draft-ietf-homenet-front-end-naming-delegation-08.txt

Homenet                                                       D. Migault
Internet-Draft                                                  Ericsson
Intended status: Informational                                  R. Weber
Expires: November 11, 2019                                       Nominum
                                                               R. Hunter
                                                    Globis Consulting BV
                                                            C. Griffiths

                                                             W. Cloetens
                                                             SoftAtHome<
                                                            May 10, 2019


         Outsourcing Home Network Authoritative Naming Service
           draft-ietf-homenet-front-end-naming-delegation-08

Abstract

   Designation of services and devices of a home network is not user
   friendly, and mechanisms should enable a user to designate services
   and devices inside a home network using names.

   In order to enable internal communications while the home network
   experiments Internet connectivity shortage, the naming service should
   be hosted on a device inside the home network.  On the other hand,
   home networks devices have not been designed to handle heavy loads.
   As a result, hosting the naming service on such home network device,
   visible on the Internet exposes this device to resource exhaustion
   and other attacks, which could make the home network unreachable, and
   most probably would also affect the internal communications of the
   home network.

   As result, home networks may prefer not serving the naming service
   for the Internet, but instead prefer outsourcing it to a third party.
   This document describes a mechanisms that enables the Home Network
   Authority (HNA) to outsource the naming service to the Outsourcing
   Infrastructure.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.




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   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
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   This Internet-Draft will expire on November 11, 2019.

Copyright Notice

   Copyright (c) 2019 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Requirements notation . . . . . . . . . . . . . . . . . . . .   3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Architecture Description  . . . . . . . . . . . . . . . . . .   6
     4.1.  Architecture Overview . . . . . . . . . . . . . . . . . .   6
     4.2.  Example: Homenet Zone . . . . . . . . . . . . . . . . . .   8
     4.3.  Example: HNA necessary parameters for outsourcing . . . .  10
   5.  Synchronization between HNA and the Synchronization Server  .  11
     5.1.  Synchronization with a Hidden Primary . . . . . . . . . .  12
     5.2.  Securing Synchronization  . . . . . . . . . . . . . . . .  13
     5.3.  HNA Security Policies . . . . . . . . . . . . . . . . . .  14
   6.  DNSSEC compliant Homenet Architecture . . . . . . . . . . . .  14
     6.1.  Zone Signing" . . . . . . . . . . . . . . . . . . . . . .  15
     6.2.  Secure Delegation"  . . . . . . . . . . . . . . . . . . .  16
   7.  Handling Different Views  . . . . . . . . . . . . . . . . . .  17
     7.1.  Misleading Reasons for Local Scope DNS Zone"  . . . . . .  17
     7.2.  Consequences" . . . . . . . . . . . . . . . . . . . . . .  18
     7.3.  Guidance and Recommendations  . . . . . . . . . . . . . .  19
     7.4.  Homenet Reverse Zone  . . . . . . . . . . . . . . . . . .  19
   8.  Renumbering . . . . . . . . . . . . . . . . . . . . . . . . .  19
     8.1.  Hidden Primary  . . . . . . . . . . . . . . . . . . . . .  20
     8.2.  Synchronization Server  . . . . . . . . . . . . . . . . .  21
   9.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  22
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  23



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     10.1.  Names are less secure than IP addresses  . . . . . . . .  23
     10.2.  Names are less volatile than IP addresses  . . . . . . .  23
     10.3.  DNS Reflection Attacks . . . . . . . . . . . . . . . . .  24
     10.4.  "Reflection Attack involving the Hidden Primary  . . . .  24
     10.5.  Reflection Attacks involving the Synchronization Server   25
     10.6.  Reflection Attacks involving the Public Authoritative
            Servers  . . . . . . . . . . . . . . . . . . . . . . . .  26
     10.7.  Flooding Attack  . . . . . . . . . . . . . . . . . . . .  26
     10.8.  Replay Attack  . . . . . . . . . . . . . . . . . . . . .  27
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28
   12. Acknowledgment  . . . . . . . . . . . . . . . . . . . . . . .  28
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  28
     13.2.  Informative References . . . . . . . . . . . . . . . . .  31
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32

1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Introduction

   IPv6 provides global end to end IP reachability.  End users prefer to
   use names instead of long and complex IPv6 addresses when accessing
   services hosted in the home network.

   Customer Edge Routers and other Customer Premises Equipment (CPEs)
   are already providing IPv6 connectivity to the home network, and
   generally provide IPv6 addresses or prefixes to the nodes of the home
   network.  In addition, [RFC7368] recommends that home networks be
   resilient to connectivity disruption from the ISP.  This could be
   achieved by a dedicated device inside the home network that builds,
   serves or manage the Homenet Zone, thus providing bindings between
   names and IP addresses.

   CPEs are of course good candidates to manage the binding between
   names and IP addresses of nodes.  However, this could also be
   performed by another device in the home network that is not a CPE.
   In addition, a given home network may have multiple nodes that may
   implement this functionality.  Since management of the Homenet Zone
   involves DNS specific mechanisms that cannot be distributed (primary
   server), when multiple nodes can potentially manage the Homenet Zone,
   a single node needs to be selected.  This selected node is designated
   as the Homenet Naming Authority (HNA).





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   CPEs, Homenet Naming Authority, as well as home network devices are
   usually low powered devices not designed not for terminating heavy
   traffic.  As a result, hosting an authoritative DNS service on the
   Internet may expose the home network to resource exhaustion and other
   attacks.  This may isolate the home network from the Internet and
   also impact the services hosted by the such an home network device,
   thus affecting overall home network communication.

   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 Homenet
   Naming Authority builds the Homenet Zone and outsources it to an
   Outsourcing Infrastructure.  The Outsourcing Infrastructure in in
   charge of publishing the corresponding Public Homenet Zone on the
   Internet.

