IPv6 Support in Home Routers

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	Introduction
	IPv6 Home LAN Topology Assumptions
	IPv6 Home Router Requirements
	Conclusion and Summary
	Resources and References

Introduction

There is a strong misconception that IPv6 support in home routers is tied to ISP deployment of a native IPv6 service. This is not true. Home routers can deliver the full IPv6 experience to users over the existing IPv4 Internet using IPv6 transition technologies. The goal of this article is to encourage independent hardware vendors (IHVs) to add IPv6 and IPv6 transition capabilities to home routers and not wait until native IPv6 service is widely deployed.

IPv6 support in home routers allows end-to-end connectivity between personal computers and other IPv6-enabled devices, which provides a better user experience in voice and video communications, peer-to-peer games, and other technologies that require end-to-end connectivity. For home router manufacturers, implementing the IPv6 features described in this article promotes a better user experience, compatibility with upcoming technologies, and integration with Microsoft Windows XP.

Home router manufacturers that would like further explanation of the architectural reasoning behind specific recommendations, or how these recommendations affect compatibility with Windows XP and future Microsoft operating systems, are encouraged to send e-mail to ipv6-fb@microsoft.com.

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IPv6 Home LAN Topology Assumptions

This article assumes that the vast majority of home network topologies have (or will have in the near future) the following properties:

Figure 1 shows a network reference topology of a home network, which consists of a single subnet, four computers, and a Voice over IP (VoIP) phone. As a growing trend, home networks now consist of multiple wired and wireless segments. Figure 1 also shows a second wireless router to illustrate a common case of wireless expansion in the home?most new wireless access points (APs) come with integrated router functionality whether the home user needs it or not. Further discussion about the differences between routers and wireless APs can be found in the following section.

Figure 1: A Single Home Router

In Figure 1, Home Router A implements network address translator (NAT) functionality for IPv4 traffic and router functionality for IPv6 traffic. The home LAN is a leaf network of the IPv6 Internet. Physical network configuration may be more complex, involving Ethernet switches, wireless APs, VoIP adapters, and other connectivity solutions.

A "pure" home router is a device with two Ethernet ports: a wide area network (WAN) port connected to the ISP and a local area network (LAN) port for the home network. However, often home routers are also integrated with other functionalities such as being a broadband modem (digital subscriber line [DSL] or cable), multi-port LAN switch, wireless AP, etc. Figure 2 illustrates the conceptual breakdown of this integration trend. Note that such integration does not alter the core router functionality.

Figure 2: Router integration with other devices

One Subnet per Household

The underlying assumption in this article is that homes consist of a single subnet. From a home network addressing perspective, multi-subnet configurations and intra-home routing are unwarranted. Exceptions to the single subnet design might include:

In a single-subnet home network, all wired or wireless segments must be bridged transparently. When an integrated router is added to this existing network (for wireless or Ethernet switching), the integrated device must either:

Microsoft further recommends including double NAT detection functionality in the home router. When an integrated router obtains a private IPv4 address for its WAN port through the Dynamic Host Configuration Protocol (DHCP), it is most likely due to a double NAT configuration. In contrast, a private IPv4 address obtained through Point-to-Point Protocol over Ethernet (PPPoE), Layer Two Tunneling Protocol (L2TP), or similar WAN/ISP mechanisms are most likely due to an ISP service that is limited to private IPv4 addresses, and is not necessarily an indication of misconfiguration. This is not an entirely accurate technique for detecting double NATs. For example, a DHCP server may be purposefully configured to hand out private IPv4 addresses. Microsoft strongly recommends that customers be warned about the potential network misconfiguration and provided guidelines for fixing the problem.

Figure 3: Router functionality bypass (LAN switching)

IPv4- and/or IPv6-capable Computers and Devices

IPv6 offers global end-to-end connectivity for peer-to-peer and other new applications and scenarios. The Windows family of operating systems starting from Windows XP with Service Pack 1 and Windows Server 2003 already supports IPv6, as will Windows Vista. Windows CE 4.2 and 5.0 also provide extensive IPv6 support. All these IPv6-enabled versions of Windows support the "Basic socket interface extensions for IPv6" (RFC 2133) and the "Advanced sockets API for IPv6" (RFC 2292) to enable applications programmers to take advantage of IPv6 today.

