Status of This Memo

This document is not an Internet Standards Track specification; it is published for examination, experimental implementation, and evaluation.¶

This document defines an Experimental Protocol for the Internet community. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are candidates for any level of Internet Standard; see Section 2 of RFC 7841.¶

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9526.¶

Copyright Notice

Copyright (c) 2024 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 (https://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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶

Table of Contents

1. Introduction

Home network owners may have devices or services hosted on their home network that they wish to access from the Internet (i.e., from a network outside of the home network). The use of IPv6 addresses in the home makes, in principle, the actual network access simpler, while on the other hand, the addresses are much harder to remember and are subject to regular renumbering. To make this situation simpler for typical home owners to manage, there needs to be an easy way for the names and IP addresses of these devices and services to be published in the public DNS.¶

As depicted in Figure 1, the names and IP address of the home network are made available in the Public Homenet Zone by the Homenet Naming Authority (HNA), which in turn instructs the DNS Outsourcing Infrastructure (DOI) to publish the zone on behalf of the HNA. This document describes how an HNA can instruct a DOI to publish a Public Homenet Zone on its behalf.¶

This document introduces the Synchronization Channel and the Control Channel between the HNA and the Distribution Manager (DM), which is the main interface to the DOI.¶

The Synchronization Channel (see Section 7) is used to synchronize the Public Homenet Zone.¶

                               Internet
.---------------------.           .-------------------.
|      Home Network   | Control   |        DOI        |
|.-------------------.| Channel   |.-----------------.|
||         HNA       |<----------->|  Distribution   ||
||.-----------------.||           ||  Manager        ||
|||  Public Homenet |||           ||                 ||
|||       Zone      ||<----------->|                 ||
||| myhome.example  ||| Synchron- |'-----------------'|
||'-----------------'|| ization   |         |         |
|'-------------------'| Channel   |         V         |
|                     |           |.-----------------.|
|                     |           ||  Public Homenet ||
'---------------------'           ||       Zone      ||
                                  || myhome.example  ||
                                  |'-----------------'|
                                  '---^--^--^--^--^---'
                                      |  |  |  |  |
                                 (served on the Internet)

The Synchronization Channel is a zone transfer, with the HNA configured as a primary server and the Distribution Manager configured as a secondary server. Some operators refer to this kind of configuration as a "hidden primary", but that term is not used in this document as it is not precisely defined anywhere, but it has many slightly different meanings to many.¶

The Control Channel (see Section 6) is used to set up the Synchronization Channel. This channel is in the form of a dynamic DNS update process, authenticated by TLS.¶

For example, to build the Public Homenet Zone, the HNA needs the authoritative servers (and associated IP addresses) of the DOI's servers (the visible primaries) that are actually serving the zone. Similarly, the DOI needs to know the IP address of the (hidden) primary (HNA) as well as potentially the hash of the Key Signing Key (KSK) in the DS RRset to secure the DNSSEC delegation with the parent zone.¶

The remainder of the document is as follows.¶

Section 2 defines the terminology. Section 3 presents the general problem of publishing names and IP addresses. Section 4 briefly describes some potential envisioned deployment scenarios. And Section 5 provides an architectural view of the HNA, DM, and DOI as well as their different communication channels (Control Channel, Synchronization Channel, and DM Distribution Channel) described in Sections 6, 7, and 8, respectively.¶

Then, Sections 6 and 7 deal with the two channels that interface to the home. Section 8 provides a set of requirements and expectations on how the distribution system works. This section is non-normative and not subject to standardization but reflects how many scalable DNS distribution systems operate.¶

Sections 9 and 11 respectively detail HNA security policies as well as DNSSEC compliance within the home network.¶

Section 12 discusses how renumbering should be handled.¶

Finally, Sections 13 and 14 respectively discuss privacy and security considerations when outsourcing the Public Homenet Zone.¶

The appendices discuss the following aspects: management (see Section 10), provisioning (see Section 10), configurations (see Appendix B), and deployment (see Section 4 and Appendix C).¶

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

Customer Premises Equipment (CPE):

A router providing connectivity to the home network.¶

Homenet Zone:

The DNS zone for use within the boundaries of the home network: "home.arpa" (see [RFC8375]). This zone is not considered public and is out of scope for this document.¶

Registered Homenet Domain:

The domain name that is associated with the home network. A given home network may have multiple Registered Homenet Domains.¶

Public Homenet Zone:

Contains the names in the home network that are expected to be publicly resolvable on the Internet. A home network can have multiple Public Homenet Zones.¶