   Section 4.1 provides an architecture description that describes the
   relation between the Homenet Naming Authority and the Outsourcing
   Architecture.  In order to keep the Public Homenet Zone up-to-date
   Section 5 describes how the Homenet Zone and the Public Homenet Zone
   can be synchronized.  The proposed architecture aims at deploying
   DNSSEC, and the Public Homenet Zone is expected to be signed with a
   secure delegation.  The zone signing and secure delegation may be
   performed either by the Homenet Naming Authority or by the
   Outsourcing Infrastructure.  Section 6 discusses these two
   alternatives.  Section 7 discusses the consequences of publishing
   multiple representations of the same zone also commonly designated as
   views.  This section provides guidance to limit the risks associated
   with multiple views.  Section 7.4 discusses management of the reverse
   zone.  Section 8 discusses how renumbering should be handled.
   Finally, Section 9 and Section 10 respectively discuss privacy and
   security considerations when outsourcing the Homenet Zone.

3.  Terminology

   o  Customer Premises Equipment: (CPE) is a router providing
      connectivity to the home network.

   o  Homenet Naming Authority: (HNA) is a home network node responsible
      to manage the Homenet Zone.  This includes building the Homenet
      Zone, as well as managing the distribution of that Homenet Zone
      through the Outsourcing Infrastructure.

   o  Registered Homenet Domain: is the Domain Name associated to the
      home network.

   o  Homenet Zone: is the DNS zone associated with the home network.
      It is designated by its Registered Homenet Domain.  This zone is



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      built by the HNA and contains the bindings between names and IP
      addresses of the nodes in the home network.  The HNA synchronizes
      the Homenet Zone with the Synchronization Server via a hidden
      primary / secondary architecture.  The Outsourcing Infrastructure
      may process the Homenet Zone - for example providing DNSSEC
      signing - to generate the Public Homenet Zone.  This Public
      Homenet Zone is then transmitted to the Public Authoritative
      Server(s) that publish it on the Internet.

   o  Public Homenet Zone: is the public version of the Homenet Zone.
      It is expected to be signed with DNSSEC.  It is hosted by the
      Public Authoritative Server(s), which are authoritative for this
      zone.  The Public Homenet Zone and the Homenet Zone might be
      different.  For example some names might not become reachable from
      the Internet, and thus not be hosted in the Public Homenet Zone.
      Another example of difference may also occur when the Public
      Homenet Zone is signed whereas the Homenet Zone is not signed.

   o  Outsourcing Infrastructure: is the combination of the
      Synchronization Server and the Public Authoritative Server(s).

   o  Public Authoritative Servers: are the authoritative name servers
      hosting the Public Homenet Zone.  Name resolution requests for the
      Homenet Domain are sent to these servers.  For resiliency the
      Public Homenet Zone SHOULD be hosted on multiple servers.

   o  Synchronization Server: is the server with which the HNA
      synchronizes the Homenet Zone.  The Synchronization Server is
      configured as a secondary and the HNA acts as primary.  There MAY
      be multiple Synchronization Servers, but the text assumes a single
      server.  In addition, the text assumes the Synchronization Server
      is a separate entity.  This is not a requirement, and when the HNA
      signs the zone, the synchronization function might also be
      operated by the Public Authoritative Servers.

   o  Homenet Reverse Zone: The reverse zone file associated with the
      Homenet Zone.

   o  Reverse Public Authoritative Servers: are the authoritative name
      server(s) hosting the Public Homenet Reverse Zone.  Queries for
      reverse resolution of the Homenet Domain are sent to this server.
      Similarly to Public Authoritative Servers, for resiliency, the
      Homenet Reverse Zone SHOULD be hosted on multiple servers.

   o  Reverse Synchronization Server: is the server with which the HNA
      synchronizes the Homenet Reverse Zone.  It is configured as a
      secondary and the HNA acts as primary.  There MAY be multiple
      Reverse Synchronization Servers, but the text assumes a single



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      server.  In addition, the text assumes the Reverse Synchronization
      Server is a separate entity.  This is not a requirement, and when
      the HNA signs the zone, the synchronization function might also be
      operated by the Reverse Public Authoritative Servers.

   o  Hidden Primary: designates the primary server of the HNA, that
      synchronizes the Homenet Zone with the Synchronization Server.  A
      primary / secondary architecture is used between the HNA and the
      Synchronization Server.  The hidden primary is not expected to
      serve end user queries for the Homenet Zone as a regular primary
      server would.  The hidden primary is only known to its associated
      Synchronization Server.

4.  Architecture Description

   Architecture Description This section describes the architecture for
   outsourcing the authoritative naming service from the HNA to the
   Outsourcing Infrastructure.  Section 4.1 describes the architecture,
   Section 4.2 and Section 4.3 illustrates this architecture and shows
   how the Homenet Zone should be built by the HNA.  It also lists the
   necessary parameters the HNA needs to be able to outsource the
   authoritative naming service.  These two sections are informational
   and non-normative.

4.1.  Architecture Overview

   Figure 1 provides an overview of the architecture.

   The home network is designated by the Registered Homenet Domain Name
   - example.com in Figure 1.  The HNA builds the Homenet Zone
   associated with the home network.  How the Homenet Zone is built is
   out of the scope of this document.  The HNA may 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 Homenet Zone.  This document
   assumes the Homenet Zone has been populated with domain names that
   are intended to be publicly published and that are publicly
   reachable.  More specifically, names associated with services or
   devices that are not expected to be reachable from outside the home
   network or names bound to non-globally reachable IP addresses MUST
   NOT be part of the Homenet Zone.

   Once the Homenet Zone has been built, the HNA does not host an
   authoritative naming service, but instead outsources it to the
   Outsourcing Infrastructure.  The Outsourcing Infrastructure takes the
   Homenet Zone as an input and publishes the Public Homenet Zone.  If
   the HNA does not sign the Homenet Zone, the Outsourcing
   Infrastructure may instead sign it on behalf of the HNA.  Figure 1



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   provides a more detailed description of the Outsourcing
   Infrastructure, but overall, it is expected that the HNA provides the
   Homenet Zone.  Then the Public Homenet Zone is derived from the
   Homenet Zone and published on the Internet.