It is expected that some devices in the home such as computers running Windows 98 will be limited to IPv4, while others (personal data assistants [PDAs], VoIP), might only communicate over IPv6. The IPv4-only and IPv6-only devices cannot communicate directly, however dual-stack computers can communicate with both.

Home Router Serving as the Network Security Boundary

The home router must provide a basic security boundary for the nodes on the home LAN. For many home network configurations, the IPv4 router performs address translation for clients on the home LAN, effectively hiding their private IPv4 addresses. However, since IPv6 provides direct connectivity to the Internet, IPv6 routers do not provide this level of address security. Consequently, since not all devices on the home LAN will have host-based firewalls, routers should provide basic firewall functionality. Such firewall functionality should include, but need not be limited to, stateful packet filtering.

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IPv6 Home Router Requirements

An IPv6-enabled home router must implement a number of technologies to be compatible with Windows operating systems and the IPv4 and IPv6 technologies that ISPs and IHVs deliver.

For simplicity, the article lists requirements separately for the WAN, LAN, and core portion of the home router. This organization has two benefits:

ISP Scenario-driven Requirements

The level of IPv6 support and requirements vary for ISP deployment scenarios. The following represents the most common ones:

Private IPv4 Connectivity (Teredo IPv6)

If the ISP provides only private IPv4 addresses, as described in RFC 1918, then IPv6 connectivity is not expected to be enabled directly by home routers. Instead, individual hosts will acquire IPv6 addresses and connectivity themselves by using Teredo technology, transparently to the home routers. Teredo is an IPv6 transition technology that tunnels IPv6 packets as IPv4-based User Datagram Protocol (UDP) messages using UDP port 3544.

Although there are no specific WAN and LAN requirements for a router to support Teredo, the router should adhere to the following behavior to be compatible with Teredo:

For more information about how Teredo works, see "Teredo Overview" at http://www.microsoft.com/technet/prodtechnol/winxppro/maintain/teredo.mspx. The Teredo RFC can be found at http://www.ietf.org/rfc/rfc4380.txt , under the title "Teredo: Tunneling IPv6 over UDP through Network Address Translations (NATs)."

Public IPv4 Connectivity (6to4 IPv6)

If the ISP provides only a single public IPv4 address, then LAN hosts have the additional and preferred option of using the 6to4 transition technology specified in RFCs 3056 and 3068. 6to4 requires the egress router to an IPv4 network to encapsulate IPv6 packets with an IPv4 header with the Protocol field value set to 41. In the home scenario, the home router is the egress router connected to the IPv4 Internet. However, the LAN itself can run in IPv6 native mode. Furthermore, some LAN hosts may still use Teredo. Therefore, a home router has the following requirements for WAN and LAN functionality:

WAN:

LAN:

Native IPv6 Connectivity

ISP support for native IPv6 connectivity is about the equivalent functionality to supporting public IPv4 connectivity. The ISP is connected to the global IPv6 Internet, allocates global unicast IPv6 addresses to their customers (in the form of a prefix), and routes IPv6 packets between the home network and the IPv6 Internet.

In this scenario, the ISP may provide a dual-stack service (providing customers with both native IPv6 and native IPv4 connectivity), or it can limit the service to native IPv6 only.

WAN:

LAN:

Native IPv6 Connectivity with Tunneled IPv4

Even if they have native IPv6 connectivity, most consumers still need IPv4 connectivity for accessing Internet content. However, from the ISP's perspective, the overhead of providing both native IPv4 and native IPv6 connectivity is high, requiring double equipment configuration, provisioning, complicated troubleshooting, etc. As an alternative to this dual stack approach, ISPs are adopting a more economical model that involves tunneling IPv4 traffic over IPv6; that is, transporting IPv4 packets as IPv6 payloads.

