| Homenet | D. Migault |
| Internet-Draft | Ericsson |
| Intended status: Informational | R. Weber |
| Expires: October 21, 2020 | Nominum |
| M. Richardson | |
| Sandelman Software Works | |
| R. Hunter | |
| Globis Consulting BV | |
| C. Griffiths | |
| W. Cloetens | |
| SoftAtHome | |
| April 19, 2020 |
Outsourcing Home Network Authoritative Naming Service
draft-ietf-homenet-front-end-naming-delegation-11
The Homenet Naming authority 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). The names of the devices accessible from the Internet are stored in the Public Homenet Zone, served by a DNS authoritative server. It is unlikely that home networks will contain sufficiently robust platforms designed to host a service such as the DNS on the Internet and as such would expose the home network to DDoS attacks.
This document describes a mechanism that enables the Home Network Authority (HNA) to outsource the naming service to the Outsourcing Infrastructure via a Distribution Master (DM).
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 October 21, 2020.
Copyright (c) 2020 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 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 to do with based upon a number of assumptions about typical home networks.
So a goal of this specification is to make 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, 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 Homenet Naming Authority (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 Outsourcing Infrastructure via a Distribution Master (DM). The Outsourcing Infrastructure 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 Distribution Master a secondary.
Section 3.1 provides an architecture description that describes the relation between the HNA and the Outsourcing Architecture. In order to keep the Public Homenet Zone up-to-date Section 5 describes how the HNA and the Outsourcing Infrastructure 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 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 10 discusses how renumbering should be handled. Finally, Section 13 and Section 14 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].
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 Outsourcing Infrastructure in Section 3.1. Section Appendix B and Appendix C illustrates this architecture with the example of a Public Homenet Zone as well as necessary parameter to configure the HNA.
Figure 1 illustrates the architecture where the HNA outsources the publication of the Public Homenet Zone to the Outsourcing Infrastructure.
The Public Homenet Zone is identified by the Registered Homenet Domain Name – example.com.
“.local” as well as “.home.arpa” are explicitly not considered as Public Homenet zones.
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.
How the Public Homenet Zone is populated is out of the scope of this document. The node providing the HNA function may also host or interact with multiple services to determine name-to-address mappings, such as a web GUI, DHCP [RFC6644] or mDNS [RFC6762]. These services may coexist and may be used to populate the Public Homenet Zone.
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 Outsourcing Infrastructure 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 Outsourcing Infrastructure 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 need 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. The function of the HNA is limited to building the zone and synchronization with the DM.
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 Outsourcing Infrastructure 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 (example.com) 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 authoritative name service of the home network implemented by 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. Such configuration is outside the scope of this document.
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
|
| +----------------------------+
| | Outsourcing Infrastructure |
Control | | |
+-----------------------+Channel | | +-----------------------+ |
| HNA |<-------------->| Distribution Master | |
|+---------------------+| | | |+---------------------+| |
|| Public Homenet Zone ||Synchronization || Public Homenet Zone || |
|| (example.com) ||Channel | | || (example.com) || |
|+---------------------+|<-------------->|+---------------------+| |
+----------------------+| | | +-----------------------+ |
| | ^ Distribution |
| | | Channel |
+-----------------------+ | | v |
| Homenet Authoritative | | | +-----------------------+ |
| Server(s) | | | | Public Authoritative | |
|+---------------------+| | | | Server(s) | |
||Public Homenet Zone || | | |+---------------------+| |
|| (example.com) || | | || Public Homenet Zone || |
|+---------------------+| | | || (example.com) || |
+-----------------------+ | | |+---------------------+| |
^ | | | +-----------------------+ |
| | | +----------^---|-------------+
| | | | |
| | name resolution | |
| v | | v
+----------------------+ | +-----------------------+
| Homenet | | | Internet |
| DNSSEC Resolver | | | DNSSEC Resolver |
+----------------------+ | +-----------------------+
Figure 1: Homenet Naming Architecture Name Resolution
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 Outsourcing Infrastructure. The entity within the Outsourcing Infrastructure 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.
The information exchanged between the HNA and the DM is using DNS messages. DNS messages can be protected using various kind of transport layers, among others, UDP:53/DTLS, TLS/TCP:53, HTTPS:443. 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 main one is that the Dynamic DNS update would also update the zone’s NS records, while the goal is to update the Distribution Master’s 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 desireable.