   As a result, DNS queries from the DNS resolvers on the Internet are
   answered by the Outsourcing Infrastructure and do not reach the HNA.
   Figure 1 illustrates the case of the resolution of node1.example.com.

   home network +-------------------+                Internet
                |                   |
                |      HNA          |
                |                   |         +-----------------------+
   +-------+    |+-----------------+|         | Public Authoritative  |
   |       |    || Homenet Zone    ||         | Server(s)             |
   | node1 |    ||                 ||         |+---------------------+|
   |       |    ||                 ||         || Public Homenet Zone ||
   +-------+    || Homenet Domain  ||=========||                     ||
                || Name            ||   ^     ||  (example.com)      ||
   node1.\      || (example.com)   ||   |     |+---------------------+|
   example.com  |+-----------------+|   |     +-----------------------+
                +-------------------+   |        ^   |
                              Synchronization    |   |
                                                 |   |
       DNSSEC resolution for node1.example.com   |   v
                                              +-----------------------+
                                              |                       |
                                              |    DNSSEC Resolver    |
                                              |                       |
                                              +-----------------------+

             Figure 1: Homenet Naming Architecture Description

   The Outsourcing Infrastructure is described in Figure 2.  The
   Synchronization Server receives the Homenet Zone as an input.  The
   received zone may be transformed to output the Public Homenet Zone.
   Various operations may be performed here, however this document only
   considers zone signing as a potential operation.  This should occur
   only when the HNA outsources this operation to the Synchronization
   Server.  On the other hand, if the HNA signs the Homenet Zone itself,
   the zone would be collected by the Synchronization Server and
   directly transferred to the Public Authoritative Server(s).  These
   policies are discussed and detailed in Section 6 and Section 7.








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                                    Internet

           +------------------------------------------------------+
           |            Outsourcing Infrastructure                |
           +------------------------------------------------------+

           +----------------------+        +----------------------+
           |                      |        |                      |
           |   Synchronization    |        | Public Authoritative |
           |       Server         |        | Server(s)            |
           |                      |        |                      |
           | +------------------+ |   X    |+--------------------+|
           | | Homenet Zone     | |   ^    || Public Homenet Zone||
   =========>|                  | |   |    ||                    ||
     ^     | |                  | |   |    ||                    ||
     |     | | (example.com)    | |   |    || (example.com)      ||
     |     | +------------------+ |   |    |+--------------------+|
     |     +----------------------+   |    +----------------------+
     |                       Homenet to Public Zone
   Synchronization                 transformation
   from the HNA

             Figure 2: Outsourcing Infrastructure Description

4.2.  Example: Homenet Zone

   This section is not normative and intends to illustrate how the HNA
   builds the Homenet Zone.

   As depicted in Figure 1 and Figure 2, the Public Homenet Zone is
   hosted on the Public Authoritative Server(s), whereas the Homenet
   Zone is hosted on the HNA.  Motivations for keeping these two zones
   identical are detailed in Section 7, and 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 3.
   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.





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   $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 3: 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 Synchronization Server and published on the
   DNS Public Authoritative Server(s)..

   o  MNAME: indicates the primary.  In our case the zone is published
      on the Public Authoritative Server(s), and its name MUST be
      included.  If multiple Public Authoritative Server(s) are
      involved, one of them MUST be chosen.  More specifically, the HNA
      MUST NOT include the name of the Hidden Primary.

   o  RNAME: indicates the email address to reach the administrator.
      [RFC2142] recommends using hostmaster@domain and replacing the '@'
      sign by '.'.

   o  REFRESH and RETRY: indicate respectively in seconds how often
      secondaries need to check the primary, and the time between two
      refresh when a refresh has failed.  Default values indicated by
      [RFC1033] are 3600 (1 hour) for refresh and 600 (10 minutes) for
      retry.  This value might be too long for highly dynamic content.
      However, the Public Authoritative Server(s) and the HNA are
      expected to implement NOTIFY [RFC1996].  So whilst shorter refresh
      timers might increase the bandwidth usage for secondaries hosting
      large number of zones, it will have little practical impact on the
      elapsed time required to achieve synchronization between the




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      Outsourcing Infrastructure and the Hidden Master.  As a result,
      the default values are acceptable.

   o  EXPIRE: is the upper limit data SHOULD be kept in absence of
      refresh.  The default value indicated by [RFC1033] is 3600000
      (approx. 42 days).  In home network architectures, the HNA
      provides both the DNS synchronization and the access to the home
      network.  This device may be plugged and unplugged by the end user
      without notification, thus we recommend a long expiry timer.

   o  MINIMUM: indicates the minimum TTL.  The default value indicated
      by [RFC1033] is 86400 (1 day).  For home network, this value MAY
      be reduced, and 3600 (1 hour) seems more appropriate.

   <<!-- ## Considerations on multiple Registered Homenet Domain Names
   ## are left for future versions When multiple Registered Homenet
   Domains are used -like example.com, example.net, example.org, a DNS
   Homenet Zone file per Registered Homenet Domain SHOULD be generated.
   In order to synchronize the zone contents, the HNA may provide all
   bindings in each zone files.  As a result, any update MUST be
   performed on all zone files, i.e. for all Registered Homenet Domains.
   To limit thees updates when multiple Registered Homenet Domains are
   involved, the HNA MAY fill all bindings in a specific zone file and
   redirect all other zones to that zone.  This can be achieved with
   redirecting mechanisms like CNAME {{RFC2181}}, {{RFC1034}}, DNAME
   {{RFC6672}} or CNAME+DNAME {{I-D.sury-dnsext-cname-dname}}. This is
   an implementation issue to determine whether redirection mechanisms
   MAY be preferred for large Homenet Zones, or when the number of
   Registered Homenet Domain becomes quite large. -->>

4.3.  Example: HNA necessary parameters for outsourcing

   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.

