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Versions: (draft-mglt-homenet-front-end-naming-delegation) 00 01 02 03 04 05

HOMENET                                                  D. Migault (Ed)
Internet-Draft                                                  Ericsson
Intended status: Standards Track                                R. Weber
Expires: January 3, 2016                                         Nominum
                                                               R. Hunter
                                                    Globis Consulting BV
                                                            C. Griffiths

                                                             W. Cloetens
                                                              SoftAtHome
                                                            July 2, 2015


         Outsourcing Home Network Authoritative Naming Service
         draft-ietf-homenet-front-end-naming-delegation-03.txt

Abstract

   RFC7368 'IPv6 Home Networking Architecture Principles' section 3.7
   describes architecture principles related to naming and service
   discovery in residential home networks.

   Customer Edge Routers and other Customer Premises Equipment (CPEs)
   are designed to provide IP connectivity to home networks.  Most CPEs
   assign IP addresses to the nodes of the home network which makes them
   good candidates for hosting the naming service.  IPv6 provides global
   connectivity, and nodes from the home network will be reachable from
   the global Internet.  As a result, the naming service is expected to
   be exposed on the Internet.

   However, CPEs have not been designed to host such a naming service
   exposed on the Internet.  Running a naming service visible on the
   Internet may expose the CPEs 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.

   In addition, regular end users may not understand, or possess the
   necessary skills to be able to perform, DNSSEC management and
   configuration.  Misconfiguration may also result in naming service
   disruption, thus these end users may prefer to rely on third party
   name service providers.

   This document describes a homenet naming architecture, where the CPEs
   manage the DNS zones associated with its own home network, and
   outsource elements of the naming service (possibly including DNSSEC
   management) to a third party running on the Internet.




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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/.

   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 January 3, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  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: CPE necessary parameters for outsourcing . . . .  10
   5.  Synchronization between CPE and the Synchronization Server  .  11
     5.1.  Synchronization with a Hidden Primary . . . . . . . . . .  11
     5.2.  Securing Synchronization  . . . . . . . . . . . . . . . .  12
     5.3.  CPE Security Policies . . . . . . . . . . . . . . . . . .  13
   6.  DNSSEC compliant Homenet Architecture . . . . . . . . . . . .  14
     6.1.  Zone Signing  . . . . . . . . . . . . . . . . . . . . . .  14
     6.2.  Secure Delegation . . . . . . . . . . . . . . . . . . . .  16



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   7.  Handling Different Views  . . . . . . . . . . . . . . . . . .  16
     7.1.  Misleading Reasons for Local Scope DNS Zone . . . . . . .  17
     7.2.  Consequences  . . . . . . . . . . . . . . . . . . . . . .  17
     7.3.  Guidance and Recommendations  . . . . . . . . . . . . . .  18
   8.  Homenet Reverse Zone  . . . . . . . . . . . . . . . . . . . .  19
   9.  Renumbering . . . . . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  Hidden Primary  . . . . . . . . . . . . . . . . . . . . .  19
     9.2.  Synchronization Server  . . . . . . . . . . . . . . . . .  21
   10. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  21
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  22
     11.1.  Names are less secure than IP addresses  . . . . . . . .  22
     11.2.  Names are less volatile than IP addresses  . . . . . . .  23
     11.3.  DNS Reflection Attacks . . . . . . . . . . . . . . . . .  23
       11.3.1.  Reflection Attack involving the Hidden Primary . . .  23
       11.3.2.  Reflection Attacks involving the Synchronization
                Server . . . . . . . . . . . . . . . . . . . . . . .  25
       11.3.3.  Reflection Attacks involving the Public
                Authoritative Servers  . . . . . . . . . . . . . . .  25
     11.4.  Flooding Attack  . . . . . . . . . . . . . . . . . . . .  26
     11.5.  Replay Attack  . . . . . . . . . . . . . . . . . . . . .  26
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  27
   13. Acknowledgment  . . . . . . . . . . . . . . . . . . . . . . .  27
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  27
     14.2.  Informational References . . . . . . . . . . . . . . . .  29
   Appendix A.  Document Change Log  . . . . . . . . . . . . . . . .  30
   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.  This makes CPEs good candidates to manage the binding
   between names and IP addresses of nodes.  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 the Homenet Zone, thus providing



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   bindings between names and IP addresses.  All this makes the CPE the
   natural candidate for populating the Homenet zone.