Homenet Naming Authority (HNA):

A function responsible for managing the Public Homenet Zone. This includes populating the Public Homenet Zone, signing the zone for DNSSEC, as well as managing the distribution of that Homenet Zone to the DOI.¶

DNS Outsourcing Infrastructure (DOI):

The infrastructure responsible for receiving the Public Homenet Zone and publishing it on the Internet. It is mainly composed of a Distribution Manager and Public Authoritative Servers.¶

Public Authoritative Servers:

The authoritative name servers for the Public Homenet Zone. Name resolution requests for the Registered Homenet Domain are sent to these servers. Some DNS operators refer to these as public secondaries, and higher resiliency networks are often implemented in an anycast fashion.¶

Homenet Authoritative Servers:

The authoritative name servers for the Homenet Zone within the Homenet network itself. These are sometimes called "hidden primary servers".¶

Distribution Manager (DM):

The server (or set of servers) that the HNA synchronizes the Public Homenet Zone to and that then distributes the relevant information to the Public Authoritative Servers. This server has been historically known as the Distribution Master.¶

Public Homenet Reverse Zone:

The reverse zone file associated with the Public Homenet Zone.¶

Reverse Public Authoritative Servers:

These are equivalent to Public Authoritative Servers, specifically for reverse resolution.¶

Reverse Distribution Manager:

This is equivalent to the Distribution Manager, specifically for reverse resolution.¶

DNS Resolver:

A resolver that performs a DNS resolution on the Internet for the Public Homenet Zone. The resolution is performed by requesting the Public Authoritative Servers. While the resolver does not necessarily perform DNSSEC resolutions, it is RECOMMENDED that DNSSEC is enabled.¶

Note that when "DNS Resolver" is used in this document, it refers to "DNS or DNSSEC Resolver".¶

Homenet DNS Resolver:

A resolver that performs a DNS or DNSSEC resolution on the home network for the Public Homenet Zone. The resolution is performed by requesting the Homenet Authoritative Servers.¶

3. Selecting Names and Addresses to Publish

While this document does not create any normative mechanism to select the names to publish, it does anticipate that the home network administrator (a human being) will be presented with a list of current names and addresses either directly on the HNA or via another device such as a smartphone.¶

The administrator will mark which devices and services (by name) are to be published. The HNA will then collect the IP address(es) associated with that device or service and put the name into the Public Homenet Zone. The address of the device or service can be collected from a number of places: Multicast DNS (mDNS) [RFC6762], DHCP [RFC8415], Universal Plug and Play (UPnP), the Port Control Protocol (PCP) [RFC6887], or manual configuration.¶

A device or service SHOULD have Global Unicast Addresses (GUAs) (IPv6 [RFC3587] or IPv4) but MAY also have IPv6 Unique Local Addresses (ULAs) [RFC4193], IPv6 Link-Local Addresses (LLAs) [RFC4291] [RFC7404], IPv4 LLAs [RFC3927], and private IPv4 addresses [RFC1918].¶

Of these, the LLAs are almost never useful for the Public Zone and should be omitted.¶

The IPv6 ULA and private IPv4 addresses may be useful to publish, if the home network environment features a VPN that would allow the home owner to reach the network. [RFC1918] addresses in public zones are generally filtered out by many DNS servers as they are considered rebind attacks [REBIND].¶

In general, one expects the GUA to be the default address to be published. A direct advantage of enabling local communication is to enable communications even in case of Internet disruption. Since communications are established with names that remain a global identifier, the communication can be protected (at the very least with integrity protection) by TLS the same way it is protected on the global Internet -- by using certificates.¶

4. Envisioned Deployment Scenarios

A number of deployment scenarios have been envisioned; this section aims at providing a brief description. The use cases are not limitations, and this section is not normative.¶

The main difference between the various deployments concerns the provisioning of the HNA -- that is, how it is configured to outsource the Public Homenet Zone to the DOI -- as well as how the Public Homenet Zone is being provisioned before being outsourced. In both cases, these configuration aspects are out of the scope of this document.¶

Provisioning the configuration related to the DOI is expected to be automated as much as possible and require interaction with the end user as little as possible. Zero configuration can only be achieved under some circumstances, and [RFC9527] provides one such example under the assumption that the ISP provides the DOI. Section 4.1 describes another variant where the Customer Premises Equipment (CPE) is provided preconfigured with the DOI. Section 4.2 describes how an agnostic CPE may be configured by the home network administrator. Of course even in this case, the configuration can leverage mechanisms to prevent the end user from manually entering all information.¶