   Synchronization Server may be configured with the following
   parameters.  These parameters are necessary to establish a secure
   channel between the HNA and the Synchronization Server as well as to
   specify the DNS zone that is in the scope of the communication:

   o  Synchronization Server: The associated FQDNs or IP addresses of
      the Synchronization Server.  IP addresses are optional and the
      FQDN is sufficient.  To secure the binding name and IP addresses,
      a DNSSEC exchange is required.  Otherwise, the IP addresses should
      be entered manually.




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   o  Authentication Method: How the HNA authenticates itself to the
      Synchronization Server.  This MAY depend on the implementation but
      this should cover at least IPsec, DTLS and TSIG

   o  Authentication data: Associated Data.  PSK only requires a single
      argument.  If other authentication mechanisms based on
      certificates are used, then HNA private keys, certificates and
      certification authority should be specified.

   o  Public Authoritative Server(s): The FQDN or IP addresses of the
      Public Authoritative Server(s).  It MAY correspond to the data
      that will be set in the NS RRsets and SOA of the Homenet Zone.  IP
      addresses are optional and the FQDN is sufficient.  To secure the
      binding between name and IP addresses, a DNSSEC exchange is
      required.  Otherwise, the IP addresses should be entered manually.

   o  Registered Homenet Domain: The domain name used to establish the
      secure channel.  This name is used by the Synchronization Server
      and the HNA for the primary / secondary configuration as well as
      to index the NOTIFY queries of the HNA when the HNA has been
      renumbered.



     Setting the Homenet Zone requires the following information.

   o  Registered Homenet Domain: The Domain Name of the zone.  Multiple
      Registered Homenet Domains may be provided.  This will generate
      the creation of multiple Public Homenet Zones.

   o  Public Authoritative Server(s): The Public Authoritative Server(s)
      associated with the Registered Homenet Domain.  Multiple Public
      Authoritative Server(s) may be provided.

5.  Synchronization between HNA and the Synchronization Server

   The Homenet Reverse Zone and the Homenet Zone MAY be updated either
   with DNS UPDATE [RFC2136] or using a primary / secondary
   synchronization.  The primary / secondary mechanism is preferred as
   it scales better and avoids DoS attacks: First the primary notifies
   the secondary that the zone must be updated and leaves the secondary
   to proceed with the update when possible.  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 query performed by the
   secondary is a small packet sent over TCP (section 4.2 [RFC5936]),
   which mitigates reflection attacks using a forged NOTIFY.  On the
   other hand, DNS UPDATE (which can be transported over UDP), requires




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   more processing than a NOTIFY, and does not allow the server to
   perform asynchronous updates.

   This document RECOMMENDS use of a primary / secondary mechanism
   instead of the use of DNS UPDATE.  This section details the primary /
   secondary mechanism.

5.1.  Synchronization with a Hidden Primary

   Uploading and dynamically updating the zone file on the
   Synchronization Server can be seen as zone provisioning between the
   HNA (Hidden Primary) and the Synchronization Server (Secondary
   Server).  This can be handled either in band or out of band.

   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 Synchronization Server 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
   Synchronization Server.  In order to set the primary / secondary
   architecture, the HNA acts as a Hidden Primary Server, which is a
   regular authoritative DNS Server listening on the WAN interface.

   The Hidden Primary Server SHOULD accept SOA [RFC1033], AXFR
   [RFC1034], and IXFR [RFC1995] queries from its configured secondary
   DNS server(s).  The Hidden Primary Server SHOULD send NOTIFY messages
   [RFC1996] in order to update Public DNS server zones as updates
   occur.  Because, the Homenet Zones are likely to be small, the HNA
   MUST implement AXFR and SHOULD implement IXFR.

   Hidden Primary Server differs from a regular authoritative server for
   the home network by:

   o  Interface Binding: the Hidden Primary Server listens on the WAN
      Interface, whereas a regular authoritative server for the home
      network would listen on the home network interface.

   o  Limited exchanges: the purpose of the Hidden Primary Server is to
      synchronize with the Synchronization Server, not to serve any
      zones to end users.  As a result, exchanges are performed with
      specific nodes (the Synchronization Server).  Further, exchange
      types are limited.  The only legitimate exchanges are: NOTIFY
      initiated by the Hidden Primary and IXFR or AXFR exchanges



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      initiated by the Synchronization Server.  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 Synchronization
      Server.  The HNA MUST listen for DNS on TCP and UDP and MUST at
      least allow SOA lookups of the Homenet Zone.

5.2.  Securing Synchronization

   Exchange between the Synchronization Server and the HNA MUST be
   secured, at least for integrity protection and for authentication.

   TSIG [RFC2845] or SIG(0) [RFC2931] MAY be used to secure the DNS
   communications between the HNA and the Synchronization Server.  TSIG
   uses a symmetric key which can be managed by TKEY [RFC2930].
   Management of the key involved in SIG(0) is performed through zone
   updates.  How keys are rolled over with SIG(0) is out-of-scope of
   this document.  The advantage of these mechanisms is that they are
   only associated with the DNS application.  Not relying on shared
   libraries eases testing and integration.  On the other hand, using
   TSIG, TKEY or SIG(0) requires these mechanisms to be implemented on
   the HNA, which adds code and complexity.  Another disadvantage is
   that TKEY does not provide authentication mechanisms.

   Protocols like TLS [RFC5246] / DTLS [RFC6347] MAY be used to secure
   the transactions between the Synchronization Server 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
   authenticate the Synchronization Server and the HNA.  On the other
   hand, using TLS/DTLS requires implementing DNS exchanges over TLS/
   DTLS, as well as a new service port.  This document therefore does
   NOT RECOMMEND this option.