This specification also assumes the same transport protocol and ports used by the DM to serve the Control Channel and by the HNA to serve the Synchronization Channel are the same.
The Distribution Channel is internal to the Outsourcing Infrastructure and as such is not the primary concern of this specification.
The DM Control Channel is used by the HNA and the Outsourcing Infrastructure to exchange information related to the configuration of the delegation which includes:
When the Homenet Naming Authority builds the public zone, it must include information that it retrieves from the Distribution Master 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:
Optionally the Outsourcing Infrastructure 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 Outsourcing Infrastructure, this information exchange is mandatory.
The HNA SHOULD provide the hash of the KSK (DS RRset), so the that Outsourcing Infrastructure provides this value to the parent zone. A common deployment use case is that the Outsourcing Infrastructure 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 Outsourcing Infrastructure 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] are used for key roll overs.
As some deployment may not provide an Outsourcing Infrastructure that will be able to update the DS in the parent zone, this information exchange is OPTIONAL.
By accepting the DS, the DM commits in taking care of advertising the DS to the parent zone. Upon refusal, the DM MUST clearly indicate the DM does not have the capacity to proceed to the update.
That information sets the primary/secondary relation between the HNA and the DM. The HNA works as a primary authoritative DNS server, and MUST provide the corresponding IP address.
The specified IP address on the HNA side and the currently used IP address of the DM defines the IP addresses involved in the Synchronization Channel. Ports and transport protocol are the same as those used by the Control Channel. By default, the same IP address used by the HNA is considered by the DM. Exchange of this information is OPTIONAL.
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 a 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.
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 SOA RR is used to indicate to the HNA the value of the MNAME of the Public Homenet Zone. The NAME of the SOA RR MUST be the Registered Homenet Domain. The MNAME value of the SOA RDATA is the value provided by the Outsourcing Infrastructure to the HNA. Other RDATA values (RNAME, REFRESH, RETRY, EXPIRE and MINIMUM) are provided by the Outsourcing Infrastructure as suggestions. The NS RRsets are used to carry the Public Authoritative Servers of the Outsourcing Infrastructure. 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 the conditions on 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 NAME in the SOA MUST be set to the parent zone of the Registered Homenet Domain - that is where the DS records should be inserted. The DS RRset MUST be placed in the Update section of the UPDATE query, and the NAME SHOULD be set to the Registered Homenet Domain. The rdata of the DS RR SHOULD correspond to the DS record to be inserted in the parent zone.
A NOERROR response from the MD is a commitment to update the parent zone with the provided DS. An error indicates the MD will not update the DS, and other method should be used by the HNA.
To provide the IP address of the primary, the HNA MAY send a DNS UPDATE message. The NAME in the SOA MUST be the parent zone of the Registered Homenet Domain. The Update section MUST be a RRset of Type NS. The NAME associated to the NS RRSet MUST be the Registered Domain Name. The RDATA MUST be a FQDN that designates the IP addresses associated to the primary. There may be multiple IP addresses. These IP addresses MUST be provided in the additional section. 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. IP addresses are provided via RRsets of type A or AAAA. The NAME associated to RRsets of type A and AAAA MUST be the Registered Homenet Domain.
A NOERROR response indicates the DM has configured the secondary and is committed to serve as a secondary. An error indicates the DM is not configured as a secondary.
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 error 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 instruct to delete the delegation the HNA MAY send a DNS UPDATE Delete message. The NAME in the SOA MUST be the parent zone of the Registered Homenet Domain. The Update section MUST be a RRset of Type NS. The NAME associated to the NS RRSet MUST be the Registered Domain Name. As indictaed 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 control channel between the HNA and the DM MUST be secured at both the HNA and the DM.
Secure protocols (like TLS [RFC5246] / DTLS [RFC6347]) SHOULD be used to secure the transactions between the DM and the HNA.
The advantage of TLS/DTLS is that this technology is widely deployed, and most of the devices already embed TLS/DTLS libraries, possibly also taking advantage of hardware acceleration. Further, TLS/DTLS provides authentication facilities and can use certificates to mutually authenticate the DM and HNA at the applicationlayer, including available API. On the other hand, using TLS/DTLS requires implementing DNS exchanges over TLS/DTLS, 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 12.
