Home Networking Architecture for IPv6
draft-chown-homenet-arch-00

Abstract

This text describes the evolving networking technology within small "residential home" networks. The goal of this memo is to define the architecture for IPv6-based home networking. The text highlights the impact of IPv6 on home networking, and illustrates some topology scenarios. The architecture shows how standard IPv6 mechanisms and addressing can be employed in home networking, lists a number of principles that should apply, and outlines the need for specific protocol extensions for certain additional functionality.

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/.

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This Internet-Draft will expire on March 24, 2012.

Copyright Notice

Copyright (c) 2011 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
• 2. Effects of IPv6 on Home Networking
• 3. Architecture
• 3.1. Network Models
• 3.2. Requirements
• 3.3. Considerations
• 3.4. Principles
• 3.5. Implementing the Architecture on IPv6
• 4. References
• 4.1. Normative References
• 4.2. Informative References
• Appendix A. Acknowledgments
• Authors' Addresses

1. Introduction

This memo focuses on the evolving networking technology within small "residential home" networks and the associated challenges. For example, a trend in home networking is the proliferation of networking technology in an increasingly broad range of devices and media. This evolution in scale and diversity sets requirements on IETF protocols. Some of these requirements relate to the need for multiple subnets for private and guest networks, the introduction of IPv6, and the introduction of specialized networks for home automation and sensors.

While advanced home networks have been built, most operate based on IPv4, employ solutions that we would like to avoid such as network address translation (NAT), or require expert assistance to set up. The architectural constructs in this document are focused on the problems to be solved when introducing IPv6 with a eye towards a better result than what we have today with IPv4, as well as a better result than if the IETF had not given this specific guidance.

This architecture document aims to provide the basis for how standard IPv6 mechanisms and addressing [RFC2460] [RFC4291] can be employed in home networking, while coexisting with existing IPv4 mechanisms. Some general principles for the architecture are listed. At this stage it is vital that introducing IPv6 does not adversely affect IPv4 operation. Future deployments, or potentially specific subnets within an otherwise dual-stack home network, may be IPv6-only.

Currently some parts of this text are somewhat "chatty", which is intended to solicit feedback on the issues presented.

2. Effects of IPv6 on Home Networking

Service providers are deploying IPv6, content is becoming available on IPv6, and support for IPv6 is increasingly available in devices and software used in the home. While IPv6 resembles IPv4 in many ways, it changes address allocation principles, makes multi-addressing the norm, and allows direct IP addressability and routing to devices in the home from the Internet. The following is an overview of some of the key areas impacted by the implementation of IPv6 into the home network that are both promising and problematic:

Multiple segments

While less complex layer 3 topologies involving as few subnets as possible are preferred in home networks for a variety of reasons including simpler management and service discovery, incorporation of dedicated segments remains necessary for some cases.

For instance, a common feature in modern home routers is the ability to support both guest and private network segments. Also, link layer networking technology is poised to become more heterogeneous, as networks begin to employ both traditional Ethernet technology and link layers designed for low-powered sensor networks. Similar needs for segmentation may occur in other cases, such as separating building control or corporate extensions from the Internet access network. Also, different segments may be associated with subnets that have different routing and security policies.

Documents that provide some more specific background and depth on this topic include: [I-D.herbst-v6ops-cpeenhancements], [I-D.baker-fun-multi-router], and [I-D.baker-fun-routing-class].

In addition to routing, rather than NATing, between subnets, there are issues of when and how to extend mechanisms such as service discovery which currently rely on link-local addressing to limit scope.

The presence of a multiple segment, multi-router network implies that there is some kind of automatic routing mechanism in place. In advanced configurations similar to those used in multihomed corporate networks, there may also be a need to discover border router(s) by an appropriate mechanism.

Multi-Addressing of devices

In an IPv6 network, devices may acquire multiple addresses, typically at least a link-local address and a globally unique address. Thus it should be considered the norm for devices on IPv6 home networks to be multi-addressed, and to also have an IPv4 address where the network is dual-stack. Default address selection mechanisms [I-D.ietf-6man-rfc3484-revise] allow a node to select appropriate src/dst address pairs for communications, though such selection may face problems in the event of multihoming, where nodes may have multiple globally unique addresses and multiple exit routers associated with them.

