| Internet-Draft | public-names | April 2021 |
| Migault, et al. | Expires 30 October 2021 | [Page] |
Home owners often have IPv6 devices that they wish to access over the Internet using names. It has been possible to register and populate a DNS Zone with names since DNS became a thing, but it has been an activity typically reserved for experts. This document automates the process through creation of a Homenet Naming Authority (HNA), whose responsibility is to select, sign and publish names to a set of publicly visible servers.¶
The use of an outsourced primary DNS server deals with possible renumbering of the home network, and with possible denial of service attacks against the DNS infrastructure.¶
This document describes the mechanism that enables the HNA to outsource the naming service to the DNS Outsourcing Infrastructure (DOI) via a Distribution Master (DM).¶
In addition, this document deals with publication of a corresponding reverse zone.¶
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 https://datatracker.ietf.org/drafts/current/.¶
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."¶
This Internet-Draft will expire on 30 October 2021.¶
Copyright (c) 2021 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 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.¶
The Homenet Naming Authority (HNA) is responsible for making devices within the home network accessible by name within the home network as well as from outside the home network (e.g. the Internet). IPv6 connectivity provides the possibility of global end to end IP connectivity. End users will be able to transparently make use of this connectivity if they can use names to access the services they want from their home network.¶
The use of a DNS zone for each home network is a reasonable and scalable way to make the set of public names visible. There are a number of ways to populate such a zone. This specification proposes a way based on a number of assumptions about typical home networks.¶
This specification makes the public names resolvable within both the home network and on the Internet, even when there are disruptions.¶
This is achieved by having a device inside the home network that builds, signs, publishes, and manages a Public Homenet Zone, thus providing bindings between public names, IP addresses, and other RR types.¶
The management of the names can be a role that the Customer Premises Equipment (CPE) does. Other devices in the home network could fulfill this role e.g. a NAS server, but for simplicity, this document assumes the function is located on one of the CPE devices.¶
The homenet architecture [RFC7368] makes it clear that a home network may have multiple CPEs. The management of the Public Homenet Zone involves DNS specific mechanisms that cannot be distributed over multiple servers (primary server), when multiple nodes can potentially manage the Public Homenet Zone, a single node needs to be selected per outsourced zone. This selected node is designated as providing the HNA function.¶
The process by which a single HNA is selected per zone is not in scope for this document. It is envisioned that a future document will describe an HNCP mechanism to elect the single HNA.¶
CPEs, which may host the HNA function, as well as home network devices, are usually low powered devices not designed for terminating heavy traffic. As a result, hosting an authoritative DNS service visible to the Internet may expose the home network to resource exhaustion and other attacks. On the other hand, if the only copy of the public zone is on the Internet, then Internet connectivity disruptions would make the names unavailable inside the homenet.¶
In order to avoid resource exhaustion and other attacks, this document describes an architecture that outsources the authoritative naming service of the home network. More specifically, the HNA builds the Public Homenet Zone and outsources it to an DNS Outsourcing Infrastructure (DOI) via a Distribution Master (DM). The DOI is in charge of publishing the corresponding Public Homenet Zone on the Internet. The transfer of DNS zone information is achieved using standard DNS mechanisms involving primary and secondary DNS servers, with the HNA hosted primary being a stealth primary, and the DM a secondary.¶
Section 3.1 provides an architecture description that describes the relation between the HNA and the DOI. In order to keep the Public Homenet Zone up-to-date Section 5 describes how the HNA and the DOI synchronizes the Pubic Homenet Zone.¶
The proposed architecture is explicitly designed to enable fully functional DNSSEC, and the Public Homenet Zone is expected to be signed with a secure delegation. DNSSEC key management and zone signing is handled by the HNA.¶
Section 10 discusses management and configuration of the Public Homenet Zone. It shows that the HNA configuration of the DOI can involve no or little interaction with the end user. More specifically, it shows that the existence of an account in the DOI is sufficient for the DOI to push the necessary configuration. In addition, when the DOI and CPE are both managed by an ISP, the configuration can be entirely automated - see Section 9.¶
Section 9 discusses management of one or more reverse zones. It shows that management of the reverse zones can be entirely automated and benefit from a pre-established relation between the ISP and the home network. Note that such scenarios may also be met for the Public Homenet Zone, but not necessarily.¶
Section 11 discusses how renumbering should be handled. Finally, Section 12 and Section 13 respectively discuss privacy and security considerations when outsourcing the Public Homenet Zone.¶
The Public Homenet Zone is expected to contain public information only in a single universal view. This document does not define how the information required to construct this view is derived.¶
