IPv6 address. As each service provided is allocated a different address space from its Internet Registry, it in-turn assigns a different address space to the end-user network or host. For example, a remote access user may use a VPN to simultaneously connect to a remote network and retain a default route to the Internet for other purposes. In IPv4 a common solution to the multihoming problem is to employ NAPT on a border router and use private address space for individual host addressing. The use of NAPT allows hosts to have exactly one IP address visible on the public network and the combination of NAPT with provider-specific outside addresses (one for each uplink) and destination-based routing insulates a host from the impacts of multiple upstream networks. The border router may also implement a DNS cache or DNS policy to resolve address queries from hosts. It is our goal to avoid the IPv6 equivalent of NAT. To reach this goal, mechanisms are needed for end-user hosts to have multiple address assignments and resolve issues such as which address to use for sourcing traffic to which destination: o If multiple routers exist on a single link the host must appropriately select next-hop for each connected network. Routing protocols that would normally be employed for router-to-router network advertisement seem inappropriate for use by individual hosts. o Source address selection also becomes difficult whenever a host has more than one address within the same address scope. Current address selection criteria may result in hosts using an arbitrary or random address when sourcing upstream traffic. Unfortunately, for the host, the appropriate source address is a function of the upstream network for which the packet is bound for. If an Troan, et al. Expires January 27, 2011 [Page 3] Internet-Draft IPv6 Multihoming without NAT July 2010 upstream service provider uses IP anti-spoofing or uRPF, it is conceivable that the packets that have inappropriate source address for the upstream network would never reach their destination. o In a multihomed environment, different DNS scopes or partitions may exist in each independent upstream network. A DNS query sent to an arbitrary upstream resolver may result in incorrect or poisoned responses. In short, while IPv6 facilitates hosts having more than one address in the same address scope, the application of this causes significant issues for a host from routing, source address selection and DNS resolution perspectives. A possible consequence of assigning a host multiple identical-scoped addresses is severely impaired IP connectivity. If a host connects to a network behind an IPv4 NAPT, the host has one private address in the local network. There is no confusion. The NAT becomes the gateway of the host and forwards the packet to an appropriate network when it is multihomed. It also operates a DNS cache server, which receives all DNS inquires, and gives a correct answer to the host. In this document, we identify the functions present in multihomed IPv4 NAPT environments and propose requirements that address multihomed IPv6 environments without using IPv6 NAT. 2. Terminology 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]. NAT66 or IPv6 NAT The terms "NAT66" and "IPv6 NAT" refer to [I-D.mrw-behave-nat66]. NAPT Network Address Port Translation as described in [RFC3022]. In other contexts, NAPT is often pronounced "NAT" or written as "NAT". Multihomed with multi-prefix (MHMP) A host implementation which supports the mechanisms described in this document. Namely source address selection policy, next-hop selection and DNS selection policy. Troan, et al. Expires January 27, 2011 [Page 4] Internet-Draft IPv6 Multihoming without NAT July 2010 3. IPv6 multihomed network scenarios In this section, we classify three scenarios of the multihoming environment. 3.1. Classification of network scenarios for multihomed host Scenario 1: In this scenario, two or more routers are present on a single link shared with the host(s). Each router is in turn connected to a different service provider network, which provides independent address assignment and DNS resolvers. A host in this environment would be offered multiple prefixes and DNS resolvers advertised from the two different routers. +------+ ___________ | | / \ +---| rtr1 |=====/ network \ | | | \ 1 / +------+ | +------+ \___________/ | | | | host |-----+ | | | +------+ | +------+ ___________ | | | / \ +---| rtr2 |=====/ network \ | | \ 2 / +------+ \___________/ Figure 1: single uplink, multiple next-hop, multiple prefix (Scenario 1) Figure 1 illustrates the host connecting to rtr1 and rtr2 via a shared link. Networks 1 and 2 are reachable via rtr1 and rtr2 respectively. When the host sends packets to network 1, the next-hop to network 1 is rtr1. Similarly, rtr2 is