Unique Local Addresses (ULAs)

[RFC4193] defines Unique Local Addresses (ULAs) for IPv6 that may be used to address devices within the scope of a single site. Support for ULAs for CPEs is described in [RFC6204].

A home network running IPv6 may deploy ULAs for communication between devices within the network. Address selection mechanisms should ensure a ULA source address is used to communicate with ULA destination address. The use of ULAs does not imply IPv6 NAT, rather that external communications should use a node's global IPv6 source address.

Security, Borders, and the elimination of NAT

The end-to-end communication that is promised with IPv6 is both an incredible opportunity for innovation and simpler network operation, but it is also a concern as it exposes nodes in the internal networks to receipt of otherwise unwanted traffic from the Internet. Firewalls that restrict incoming connections may be used to prevent exposure, however, this reduces the efficacy of end-to-end connectivity that IPv6 has the potential to restore. [RFC6092] provides recommendations for an IPv6 firewall that applies "limitations on end-to-end transparency where security considerations are deemed important to promote local and Internet security." The firewall operation is "simple" in that there is an assumption that traffic which is to be blocked by default is defined in the RFC and not expected to be updated by the user or otherwise. The RFC also discusses an option for CPEs to have an option to be put into a "transparent mode" of operation.

It is important to distinguish between addressability and reachability; i.e. IPv6 through use of globally unique addressing in the home makes all devices potentially reachable from anywhere. Whether they are or not should depend on firewall or filtering behaviour, and not the presence or use of NAT.

Advanced Security for IPv6 CPE [I-D.vyncke-advanced-ipv6-security] takes the approach that in order to provide the greatest end-to-end transparency as well as security, security polices must be updated by a trusted party which can provide intrusion signatures an other "active" information on security threats. This is much like a virus-scanning tool which must receive updates in order to detect and/or neutralize the latest attacks as they arrive. As the name implies "advanced" security requires significantly more resources and infrastructure (including a source for attack signatures) vs. "simple" security.

In addition to the security mechanisms themselves, it is important to know where to enable them. If there is some indication as to which router is connected to the "outside" of the home network, this is feasible. Otherwise, it can be difficult to know which security policies to apply where. Further, security policies may be different for various address ranges if ULA addressing is setup to only operate within the homenet itself and not be routed to the Internet at large. Finally, such policies must be able to be applied by typical home users, e.g. to give a visitor in a 'guest' network access to media services in the home.

It may be useful to classify the border of the home network as a unique logical interface separating the home network from service provider network/s. This border interface may be a single physical interface to a single service provider, multiple layer 2 sub-interfaces to a single service provider, or multiple connections to a single or multiple providers. This border is useful for describing edge operations and interface requirements across multiple functional areas including security, routing, service discovery, and router discovery.

Naming, and manual configuration of IP addresses

In IPv4, a single subnet NATed home network environment is currently the norm. As a result, it is common practice to reach a router for configuration, DNS resolver functions, or otherwise via 192.168.1.1 or some other commonly used RFC 1918 address. In IPv6, while ULAs exist and could potentially be used to address internally-reachable services, little deployment experience exists to date. In addition, generally IPv6 addresses are more cumbersome for humans to manually configure, with a true ULA prefix effectively being a random 48-bit prefix. As such, even for the simplest of functions, naming and the associated discovery of services is imperative for an easy to administer homenet.

Naming and service discovery are thus important, but they may also be expected to operate across the scope of the entire home network, despite crossing subnet boundaries. It should be noted that in IPv4, these services do not generally function across home router NAT boundaries, so this would be one area where there is room for an improvement in IPv6.

3. Architecture

An architecture outlines how to construct home networks involving multiple routers and subnets. In the next section this text presents a few typical home network topology models/scenarios, followed by a list of topics that may influence the architecture discussions. This is followed by a set of architectural principles that govern how the various nodes should work together. Finally, some guidelines are given for realizing the architecture with the IPv6 addressing architecture, prefix delegation, global and ULA addresses, source address selection rules and other existing components of the IPv6 architecture. The architecture also drives what protocols extensions are necessary, as will be discussed in Section 3.5.

3.1. Network Models

Figure 1 shows the simplest possible home network topology, involving just one router, a local area network, and a set of hosts. Setting up such networks is in principle well understood today [RFC6204].