It is also not in the scope of this document to define names for exclusive use within the boundaries of the local home network. Instead, local scope information is expected to be provided to the home network using local scope naming services. mDNS [RFC6762] DNS-SD [RFC6763] are two examples of these services. Currently mDNS is limited to a single link network. However, future protocols and architectures [I-D.ietf-homenet-simple-naming] are expected to leverage this constraint as pointed out in [RFC7558].¶
While this document does not create any normative mechanism by which the selection of names to publish, this document anticipates that the home network administrator (a humuan), will be presented with a list of current names and addresses present on the inside of the home network.¶
The administrator would mark which devices (by name), are to be published. The HNA would then collect the IPv6 address(es) associated with that device, and put the name into the Public Homenet Zone. The address of the device can be collected from a number of places: mDNS [RFC6762], DHCP [RFC6644], UPnP, PCP [RFC6887], or manual configuration.¶
A device may have a Global Unicast Address (GUA), a Unique Local IPv6 Address (ULA), as as well IPv6-Link-Local addresses, IPv4-Link-Local Addresses, and RFC1918 addresses. Of these the link-local are never useful for the Public Zone, and should be omitted. The IPv6 ULA and the RFC1918 addresses may be useful to publish, if the home network environment features a VPN that would allow the home owner to reach the network.¶
The IPv6 ULA addressees are significantly safer to publish, as the RFC1918 addressees are likely to be confusing to any other entity.¶
In general, one expects the GUA to be the default address to be published. However, during periods when the home network has connectivity problems, the ULA and RFC1918 addressees can be used inside the home, and the mapping from public name to locally useful location address would permit many services secured with HTTPS to continue to operate.¶
An alternative existing solution in IPv4 is to have a single zone, where a host uses a RESTful HTTP service to register a single name into a common public zone. This is often called "Dynamic DNS", and there are a number of commercial providers, including Dyn, Gandi etc. These solutions were typically used by a host behind the CPE to make it's CPE IPv4 address visible, usually in order to enable incoming connections.¶
For a small number (one to three) of hosts, use of such a system provides an alternative to the architecture described in this document.¶
The alternative does suffer from some severe limitations:¶
There is no technical reason why a RESTful cloud service could not provide solutions to many of these problems, but this document describes a DNS based solution.¶
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.¶
This section provides an overview of the architecture for outsourcing the authoritative naming service from the HNA to the DOI in Section 3.1. Section 14 defines necessary parameter to configure the HNA.¶
Figure 1 illustrates the architecture where the HNA outsources the publication of the Public Homenet Zone to the DOI.¶
The Public Homenet Zone is identified by the Registered Homenet Domain Name - myhome.example. The ".local" as well as ".home.arpa" are explicitly not considered as Public Homenet zones and represented as Homenet Zone in Figure 1.¶
The HNA SHOULD build the Public Homenet Zone in a single view populated with all resource records that are expected to be published on the Internet. As explained in Section 1.1, how the Public Homenet Zone is populated is out of the scope of this document. The HNA also signs the Public Homenet Zone. The HNA handles all operations and keying material required for DNSSEC, so there is no provision made in this architecture for transferring private DNSSEC related keying material between the HNA and the DM.¶
Once the Public Homenet Zone has been built, the HNA outsources it to the DOI as described in Figure 1. The HNA acts as a hidden primary while the DM behaves as a secondary responsible to distribute the Public Homenet Zone to the multiple Public Authoritative Servers that DOI is responsible for. The DM has 3 communication channels:¶
There MAY be multiple DM's, and multiple servers per DM. This text assumes a single DM server for simplicity, but there is no reason why each channel needs to be implemented on the same server, or indeed use the same code base.¶
It is important to note that while the HNA is configured as an authoritative server, it is not expected to answer to DNS requests from the public Internet for the Public Homenet Zone. More specifically, the addresses associated with the HNA SHOULD NOT be mentioned in the NS records of the Public Homenet zone, unless additional security provisions necessary to protect the HNA from external attack have been taken.¶
The DOI is also responsible for ensuring the DS record has been updated in the parent zone.¶
Resolution is performed by the DNSSEC resolvers. When the resolution is performed outside the home network, the DNSSEC Resolver resolves the DS record on the Global DNS and the name associated to the Public Homenet Zone (myhome.example) on the Public Authoritative Servers.¶
When the resolution is performed from within the home network, the Homenet DNSSEC Resolver may proceed similarly. On the other hand, to provide resilience to the Public Homenet Zone in case of disruption, the Homenet DNSSEC Resolver SHOULD be able to perform the resolution on the Homenet Authoritative Servers. These servers are not expected to be mentioned in the Public Homenet Zone, nor to be accessible from the Internet. As such their information as well as the corresponding signed DS record MAY be provided by the HNA to the Homenet DNSSEC Resolvers, e.g., using HNCP [RFC7788]. Such configuration is outside the scope of this document. Since the scope of the Homenet Authoritative Servers is limited to the home network, these servers are expected to serve the Homenet Zone as represented in Figure 1.¶