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 12 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 10, 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. This should apply to any OAUTH2 token produced as envisioned by Section 12.
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 listen for DNS on TCP and UDP and 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 addresses. 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 MD at port XX (well known port). On the other hand, the Synchronization Channel is set between the MD 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 disc tint 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 Homenet Domain Name. This secondary configuration has been previously agreed between the end user and the provider of the Outsourcing Infrastructure as part of either the provisioning or due to receipt of 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. DNS over TLS [RFC7858] is RECOMMENDED.
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}}
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 Hidden Primary, as described in this document 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 Outsourcing Infrastructures.
The DS RRset can be updated manually with nsupdate for example. This requires the HNA or the Outsourcing Infrastructure 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 Outsourcing Infrastructure. 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 Outsourcing Infrastructure 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 Outsourcing Infrastructure. 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 be not 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 Outsourcing Infrastructure of the associated reverse zone. This leave place for setting up automatically the relation between HNA and the Outsourcing infrastructure as described in [I-D.ietf-homenet-naming-architecture-dhc-options].
With this relation automatically configured, the synchronization between the Home network and the Outsourcing infrastructure 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 Outsourcing Infrastructure 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 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”.
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 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.
Once the Public Homenet Zone file has been updated on the Hidden Primary, the Hidden Primary needs to inform the Outsourcing Infrastructure 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.
The Hidden Primary SHOULD inform the DM that the Public Homenet Zone has been updated by sending a NOTIFY payload with the new IP address. In addition, this NOTIFY payload SHOULD be authenticated using SIG(0) or TSIG. When the DM receives the NOTIFY payload, it MUST authenticate it. Note that the cryptographic key used for the authentication SHOULD be indexed by the Registered Homenet Domain contained in the NOTIFY payload as well as the RRSIG. In other words, the IP address SHOULD NOT be used as an index. If authentication succeeds, the DM MUST also notice the IP address has been modified and perform a reachability check before updating its primary configuration. The routability check MAY performed by sending a SOA request to the Hidden Primary using the source IP address of the NOTIFY. This exchange is also secured, and if an authenticated response is received from the Hidden Primary with the new IP address, the DM SHOULD update its configuration file and retrieve the Public Homenet Zone using an AXFR or a IXFR exchange.
Note that the primary reason for providing the IP address is that the Hidden Primary is not publicly announced in the DNS. If the Hidden Primary were publicly announced in the DNS, then the IP address update could have been performed using the DNS as described in Section 10.2.
Renumbering of the Distribution Master results in it changing its IP address. As the DM is a secondary, the destination of DNS NOTIFY payloads MUST be changed, and any configuration/firewalling that restricts DNS AXFR/IXFR operations MUST be updated.
If the DM is configured in the Hidden Primary configuration file using a FQDN, then the update of the IP address is performed by DNS. More specifically, before sending the NOTIFY, the Hidden Primary performs a DNS resolution to retrieve the IP address of the secondary.
As described in Section 10.1, the DM DNS information SHOULD be coherent with the IP plane. The TTL of the Distribution Master name SHOULD be adjusted appropriately prior to changing the IP address.
Some DNS infrastructure uses the IP address to designate the secondary, in which case, other mechanisms must be found. The reason for using IP addresses instead of names is generally to reach an internal interface that is not designated by a FQDN, and to avoid potential bootstrap problems. Such scenarios are considered as out of scope in the case of home networks.
This section is non-normative. It provides suggestions on operational consideration. TBD.
This document does not deal with how the HNA is provisioned with a trusted relationship to the Distribution Master for the forward zone. Provisioning of the relationship with an ISP-connection specific Distribution Master for reverse zones is dealt with in [I-D.ietf-homenet-naming-architecture-dhc-options]
This section details what needs to be provisioned into the HNA and serves as a requirements statement for mechanisms.
Outsourcing the DNS Authoritative service from the HNA to a third party raises a few privacy related concerns.