On the other hand, provisioning the Public Homenet Zone needs to combine the ability to closely reflect what the end user wishes to publish on the Internet while easing such interaction. The HNA may implement such interactions using web-based GUIs or specific mobile applications.¶

With the CPE configured with the DOI, the HNA contacts the DOI to build a template for the Public Homenet Zone and then provisions the Public Homenet Zone. Once the Public Homenet Zone is built, the HNA starts synchronizing it with the DOI on the Synchronization Channel.¶

5. Architecture Description

This section provides an overview of the architecture for outsourcing the authoritative naming service from the HNA to the DOI. As a consequence, this prevents HNA from handling the DNS traffic from the Internet that is associated with the resolution of the Homenet Zone.¶

The device-assigned zone or user-configurable zone that is used as the domain to publicly serve hostnames in the home network is called the Public Homenet Zone. In this document, "myhome.example" is used as the example for an end-user-owned domain configured as a Public Homenet Zone.¶

More specifically, DNS resolution for the Public Homenet Zone (here "myhome.example") from Internet DNSSEC resolvers is handled by the DOI as opposed to the HNA. The DOI benefits from a cloud infrastructure while the HNA is dimensioned for a home network and, as such, is likely unable to support any load. In the case where the HNA is a CPE, outsourcing to the DOI reduces the attack surface of the home network to DDoS, for example. Of course, the DOI needs to be informed dynamically about the content of myhome.example. The description of such a synchronization mechanism is the purpose of this document.¶

Note that Appendix B shows the necessary parameters to configure the HNA.¶

.----------------------------.         .-----------------------------.
|        Home Network        |         |          Internet           |
| .-----------------------.  | Control |  .-----------------------.  |
| |          HNA          |  | Channel |  |          DOI          |  |
| |   (hidden primary)    |<------------->|   (hidden secondary)  |  |
| |                       |  | DNSUPD  |  |  Distribution Manager |  |
| | .-------------------. |  |         |  |                       |  |
| | |  Public Homenet   | |  |         |  |  .-------------------.|  |
| | |       Zone        |<------------------>|Public Homenet Zone||  |
| | | myhome.example    | |  |Synchron-|  |  | myhome.example    ||  |
| | '-------------------' |  |ization  |  |  '-------------------'|  |
| '-----------------------'  |Channel  |  |             |         |  |
|             ^              |  AXFR   |  |             |         |  |
|             |              |         |  |             v         |  |
| .-----------------------.  |         |  |.---------------------.|  |
| | Homenet Authoritative |  |         |  || Public Authoritative||  |
| |        Server         |  |         |  || (secondary) Servers ||  |
| | + myhome.example      |  |         |  || + myhome.example    ||  |
| | + home.arpa           |  |         |  || + x.y.z.ip6.arpa    ||  |
| | + x.y.z.ip6.arpa      |  |         |  ||                     ||  |
| '-----------------------'  |         |  ||                     ||  |
|        |       ^           |         |  |'---------------------'|  |
|        |       |           |         |  |  ^            |       |  |
|        |       |           |         |  '--|------------|-------'  |
|        v       |           |         |     |            v          |
|  .----------------------.  |         | .------------------------.  |
|  | Homenet DNS Resolver |  |         | |   Internet Resolvers   |  |
|  '----------------------'  |         | '------------------------'  |
|                            |         |                             |
'----------------------------'         |                             |
                                       '-----------------------------'

6. Control Channel

The DM Control Channel is used by the HNA and the DOI to exchange information related to the configuration of the delegation, which includes information to build the Public Homenet Zone (Section 6.1), to build the DNSSEC chain of trust (Section 6.2), and to set the Synchronization Channel (Section 6.3).¶

Some information is carried from the DOI to the HNA, as described in the next section. The HNA updates the DOI with the IP address on which the zone is to be transferred using the Synchronization Channel. The HNA is always initiating the exchange in both directions.¶

As such, the HNA has a prior knowledge of the DM identity (via an X.509 certificate), the IP address and port number to use, and the protocol to establish a secure session. The DM acquires knowledge of the identity of the HNA (X.509 certificate) as well as the Registered Homenet Domain. For more detail on how this can be achieved, please see Appendix A.1.¶