   CPEs are usually low powered devices designed for the home network,
   but 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
   CPEs, 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
   Zone built by the CPE is outsourced to an Outsourcing Infrastructure.
   The Outsourcing Infrastructure publishes the corresponding Public
   Homenet Zone on the Internet.  Section 4.1 describes the
   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 CPE 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 8 discusses
   management of the reverse zone.  Section 9 discusses how renumbering
   should be handled.  Finally, Section 10 and Section 11 respectively
   discuss privacy and security considerations when outsourcing the
   Homenet Zone.

3.  Terminology

   - Customer Premises Equipment:   (CPE) is the router providing
         connectivity to the home network.  It might be configured and
         managed by the end user.  In this document, the CPE might also
         host services such as DHCPv6.  This device might be provided by
         the ISP.

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

   - Homenet Zone:   is the DNS zone associated with the home network.
         It is designated by its Registered Homenet Domain.  This zone
         is built by the CPE and contains the bindings between names and
         IP addresses of the nodes in the home network.  The CPE
         synchronizes the Homenet Zone with the Synchronization Server
         via a hidden primary / secondary architecture.  The Outsourcing



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         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.

   - 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.

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

   - 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.

   - Synchronization Server:   is the server with which the CPE
         synchronizes the Homenet Zone.  The Synchronization Server is
         configured as a secondary and the CPE 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 CPE signs the zone, the
         synchronization function might also be operated by the Public
         Authoritative Servers.

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

   - 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.

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



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         Synchronization Server is a separate entity.  This is not a
         requirement, and when the CPE signs the zone, the
         synchronization function might also be operated by the Reverse
         Public Authoritative Servers.

   - Hidden Primary:   designates the primary server of the CPE, that
         synchronizes the Homenet Zone with the Synchronization Server.
         A primary / secondary architecture is used between the CPE 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

   This section describes the architecture for outsourcing the
   authoritative naming service from the CPE 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 CPE.  It also lists the necessary
   parameters the CPE 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 CPE builds the Homenet Zone
   associated with the home network.  How the Homenet Zone is built is
   out of the scope of this document.  The CPE 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 CPE 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 CPE does not sign the Homenet Zone, the Outsourcing
   Infrastructure may instead sign it on behalf of the CPE.  Figure 1



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   provides a more detailed description of the Outsourcing
   Infrastructure, but overall, it is expected that the CPE 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 CPE.
   Figure 1 illustrates the case of the resolution of node1.example.com.

   home network +-------------------+                Internet
                |                   |
                |      CPE          |
                |                   |         +-----------------------+
   +-------+    |+-----------------+|         | 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 CPE outsources this operation to the Synchronization
   Server.  On the other hand, if the CPE 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 CPE

             Figure 2: Outsourcing Infrastructure Description

4.2.  Example: Homenet Zone

   This section is not normative and intends to illustrate how the CPE
   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 CPE.  Motivations for keeping these two zones
   identical are detailed in Section 7, and this section considers that
   the CPE 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 CPE 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)..

   - 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
         CPE MUST NOT include the name of the Hidden Primary.

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

   - 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
         CPE 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




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

   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 CPE
         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.

   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.

4.3.  Example: CPE necessary parameters for outsourcing

   This section specifies the various parameters required by the CPE to
   configure the naming architecture of this document.  This section is
   informational, and is intended to clarify the information handled by
   the CPE 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 CPE and the Synchronization Server as well as to
   specify the DNS zone that is in the scope of the communication:

   - 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.

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

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

   - 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




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         exchange is required.  Otherwise, the IP addresses should be
         entered manually.

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

   Setting the Homenet Zone requires the following information.

   - 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.

   - 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 CPE 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
   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
   CPE (Hidden Primary) and the Synchronization Server (Secondary
   Server).  This can be handled either in band or out of band.