the next-hop to network 2. - e.g., broadband service (Internet, VoIP, IPTV, etc.) Scenario 2: In this scenario, a single gateway router connects the host to two or more upstream service provider networks. This gateway router would receive prefix delegations from each independent service provider network and a different set of DNS resolvers. The gateway in turn advertises the provider prefixes to the host, and for DNS, may either Troan, et al. Expires January 27, 2011 [Page 5] Internet-Draft IPv6 Multihoming without NAT July 2010 act as a lightweight DNS resolver/cache or may advertise the complete set of service provider DNS resolvers to the hosts. +------+ ___________ | | / \ +---| rtr1 |=====/ network \ | | | \ 1 / +------+ +-----+ | +------+ \___________/ | | | | | | host |-----| GW |---+ | | | rtr | | +------+ +-----+ | +------+ ___________ | | | / \ +---| rtr2 |=====/ network \ | | \ 2 / +------+ \___________/ Figure 2: single uplink, single next-hop, multiple prefix (Scenario 2) Figure 2 illustrates the host connected to GW rtr. GW rtr connects to networks 1 and 2 via rtr1 and rtr2, respectively. When the host sends packets to either network 1 or 2, the next-hop is GW rtr. When the packets are sent to network 1 (network 2), GW rtr forwards the packets to rtr1 (rtr2). - e.g, Internet + VPN/ASP Scenario 3: In this scenario, a host has more than one active interfaces that connects to different routers and service provider networks. Each router provides the host with a different address prefix and set of DNS resolvers, resulting in a host with a unique address per link/ interface. Troan, et al. Expires January 27, 2011 [Page 6] Internet-Draft IPv6 Multihoming without NAT July 2010 +------+ +------+ ___________ | | | | / \ | |-----| rtr1 |=====/ network \ | | | | \ 1 / | | +------+ \___________/ | | | host | | | | | +------+ ___________ | | | | / \ | |=====| rtr2 |=====/ network \ | | | | \ 2 / +------+ +------+ \___________/ Figure 3: Multiple uplink, multiple next-hop, multiple prefix (Scenario 3) Figure 3 illustrates the host connecting to rtr1 and rtr2 via a direct connection or a virtual link. When the host sends packets network 1, the next-hop to network 1 is rtr1. Similarly, rtr2 is the next-hop to network 2. - e.g., Mobile Wifi + 3G, ISP A + ISP B 3.2. Multihomed network environment In an IPv6 multihomed network, a host is assigned two or more IPv6 addresses and DNS resolvers from independent service provider networks. When this multihomed host attempts to connect with other hosts, it may incorrectly resolve the next-hop router, use an inappropriate source address, or use a DNS response from an incorrect service provider that may result in impaired IP connectivity. Multihomed networks in IPv4 have been commonly implemented through the use of a gateway router with NAPT function (scenario 2 with NAPT). An analysis of the current IPv4 NAPT and DNS functions within the gateway router should provide a baseline set of requirements for IPv6 multihomed environments. A destination prefix/route is often used on the gateway router to separate traffic between the networks. Troan, et al. Expires January 27, 2011 [Page 7] Internet-Draft IPv6 Multihoming without NAT July 2010 +------+ ___________ | | / \ +---| rtr1 |=====/ network \ | | | \ 1 / +------+ +-----+ | +------+ \___________/ | IPv4 | | | | | host |-----| GW |---+ | | | rtr | | +------+ +-----+ | +------+ ___________ (NAPT&DNS) | | | / \ (private +---| rtr2 |=====/ network \ address | | \ 2 / space) +------+ \___________/ Figure 4: IPv4 Multihomed environment with Gateway Router performing NAPT 3.3. Multihomed Problem Statement A multihomed IPv6 host has one or more assigned IPv6 addresses and DNS resolvers from each upstream service provider, resulting in the host having multiple valid IPv6 addresses and DNS resolvers. The host must be able to resolve the appropriate next-hop, the correct source address and DNS resolver to use based on the destination prefix. To prevent IP spoofing, operators will often implement IP filters and uRPF to discard traffic with an inappropriate source address, making it essential for the host to correctly resolve these three criteria before sourcing the first packet. IPv6 has mechanisms for the provision of multiple routers on a single link and multiple address assignments to a single host. However, when these mechanisms are applied to the three scenarios in Section 3.1 a number of connectivity issues are identified: Scenario 1: The host has been assigned an address from each router and recognizes both rtr1 and rtr2 as valid default routers (in the default routers list). o The source address selection policy on the host does not deterministically resolve a source address. Upstream uRPF or filter policies will discard traffic with source addresses