   IPsec [RFC4301] IKEv2 [RFC7296] MAY also be used to secure
   transactions between the HNA and the Synchronization Server.
   Similarly to TLS/DTLS, most HNAs already embed an IPsec stack, and
   IKEv2 supports multiple authentication mechanisms via the EAP
   framework.  In addition, IPsec can be used to protect DNS exchanges
   between the HNA and the Synchronization Server without any
   modifications of the DNS server or client.  DNS integration over
   IPsec only requires an additional security policy in the Security
   Policy Database (SPD).  One disadvantage of IPsec is that NATs and
   firewall traversal may be problematic.  However, in our case, the HNA
   is connected to the Internet, and IPsec communication between the HNA
   and the Synchronization Server should not be impacted by middle
   boxes.



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   <<!-- As mentioned above, TSIG, IPsec and TLS/DTLS MAY be used to
   secure transactions between the HNA and the Public Authentication
   Servers.  The HNA and the Synchronization Server SHOULD implement
   TSIG and IPsec.  -->>

   How the PSK can be used by any of the TSIG, TLS/DTLS or IPsec
   protocols: Authentication based on certificates implies a mutual
   authentication and thus requires the HNA to manage a private key, a
   public key, or certificates, as well as Certificate Authorities.
   This adds complexity to the configuration especially on the HNA side.
   For this reason, we RECOMMEND that the HNA MAY use PSK or certificate
   base authentication, and that the Synchronization Server MUST support
   PSK and certificate based authentication.

   Note also that authentication of message exchanges between the HNA
   and the Synchronization Server SHOULD NOT use the external IP address
   of the HNA to index the appropriate keys.  As detailed in Section 8,
   the IP addresses of the Synchronization Server 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.

5.3.  HNA Security Policies

   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
   Synchronization Server.  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.

6.  DNSSEC compliant Homenet Architecture

   [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.





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   Deploying DNSSEC requires signing the zone and configuring a secure
   delegation.  As described in Section 4.1, signing can be performed
   either by the HNA or by the Outsourcing Infrastructure.  Section 6.1
   details the implications of these two alternatives.  Similarly, the
   secure delegation can be performed by the HNA or by the Outsourcing
   Infrastructure.  Section 6.2 discusses these two alternatives.

6.1.  Zone Signing"

   This section discusses the pros and cons when zone signing is
   performed by the HNA or by the Outsourcing Infrastructure.  It is
   RECOMMENDED that the HNA signs the zone unless there is a strong
   argument against this, such as a HNA that is not capable of signing
   the zone.  In that case zone signing MAY be performed by the
   Outsourcing Infrastructure on behalf of the HNA.

   Reasons for signing the zone by the HNA are:

   o  1) Keeping the Homenet Zone and the Public Homenet Zone equal to
      securely optimize DNS resolution.  As the Public Zone is signed
      with DNSSEC, RRsets are authenticated, and thus DNS responses can
      be validated even though they are not provided by the
      authoritative server.  This provides the HNA the ability to
      respond on behalf of the Public Authoritative Server(s).  This
      could be useful for example if, in the future, the HNA announces
      to the home network that the HNA can act as a local authoritative
      primary or equivalent for the Homenet Zone.  Currently the HNA is
      not expected to receive authoritative DNS queries, as its IP
      address is not mentioned in the Public Homenet Zone.  On the other
      hand most HNAs host a resolving function, and could be configured
      to perform a local lookup to the Homenet Zone instead of
      initiating a DNS exchange with the Public Authoritative Server(s).
      Note that outsourcing the zone signing operation means that all
      DNSSEC queries SHOULD be cached to perform a local lookup,
      otherwise a resolution with the Public Authoritative Server(s)
      would be performed.

   o  2) Keeping the Homenet Zone and the Public Homenet Zone equal to
      securely address the connectivity disruption independence detailed
      in [RFC7368] section 4.4.1 and 3.7.5.  As local lookups are
      possible in case of network disruption, communications within the
      home network can still rely on the DNSSEC service.  Note that
      outsourcing the zone signing operation does not address
      connectivity disruption independence with DNSSEC.  Instead local
      lookup would provide DNS as opposed to DNSSEC responses provided
      by the Public Authoritative Server(s).





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   o  3) Keeping the Homenet Zone and the Public Homenet Zone equal to
      guarantee coherence between DNS responses.  Using a unique zone is
      one way to guarantee uniqueness of the responses among servers and
      places.  Issues generated by different views are discussed in more
      details in Section 7.

   4) Privacy and Integrity of the DNSSEC Homenet Zone are better
   guaranteed.  When the Zone is signed by the HNA, it makes
   modification of the DNS data - for example for flow redirection -
   impossible.  As a result, signing the Homenet Zone by the HNA
   provides better protection for end user privacy.

   Reasons for signing the zone by the Outsourcing Infrastructure are:

   1) The HNA may not be capable of signing the zone, most likely
   because its firmware does not support this function.  However this
   reason is expected to become less and less valid over time.

   2) Outsourcing DNSSEC management operations.  Management operations
   involve key roll-over, which can be performed automatically by the
   HNA and transparently for the end user.  Avoiding DNSSEC management
   is mostly motivated by bad software implementations.

   3) Reducing the impact of HNA replacement on the Public Homenet Zone.
   Unless the HNA private keys can be extracted and stored off-device,
   HNA hardware replacement will result in an emergency key roll-over.
   This can be mitigated by using relatively small TTLs.

   4) Reducing configuration impact on the end user.  Unless there are
   zero configuration mechanisms in place to provide credentials between
   the new HNA and the Synchronization Server, authentication
   associations between the HNA and the Synchronization Server would
   need to be re-configured.  As HNA replacement is not expected to
   happen regularly, end users may not be at ease with such
   configuration settings.  However, mechanisms as described in
   [I-D.ietf-homenet-naming-architecture-dhc-options] use DHCP Options
   to outsource the configuration and avoid this issue.

   5) The Outsourcing Infrastructure is more likely to handle private
   keys more securely than the HNA.  However, having all private keys in
   one place may also nullify that benefit.