The Public Homenet Zone contains a full description of the services hosted in the network. These services may not be expected to be publicly shared although their names remain accessible through the Internet. Even though DNS makes information public, the DNS does not expect to make the complete list of services public. In fact, making information public still requires the key (or FQDN) of each service to be known by the resolver in order to retrieve information about the services. More specifically, making mywebsite.example.com public in the DNS, is not sufficient to make resolvers aware of the existence web site. However, an attacker may walk the reverse DNS zone, or use other reconnaissance techniques to learn this information as described in [RFC7707].
In order to prevent the complete Public Homenet Zone being published on the Internet, AXFR queries SHOULD be blocked on the Public Authoritative Server(s). Similarly, to avoid zone-walking NSEC3 [RFC5155] SHOULD be preferred over NSEC [RFC4034]. When the Public Homenet Zone is outsourced, the end user should be aware that it provides a complete description of the services available on the home network. More specifically, names usually provides a clear indication of the service and possibly even the device type, and as the Public Homenet Zone contains the IP addresses associated with the service, they also limit the scope of the scan space.
In addition to the Public Homenet Zone, the third party 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.
The Homenet Naming Architecture described in this document solves exposing the HNA’s DNS service as a DoS attack vector.
The HNA DM channels are specified to include their own security mechanisms that are designed to provide the minimum attacke surface, and to authenticate transactions where necessary.
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 HNA and the DM MAY belong to the same administrative domain, i.e. the ISP. More specifically, the WAN interface is located in the ISP network. As a result, if provisioned using DHCPv6, the security credential may not even transit in the home network. On the other hand, if the HNA is not hosted at the border of the home network, the credential may rely on the security associated to DHCPv6. Even if HNA and DM are in the same administrative domain it is strongly RECOMMENDED to use a secure channel.
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.
An attacker performs a reflection attack when it sends traffic to one or more intermediary nodes (reflectors), that in turn send back response traffic to the victim. Motivations for using an intermediary node might be anonymity of the attacker, as well as amplification of the traffic. Typically, when the intermediary node is a DNSSEC server, the attacker sends a DNSSEC query and the victim is likely to receive a DNSSEC response. This section analyzes how the different components may be involved as a reflector in a reflection attack. Section 14.5 considers the Hidden Primary, Section 14.6 the Synchronization Server, and Section 14.7 the Public Authoritative Server(s).
With the specified architecture, the Hidden Primary is only expected to receive DNS queries of type SOA, AXFR or IXFR. This section analyzes how these DNS queries may be used by an attacker to perform a reflection attack.
DNS queries of type AXFR and IXFR use TCP and as such are less subject to reflection attacks. This makes SOA queries the only remaining practical vector of attacks for reflection attacks, based on UDP.
SOA queries are not associated with a large amplification factor compared to queries of type “ANY” or to query of non existing FQDNs. This reduces the probability a DNS query of type SOA will be involved in a DDoS attack.
SOA queries are expected to follow a very specific pattern, which makes rate limiting techniques an efficient way to limit such attacks, and associated impact on the naming service of the home network.
Motivations for such a flood might be a reflection attack, but could also be a resource exhaustion attack performed against the Hidden Primary. The Hidden Primary only expects to exchange traffic with the DM, that is its associated secondary. Even though secondary servers may be renumbered as mentioned in Section 10, the Hidden Primary is likely to perform a DNSSEC resolution and find out the associated secondary’s IP addresses in use. As a result, the Hidden Primary is likely to limit the origin of its incoming traffic based on the origin IP address.
With filtering rules based on IP address, SOA flooding attacks are limited to forged packets with the IP address of the secondary server. In other words, the only victims are the Hidden Primary itself or the secondary. There is a need for the Hidden Primary to limit that flood to limit the impact of the reflection attack on the secondary, and to limit the resource needed to carry on the traffic by the HNA hosting the Hidden Primary. On the other hand, mitigation should be performed appropriately, so as to limit the impact on the legitimate SOA sent by the secondary.
The main reason for the DM sending a SOA query is to update the SOA RRset after the TTL expires, to check the serial number upon the receipt of a NOTIFY query from the Hidden Primary, or to re-send the SOA request when the response has not been received. When a flood of SOA queries is received by the Hidden Primary, the Hidden Primary may assume it is involved in an attack.