that the operator did not assign. o The host will select one of the two routers as the active default router. No traffic is sent to the other router. Troan, et al. Expires January 27, 2011 [Page 8] Internet-Draft IPv6 Multihoming without NAT July 2010 Scenario 2: The host has been assigned two different addresses from the single gateway router. The gateway router is the only default router on the link. o The source address selection policy on the host does not deterministically resolve a source address. Upstream uRPF or filter policies will discard traffic with source addresses that the operator did not assign. o The gateway router does not have a mechanism for determining which traffic should be sent to which network. If the gateway router is implementing host functions (ie, processing RA) then two valid default routers may be recognized. Scenario 3: A host has two separate interfaces and on each interface a different address is assigned. Each link has its own router. o The host does not have enough information for determining which traffic should be sent to which upstream routers. The host will select one of the two routers as the active default router, and no traffic is sent to the other router. o The default address selection rules select the address assigned to the outgoing interface as the source address. So, if a host has an appropriate routing table, an appropriate source address will be selected. All scenarios: o The host may use an incorrect DNS resolver for DNS queries. 4. Problem statement and analysis The problems described in Section 3 can be classified into these three types: o Wrong source address selection o Wrong next-hop selection o Wrong DNS server selection This section reviews the problem statements presented above and the Troan, et al. Expires January 27, 2011 [Page 9] Internet-Draft IPv6 Multihoming without NAT July 2010 proposed functional requirements to resolve the issues without employing IPv6 NAT. 4.1. Source address selection A multihomed IPv6 host will typically have different addresses assigned from each service provider either on the same link (scenarios 1 & 2) or different links (scenario 3). When the host wishes to send a packet to any given destination, the current source address selection rules [RFC3484] may not deterministically resolve the correct source address when the host addressing was via RA or DHCPv6. [I-D.ietf-6man-addr-select-sol] describes the use of the policy table [RFC3484] to resolve this problem, but there is no mechanism defined to disseminate the policy table information to a host. A proposal is in [I-D.fujisaki-dhc-addr-select-opt] to provide a DHCPv6 mechanism for host policy table management. Again, by employing DHCPv6, the server could restrict address assignment (of additional prefixes) only to hosts that support policy table management. Scenario 1: "Host" needs to support the solution for this problem Scenario 2: "Host" needs to support the solution for this problem Scenario 3: If "Host" support the next-hop selection solution, there is no need to support the address selection functionality on the host. 4.2. Next-hop selection A multihomed IPv6 host or gateway may have multiple uplinks to different service providers. Here each router would use Router Advertisements [RFC4861] for distributing default route/next-hop information to the host or gateway router. In this case, the host or gateway router may select any valid default router from the default routers list, resulting in traffic being sent to the wrong router and discarded by the upstream service provider. Using the above scenarios as an example, whenever the host wishes to reach a destination in network 2 and there is no connectivity between networks 1 and 2 (as is the case for a walled-garden or closed service), the host or gateway router does not know whether to forward traffic to rtr1 or rtr2 to reach a destination in network 2. The host or gateway router may choose rtr1 as the default router, and traffic fails to reach the destination server. The host or gateway router requires route information for each upstream service provider, but the use of a routing protocol between a host and router causes Troan, et al. Expires January 27, 2011 [Page 10] Internet-Draft IPv6 Multihoming without NAT July 2010 both configuration and scaling issues. For IPv4 hosts, the gateway router is often pre-configured with static route information or uses of Classless Static Route Options [RFC3442] for DHCPv4. Extensions to Router Advertisements through Default Router Preference and More- Specific Routes [RFC4191] provides for link-specific preferences but does not address per-host configuration in a multi-access topology because of its reliance on Router Advertisements. A DHCPv6 option, such as that in [I-D.dec-dhcpv6-route-option], is