How the Homenet Authoritative Servers are provisioned is also out of scope of this specification. It could be implemented using primary secondaries servers, or via rsync. In some cases, the HNA and Homenet Authoritative Servers may be combined together which would result in a common instantiation of an authoritative server on the WAN and inner interface. Other mechanisms may also be used.¶
Home network | Internet
|
| +----------------------------+
| | DOI |
Control | | |
+-----------------------+ Channel | | +-----------------------+ |
| HNA |<-------------->| Distribution Master | |
|+---------------------+| | | |+---------------------+| |
|| Public Homenet Zone ||Synchronization || Public Homenet Zone || |
|| (myhome.example) || Channel | | || (myhome.example) || |
|+---------------------+|<-------------->|+---------------------+| |
+-----------^-----------+ | | +-----------------------+ |
. | | ^ Distribution |
. | | | Channel |
+-----------v-----------+ | | v |
| Homenet Authoritative | | | +-----------------------+ |
| Server(s) | | | | Public Authoritative | |
|+---------------------+| | | | Server(s) | |
||Public Homenet Zone || | | |+---------------------+| |
|| (myhome.example) || | | || Public Homenet Zone || |
|+---------------------+| | | || (myhome.example) || |
|| Homenet Zone || | | |+---------------------+| |
|| (home.arpa) || | | +-----------------------+ |
|+---------------------+| | +----------^---|-------------+
+----------^---|--------+ | | |
| | name resolution | |
| v | | v
+----------------------+ | +-----------------------+
| Homenet | | | Internet |
| DNSSEC Resolver | | | DNSSEC Resolver |
+----------------------+ | +-----------------------+
This section details the interfaces and channels of the DM, that is the Control Channel, the Synchronization Channel and the Distribution Channel.¶
The Control Channel and the Synchronization Channel are the interfaces used between the HNA and the DOI. The entity within the DOI responsible to handle these communications is the DM and communications between the HNA and the DM SHOULD be protected and mutually authenticated. While section Section 4.6 discusses in more depth the different security protocols that could be used to secure, this specification RECOMMENDS the use of TLS with mutually authentication based on certificates to secure the channel between the HNA and the DM.¶
The Control Channel is used to set up the Synchronization Channel. We assume that the HNA initiates the Control Channel connection with the DM and as such has a prior knowledge of the DM identity (X509 certificate), the IP address and port to use and protocol to set secure session. We also assume the DM has knowledge of the identity of the HNA (X509 certificate) as well as the Registered Homenet Domain. For more detail to see how this can be achieved, please see section Section 10.¶
The information exchanged between the HNA and the DM is using DNS messages protected by DNS over TLS (DoT) [RFC7858]. Further specifications may consider protecting DNS messages with other transport layers, among others, DNS over DTLS [RFC8094], or DNS over HTTPs (DoH) [RFC8484] or DNS over QUIC [I-D.ietf-dprive-dnsoquic]. There was consideration to using a standard TSIG [RFC2845] or SIG(0) [RFC2931] to perform a dynamic DNS update to the DM. There are a number of issues with this. The first one is that TSIG or SIG(0) make scenarios where the end user needs to interact via its web browser more complex. More precisely, authorization and access control granted via OAUTH would be unnecessarily complex with TSIG or SIG(0).¶
The main one is that the Dynamic DNS update would also update the parent zone's (NS, DS and associated A or AAAA records) while the goal is to update the DM configuration files. The visible NS records SHOULD remain pointing at the cloud provider's anycast addresses. Revealing the address of the HNA in the DNS is not desirable. Please see section Section 4.2 for more details.¶
This specification assumes:¶
The Distribution Channel is internal to the DOI and as such is not the primary concern of this specification.¶
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 (see Section 4.1), information to build the DNSSEC chain of trust (see Section 4.2) and information to set the Synchronization Channel (see Section 4.3).¶
When the HNA builds the Public Homenet Zone, it must include information that it retrieves from the DM relating to how the zone is to be published.¶
The information includes at least names and IP addresses of the Public Authoritative Name Servers. In term of RRset information this includes:¶
Optionally the DOI MAY also provide operational parameters such as other fields of SOA (SERIAL, RNAME, REFRESH, RETRY, EXPIRE and MINIMUM). As the information is necessary for the HNA to proceed and the information is associated to the DOI, this information exchange is mandatory.¶
The HNA SHOULD provide the hash of the KSK (DS RRset), so the that DOI provides this value to the parent zone. A common deployment use case is that the DOI is the registrar of the Registered Homenet Domain, and as such, its relationship with the registry of the parent zone enables it to update the parent zone. When such relation exists, the HNA should be able to request the DOI to update the DS RRset in the parent zone. A direct update is especially necessary to initialize the chain of trust.¶
Though the HNA may also later directly update the values of the DS via the Control Channel, it is RECOMMENDED to use other mechanisms such as CDS and CDNSKEY [RFC7344] for transparent updates during key roll overs.¶
As some deployment may not provide a DOI that will be able to update the DS in the parent zone, this information exchange is OPTIONAL.¶
By accepting the DS RR, the DM commits in taking care of advertising the DS to the parent zone. Upon refusal, the DM clearly indicates it does not have the capacity to proceed to the update.¶