There are few legitimate time slots when the secondary is expected to send a SOA query. Suppose T_NOTIFY is the time a NOTIFY is sent by the Hidden Primary, T_SOA the last time the SOA has been queried, TTL the TTL associated to the SOA, and T_REFRESH the refresh time defined in the SOA RRset. The specific time SOA queries are expected can be for example T_NOTIFY, T_SOA + 2/3 TTL, T_SOA + TTL, T_SOA + T_REFRESH., and. Outside a few minutes following these specific time slots, the probability that the HNA discards a legitimate SOA query is very low. Within these time slots, the probability the secondary may have its legitimate query rejected is higher. If a legitimate SOA is discarded, the secondary will re-send SOA query every “retry time” second until “expire time” seconds occurs, where “retry time” and “expire time” have been defined in the SOA.
As a result, it is RECOMMENDED to set rate limiting policies to protect HNA resources. If a flood lasts more than the expired time defined by the SOA, it is RECOMMENDED to re-initiate a synchronization between the Hidden Primary and the secondaries.
The DM acts as a secondary coupled with the Hidden Primary. The secondary expects to receive NOTIFY query, SOA responses, AXFR and IXFR responses from the Hidden Primary.
Sending a NOTIFY query to the secondary generates a NOTIFY response as well as initiating an SOA query exchange from the secondary to the Hidden Primary. As mentioned in [RFC1996], this is a known “benign denial of service attack”. As a result, the DM SHOULD enforce rate limiting on sending SOA queries and NOTIFY responses to the Hidden Primary. Most likely, when the secondary is flooded with valid and signed NOTIFY queries, it is under a replay attack which is discussed in Section 14.9. The key thing here is that the secondary is likely to be designed to be able to process much more traffic than the Hidden Primary hosted on a HNA.
This paragraph details how the secondary may limit the NOTIFY queries. Because the Hidden Primary may be renumbered, the secondary SHOULD NOT perform permanent IP filtering based on IP addresses. In addition, a given secondary may be shared among multiple Hidden Primaries which make filtering rules based on IP harder to set. The time at which a NOTIFY is sent by the Hidden Primary is not predictable. However, a flood of NOTIFY messages may be easily detected, as a NOTIFY originated from a given Homenet Zone is expected to have a very limited number of unique source IP addresses, even when renumbering is occurring. As a result, the secondary, MAY rate limit incoming NOTIFY queries.
On the Hidden Primary side, it is recommended that the Hidden Primary sends a NOTIFY as long as the zone has not been updated by the secondary. Multiple SOA queries may indicate the secondary is under attack.
Reflection attacks involving the Public Authoritative Server(s) are similar to attacks on any Outsourcing Infrastructure. This is not specific to the architecture described in this document, and thus are considered as out of scope.
In fact, one motivation of the architecture described in this document is to expose the Public Authoritative Server(s) to attacks instead of the HNA, as it is believed that the Public Authoritative Server(s) will be better able to defend itself.
The purpose of flooding attacks is mostly resource exhaustion, where the resource can be bandwidth, memory, or CPU for example.
One goal of the architecture described in this document is to limit the surface of attack on the HNA. This is done by outsourcing the DNS service to the Public Authoritative Server(s). By doing so, the HNA limits its DNS interactions between the Hidden Primary and the DM. This limits the number of entities the HNA interacts with as well as the scope of DNS exchanges - NOTIFY, SOA, AXFR, IXFR.
The use of an authenticated channel with SIG(0) or TSIG between the HNA and the DM, enables detection of illegitimate DNS queries, so appropriate action may be taken - like dropping the queries. If signatures are validated, then most likely, the HNA is under a replay attack, as detailed in Section 14.9
In order to limit the resource required for authentication, it is recommended to use TSIG that uses symmetric cryptography over SIG(0) that uses asymmetric cryptography.
Replay attacks consist of an attacker either resending or delaying a legitimate message that has been sent by an authorized user or process. As the Hidden Primary and the DM use an authenticated channel, replay attacks are mostly expected to use forged DNS queries in order to provide valid traffic.
From the perspective of an attacker, using a correctly authenticated DNS query may not be detected as an attack and thus may generate a response. Generating and sending a response consumes more resources than either dropping the query by the defender, or generating the query by the attacker, and thus could be used for resource exhaustion attacks. In addition, as the authentication is performed at the DNS layer, the source IP address could be impersonated in order to perform a reflection attack.