             +-------+-------+                      \
             |   Service     |                       \
             |   Provider    |                        | Service
             |    Router     |                        | Provider
             +-------+-------+                        | network
                     |                               /
                     | Customer                     /
                     | Internet connection         /
                     |
              +------+--------+                    \
              |     IPv6      |                     \
              | Customer Edge |                      \
              |    Router     |                      /
              +------+--------+                     /
                     |                             | End-User
       Local Network |                             | network(s)
            ---+-----+-------+---                   \ 
               |             |                       \
          +----+-----+ +-----+----+                   \
          |IPv6 Host | |IPv6 Host |                   /
          |          | |          |                  /
          +----------+ +-----+----+                 /

Figure 2 shows another network that now introduces multiple local area networks. These may be needed for reasons relating to different link layer technology or for policy reasons. Note that a common arrangement is to have different link types supported on the same router, bridged together. For the purposes of this memo and IP layer operation this arrangement is considered equivalent to the topology in Figure 1.

This topology is also relatively well understood today [RFC6204], though it certainly presents additional demands with regards suitable firewall policies and limits the operation of certain applications and discovery mechanisms (which may typically today only succeed within a single subnet).

                   +-------+-------+                    \
                   |   Service     |                     \
                   |   Provider    |                      | Service
                   |    Router     |                      | Provider
                   +------+--------+                      | network
                          |                              /
                          | Customer                    /
                          | Internet connection        /
                          |
                   +------+--------+                     \
                   |     IPv6      |                      \
                   | Customer Edge |                       \
                   |    Router     |                       /
                   +----+-------+--+                      /
        Network A       |       |   Network B            | End-User
  ---+-------------+----+-    --+--+-------------+---    | network(s)
     |             |               |             |        \
+----+-----+ +-----+----+     +----+-----+ +-----+----+    \
|IPv6 Host | |IPv6 Host |     | IPv6 Host| |IPv6 Host |    /
|          | |          |     |          | |          |   /
+----------+ +-----+----+     +----------+ +----------+  /

Figure 3 shows a little bit more complex network with two routers and eight devices connected to one ISP. This network is similar to the one discussed in [I-D.ietf-v6ops-ipv6-cpe-router-bis]. The main complication in this topology compared to the ones described earlier is that there is no longer a single router that a priori understands the entire topology. The topology itself may also be complex. It may not be possible to assume a pure tree form, for instance. This would be a consideration if there was an assumption that home users may plug routers together to form arbitrary topologies.

                  +-------+-------+                     \
                  |   Service     |                      \
                  |   Provider    |                       | Service
                  |    Router     |                       | Provider
                  +-------+-------+                       | network
                          |                              /
                          | Customer                    /
                          | Internet connection        
                          |                            
                   +------+--------+                    \
                   |     IPv6      |                     \
                   | Customer Edge |                      \
                   |    Router     |                      |
                   +----+-+---+----+                      |
       Network A        | |   |      Network B/E          |
 ----+-------------+----+ |   +---+-------------+------+  |
     |             |    | |       |             |      |  |
+----+-----+ +-----+----+ |  +----+-----+ +-----+----+ |  |
|IPv6 Host | |IPv6 Host | |  | IPv6 Host| |IPv6 Host | |  |
|          | |          | |  |          | |          | |  |
+----------+ +-----+----+ |  +----------+ +----------+ |  |
                          |        |             |     |  |
                          |     ---+------+------+-----+  |
                          |               | Network B/E   |
                   +------+--------+      |               | End-User
                   |     IPv6      |      |               | networks
                   |   Interior    +------+               |
                   |    Router     |                      |
                   +---+-------+-+-+                      |
       Network C       |       |   Network D              |
 ----+-------------+---+-    --+---+-------------+---     |
     |             |               |             |        |
+----+-----+ +-----+----+     +----+-----+ +-----+----+   |
|IPv6 Host | |IPv6 Host |     | IPv6 Host| |IPv6 Host |   |
|          | |          |     |          | |          |   /
+----------+ +-----+----+     +----------+ +----------+  /