The HNA works as a primary authoritative DNS server, while the DM works like a secondary. As a result, the HNA MUST provide the IP address the DM is using to reach the HNA. The synchronization Channel will be set between that IP address and the IP address of the DM. By default, the IP address used by the HNA in the Control Channel is considered by the DM and the specification of the IP by the HNA is only OPTIONAL. The transport channel (including port) is the same as the one used between the HNA and the DM for the Control Channel.¶
The purpose of the previous sections were to exchange information in order to set a delegation. The HNA MUST also be able to delete a delegation with a specific DM. Upon an instruction of deleting the delegation, the DM MUST stop serving the Public Homenet Zone.¶
There are multiple ways these information could be exchanged between the HNA and the DM. This specification defines a mechanism that re-use the DNS exchanges format. The intention is to reuse standard libraries especially to check the format of the exchanged fields as well as to minimize the additional libraries needed for the HNA. The re-use of DNS exchanges achieves these goals. Note that while information is provided using DNS exchanges, the exchanged information is not expected to be set in any zone file, instead this information is expected to be processed appropriately.¶
The Control Channel is not expected to be a long term session. After a predefined timer the Control Channel is expected to be terminated. The Control Channel MAY Be re-opened at any time later.¶
The provisioning process SHOULD provide a method of securing the Control Channel, so that the content of messages can be authenticated. This authentication MAY be based on certificates for both the DM and each HNA. The DM may also create the initial configuration for the delegation zone in the parent zone during the provisioning process.¶
The information provided by the DM to the HNA is retrieved by the HNA with an AXFR exchange. The AXFR message enables the response to contain any type of RRsets. The response might be extended in the future if additional information will be needed. Alternatively, the information provided by the HNA to the DM is pushed by the HNA via a DNS update exchange [RFC2136].¶
To retrieve the necessary information to build the Public Homenet Zone, the HNA MUST send an DNS request of type AXFR associated to the Registered Homenet Domain. The DM MUST respond with a zone template. The zone template MUST contain a RRset of type SOA, one or multiple RRset of type NS and zero or more RRset of type A or AAAA.¶
The NS RRsets are used to carry the Public Authoritative Servers of the DOI. Their associated NAME MUST be the Registered Homenet Domain.¶
The TTL and RDATA are those expected to be published on the Public Homenet Zone. The RRsets of Type A and AAAA MUST have their NAME matching the NSDNAME of one of the NS RRsets.¶
Upon receiving the response, the HNA MUST validate format and properties of the SOA, NS and A or AAAA RRsets. If an error occurs, the HNA MUST stop proceeding and MUST report an error. Otherwise, the HNA builds the Public Homenet Zone by setting the MNAME value of the SOA as indicated by the SOA provided by the AXFR response. The HNA SHOULD set the value of NAME, REFRESH, RETRY, EXPIRE and MINIMUM of the SOA to those provided by the AXFR response. The HNA MUST insert the NS and corresponding A or AAAA RRset in its Public Homenet Zone. The HNA MUST ignore other RRsets. If an error message is returned by the DM, the HNA MUST proceed as a regular DNS resolution. Error messages SHOULD be logged for further analysis. If the resolution does not succeed, the outsourcing operation is aborted and the HNA MUST close the Control Channel.¶
To provide the DS RRset to initialize the DNSSEC chain of trust the HNA MAY send a DNS update [RFC2136] message.¶
The DNS update message is composed of a Header section, a Zone section, a Pre-requisite section, and Update section and an additional section. The Zone section MUST set the ZNAME to the parent zone of the Registered Homenet Domain - that is where the DS records should be inserted. As described [RFC2136], ZTYPE is set to SOA and ZCLASS is set to the zone's class. The Pre-requisite section MUST be empty. The Update section is a DS RRset with its NAME set to the Registered Homenet Domain and the associated RDATA corresponds to the value of the DS. The Additional Data section MUST be empty.¶
Though the pre-requisite section MAY be ignored by the DM, this value is fixed to remain coherent with a standard DNS update.¶
Upon receiving the DNS update request, the DM reads the DS RRset in the Update section. The DM checks ZNAME corresponds to the parent zone. The DM SHOULD ignore non empty the Pre-requisite and Additional Data section. The DM MAY update the TTL value before updating the DS RRset in the parent zone. Upon a successful update, the DM should return a NOERROR response as a commitment to update the parent zone with the provided DS. An error indicates the MD does not update the DS, and other method should be used by the HNA.¶
The regular DNS error message SHOULD be returned to the HNA when an error occurs. In particular a FORMERR is returned when a format error is found, this includes when unexpected RRSets are added or when RRsets are missing. A SERVFAIL error is returned when a internal error is encountered. A NOTZONE error is returned when update and Zone sections are not coherent, a NOTAUTH error is returned when the DM is not authoritative for the Zone section. A REFUSED error is returned when the DM refuses to proceed to the configuration and the requested action.¶
To provide a non default IP address used by the HNA for the Synchronization Channel, the HNA MAY send a DNS Update message. Such exchange is OPTIONAL.¶