This practice is already well established in many regions such as the European Union where government regulation restricts the ability of companies to provide both broadband and Internet services. In these regions, IPv4 customers already have dual connectivity: native IPv4 connectivity to their broadband provider (for added value services and content), and tunneled connectivity (over PPPoE, L2TP, or IPsec) to their chosen Internet provider. In these regions, the broadband network can be upgraded transparently to native IPv6 while users continue to receive their IPv4 Internet service over the same network through IPv4-over-IPv6 tunnels.

WAN:

LAN:

Other Home Router Considerations

Name Resolution (DNS)

IPv6 addresses are too long to be typed by a user on a regular basis. For example, typing http://192.168.2.1 may be acceptable for IPv4, but IPv6 usability mandates using name-based URLs such as (http://myrouter). Therefore, on the LAN side, routers must support multicast DNS (mDNS), also known as Link-Local Multicast Name Resolution (LLMNR) (Linklocal Multicast Name Resolution (LLMNR) Internet draft) . Routers should:

Although there are no specific WAN and LAN requirements for a router to support Teredo, the router should adhere to the following behavior to be compatible with Teredo:

It is highly recommended that IPv6 configuration and reports include DNS names alongside (or instead of) IPv6 address.

DNS proxy functionality is not generally needed in the common single subnet case:

A stateless DNS relay/proxy is needed for two cases: multi-subnet homes and when IPv6 resource record queries (DNS AAAA records) are sent over IPv4 (with Windows XP with Service Pack 2 and Windows XP with Service Pack 1).

For more information about how Teredo works, see "Teredo Overview" at http://www.microsoft.com/technet/prodtechnol/winxppro/maintain/teredo.mspx. The Teredo RFC can be found at http://www.ietf.org/html.charters/ngtrans-charter.html , under the title "Teredo: Tunneling IPv6 over UDP through Network Address Translations (NATs)."

UPnP-enabled Firewall Capabilities

As mentioned earlier, home routers must provide at least stateful packet filtering to make up for the fact that the address translation and concealment functionality provided by IPv4 NATs is no longer available.

Furthermore it is important that the router's firewall functionality be able to seamlessly co-exist with host-based (personal) firewalls and end-user applications to provide the best user experience. To this end, Microsoft recommends that the router be UPnP enabled, for example, to allow ports to be dynamically opened and closed. More information about the UPnP protocol can be found at http://www.upnp.org . UPnP is supported on Windows XP, Windows 2003 Server, and Windows CE versions 4.2 and 5.0.

Configured Tunnels

Configured IPv6 over IPv4 tunnels can extend native IPv6 connectivity, but given their poor scaling properties and the need for individual configuration, they are optional. The 6to4 service does require relaying into the native IPv6 Internet but has better scaling properties for homes.

IPv6-to-IPv4 Translation (NAT-PT)

Microsoft does not recommend that routers support IPv6-to-IPv4 Network Address Translation Protocol Translation (NAT-PT) because it is known to break end-to-end connectivity. The IETF has been working to resolve these issues, but NAT-PT may be deprecated.

Interoperability and Conformance Testing

As noted, there are various IPv6 standards that home routers must implement. To assist in testing conformance to these standards, Microsoft recommends the use of the third-party Tahi suite of interoperability tests available at http://www.tahi.org/ . Microsoft will provide further information on Microsoft-specific tools and hardware compatibility tests when available.

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Conclusion and Summary

Even if ISPs do not all support IPv6 natively, it is possible to take advantage of IPv6 features through transition technologies, such as Teredo and 6to4, that support IPv6 communications over an IPv4 network infrastructure such as the IPv4 Internet. In order to take advantage of IPv6, however, home routers need to provide a basic set of IPv6 features depending on the targeted ISP scenario. Table 1 summarizes these requirements. IPv6 support in home routers will ultimately provide a better user experience in voice and video communications, peer-to-peer games, and other technologies that require end-to-end connectivity.

Table 1: Summary of home router functional requirements

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Resources and References

For questions about this document, please send e-mail to ipv6-fb@microsoft.com.

For additional information, see the following:

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