7. Synchronization Channel

The DM Synchronization Channel is used for communication between the HNA and the DM for synchronizing the Public Homenet Zone. Note that the Control Channel and the Synchronization Channel are different channels by construction even though they may use the same IP address. Suppose the HNA and the DM are using a single IP address designated by XX, and YYYYY and ZZZZZ are the various ports involved in the communications.¶

The Control Channel is between¶

• the HNA working as a client using port number YYYYY (an ephemeral also commonly designated as a high range port) and¶
• a service provided by the DM at port 853, when using DoT.¶

On the other hand, the Synchronization Channel is between¶

• the DM working as a client using port ZZZZZ (another ephemeral port) and¶
• a service provided by the HNA at port 853.¶

As a result, even though the same pair of IP addresses may be involved, the Control Channel and the Synchronization Channel are always distinct channels.¶

Uploading and dynamically updating the zone file on the DM can be seen as zone provisioning between the HNA (hidden primary server) and the DM (secondary server). This is handled using the normal zone transfer mechanism involving the AXFR and Incremental Zone Transfer (IXFR).¶

Part of the process to update the zone involves the owner of the zone (the hidden primary server, the HNA) sending a DNS Notify to the secondaries. In this situation, the only destination that is known by the HNA is the DM's Control Channel, so DNS Notifies are sent over the Control Channel, secured by a mutually authenticated TLS.¶

Please note that DNS Notifies are not critical to normal operation, as the DM will be checking the zone regularly based upon SOA record comments. DNS Notifies do speed things up as they cause the DM to use the Synchronization Channel to immediately do an SOA query to detect any updates. If there are any changes, then the DM immediately transfers the zone updates.¶

This specification standardizes the use of a primary/secondary mechanism [RFC1996] rather than an extended series of DNS update messages. The primary/secondary mechanism was selected as it scales better and avoids DoS attacks. Because this AXFR runs over a TCP channel secured by a mutually authenticated TLS, the DNS update is more complicated.¶

Note that this document provides no standard way to distribute a DNS primary between multiple devices. As a result, if multiple devices are candidates for hosting the hidden primary server, some specific mechanisms should be designed so the home network only selects a single HNA for the hidden primary server. Selection mechanisms based on HNCP [RFC7788] are good candidates for future work.¶

8. DM Distribution Channel

The DM Distribution Channel is used for communication between the DM and the Public Authoritative Servers. The architecture and communication used for the DM Distribution Channels are outside the scope of this document, but there are many existing solutions available, e.g., rsync, DNS AXFR, REST, and DB copy.¶

9. HNA Security Policies

The HNA, as the hidden primary server, processes only limited message exchanges on its Internet-facing interface. This should be enforced using security policies to allow only a subset of DNS requests to be received by HNA.¶

The hidden primary server on the HNA differs from the regular authoritative server for the home network due to the following:¶

Interface Binding:

The hidden primary server will almost certainly listen on the WAN Interface, whereas a regular Homenet Authoritative Server will listen on the internal home network interface.¶

Limited Exchanges:

The purpose of the hidden primary server is to synchronize with the DM, not to serve any zones to end users or the public Internet. This results in a limited number of possible exchanges (AXFR/IXFR) with a small number of IP addresses, and an implementation MUST enable filtering policies: it should only respond to queries that are required to do zone transfers. That list includes SOA queries and AXFR/IXFR queries.¶

10. Public Homenet Reverse Zone

The Public Homenet Reverse Zone works similarly to the Public Homenet Zone. The main difference is that the ISP that provides the IPv6 connectivity is likely to also be the owner of the corresponding IPv6 reverse zone who administrates the Reverse Public Authoritative Servers. The configuration and the setting of the Synchronization Channel and Control Channel can largely be automated using DHCPv6 messages that are a part of the IPv6 prefix delegation process.¶

The Public Homenet Zone is associated with a Registered Homenet Domain, and the ownership of that domain requires a specific registration from the end user as well as the HNA being provisioned with some authentication credentials. Such steps are mandatory unless the DOI has some other means to authenticate the HNA. Such situation may occur, for example, when the ISP provides the Homenet Domain as well as the DOI.¶

In this case, the HNA may be authenticated by the physical link layer, in which case the authentication of the HNA may be performed without additional provisioning of the HNA. While this may not be so common for the Public Homenet Zone, this situation is expected to be quite common for the Reverse Homenet Zone as the ISP owns the IP address or IP prefix.¶

More specifically, a common case is that the upstream ISP provides the IPv6 prefix to the Homenet with an identity association for a prefix delegation (IA_PD) option [RFC8415] and manages the DOI of the associated reverse zone.¶