Similarly to the Section 4.5.2, the HNA MAY optionally specify the IP address using a DNS update message. The Zone section sets its ZNAME to the parent zone of the Registered Homenet Domain, ZTYPE is set to SOA and ZCLASS is set to the zone's type. Pre-requisite is empty. The Update section is a RRset of type NS. The Additional Data section contains the RRsets of type A or AAAA that designates the IP addresses associated to the primary (or the HNA).¶
The reason to provide these IP addresses is that it is NOT RECOMMENDED to publish these IP addresses. As a result, it is not expected to resolve them.¶
Upon receiving the DNS update request, the DM reads the IP addresses and checks the ZNAME corresponds to the parent zone. The DM SHOULD ignore a non empty Pre-requisite section. The DM configures the secondary with the IP addresses and returns a NOERROR response to indicate it is committed to serve as a secondary.¶
Similarly to Section 4.5.2, DNS errors are used and an error indicates the DM is not configured as a secondary.¶
To instruct to delete the delegation the HNA SHOULD send a DNS UPDATE Delete message.¶
The Zone section sets its ZNAME to the Registered Homenet Domain, the ZTYPE to SOA and the ZCLASS to zone's type. The Pre-requisite section is empty. The Update section is a RRset of type NS with the NAME set to the Registered Domain Name. As indicated by [RFC2136] section 2.5.2 the delete instruction is set by setting the TTL to 0, the Class to ANY, the RDLENGTH to 0 and the RDATA MUST be empty. The Additional Data section is empty.¶
Upon receiving the DNS update request, the DM checks the request and removes the delegation. The DM returns a NOERROR response to indicate the delegation has been deleted. Similarly to Section 4.5.2, DNS errors are used and an error indicates the delegation has not been deleted.¶
The control channel between the HNA and the DM MUST be secured at both the HNA and the DM.¶
Secure protocols (like TLS [RFC8446] SHOULD be used to secure the transactions between the DM and the HNA.¶
The advantage of TLS is that this technology is widely deployed, and most of the devices already embed TLS libraries, possibly also taking advantage of hardware acceleration. Further, TLS provides authentication facilities and can use certificates to mutually authenticate the DM and HNA at the application layer, including available API. On the other hand, using TLS requires implementing DNS exchanges over TLS, as well as a new service port.¶
The HNA SHOULD authenticate inbound connections from the DM using standard mechanisms, such as a public certificate with baked-in root certificates on the HNA, or via DANE [RFC6698]. The HNA is expected to be provisioned with a connection to the DM by the manufacturer, or during some user-initiated onboarding process, see Section 10.¶
The DM SHOULD authenticate the HNA and check that inbound messages are from the appropriate client. The DM MAY use a self-signed CA certificate mechanism per HNA, or public certificates for this purpose.¶
IPsec [RFC4301] and IKEv2 [RFC7296] were considered. They would need to operate in transport mode, and the authenticated end points would need to be visible to the applications, and this is not commonly available at the time of this writing.¶
A pure DNS solution using TSIG and/or SIG(0) to authenticate message was also considered. Section 10 envisions one mechanism would involve the end user, with a browser, signing up to a service provider, with a resulting OAUTH2 token to be provided to the HNA. A way to translate this OAUTH2 token from HTTPS web space to DNS SIG(0) space seems overly problematic, and so the enrollment protocol using web APIs was determined to be easier to implement at scale.¶
Note also that authentication of message exchanges between the HNA and the DM SHOULD NOT use the external IP address of the HNA to index the appropriate keys. As detailed in Section 11, the IP addresses of the DM and the Hidden Primary are subject to change, for example while the network is being renumbered. This means that the necessary keys to authenticate transaction SHOULD NOT be indexed using the IP address, and SHOULD be resilient to IP address changes.¶
The Hidden Primary Server on the HNA differs from a regular authoritative server for the home network due to:¶
As a result, exchanges are performed with specific nodes (the DM). Further, exchange types are limited. The only legitimate exchanges are: NOTIFY initiated by the Hidden Primary and IXFR or AXFR exchanges initiated by the DM.¶
On the other hand, regular authoritative servers would respond to any hosts, and any DNS query would be processed. The HNA SHOULD filter IXFR/AXFR traffic and drop traffic not initiated by the DM. The HNA MUST MUST at least allow SOA lookups of the Homenet Zone.¶
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 by construction different channels even though there they MAY use the same IP addresse. In fact the Control Channel is set between the HNA working as a client using port YYYY (a high range port) toward a service provided by the DM at port XX (well known port).¶
On the other hand, the Synchronization Channel is set between the DM working as a client using port ZZZZ ( a high range port) toward a service a service provided by the HNA at port XX.¶
As a result, even though the same couple 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) and the DM (Secondary Server). This can be handled via AXFR + DNS Update.¶
This document RECOMMENDS use of a primary / secondary mechanism instead of the use of DNS Update. The primary / secondary mechanism is RECOMMENDED as it scales better and avoids DoS attacks. Note that even when UPDATE messages are used, these messages are using a distinct channel as those used to set the configuration.¶