6.2.  Secure Delegation"

   Secure delegation is achieved only if the DS RRset is properly set in
   the parent zone.  Secure delegation can be performed by the HNA or
   the Outsourcing Infrastructures (that is the Synchronization Server
   or the Public Authoritative Server(s)).



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   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].

7.  Handling Different Views

   The Homenet Zone provides information about the home network.  Some
   users may be tempted to have provide responses dependent on the
   origin of the DNS query.  More specifically, some users may be
   tempted to provide a different view for DNS queries originating from
   the home network and for DNS queries coming from the Internet.  Each
   view could then be associated with a dedicated Homenet Zone.

   <!--Regarding {{fig-naming-arch}}, an example of an implementation of
   two distinct view could be the Homenet Zone that describes the
   homenet view and the Public Homenet Zone that contains the Internet
   view, with these two zones being different.-->

   Note that this document does not specify how DNS queries originating
   from the home network are addressed to the Homenet Zone.  This could
   be done via hosting the DNS resolver on the HNA for example.

   This section is not normative.  Section 7.1 details why some nodes
   may only be reachable from the home network and not from the global
   Internet.  Section 7.2 briefly describes the consequences of having
   distinct views such as a "home network view" and an "Internet view".
   Finally, Section 7.3 provides guidance on how to resolve names that
   are only significant in the home network, without creating different
   views.

7.1.  Misleading Reasons for Local Scope DNS Zone"

   The motivation for supporting different views is to provide different
   answers dependent on the origin of the DNS query, for reasons such
   as:

   1: An end user may want to have services not published on the
   Internet.  Services like the HNA administration interface that
   provides the GUI to administer your HNA might not seem advisable to
   publish on the Internet.  Similarly, services like the mapper that
   registers the devices of your home network may also not be desirable
   to be published on the Internet.  In both cases, these services
   should only be known or used by the network administrator.  To



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   restrict the access of such services, the home network administrator
   may choose to publish these pieces of information only within the
   home network, where it might be assumed that the users are more
   trusted than on the Internet.  Even though this assumption may not be
   valid, at least this may reduce the surface of any attack.

   2: Services within the home network may be reachable using non global
   IP addresses.  IPv4 and NAT may be one reason.  On the other hand
   IPv6 may favor link-local or site-local IP addresses.  These IP
   addresses are not significant outside the boundaries of the home
   network.  As a result, they MAY be published in the home network
   view, and SHOULD NOT be published in the Public Homenet Zone.

7.2.  Consequences"

   Enabling different views leads to a non-coherent naming system.
   Depending on where resolution is performed, some services will not be
   available.  This may be especially inconvenient with devices with
   multiple interfaces that are attached both to the Internet via a
   3G/4G interface and to the home network via a WLAN interface.
   Devices may also cache the results of name resolution, and these
   cached entries may no longer be valid if a mobile device moves
   between a homenet connection and an internet connection e.g. a device
   temporarily loses wifi signal and switches to 3G.

   Regarding local-scope IP addresses, such devices may end up with poor
   connectivity.  Suppose, for example, that DNS resolution is performed
   via the WLAN interface attached to the HNA, and the response provides
   local-scope IP addresses, but the communication is initiated on the
   3G/4G interface.  Communications with local-scope addresses will be
   unreachable on the Internet, thus aborting the communication.  The
   same situation occurs if a device is flip / flopping between various
   WLAN networks.

   Regarding DNSSEC, if the HNA does not sign the Homenet Zone and
   outsources the signing process, the two views are different, because
   one is protected with DNSSEC whereas the other is not.  Devices with
   multiple interfaces will have difficulty securing the naming
   resolution, as responses originating from the home network may not be
   signed.

   For devices with all its interfaces attached to a single
   administrative domain, that is to say the home network, or the
   Internet.  Incoherence between DNS responses may still also occur if
   the device is able to perform DNS resolutions both using the DNS
   resolving server of the home network, or one of the ISP.  DNS
   resolution performed via the HNA or the ISP resolver may be different
   than those performed over the Internet.



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7.3.  Guidance and Recommendations

   As documented in Section 7.2, it is RECOMMENDED to avoid different
   views.  If network administrators choose to implement multiple views,
   impacts on devices' resolution SHOULD be evaluated.

   As a consequence, the Homenet Zone is expected to be an exact copy of
   the Public Homenet Zone.  As a result, services that are not expected
   to be published on the Internet SHOULD NOT be part of the Homenet
   Zone, local-scope addresses SHOULD NOT be part of the Homenet Zone,
   and when possible, the HNA SHOULD sign the Homenet Zone.

   The Homenet Zone is expected to host public information only.  It is
   not the scope of the DNS service to define local home network
   boundaries.  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 are expected to leverage this constraint as pointed out in
   [RFC7558].

7.4.  Homenet Reverse Zone

   This section is focused on the Homenet Reverse Zone.

   Firstly, all considerations for the Homenet Zone apply to the Homenet
   Reverse Zone.  The main difference between the Homenet Reverse Zone
   and the Homenet Zone is that the parent zone of the Homenet Reverse
   Zone is most likely managed by the ISP.  As the ISP also provides the
   IP prefix to the HNA, it may be able to authenticate the HNA using
   mechanisms outside the scope of this document e.g. the physical
   attachment point to the ISP network.  If the Reverse Synchronization
   Server is managed by the ISP, credentials to authenticate the HNA for
   the zone synchronization may be set automatically and transparently
   to the end user.  [I-D.ietf-homenet-naming-architecture-dhc-options]
   describes how automatic configuration may be performed.

   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.

8.  Renumbering

   This section details how renumbering is handled by the Hidden Primary
   server or the Synchronization Server.  Both types of renumbering are
   discussed i.e. "make-before-break" and "break-before-make".



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   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.

8.1.  Hidden Primary

   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 Homenet Zone will also
   be updated.  Although the new and old IP addresses may be stored in
   the 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 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 Homenet Zone file has been updated on the Hidden Primary,
   the Hidden Primary needs to inform the Outsourcing Infrastructure
   that the 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 Synchronization Server that the
   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 Synchronization Server



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   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 Synchronization Server
   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
   Synchronization Server SHOULD update its configuration file and
   retrieve the 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 8.2.