This leaves a place for setting up the relation between the HNA and DOI automatically as described in [RFC9527].¶

In the case of the reverse zone, the DOI authenticates the source of the updates by IPv6 ACLs, and the ISP knows exactly what addresses have been delegated. Therefore, the HNA SHOULD always originate Synchronization Channel updates from an IP address within the zone that is being updated. Exceptionally, the Synchronization Channel might be from a different zone delegated to the HNA (if there were multiple zones or renumbering events were in progress).¶

For example, if the ISP has assigned 2001:db8:f00d:1234::/64 to the WAN interface (by DHCPv6 or PPP with Router Advertisement (RA)), then the HNA should originate Synchronization Channel updates from, for example, 2001:db8:f00d:1234::2.¶

If an ISP has delegated 2001:db8:aeae::/56 to the HNA via DHCPv6-PD, then the HNA should originate Synchronization Channel updates to an IP address within that subnet, such as 2001:db8:aeae:1::2.¶

With this relation automatically configured, the synchronization between the Home network and the DOI happens in a similar way to the synchronization of the Public Homenet Zone described earlier in this document.¶

Note that for home networks connected to multiple ISPs, each ISP provides only the DOI of the reverse zones associated with the delegated prefix. It is also likely that the DNS exchanges will need to be performed on dedicated interfaces to be accepted by the ISP. More specifically, the reverse zone update associated with prefix 1 cannot be performed by the HNA using an IP address that belongs to prefix 2. Such constraints do not raise major concerns for hot standby or load-sharing configuration.¶

With IPv6, the reverse domain space for IP addresses associated with a subnet such as ::/64 is so large that the reverse zone may be confronted with scalability issues. How the reverse zone is generated is out of scope of this document. [RFC8501] provides guidance on how to address scalability issues.¶

11. DNSSEC-Compliant Homenet Architecture

Section 3.7.3 of [RFC7368] recommends that DNSSEC be deployed on both the authoritative server and the resolver.¶

The resolver side is out of scope of this document, and only the authoritative part of the server is considered. Other documents such as [RFC5011] deal with the continuous update of trust anchors required for operation of a DNSSEC Resolver.¶

The Public Homenet Zone and the Public Reverse Zone MUST be DNSSEC signed by the HNA.¶

Secure delegation is achieved only if the DS RRset is properly set in the parent zone. Secure delegation can be performed by the HNA or the DOIs, and the choice highly depends on which entity is authorized to perform such updates. Typically, the DS RRset is updated manually through a registrar interface and can be maintained with mechanisms such as CDS [RFC7344].¶

When the operator of the DOI is also the registrar for the domain, then it is a trivial matter for the DOI to initialize the relevant DS records in the parent zone. In other cases, some other initialization will be required, and that will be specific to the infrastructure involved. It is beyond the scope of this document.¶

There may be some situations where the HNA is unable to arrange for secure delegation of the zones, but the HNA MUST still sign the zones.¶

12. Renumbering

During a renumbering of the home network, the HNA IP address may be changed and the Public Homenet Zone will be updated by the HNA with new AAAA records.¶

The HNA will then advertise to the DM via a NOTIFY on the Control Channel. The DM will need to note the new originating IP for the connection, and it will need to update its internal database of Synchronization Channels. A new zone transfer will occur with the new records for the resources that the HNA wishes to publish.¶

The remainder of the section provides recommendations regarding the provisioning of the Public Homenet Zone, especially the IP addresses.¶

Renumbering has been extensively described in [RFC4192] and analyzed in [RFC7010], and the reader is expected to be familiar with them before reading this section. In the make-before-break renumbering scenario, the new prefix is advertised, and the network is configured to prepare the transition to the new prefix. During a period of time, the two prefixes (old and new) coexist before the old prefix is completely removed. New resource records containing the new prefix SHOULD be published, while the old resource records with the old prefixes SHOULD be withdrawn. If the HNA anticipates that the period of overlap will be long (perhaps due to the knowledge of router and DHCPv6 lifetimes), it MAY publish the old prefixes with a significantly lower TTL.¶

In break-before-make renumbering scenarios, including flash renumbering scenarios [RFC8978], the old prefix becomes unusable before the new prefix is known or advertised. As explained in [RFC8978], some flash renumberings occur due to power cycling of the HNA, where ISPs do not properly remember what prefixes have been assigned to which user.¶