Note that there is no standard way to distribute a DNS primary between multiple devices. As a result, if multiple devices are candidate for hosting the Hidden Primary, some specific mechanisms should be designed so the home network only selects a single HNA for the Hidden Primary. Selection mechanisms based on HNCP [RFC7788] are good candidates.¶
The HNA acts as a Hidden Primary Server, which is a regular authoritative DNS Server listening on the WAN interface.¶
The DM is configured as a secondary for the Registered Homenet Domain Name. This secondary configuration has been previously agreed between the end user and the provider of the DOI as part of either the provisioning or due to receipt of DNS Update messages on the DM Control Channel.¶
The Homenet Reverse Zone MAY also be updated either with DNS UPDATE [RFC2136] or using a primary / secondary synchronization.¶
The Synchronization Channel used standard DNS request.¶
First the primary notifies the secondary that the zone must be updated and eaves the secondary to proceed with the update when possible/convenient.¶
Then, a NOTIFY message is sent by the primary, which is a small packet that is less likely to load the secondary.¶
Finally, the AXFR [RFC1034] or IXFR [RFC1995] query performed by the secondary is a small packet sent over TCP (section 4.2 [RFC5936]), which mitigates reflection attacks using a forged NOTIFY.¶
The AXFR request from the DM to the HNA SHOULD be secured and the use of TLS is RECOMMENDED [I-D.ietf-dprive-xfr-over-tls]¶
When using TLS, the HNA MAY authenticate inbound connections from the DM using standard mechanisms, such as a public certificate with baked-in root certificates on the HNA, or via DANE [RFC6698]. In addition, to guarantee the DM remains the same across multiple TLS session, the HNA and DM MAY implement [RFC8672].¶
The HNA MAY apply a simple IP filter on inbound AXFR requests to ensure they only arrive from the DM Synchronization Channel. In this case, the HNA SHOULD regularly check (via DNS resolution) that the address of the DM in the filter is still valid.¶
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 is outside the scope of this document, and there are many existing solutions available e.g. rsynch, DNS AXFR, REST, DB copy.¶
This section details security policies related to the Hidden Primary / Secondary synchronization.¶
The HNA, as Hidden Primary SHOULD drop any queries from the home network. This could be implemented via port binding and/or firewall rules. The precise mechanism deployed is out of scope of this document. The Hidden Primary SHOULD drop any DNS queries arriving on the WAN interface that are not issued from the DM. The Hidden Primary SHOULD drop any outgoing packets other than DNS NOTIFY query, SOA response, IXFR response or AXFR responses. The Hidden Primary SHOULD drop any incoming packets other than DNS NOTIFY response, SOA query, IXFR query or AXFR query. The Hidden Primary SHOULD drop any non protected IXFR or AXFR exchange,depending on how the synchronization is secured.¶
[RFC7368] in Section 3.7.3 recommends DNSSEC to 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.¶
This document assumes the HNA signs the Public Homenet Zone.¶
Secure delegation is achieved only if the DS RRset is properly set in the parent zone. Secure delegation is performed by the HNA or the DOIs.¶
The DS RRset can be updated manually with nsupdate for example. This requires the HNA or the DOI to be authenticated by the DNS server hosting the parent of the Public Homenet Zone. Such a trust channel between the HNA and the parent DNS server may be hard to maintain with HNAs, and thus may be easier to establish with the DOI. In fact, the Public Authoritative Server(s) may use Automating DNSSEC Delegation Trust Maintenance [RFC7344].¶
The Public Homenet Zone is associated to 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.¶
More specifically, a common case is that the upstream ISP provides the IPv6 prefix to the Homenet with a IA_PD [RFC8415] option and manages the DOI of the associated reverse zone.¶
This leave place for setting up automatically the relation between HNA and the DNS Outsourcing infrastructure as described in [I-D.ietf-homenet-naming-architecture-dhc-options].¶
In the case of the reverse zone, the DOI authenticates the source of the updates by IPv6 Access Control Lists. In the case of the reverse zone, the ISP knows exactly what addresses have been delegated. The HNA SHOULD therefore always originate Synchronization Channel updates from an IP address within the zone that is being updated.¶
For example, if the ISP has assigned 2001:db8:f00d::2/64 to the WAN interface (by DHCPv6, or PPP/RA), then the HNA should originate Synchronization Channel updates from 2001:db8:f00d::2.¶
An ISP that has delegated 2001:db8:babe::/56 to the HNA via DHCPv6-PD, then HNA should originate Synchronization Channel updates an IP within that subnet, such as 2001:db8:babe:0001::2.¶
With this relation automatically configured, the synchronization between the Home network and the DOI happens similarly as for the Public Homenet Zone described earlier in this document.¶
Note that for home networks hosted by multiple ISPs, each ISP provides only the DOI of the reverse zones associated to the delegated prefix. It is also likely that the DNS exchanges will need to be performed on dedicated interfaces as to be accepted by the ISP. More specifically, the reverse zone associated to prefix 1 will not be possible to be performs by the HNA using an IP address that belongs to prefix 2. Such constraints does not raise major concerns either for hot standby or load sharing configuration.¶
With IPv6, the domain space for IP addresses is so large that reverse zone may be confronted with scalability issues. How the reverse zone is generated is out of scope of this document. [I-D.howard-dnsop-ip6rdns] provides guidance on how to address scalability issues.¶
This document does not deal with how the HNA is provisioned with a trusted relationship to the Distribution Master for the forward zone.¶