        +-------+-------+     +-------+-------+         \
        |   Service     |     |   Service     |          \
        |  Provider A   |     |  Provider B   |           | Service
        |    Router     |     |    Router     |           | Provider
        +------+--------+     +-------+-------+           | network
               |                      |                   /
               |      Customer        |                  /
               | Internet connections |                 /
               |                      |
        +------+--------+     +-------+-------+         \
        |     IPv6      |     |    IPv6       |          \
        | Customer Edge |     | Customer Edge |           \
        |   Router 1    |     |   Router 2    |           / 
        +------+--------+     +-------+-------+          /
               |                      |                 /
               |                      |                | End-User
  ---+---------+---+---------------+--+----------+---  | network(s)
     |             |               |             |      \
+----+-----+ +-----+----+     +----+-----+ +-----+----+  \
|IPv6 Host | |IPv6 Host |     | IPv6 Host| |IPv6 Host |  /
|          | |          |     |          | |          | /
+----------+ +-----+----+     +----------+ +----------+ 

Figure 4 illustrates a multihomed home network model, where the customer has connectivity via CPE1 to ISP A and via CPE2 to ISP B. This example shows one shared subnet where IPv6 nodes would potentially be multihomed and received multiple IPv6 global addresses, one per ISP. This model may also be combined with that shown in Figure 3 for example to create a more complex scenario.

        +-------+-------+     +-------+-------+         \
        |   Service     |     |   Service     |          \
        |  Provider A   |     |  Provider B   |           | Service
        |    Router     |     |    Router     |           | Provider
        +-------+-------+     +-------+-------+           | network
                 |                 |                     /
                 |    Customer     |                   /
                 |    Internet     |                  /
                 |   connections   |                 |
                +---------+---------+                 \
                |       IPv6        |                   \
                |   Customer Edge   |                    \
                |     Router 1      |                    / 
                +---------+---------+                   /
                   |             |                     /
                   |             |                     | End-User
  ---+---------+---+--           --+--+----------+---  | network(s)
     |             |               |             |      \
+----+-----+ +-----+----+     +----+-----+ +-----+----+  \
|IPv6 Host | |IPv6 Host |     | IPv6 Host| |IPv6 Host |  /
|          | |          |     |          | |          | /
+----------+ +-----+----+     +----------+ +----------+ 

Figure 5 illustrates a model where a home network may have multiple connections to multiple providers or multiple logical connections to the same provider, but the associated subnet(s) are isolated. Some deployment scenarios may require this model.

3.2. Requirements

[RFC6204] defines "basic" requirements for IPv6 Customer Edge Routers, while [I-D.ietf-v6ops-ipv6-cpe-router-bis] describes "advanced" features. In general, home network equipment needs to cope with the different types of network topologies discussed above. Manual configuration is rarely, if at all, possible, given the knowledge lying with typical home users. The equipment needs to be prepared to handle at least

• Prefix configuration for routers
• Managing routing
• Name resolution
• Service discovery
• Network security

3.3. Considerations

This section lists some considerations for home networking that may affect the architecture depending on how or if they are included. Comments are certainly required here.

Multihoming

A home network may be multihomed to multiple providers. This may either take a form where there are multiple isolated networks within the home or a more integrated network where the connectivity selection is dynamic. Current practice is typically of the former kind.

In an integrated network, specific appliances or applications may use their own external connectivity, or the entire network may change its connectivity based on the status of the different upstream connections. Many general solutions for IPv6 multihoming have been worked for years in the IETF and to date there is little deployment of these mechanisms. An argument can be made that home networking standards should not make another attempt at this. An obvious counter-argument is that multihoming support may be necessary for many deployment situations.

In any case, if multihoming is supported, additional requirements are necessary as described in [I-D.baker-fun-multi-router]. In the case of multiple exit routers, either the use of NAT66 [RFC6296] or an alternative approach may be needed, e.g. [I-D.v6ops-multihoming-without-ipv6nat]. One could also argue that a "happy eyeballs" viewpoint, not too dissimilar to that proposed for multiple interface (mif) scenarios is also acceptable. The central part of the arguments about IPv6 multihoming is whether all devices exist in the same multihomed network, and if they, do they have one or multiple IPv6 addresses.

Quality of Service in multi-service home networks

Support for QoS between multiple services may be a requirement, e.g. for a critical system (perhaps healthcare related), or for differentiation between different types of traffic (file sharing, cloud storage, live streaming, VoIP, etc). Different media types may have different QoS properties or capabilities.