An HNA that boots up MUST immediately use the Control Channel to update the location for the Synchronization Channel. This is a reasonable thing to do on every boot, as the HNA has no idea how long it has been offline or if the (DNSSEC) zone has perhaps expired during the time the HNA was powered off.¶

The HNA will have a list of names that should be published, but it might not yet have IP addresses for those devices. This could be because at the time of power on, the other devices were not yet online. If the HNA is sure that the prefix has not changed, then it should use the previously known addresses, with a very low TTL.¶

Although the new and old IP addresses may be stored in the Public Homenet Zone, it is RECOMMENDED that only the newly reachable IP addresses be published.¶

Regarding the Public Homenet Reverse Zone, the new Public Homenet Reverse Zone has to be populated as soon as possible, and the old Public Homenet Reverse Zone will be deleted by the owner of the zone (and the owner of the old prefix, which is usually the ISP) once the prefix is no longer assigned to the HNA. The ISP MUST ensure that the DNS cache has expired before reassigning the prefix to a new home network. This may be enforced by controlling the TTL values.¶

To avoid reachability disruption, IP connectivity information provided by the DNS MUST be coherent with the IP in use. In our case, this means the old IP address MUST NOT be provided via the DNS when it is not reachable anymore.¶

In the make-before-break scenario, it is possible to make the transition seamless. Let T be the TTL associated with an RRset of the Public Homenet Zone; Time_NEW be the time the new IP address replaces the old IP address in the Homenet Zone; and Time_OLD_UNREACHABLE be the time the old IP will not be reachable anymore.¶

In the case of the make-before-break scenario, seamless reachability is provided as long as Time_OLD_UNREACHABLE - T_NEW > (2 * T). If this is not satisfied, then devices associated with the old IP address in the home network may become unreachable for 2 * T - (Time_OLD_UNREACHABLE - Time_NEW).¶

In the case of a break-before-make scenario, Time_OLD_UNREACHABLE = Time_NEW, and the device may become unreachable up to 2 * T. Of course, if Time_NEW >= Time_OLD_UNREACHABLE, then the outage is not seamless.¶

13. Privacy Considerations

Outsourcing the DNS Authoritative service from the HNA to a third party raises a few privacy-related concerns.¶

The Public Homenet Zone lists the names of services hosted in the home network. Combined with blocking of AXFR queries, the use of NSEC3 [RFC5155] (vs. NSEC [RFC4034]) prevents an attacker from being able to walk the zone to discover all the names. However, recent work [GPUNSEC3] [ZONEENUM] has shown that the protection provided by NSEC3 against dictionary attacks should be considered cautiously, and [RFC9276] provides guidelines to configure NSEC3 properly. In addition, the attacker may be able to walk the reverse DNS zone or use other reconnaissance techniques to learn this information as described in [RFC7707].¶

The zone may be also exposed during the synchronization between the primary and the secondary. The casual risk of this occurring is low, and the use of [RFC9103] significantly reduces this. Even if DNS zone transfer over TLS [RFC9103] is used by the DOI, it may still leak the existence of the zone through Notifies. The protocol described in this document does not increase that risk, as all Notifies use the encrypted Control Channel.¶

In general, a home network owner is expected to publish only names for which there is some need to reference them externally. Publication of the name does not imply that the service is necessarily reachable from any or all parts of the Internet. [RFC7084] mandates that the outgoing-only policy [RFC6092] be available, and in many cases, it is configured by default. A well-designed user interface would combine a policy for making a service public by a name with a policy on who may access it.¶

In many cases, and for privacy reasons, the home network owner has wanted to publish names only for services that they will be able to access. The access control may consist of an IP source address range, or access may be restricted via some VPN functionality. The main advantages of publishing the names are that the service may be accessed by the same name both within and outside the home, and the DNS resolution can be handled similarly both within and outside the home. This considerably eases the ability to use VPNs where the VPN can be chosen according to the IP address of the service. Typically, a user may configure its device to reach its Homenet devices via a VPN while the remaining traffic is accessed directly.¶

Enterprise networks have generally adopted another strategy designated as split-horizon-DNS. While such strategy might appear as providing more privacy at first sight, its implementation remains challenging and the privacy advantages need to be considered carefully. In split-horizon-DNS, names are designated with internal names that can only be resolved within the corporate network. When such strategy is applied to the homenet, VPNs need to be configured with naming resolution policies and routing policies. Such an approach might be reasonable with a single VPN, but maintaining a coherent DNS space and IP space among various VPNs comes with serious complexities. Firstly, if multiple homenets are using the same domain name -- like home.arpa -- it becomes difficult to determine on which network the resolution should be performed. As a result, homenets should at least be differentiated by a domain name. Secondly, the use of split-horizon-DNS requires each VPN to be associated with a resolver and specific resolutions to be performed by the dedicated resolver. Such policies can easily raise some conflicts (with significant privacy issues) while remaining hard to be implemented.¶