Section 14.4 details how to mitigate reflection attacks and Section 14.8 details how to mitigate resource exhaustion. Both sections assume a context of DoS with a flood of DNS queries. This section suggests a way to limit the attack surface of replay attacks.
As SIG(0) and TSIG use inception and expiration time, the time frame for replay attack is limited. SIG(0) and TSIG recommends a fudge value of 5 minutes. This value has been set as a compromise between possibly loose time synchronization between devices and the valid lifetime of the message. As a result, better time synchronization policies could reduce the time window of the attack.
[](<!– <section title=”DNSSEC is recommended to authenticate DNS hosted data
Deploying DNSSEC is recommended, since in some cases the information stored in the DNS is used by the ISP or an IT department to grant access. For example some servers may perform PTR DNS queries to grant access based on host names. DNSSEC mitigates lack of trust in DNS, and it is RECOMMENDED to deploy DNSSEC on HNAs.
–>)
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, Michael Richardson 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.
| [I-D.howard-dnsop-ip6rdns] | Howard, L., "Reverse DNS in IPv6 for Internet Service Providers", Internet-Draft draft-howard-dnsop-ip6rdns-00, June 2014. |
| [I-D.ietf-homenet-naming-architecture-dhc-options] | Migault, D., Mrugalski, T., Griffiths, C., Weber, R. and W. Cloetens, "DHCPv6 Options for Homenet Naming Architecture", Internet-Draft draft-ietf-homenet-naming-architecture-dhc-options-06, June 2018. |
| [I-D.ietf-homenet-simple-naming] | Lemon, T., Migault, D. and S. Cheshire, "Homenet Naming and Service Discovery Architecture", Internet-Draft draft-ietf-homenet-simple-naming-03, October 2018. |
| [I-D.sury-dnsext-cname-dname] | Sury, O., "CNAME+DNAME Name Redirection", Internet-Draft draft-sury-dnsext-cname-dname-00, April 2010. |
A number of deployment have been envisionned, this section aims at providing a brief description. The use cases are not limitatives 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 outsourcing infrastructure 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 advanatge to the protocol defined in this document but some configuration steps will be needed.
This section is not normative and intends to illustrate how the HNA builds the Homenet Zone.
As depicted in Figure 1, the Public Homenet Zone is hosted on the Public Authoritative Server(s), whereas the Homenet Zone is hosted on the HNA. This section considers that the HNA builds the zone that will be effectively published on the Public Authoritative Server(s). In other words “Homenet to Public Zone transformation” is the identity also commonly designated as “no operation” (NOP).
In that case, the Homenet Zone should configure its Name Server RRset (NS) and Start of Authority (SOA) with the values associated with the Public Authoritative Server(s). This is illustrated in Figure 2. public.primary.example.net is the FQDN of the Public Authoritative Server(s), and IP1, IP2, IP3, IP4 are the associated IP addresses. Then the HNA should add the additional new nodes that enter the home network, remove those that should be removed, and sign the Homenet Zone.
$ORIGIN example.com
$TTL 1h
@ IN SOA public.primary.example.net
hostmaster.example.com. (
2013120710 ; serial number of this zone file
1d ; secondary refresh
2h ; secondary retry time in case of a problem
4w ; secondary expiration time
1h ; maximum caching time in case of failed
; lookups
)
@ NS public.authoritative.servers.example.net
public.primary.example.net A @IP1
public.primary.example.net A @IP2
public.primary.example.net AAAA @IP3
public.primary.example.net AAAA @IP4
Figure 2: Homenet Zone
The SOA RRset is defined in [RFC1033], [RFC1035] and [RFC2308]. This SOA is specific, as it is used for the synchronization between the Hidden Primary and the DM and published on the DNS Public Authoritative Server(s)..
This section specifies the various parameters required by the HNA to configure the naming architecture of this document. This section is informational, and is intended to clarify the information handled by the HNA and the various settings to be done.
DM may be configured with the following parameters. 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:
Setting the Homenet Zone requires the following information.
Two possible methods of providing the required information would be:
JSON for forward zones should be standardized in a similar way to zone file layout in RFC1035
DHCP for reverse zones needs a separate draft