This section details what needs to be provisioned into the HNA and serves as a requirements statement for mechanisms.¶
The HNA needs to be provisioned with:¶
The HNA will need to select an IP address for communication for the Synchronization Channel. This is typically the outside WAN address of the router, but could be an IPv6 LAN address in the case of a home with multiple ISPs (and multiple border routers). This is communicated in section Section 4.5.3 when the NS and A or AAAA RRsets are communicated.¶
The above parameters MUST be be provisioned for ISP-specific reverse zones, as per [I-D.ietf-homenet-naming-architecture-dhc-options]. ISP-specific forward zones MAY also be provisioned using [I-D.ietf-homenet-naming-architecture-dhc-options], but zones which are not related to a specific ISP zone (such as with a DNS provider) must be provisioned through other means.¶
Similarly, if the HNA is provided by a registrar, the HNA may be given configured to end user.¶
In the absence of specific pre-established relation, these pieces of information may be entered manually by the end user. In order to ease the configuration from the end user the following scheme may be implemented.¶
The HNA may present the end user a web interface where it provides the end user the ability to indicate the Registered Homenet Domain or the registrar for example a preselected list. Once the registrar has been selected, the HNA redirects the end user to that registrar in order to receive a access token. The access token will enable the HNA to retrieve the DM parameters associated to the Registered Domain. These parameters will include the credentials used by the HNA to establish the Control and Synchronization Channels.¶
Such architecture limits the necessary steps to configure the HNA from the end user.¶
This section details how renumbering is handled by the Hidden Primary server or the DM. Both types of renumbering are discussed i.e. "make-before-break" and "break-before-make" (aka flash renumbering).¶
In the make-before-break renumbering scenario, the new prefix is advertised, 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.¶
In the break-before-make renumbering scenario, the new prefix is advertised making the old prefix obsolete.¶
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 a renumbering scenario, the HNA or Hidden Primary is informed it is being renumbered. In most cases, this occurs because the whole home network is being renumbered. As a result, the Public Homenet Zone will also be updated. Although the new and old IP addresses may be stored in the Public Homenet Zone, we recommend that only the newly reachable IP addresses be published.¶
To avoid reachability disruption, IP connectivity information provided by the DNS SHOULD be coherent with the IP plane. In our case, this means the old IP address SHOULD NOT be provided via the DNS when it is not reachable anymore. Let for example TTL be the TTL associated with a RRset of the Public Homenet Zone, it may be cached for TTL seconds. Let T_NEW be the time the new IP address replaces the old IP address in the Homenet Zone, and T_OLD_UNREACHABLE the time the old IP is not reachable anymore.¶
In the case of the make-before-break, seamless reachability is provided as long as T_OLD_UNREACHABLE - T_NEW > 2 * TTL. If this is not satisfied, then devices associated with the old IP address in the home network may become unreachable for 2 * TTL - (T_OLD_UNREACHABLE - T_NEW). In the case of a break-before-make, T_OLD_UNREACHABLE = T_NEW, and the device may become unreachable up to 2 * TTL. Of course if T_NEW >= T_OLD_UNREACHABLE, the disruption is increased.¶
Once the Public Homenet Zone file has been updated on the Hidden Primary, the Hidden Primary needs to inform the DOI that the Public Homenet Zone has been updated and that the IP address to use to retrieve the updated zone has also been updated. Both notifications are performed using regular DNS exchanges. Mechanisms to update an IP address provided by lower layers with protocols like SCTP [RFC4960], MOBIKE [RFC4555] are not considered in this document. Instead the IP address of the HNA is updated using the Synchronization Channel as described in Section 4.3.¶
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, the attacker may be able to walk the reverse DNS zone, or use other reconnaissance techniques to learn this information as described in [RFC7707].¶
In general a home network owner is expected to publish only names for which there is some need to be able to reference 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, the home network owner wishes to publish names for services that only 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 purpose of publishing the name is so that the service may be access by the same name both within the home, and outside the home. Sending traffic to the relevant IPv6 address causes the relevant VPN policy to be enacted upon.¶
While the problem of getting access to internal names has been solved in Enterprise configurations with a split-DNS, and such a thing could be done in the home, many recent improvements to VPN user interfaces make it more likely that an individual might have multiple connections configured. For instance, an adult child checking on the state of a home automation system for a parent.¶
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 outside your home network this information will not be cached.¶
This document exposes a mechanism that prevents the HNA from being exposed to the Internet and served DNS request from the Internet. These requests are instead served by the DOI. While this limits the level of exposure of the HNA, the HNA remains exposed to the Internet with communications with the DOI. This section analyses the attack surface associated to these communications. In addition, the DOI exposes data that are related to the home network. This section also analyses the implication of such exposure.¶