A counter-argument for adding any specific support for home networking related standards is that again, there is little practical deployment of QoS mechanism even in the general networking world, let alone home networks. It could also be argued that simpler mechanisms are more cost-effective, such as ensuring proper buffering algorithms to avoid the bufferbloat problem as described in [Gettys11].

DNS services

Consideration will need to be given for existing protocols that may be used within a network, e.g. mDNS. With the introduction of new top level domains, there is potential for ambiguity between for example a local host called apple and (if it is registered) an apple gTLD, so some local name space is probably required, and one that may be configurable by a home user. It is probably desirable to have DNS treated the same within a home network for IPv4 and IPv6. This will fall under the naming and service discovery requirements. More input needed here.

Privacy considerations

There has been some suggestion to include privacy consideration in homenet. What do we want to say about that here?

3.4. Principles

There is little that the Internet standards community can do about the physical topologies or the need for some networks to be separated at the network layer for policy or link layer compatibility reasons. However, there is a lot of flexibility in using IP addressing and inter-networking mechanisms. It would be desirable to provide some guidance on how this flexibility should be used to provide the best user experience and ensure that the network can evolve with new applications in the future.

The authors believe that the following principles guide us in designing these networks in the correct manner. There is no implied priority by the order in which the principles are listed.

Reuse existing protocols

It is desirable to reuse existing protocols where possible, but at the same time to avoid consciously precluding the introduction of new or emerging protocols. For example, [I-D.baker-fun-routing-class] suggests introducing a routing protocol that may may route on both source and destination addresses. Protocols used should be backwardly compatible.

Do we wish to say anything about other home networking related standards or groups, e.g. DLNA?

Dual-stack Operation

Any solutions for IPv6 must not adversely affect IPv4 operation. While RFC 6204 is targeted at IPv6-only networks, it is likely that dual-stack home networks will be the norm for some period of time, but IPv6-only home networks will be deployed in due course, perhaps first in "greenfield" scenarios, or may appear as one element of an otherwise dual-stack network. It is likely that topologies of IPv4 and IPv6 networks would be as congruent as possible.

Should the text say anything to say about transition tool use? Some discussion has also happened on mapping of external IPv6 addresses to internal IPv4 ones.

Largest Possible Subnets

Today's IPv4 home networks generally have a single subnet, and early dual-stack deployments have a single congruent IPv6 subnet, possibly with some bridging functionality. Future home networks are highly likely to need multiple subnets, for reasons described earlier. As part of the self-organization of the network, the network should subdivide itself to the largest possible subnets that can be constructed with the constraints of link layer mechanisms, bridging, physical connectivity, and policy. For instance, separate subnetworks are necessary where two different links cannot be bridged, or when a policy requires the separation of a private and visitor parts of the network.

While it may be desirable to maximise the chance of link-local protocols succeeding, multiple subnet home networks are inevitable, so their support must be included. A general recommendation is to follow the same topology for IPv6 as is used for IPv4, but not to use NAT. Thus there should be routed IPv6 where an IPv4 NAT is used, and where there is no NAT there should be bridging.

** Perhaps add a Figure here to illustrate the principle.

Transparent End-to-End Communications

An IPv6-based home network architecture should naturally offer a transparent end-to-end communications model. Each device should be addressable by a unique address. Security perimeters can of course restrict the end-to-end communications, but it is much easier to block certain nodes from communicating than it is to re-enable nodes to communicate if they have been hidden behind address translation devices.

As discussed previously, it is important to note the difference between addressable and reachable. So filtering is to be expected, but NAT is not. For configuring filters, protocols for securely associating devices would be desirable. The use of protocols including uPnP or PCP may be expected. A default 'transparent mode' (as per RFC6092) may be used.

Local addressing (ULAs) may be used within the scope of a home network. Should ULAs be encouraged for all devices or only those intended to have internal connectivity only? IPv4 "thinking" would incorrectly associate ULAs with use of NAT.

IP Connectivity between All Nodes

A logical consequence of the end-to-end communications model is that the network should attempt to provide IP-layer connectivity between all internal parts as well as between the internal parts and the Internet. This connectivity should be established at the link layer, if possible, and using routing at the IP layer otherwise.