preferred for host- specific configuration. By employing a DHCPv6 solution, a DHCPv6 server could restrict address assignment (of additional prefixes) only to hosts that support more advanced next-hop and address selection requirements. Scenario 1: "Host" needs to support the solution for this problem Scenario 2: "GW rtr" needs to support the solution for this problem Scenario 3: "Host" needs to support the solution for this problem 4.3. DNS server selection A multihomed IPv6 host or gateway router may be provided multiple DNS resolvers through DHCPv6 or the experimental [RFC5006]. When the host or gateway router sends a DNS query, it would normally choose one of the available DNS resolvers for the query. In the IPv6 gateway router scenario, the Broadband Forum [TR124] required that the query be sent to all DNS resolvers, and the gateway waits for the first reply. In IPv6, given our use of specific destination-based policy for both routing and source address selection, it is desirable to extend a policy-based concept to DNS resolver selection. Doing so can minimize DNS resolver load and avoid issues where DNS resolvers in different networks have connectivity issues, or the DNS resolvers are not publicly accessible. In the worst case, a DNS query may be unanswered if sent towards an incorrect resolver, resulting in a lack of connectivity. An IPv6 multihomed host or gateway router should have the ability to select appropriate DNS resolvers for each service based on the domain space for the destination, and each service should provide rules specific to that network. [I-D.savolainen-mif-dns-server-selection] proposes a solution for DNS server selection policy enforcement solution with a DHCPv6 option. Scenario 1: "Host" needs to support the solution for this problem Scenario 2: "GW rtr" needs to support the solution for this problem Troan, et al. Expires January 27, 2011 [Page 11] Internet-Draft IPv6 Multihoming without NAT July 2010 Scenario 3: "Host" needs to support the solution for this problem 5. Requirements This section describes requirements that any solution multi-address and multi-uplink architectures need to meet. 5.1. End-to-End transparency End-to-end transparency is a basic concept of the Internet. [RFC4966] states, "One of the major design goals for IPv6 is to restore the end-to-end transparency of the Internet. Therefore, because IPv6 is expected to remove the need for NATs and similar impediments to transparency, developers creating applications to work with IPv6 may be tempted to assume that the complex mechanisms employed by an application to work in a 'NATted' IPv4 environment are not required." The IPv6 multihoming solution SHOULD guarantee end- to-end transparency by avoiding IPv6 NAT. 5.2. Policy enforcement The solution SHOULD have a function to enforce a policy on sites/ nodes. In particular, in a managed environment such as enterprise networks, an administrator has to control all nodes in his or her network. The enforcement mechanisms should have: o a function to distribute policies to nodes dynamically to update their behavior. When the network environment changes and the nodes' behavior has to be changed, a network administrator can modify the behavior of the nodes. o a function to control every node centrally. A site administrator or a service provider could determine or could have an effect on the behavior at their users' hosts. o a function to control node-specific behavior. Even when multiple nodes are on the same subnet, the mechanism should be able to provide a method for the network administrator to make nodes behave differently. For example, each node may have a different set of assigned prefixes. In such a case, the appropriate behavior may be different. Troan, et al. Expires January 27, 2011 [Page 12] Internet-Draft IPv6 Multihoming without NAT July 2010 5.3. Scalability The solution will have to be able to manage a large number of sites/ nodes. In services for residential users, provider edge devices have to manage thousands of sites. In such environments, sending packets periodically to each site may affect edge system performance. 6. Implementation approach As mentioned in Section 4, in the multi-prefix environment, we have three problems in source address selection, next-hop selection, and DNS resolver selection. In this section, possible solution mechanisms for each problem are introduced and evaluated against the requirements in Section 5. 6.1. Source address selection Possible solutions and their evaluation are summarized in [I-D.ietf-6man-addr-select-sol]. When those solutions are examined against the requirements in Section 5, the proactive approaches, such as the policy table distribution mechanism and the routing system assistance mechanism, are more appropriate in that they can propagate the network administrator's policy directly. The policy distribution mechanism has an advantage with regard to the host's protocol stack impact and the staticness of the assumed target network environment. 