The channels between HNA and DM are mutually authenticated and encrypted with TLS [RFC8446] and its associated security considerations apply. To ensure the multiple TLS session are are continuously authenticating the same entity, TLS may take advantage of second factor authentication as described in [RFC8672].¶
At the time of writing TLS 1.2 or TLS 1.3 can be used and TLS 1.3 (or newer) SHOULD be supported.¶
The DNS protocol is subject to reflection attacks, however, these attacks are largely applicable when DNS is carried over UDP. The interfaces between the HNA and DM are using TLS over TCP, which prevents such reflection attacks. Note that Public Authoritative servers hosted by the DOI are subject to such attacks, but that is out of scope of our document.¶
Note that in the case of the Reverse Homenet Zone, the data is less subject to attacks than in the Public Homenet Zone. In addition, the DM and RDM may be provided by the ISP - as described in [I-D.ietf-homenet-naming-architecture-dhc-options], in which case DM and RDM might be less exposed to attacks - as communications within a network.¶
This document describes how an end user can make their services and devices from his home network reachable on the Internet by using names rather than IP addresses. This exposes the home network to attackers, since names are expected to include less entropy than IP addresses. In fact, with IP addresses, the Interface Identifier is 64 bits long leading to up to 2^64 possibilities for a given subnetwork. This is not to mention that the subnet prefix is also of 64 bits long, thus providing up to 2^64 possibilities. On the other hand, names used either for the home network domain or for the devices present less entropy (livebox, router, printer, nicolas, jennifer, ...) and thus potentially exposes the devices to dictionary attacks.¶
IP addresses may be used to locate a device, a host or a service. However, home networks are not expected to be assigned a time invariant prefix by ISPs. As a result, observing IP addresses only provides some ephemeral information about who is accessing the service. On the other hand, names are not expected to be as volatile as IP addresses. As a result, logging names over time may be more valuable than logging IP addresses, especially to profile an end user's characteristics.¶
PTR provides a way to bind an IP address to a name. In that sense, responding to PTR DNS queries may affect the end user's privacy. For that reason end users may choose not to respond to PTR DNS queries and MAY instead return a NXDOMAIN response.¶
This section is non-normative for the front-end protocol. It 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 just 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 OAUTH2 [RFC6749] flow that could do the setup automatically.¶
The HNA needs to be configured with the following parameters as described by this CDDL [RFC8610]. These are the 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:21c::/64"
or [ "2001:db8:1f15:62e:21c::/64", ... ]
"hna_auth_method" : "certificate",
"hna_certificate" : "-----BEGIN CERTIFICATE-----\nMIIDTjCCFGy....",
}
¶
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.¶
Note that HNA does not defines ports for the Synchronization Channel. In any case, this is not expected to part of the configuration, but 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 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.¶
For forward zones, the relationship between the HNA and the forward zone provider may be the result of a number of transactions:¶
For reverse zones, the relationship is always with the upstream ISP (although there may be more than one), and so [I-D.ietf-homenet-naming-architecture-dhc-options] is always the appropriate interface.¶
The following is an abbridged example of a set of data that represents the needed configuration parameters for outsourcing.¶
This document has no actions for IANA.¶
The authors wish to thank Philippe Lemordant for its contributions on the early versions of the draft; 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, 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; Mark Andrew and Peter Koch for clarifying the renumbering.¶
The co-authors would like to thank Chris Griffiths and Wouter Cloetens that provided a significant contribution in the early versions of the document.¶
A number of deployment have been envisioned, this section aims at providing a brief description. The use cases are not limitations and this section is not normative.¶
A specific vendor with specific relations with a registrar or a registry may sell a CPE that is provisioned with provisioned domain name. Such domain name does not need to be necessary human readable.¶
One possible way is that the vendor also provisions the HNA with a private and public keys as well as a certificate. Note that these keys are not expected to be used for DNSSEC signing. Instead these keys are solely used by the HNA to proceed to the authentication. Normally the keys should be necessary and sufficient to proceed to the authentication. The reason to combine the domain name and the key is that DOI are likely handle names better than keys and that domain names might be used as a login which enables the key to be regenerated.¶
When the home network owner plugs the CPE at home, the relation between HNA and DM is expected to work out-of-the-box.¶
An CPE that is not preconfigured may also take advantage to the protocol defined in this document but some configuration steps will be needed.¶
This scenario is one where a homenet router device manufacturer decides to offer DNS hosting as a value add.¶
[I-D.richardson-homerouter-provisioning] 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 a assymmetric 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 wishes a better name, they can arrange for it.¶
The configuration would look like:¶
{
"dm_notify" : "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.¶