8.2.  Synchronization Server

   Renumbering of the Synchronization Server results in the
   Synchronization Server changing its IP address.  The Synchronization
   Server is a secondary, so its renumbering does not impact the Homenet
   Zone.  In fact, exchanges to the Synchronization Server are
   restricted to the Homenet Zone synchronization.  In our case, the
   Hidden Primary MUST be able to send NOTIFY payloads to the
   Synchronization Server.

   If the Synchronization Server 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 8.1, the Synchronization Server DNS
   information SHOULD be coherent with the IP plane.  Let TTL be the TTL
   associated with the Synchronization Server FQDN, T_NEW the time the
   new IP address replaces the old one and T_OLD_UNREACHABLE the time
   the Synchronization Server is not reachable anymore with its old IP
   address.  Seamless reachability is provided as long as
   T_OLD_UNREACHABLE - T_NEW > 2 * TTL.  If this condition is not met,
   the Synchronization Server may be unreachable during 2 * TTL -
   (T_OLD_UNREACHABLE - T_NEW).  In the case of a break-before-make,
   T_OLD_UNREACHABLE = T_NEW, and it may become unreachable up to 2 *
   TTL.




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   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.

   []( <!- <section {#sec-dnssec-outsrc" title="DNSSEC outsourcing
   configuration}

    In this document we assume that the Outsourcing Infrastructure MAY sign the Homenet Zone. Multiple variants MAY be proposed by the Outsourcing Infrastructure. The Outsourcing Infrastructure MAY propose signing the DNS Homenet Zone with keys generated by the Outsourcing Infrastructure and which are unknown to the HNA. Alternatively the Outsourcing Infrastructure MAY propose that the end user provides the private keys. Although not considered in this document, some end users MAY still prefer to sign their zone with their own keys that they do not communicate to the Outsourcing Infrastructure. All these alternatives result from a negotiation between the end user and the Outsourcing Infrastructure. This negotiation is performed out-of-band and is out of scope of this document.

    In this document, we consider that the Outsourcing Infrastructure has all the necessary cryptographic elements to perform zone signing and key management operations.

    Note that Outsourcing Infrastructure described in this document implements various functions, and thus different entities may be involved.
    <list hangIndent="6" style="hanging
            <t hangText="- DNS Slave functionsynchronizes the Homenet Zone
            between the HNA and the Outsourcing Infrastructures. The DNS Homenet Zone SHOULD  NOT be published directly on the Public Authoritative Servers, and the Public Authoritative Server(s MUST NOT respond to  any DNS queries for that zone. Instead, the Outsourcing Infrastructure chooses a dedicated set of servers to serve the Public Homenet Zone: the Public Authoritative Server(s.
            <t hangText="- DNS Zone Signing functionsigns the DNS Zone Homenet Zone to generate an Public Homenet Zone.
            <t hangText="- Public Authoritative Server hosts the naming service for the Public Homenet Zone. Any DNS query associated with the Homenet Zone SHOULD be performed using the specific servers designated as the Public Authoritative Servers
    </list>

   ->)

9.  Privacy Considerations

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

   The 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 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 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



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   specifically, names usually provides a clear indication of the
   service and possibly even the device type, and as the Homenet Zone
   contains the IP addresses associated with the service, they also
   limit the scope of the scan space.

   In addition to the Homenet Zone, the third party can also monitor the
   traffic associated with the 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.

10.  Security Considerations

   The Homenet Naming Architecture described in this document solves
   exposing the HNA's DNS service as a DoS attack vector.

10.1.  Names are less secure than IP addresses

   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.

10.2.  Names are less volatile than IP addresses

   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.




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10.3.  DNS Reflection Attacks

   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 10.4 considers the Hidden Primary,
   Section 10.5 the Synchronization Server, and Section 10.6 the Public
   Authoritative Server(s).

10.4.  "Reflection Attack involving the Hidden Primary

   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 Synchronization Server, that is its associated secondary.  Even
   though secondary servers may be renumbered as mentioned in Section 8,
   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



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   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 Synchronization Server 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.

10.5.  Reflection Attacks involving the Synchronization Server

   The Synchronization Server 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 Synchronization Server
   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 10.8.  The key thing here is



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   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.

10.6.  Reflection Attacks involving the Public Authoritative Servers

   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.

10.7.  Flooding Attack

   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
   Synchronization Server.  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 Synchronization Server, enables detection of illegitimate
   DNS queries, so appropriate action may be taken - like dropping the



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   queries.  If signatures are validated, then most likely, the HNA is
   under a replay attack, as detailed in Section 10.8

   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.

10.8.  Replay Attack

   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 Synchronization Server 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 10.3 details how to mitigate reflection attacks and
   Section 10.7 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.

       -->)





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11.  IANA Considerations

   This document has no actions for IANA.

12.  Acknowledgment

   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.

13.  References

13.1.  Normative References

   [RFC1033]  Lottor, M., "Domain Administrators Operations Guide",
              RFC 1033, DOI 10.17487/RFC1033, November 1987,
              <https://www.rfc-editor.org/info/rfc1033>.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/info/rfc1034>.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/info/rfc1035>.

   [RFC1995]  Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
              DOI 10.17487/RFC1995, August 1996, <https://www.rfc-
              editor.org/info/rfc1995>.

   [RFC1996]  Vixie, P., "A Mechanism for Prompt Notification of Zone
              Changes (DNS NOTIFY)", RFC 1996, DOI 10.17487/RFC1996,
              August 1996, <https://www.rfc-editor.org/info/rfc1996>.







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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
              editor.org/info/rfc2119>.

   [RFC2136]  Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
              "Dynamic Updates in the Domain Name System (DNS UPDATE)",
              RFC 2136, DOI 10.17487/RFC2136, April 1997,
              <https://www.rfc-editor.org/info/rfc2136>.