In addition to the Public Homenet Zone, pervasive DNS monitoring can also monitor the traffic associated with the Public Homenet Zone. This traffic may provide an indication of the services an end user accesses, plus how and when they use these services. Although, caching may obfuscate this information inside the home network, it is likely that this information will not be cached outside the home network.¶

14. Security Considerations

The HNA never answers DNS requests from the Internet. These requests are instead served by the DOI.¶

While this limits the level of exposure of the HNA, the HNA still has some exposure to attacks from the Internet. This section analyses the attack surface associated with these communications, the data published by the DOI, as well as operational considerations.¶

15. IANA Considerations

This document has no IANA actions.¶

Appendix A. HNA Channel Configurations

Appendix B. Information Model for Outsourced Information

This section specifies an optional format for the set of parameters required by the HNA to configure the naming architecture of this document.¶

In cases where a home router has not been provisioned by the manufacturer (when forward zones are provided by the manufacturer) or by the ISP (when the ISP provides this service), then a home user/owner will need to configure these settings via an administrative interface.¶

By defining a standard format (in JSON) for this configuration information, the user/owner may be able to copy and paste a configuration blob from the service provider into the administrative interface of the HNA.¶

This format may also provide the basis for a future OAuth 2.0 [RFC6749] flow that could do the set up automatically.¶

The HNA needs to be configured with the following parameters as described by the Concise Data Definition Language (CDDL) [RFC8610]. These parameters are necessary to establish a secure channel between the HNA and the DM as well as to specify the DNS zone that is in the scope of the communication.¶

hna-configuration = {
  "registered_domain" : tstr,
  "dm"                : tstr,
  ? "dm_transport" : "DoT"
  ? "dm_port"        : uint,
  ? "dm_acl"         : hna-acl / [ +hna-acl ]
  ? "hna_auth_method": hna-auth-method
  ? "hna_certificate": tstr
}

hna-acl          = tstr
hna-auth-method  /= "certificate"

For example:¶

{
  "registered_domain" : "n8d234f.r.example.net",
  "dm"                : "2001:db8:1234:111:222::2",
  "dm_transport"      : "DoT",
  "dm_port"           : 4433,
  "dm_acl"            : "2001:db8:1f15:62e::/64"
                   or [ "2001:db8:1f15:62e::/64", ... ]
  "hna_auth_method"   : "certificate",
  "hna_certificate"   : "-----BEGIN CERTIFICATE-----\nMIIDTjCCFGy..",
}

Registered Homenet Domain (registered_domain):

The Domain Name of the zone. Multiple Registered Homenet Domains may be provided. This will generate the creation of multiple Public Homenet Zones. This parameter is mandatory.¶

Distribution Manager notification address (dm):

The associated FQDNs or IP addresses of the DM to which DNS Notifies should be sent. This parameter is mandatory. IP addresses are optional, and the FQDN is sufficient and preferred. If there are concerns about the security of the name to IP translation, then DNSSEC should be employed.¶

As the session between the HNA and the DM is authenticated with TLS, the use of names is easier.¶

As certificates are more commonly emitted for FQDN than for IP addresses, it is preferred to use names and authenticate the name of the DM during the TLS session establishment.¶

Supported Transport (dm_transport):

The transport that carries the DNS exchanges between the HNA and the DM. The typical value is "DoT", but it may be extended in the future with "DoH" or "DoQ", for example. This parameter is optional, and the HNA uses DoT by default.¶

Distribution Manager Port (dm_port):

Indicates the port used by the DM. This parameter is optional, and the default value is provided by the Supported Transport. In the future, an additional transport may not have a default port, in which case either a default port needs to be defined or this parameter becomes mandatory.¶

Note that HNA does not define ports for the Synchronization Channel. In any case, this is not expected to be a part of the configuration but is instead negotiated through the Configuration Channel. Currently, the Configuration Channel does not provide this and limits its agility to a dedicated IP address. If such agility is needed in the future, additional exchanges will need to be defined.¶

Authentication Method ("hna_auth_method"):

How the HNA authenticates itself to the DM within the TLS connection(s). The authentication method can typically be "certificate", "psk", or "none". This parameter is optional, and the Authentication Method is "certificate" by default.¶