6.2. Next-hop selection As for the source address selection problem, both a policy-based approach and a non policy-based approach are possible with regard to the next-hop selection problem. Because of the same requirements, the policy propagation-based solution mechanism, whatever the policy, should be more appropriate. Routing information is a typical example of policy related to next- hop selection. If we assume source address-based routing at hosts or intermediate routers, the pairs of source prefixes and next-hops can be another example of next-hop selection policy. The routing information-based approach has a clear advantage in implementation and is already commonly used. The existing proposed or standardized routing information distribution mechanisms are routing protocols, such as RIPng and OSPFv3, the router advertisement (RA) extension option defined in [RFC4191], the DHCPv6 route information option proposed in [I-D.dec-dhcpv6-route-option], and the [TR069] standardized at BBF. Troan, et al. Expires January 27, 2011 [Page 13] Internet-Draft IPv6 Multihoming without NAT July 2010 The RA-based mechanism has difficulty in per-host routing information distribution. The dynamic routing protocols such as RIPng are not usually used between the residential users and ISP networks because of their scalability implications. The DHCPv6 mechanism does not have these difficulties and has the advantages of its relaying functionality. It is commonly used and is thus easy to deploy. [TR069], mentioned above, is a possible solution mechanism for routing information distribution to customer-premises equipment (CPE). It assumes, however, IP reachability to the Auto Configuration Server (ACS) is established. Therefore, if the CPE requires routing information to reach the ACS, [TR069] cannot be used to distribute this information. 6.3. DNS resolver selection As in the above two problems, a policy-based approach and non policy- based approach are possible. In a non policy-based approach, a host or a home gateway router is assumed to send DNS queries to several DNS servers at once or to select one of the available servers. In the non policy-based approach, by making a query to a resolver in a different service provider to that which hosts the service, a user could be directed to unexpected IP address or receive an invalid response, and thus cannot connect to the service provider's private and legitimate service. For example, some DNS servers reply with different answers depending on the source address of the DNS query, which is sometimes called split-horizon. When the host mistakenly makes a query to a different provider's DNS to resolve a FQDN of another provider's private service, and the DNS resolver adopts the split-horizon configuration, the queried server returns an IP address of the non-private side of the service. Another problem with this approach is that it causes unnecessary DNS traffic to the DNS resolvers that are visible to the users. The alternative of a policy-based approach is documented in [I-D.savolainen-mif-dns-server-selection], where several pairs of DNS resolver addresses and DNS domain suffixes are defined as part of a policy and conveyed to hosts in a new DHCP option. In an environment where there is a home gateway router, that router can act as a DNS proxy, interpret this option and distribute DNS queries to the appropriate DNS servers according to the policy. 7. Considerations for host without multi-prefix support This section presents an alternative approach to mitigate the problem in a multihomed network. This approach will help IPv6 hosts that are Troan, et al. Expires January 27, 2011 [Page 14] Internet-Draft IPv6 Multihoming without NAT July 2010 not capable of the enhancements for the source address selection policy, next-hop selection policy, and DNS selection policy described in Section 6. 7.1. IPv6 NAT In a typical IPv4 multihomed network deployment, IPv4 NAPT is practically used and it can eventually avoid assigning multiple addresses to the hosts and solve the next-hop selection problem. In a similar fashion, IPv6 NAT can be used as a last resort for IPv6 multihomed network deployments where one needs to assign a single IPv6 address to a host. __________ / \ +---/ Internet \ gateway router | \ / +------+ +---------------------+ | \__________/ | | | | | WAN1 +--+ | host |-----|LAN| Router |--------| | | | | |NAT|WAN2+--+ +------+ +---------------------+ | __________ | / \ +---/ ASP \ \ / \__________/ Figure 5: Legacy Host The gateway router also has to support the two features, next-hop selection and DNS server selection, shown in Section 6. The implementation and issues of IPv6 NAT are out of the scope of this document. They may be covered by another document under discussion [I-D.mrw-behave-nat66]. 