   [RFC2142]  Crocker, D., "Mailbox Names for Common Services, Roles and
              Functions", RFC 2142, DOI 10.17487/RFC2142, May 1997,
              <https://www.rfc-editor.org/info/rfc2142>.

   [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
              Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
              <https://www.rfc-editor.org/info/rfc2181>.

   [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS
              NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,
              <https://www.rfc-editor.org/info/rfc2308>.

   [RFC2845]  Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
              Wellington, "Secret Key Transaction Authentication for DNS
              (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,
              <https://www.rfc-editor.org/info/rfc2845>.

   [RFC2930]  Eastlake 3rd, D., "Secret Key Establishment for DNS (TKEY
              RR)", RFC 2930, DOI 10.17487/RFC2930, September 2000,
              <https://www.rfc-editor.org/info/rfc2930>.

   [RFC2931]  Eastlake 3rd, D., "DNS Request and Transaction Signatures
              ( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September
              2000, <https://www.rfc-editor.org/info/rfc2931>.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,
              <https://www.rfc-editor.org/info/rfc4034>.

   [RFC4192]  Baker, F., Lear, E., and R. Droms, "Procedures for
              Renumbering an IPv6 Network without a Flag Day", RFC 4192,
              DOI 10.17487/RFC4192, September 2005, <https://www.rfc-
              editor.org/info/rfc4192>.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <https://www.rfc-editor.org/info/rfc4301>.



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   [RFC4555]  Eronen, P., "IKEv2 Mobility and Multihoming Protocol
              (MOBIKE)", RFC 4555, DOI 10.17487/RFC4555, June 2006,
              <https://www.rfc-editor.org/info/rfc4555>.

   [RFC4960]  Stewart, R., Ed., "Stream Control Transmission Protocol",
              RFC 4960, DOI 10.17487/RFC4960, September 2007,
              <https://www.rfc-editor.org/info/rfc4960>.

   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
              Security (DNSSEC) Hashed Authenticated Denial of
              Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
              <https://www.rfc-editor.org/info/rfc5155>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008, <https://www.rfc-
              editor.org/info/rfc5246>.

   [RFC5936]  Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
              (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
              <https://www.rfc-editor.org/info/rfc5936>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <https://www.rfc-editor.org/info/rfc6347>.

   [RFC6644]  Evans, D., Droms, R., and S. Jiang, "Rebind Capability in
              DHCPv6 Reconfigure Messages", RFC 6644,
              DOI 10.17487/RFC6644, July 2012, <https://www.rfc-
              editor.org/info/rfc6644>.

   [RFC6672]  Rose, S. and W. Wijngaards, "DNAME Redirection in the
              DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012,
              <https://www.rfc-editor.org/info/rfc6672>.

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              DOI 10.17487/RFC6762, February 2013, <https://www.rfc-
              editor.org/info/rfc6762>.

   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
              Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
              <https://www.rfc-editor.org/info/rfc6763>.

   [RFC7010]  Liu, B., Jiang, S., Carpenter, B., Venaas, S., and W.
              George, "IPv6 Site Renumbering Gap Analysis", RFC 7010,
              DOI 10.17487/RFC7010, September 2013, <https://www.rfc-
              editor.org/info/rfc7010>.




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   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <https://www.rfc-editor.org/info/rfc7296>.

   [RFC7344]  Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
              DNSSEC Delegation Trust Maintenance", RFC 7344,
              DOI 10.17487/RFC7344, September 2014, <https://www.rfc-
              editor.org/info/rfc7344>.

   [RFC7368]  Chown, T., Ed., Arkko, J., Brandt, A., Troan, O., and J.
              Weil, "IPv6 Home Networking Architecture Principles",
              RFC 7368, DOI 10.17487/RFC7368, October 2014,
              <https://www.rfc-editor.org/info/rfc7368>.

   [RFC7558]  Lynn, K., Cheshire, S., Blanchet, M., and D. Migault,
              "Requirements for Scalable DNS-Based Service Discovery
              (DNS-SD) / Multicast DNS (mDNS) Extensions", RFC 7558,
              DOI 10.17487/RFC7558, July 2015, <https://www.rfc-
              editor.org/info/rfc7558>.

   [RFC7707]  Gont, F. and T. Chown, "Network Reconnaissance in IPv6
              Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016,
              <https://www.rfc-editor.org/info/rfc7707>.

   [RFC7788]  Stenberg, M., Barth, S., and P. Pfister, "Home Networking
              Control Protocol", RFC 7788, DOI 10.17487/RFC7788, April
              2016, <https://www.rfc-editor.org/info/rfc7788>.

13.2.  Informative References

   [I-D.howard-dnsop-ip6rdns]
              Howard, L., "Reverse DNS in IPv6 for Internet Service
              Providers", draft-howard-dnsop-ip6rdns-00 (work in
              progress), 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", draft-ietf-homenet-naming-architecture-dhc-
              options-06 (work in progress), June 2018.

   [I-D.sury-dnsext-cname-dname]
              Sury, O., "CNAME+DNAME Name Redirection", draft-sury-
              dnsext-cname-dname-00 (work in progress), April 2010.






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Authors' Addresses

   Daniel Migault
   Ericsson
   8275 Trans Canada Route
   Saint Laurent, QC  4S 0B6
   Canada

   EMail: daniel.migault@ericsson.com


   Ralf Weber
   Nominum
   2000 Seaport Blvd
   Redwood City  94063
   US

   EMail: ralf.weber@nominum.com


   Ray Hunter
   Globis Consulting BV
   Weegschaalstraat 3
   Eindhoven  5632CW
   NL

   EMail: v6ops@globis.net


   Chris Griffiths

   EMail: cgriffiths@gmail.com


   Wouter Cloetens
   SoftAtHome<
   vaartdijk 3 701
   Wijgmaal  3018
   BE

   EMail: cgriffiths@gmail.com










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