Authentication data ("hna_certificate", "hna_key"):

The certificate chain used to authenticate the HNA. This parameter is optional, and when not specified, a self-signed certificate is used.¶

Distribution Manager AXFR permission netmask (dm_acl):

The subnet from which the CPE should accept SOA queries and AXFR requests. A subnet is used in the case where the DOI consists of a number of different systems. An array of addresses is permitted. This parameter is optional, and if unspecified, the CPE uses the IP addresses provided by the dm parameter either directly when the dm indicates the IP address(es) returned by the DNS or DNSSEC resolution when dm indicates an FQDN.¶

For forward zones, the relationship between the HNA and the forward zone provider may be the result of a number of transactions:¶

1. The forward zone outsourcing may be provided by the maker of the Homenet router. In this case, the identity and authorization could be built in the device at the manufacturer provisioning time. The device would need to be provisioned with a device-unique credential, and it is likely that the Registered Homenet Domain would be derived from a public attribute of the device, such as a serial number (see Appendix C or [HOMEROUTER-PROVISION] for more details).¶
2. The forward zone outsourcing may be provided by the ISP. In this case, the use of [RFC9527] to provide the credentials is appropriate.¶
3. The forward zone may be outsourced to a third party, such as a domain registrar. In this case, the use of the JSON-serialized YANG data model described in this section is appropriate, as it can easily be copy and pasted by the user or downloaded as part of a web transaction.¶

For reverse zones, the relationship is always with the upstream ISP (although there may be more than one), so [RFC9527] always applies.¶

The following is an abridged example of a set of data that represents the needed configuration parameters for outsourcing.¶

Appendix C. Example: A Manufacturer-Provisioned HNA Product Flow

This scenario is one where a Homenet router device manufacturer decides to offer DNS hosting as a value add.¶

[HOMEROUTER-PROVISION] describes a process for a home router credential provisioning system. The outline of it is that near the end of the manufacturing process, as part of the firmware loading, the manufacturer provisions a private key and certificate into the device.¶

In addition to having an asymmetric credential known to the manufacturer, the device also has been provisioned with an agreed-upon name. In the example in the above document, the name "n8d234f.r.example.net" has already been allocated and confirmed with the manufacturer.¶

The HNA can use the above domain for itself. It is not very pretty or personal, but if the owner would like to have a better name, they can arrange it.¶

The configuration would look like the following:¶

{
  "dm" : "2001:db8:1234:111:222::2",
  "dm_acl"    : "2001:db8:1234:111:222::/64",
  "dm_ctrl"   : "manufacturer.example.net",
  "dm_port"   : "4433",
  "ns_list"   : [ "ns1.publicdns.example", "ns2.publicdns.example"],
  "zone"      : "n8d234f.r.example.net",
  "auth_method" : "certificate",
  "hna_certificate":"-----BEGIN CERTIFICATE-----\nMIIDTjCCFGy....",
}

The dm_ctrl and dm_port values would be built into the firmware.¶

Acknowledgments

The authors wish to thank Philippe Lemordant for his contributions to the earlier draft versions of this document; Ole Troan for pointing out issues with the IPv6-routed home concept and placing the scope of this document in a wider picture; Mark Townsley for encouragement and injecting a healthy debate on the merits of the idea; Ulrik de Bie for providing alternative solutions; Paul Mockapetris, Christian Jacquenet, Francis Dupont, and Ludovic Eschard for their remarks on HNA and low power devices; Olafur Gudmundsson for clarifying DNSSEC capabilities of small devices; Simon Kelley for its feedback as dnsmasq implementer; Andrew Sullivan, Mark Andrew, Ted Lemon, Mikael Abrahamson, Stephen Farrell, and Ray Bellis for their feedback on handling different views as well as clarifying the impact of outsourcing the zone-signing operation outside the HNA; and Mark Andrew and Peter Koch for clarifying the renumbering.¶

The authors would like to thank Kiran Makhijani for her in-depth review that contributed to shaping the final version of this document.¶

The authors would also like to thank our Area Director Éric Vyncke for his constant support and pushing the document through the IESG process and the many reviewers from various directorates including Anthony Somerset, Geoff Huston, Tim Chown, Tim Wicinski, Matt Brown, Darrel Miller, and Christer Holmberg.¶

Contributors

The coauthors would like to thank Chris Griffiths and Wouter Cloetens for providing significant contributions to the earlier draft versions of this document.¶

Authors' Addresses