Some home networking scenarios/models may involve isolated subnet(s) with their own CPEs. In such cases connectivity would only be expected within each isolated network (though traffic may potentially pass between them via external providers).

Routing functionality

Routing functionality is required when multiple subnets are in use. This functionality could be as simple as the current "default route is up" model of IPv4 NAT, or it could be running an actual routing protocol.

The requirements for solutions in this area are unclear, but it seems likely that a solution is required and that it should be something that can work across different types of devices in the same home network.

If an actual routing protocol is needed, is it necessary to pick one? If there are multiple protocols, will some kind of negotiation be needed?

If one routing protocol is recommended, which one should it be? Should the selection of the solution be guided by what already exists in most devices (the running code approach) or what satisfies the full requirements (the design principle)?

Should sensor and machine-to-machine communication networks be dealt with as separate networks, or as a part of the routing mechanisms that handle the entire home network? Or are the requirements and mechanisms for home networks too different from these specialized, low-power networks that attempting to use one solution would merely cause harm? Current home deployments use largely different mechanisms in sensor and basic Internet connectivity networks.

Self-Organization

A home network architecture should be naturally self-organizing and self-configuring under different circumstances relating to connectivity status to the Internet, number of devices, and physical topology.

Least Topology Assumptions

There should be ideally no built-in assumptions about the topology in home networks, as users are capable of connecting their devices in ingenious ways. Thus arbitrary topologies will need to be supported.

Discovery

The most natural way to think about naming and service discovery within a home is to enable it to work across the entire residence, disregarding technical borders such as subnets but respecting policy borders such as those between visitor and internal networks.

This implies support for IPv6 multicast across the scope of the home network, and thus at least all routing devices in the network.

Proxy or Extend?

Related to the above, it would be desirable to decide whether in general existing protocols that are designed to only work within a subnet are modified/extended to work across subnets, or whether proxy capabilities are defined for those functions.

We may need to do more analysis (a survey?) on which functions/protocols assume subnet-only operation, in the context of existing home networks (which today are most commonly a single subnet). Some experience from enterprises may be relevant here.

Adapt to ISP constraints

The home network may receive an arbitrary length IPv6 prefix from its provider, e.g. /60 or /56. The offered prefix may be static or dynamic. The home network needs to be adaptable to such ISP policies, e.g. on constraints placed by the size of prefix offered by the ISP. The ISP may use [I-D.ietf-dhc-pd-exclude] for example.

The internal operation of the home network should not also depend on the availability of the ISP network at any given time, other than for connectivity to services or systems off the home network.

Intelligent Policy

As the Internet continues to evolve, no part of the architecture or security design should depend on hard coding acceptable or unacceptable traffic patterns into the devices. Rather, these traffic patterns should be driven off up-to-date databases in the Internet.

This principle should also cover consideration to avoid hard coding IP literals or taking other actions that unnecessarily complicate any required home network renumbering operation.

3.5. Implementing the Architecture on IPv6

The necessary mechanisms are largely already part of the IPv6 protocol set and common implementations. The few known counter-examples are discussed in the following section. For automatic routing, it is expected that existing routing protocols can be used as is. However, a new mechanism may be needed in order to turn a selected protocol on by default. Support for multiple exit routers and multi-homing would also require extensions. For name resolution and service discovery, extensions to existing multicast-based name resolution protocols are needed to enable them to work across subnets, within the scope of the home network.

The hardest problems in developing solutions for home networking IPv6 architectures include discovering the right borders where the domain "home" ends and the service provider domain begins, deciding whether some of necessary discovery mechanism extensions should affect only the network infrastructure or also hosts, and the ability to turn on routing, prefix delegation and other functions in a backwards compatible manner.

4. References

4.1. Normative References

4.2. Informative References

Appendix A. Acknowledgments

The authors would like to thank to Stuart Cheshire, James Woodyatt, Lars Eggert, Ray Bellis, David Harrington, Wassim Haddad, Heather Kirksey, Dave Thaler, Fred Baker, and Ralph Droms for interesting discussions in this problem space, and Mark Townsley for being an initial editor/author of this text before taking his position as homenet WG co-chair.

** Additional acknowledgements TBA.

Authors' Addresses