7.2. Co-exisitence consideration The above scenario relies on the assumption that only hosts without multi-prefix support are connected to the GW rtr in scenario 2. To allow the coexistence of non-MHMP hosts and MHMP hosts(i.e. hosts supporting multi-prefix with the enhancements for the source address selection), GW-rtr may need to treat those hosts separately. An idea to achieve this is that GW-rtr identifies the hosts, and then assigns single prefix to non-MHMP hosts and assigns multiple prefix to MHMP hosts. In this case, GW-rtr can perform IPv6 NAT only for Troan, et al. Expires January 27, 2011 [Page 15] Internet-Draft IPv6 Multihoming without NAT July 2010 the traffic from MHMP hosts if its source address is not appropriate. Another idea is that GW-rtr assigns multiple prefix to the both hosts, and it performs IPv6 NAT for the traffic from non-MHMP hosts if its source address is not appropriate. In scenario 1 and 3, the non-MHMP hosts can be placed behind the NAT box. In this case, non-MHMP host can access the service through the NAT box. The implementation of identifying non-MHMP hosts and NAT policy is outside the scope of this document. 8. Security Considerations This document does not define any new mechanisms. Each solution mechanisms should consider security risks independently. Security risks that occur as a result of combining solution mechanisms should be considered in another document. 9. IANA Considerations This document has no IANA actions. 10. Contributors The following people contributed to this document: Akiko Hattori, Arifumi Matsumoto, Frank Brockners, Fred Baker, Tomohiro Fujisaki, Jun-ya Kato, Shigeru Akiyama, Seiichi Morikawa, Mark Townsley, Wojciech Dec, Yasuo Kashimura, Yuji Yamazaki 11. References 11.1. Normative References [I-D.dec-dhcpv6-route-option] Dec, W. and R. Johnson, "DHCPv6 Route Option", draft-dec-dhcpv6-route-option-03 (work in progress), March 2010. [I-D.fujisaki-dhc-addr-select-opt] Fujisaki, T., Matsumoto, A., and R. Hiromi, "Distributing Address Selection Policy using DHCPv6", draft-fujisaki-dhc-addr-select-opt-09 (work in progress), Troan, et al. Expires January 27, 2011 [Page 16] Internet-Draft IPv6 Multihoming without NAT July 2010 March 2010. [I-D.ietf-6man-addr-select-sol] Matsumoto, A., Fujisaki, T., and R. Hiromi, "Solution approaches for address-selection problems", draft-ietf-6man-addr-select-sol-03 (work in progress), March 2010. [I-D.mrw-behave-nat66] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Address Translation (NAT66)", draft-mrw-behave-nat66-02 (work in progress), March 2009. [I-D.savolainen-mif-dns-server-selection] Savolainen, T., "DNS Server Selection on Multi-Homed Hosts", draft-savolainen-mif-dns-server-selection-02 (work in progress), February 2010. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3484] Draves, R., "Default Address Selection for Internet Protocol version 6 (IPv6)", RFC 3484, February 2003. [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and More-Specific Routes", RFC 4191, November 2005. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. 11.2. Informative References [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network Address Translator (Traditional NAT)", RFC 3022, January 2001. [RFC3442] Lemon, T., Cheshire, S., and B. Volz, "The Classless Static Route Option for Dynamic Host Configuration Protocol (DHCP) version 4", RFC 3442, December 2002. [RFC4966] Aoun, C. and E. Davies, "Reasons to Move the Network Address Translator - Protocol Translator (NAT-PT) to Historic Status", RFC 4966, July 2007. [RFC5006] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, "IPv6 Router Advertisement Option for DNS Configuration", RFC 5006, September 2007. Troan, et al. Expires January 27, 2011 [Page 17] Internet-Draft IPv6 Multihoming without NAT July 2010 [TR069] The BroadBand Forum, "TR-069, CPE WAN Management Protocol v1.1, Version: Issue 1 Amendment 2", December 2007. [TR124] The BroadBand Forum, "TR-124i2, Functional Requirements for Broadband Residential Gateway Devices (work in progress)", May 2010. Authors' Addresses Ole Troan (editor) Cisco Bergen Norway Email: ot@cisco.com David Miles Alcatel-Lucent Melbourne Australia Email: david.miles@alcatel-lucent.com Satoru Matsushima SOFTBANK TELECOM Corp. Tokyo Japan Email: satoru.matsushima@tm.softbank.co.jp Tadahisa Okimoto NTT Tokyo Japan Email: t.okimoto@hco.ntt.co.jp Troan, et al. Expires January 27, 2011 [Page 18] Internet-Draft IPv6 Multihoming without NAT July 2010 Dan Wing Cisco 170 West Tasman Drive San Jose USA Email: dwing@cisco.com Troan, et al. Expires January 27, 2011 [Page 19]