   The Synchronization Server is configured as a secondary for the
   Homenet Domain Name.  This secondary configuration has been



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   previously agreed between the end user and the provider of the
   Synchronization Server.  In order to set the primary / secondary
   architecture, the CPE 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 CPE
   MUST implement AXFR and SHOULD implement IXFR.

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

   - 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.

   - 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
         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 CPE SHOULD filter IXFR/
         AXFR traffic and drop traffic not initiated by the
         Synchronization Server.  The CPE 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 CPE 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 CPE 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 CPE, which adds code and complexity.  Another disadvantage is
   that TKEY does not provide authentication mechanisms.



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   Protocols like TLS [RFC5246] / DTLS [RFC6347] MAY be used to secure
   the transactions between the Synchronization Server and the CPE.  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 CPE.  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 CPE and the Synchronization Server.
   Similarly to TLS/DTLS, most CPEs 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 CPE 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 CPE
   is connected to the Internet, and IPsec communication between the CPE
   and the Synchronization Server should not be impacted by middle
   boxes.

   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 CPE to manage a private key, a
   public key, or certificates, as well as Certificate Authorities.
   This adds complexity to the configuration especially on the CPE side.
   For this reason, we RECOMMEND that the CPE 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 CPE
   and the Synchronization Server SHOULD NOT use the external IP address
   of the CPE to index the appropriate keys.  As detailed in Section 9,
   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.  CPE Security Policies

   This section details security policies related to the Hidden Primary
   / Secondary synchronization.




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   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.

   Deploying DNSSEC requires signing the zone and configuring a secure
   delegation.  As described in Section 4.1, signing can be performed
   either by the CPE or by the Outsourcing Infrastructure.  Section 6.1
   details the implications of these two alternatives.  Similarly, the
   secure delegation can be performed by the CPE 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 CPE or by the Outsourcing Infrastructure.  It is
   RECOMMENDED that the CPE signs the zone unless there is a strong
   argument against this, such as a CPE that is not capable of signing
   the zone.  In that case zone signing MAY be performed by the
   Outsourcing Infrastructure on behalf of the CPE.

   Reasons for signing the zone by the CPE are:

   - 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 CPE the ability to
         respond on behalf of the Public Authoritative Server(s).  This



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         could be useful for example if, in the future, the CPE
         announces to the home network that the CPE can act as a local
         authoritative primary or equivalent for the Homenet Zone.
         Currently the CPE 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 CPEs 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.

   - 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).

   - 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.

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

   Reasons for signing the zone by the Outsourcing Infrastructure are:

   - 1:  The CPE 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 CPE and transparently for the end user.




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         Avoiding DNSSEC management is mostly motivated by bad software
         implementations.

   - 3:  Reducing the impact of CPE replacement on the Public Homenet
         Zone.  Unless the CPE private keys can be extracted and stored
         off-device, CPE 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 CPE and the Synchronization Server,
         authentication associations between the CPE and the
         Synchronization Server would need to be re-configured.  As CPE
         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 CPE.  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 CPE or
   the Outsourcing Infrastructures (that is the Synchronization Server
   or the Public Authoritative Server(s)).

   The DS RRset can be updated manually with nsupdate for example.  This
   requires the CPE 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 CPE and the parent
   DNS server may be hard to maintain with CPEs, 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.  Note



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   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 CPE 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 CPE administration interface that
         provides the GUI to administer your CPE 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 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



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   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 CPE, 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 CPE 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 CPE or the ISP resolver may be different
   than those performed over the Internet.

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 CPE 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
   [I-D.ietf-dnssd-requirements].



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8.  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 CPE, it may be able to authenticate the CPE 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 CPE 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.

9.  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".

   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.

9.1.  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.




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   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
   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 9.2.





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9.2.  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 9.1, 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.

   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.

10.  Privacy Considerations

   Outsourcing the DNS Authoritative service from the CPE 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



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   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 [I-D.ietf-opsec-ipv6-host-scanning].

   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 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.

11.  Security Considerations

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

11.1.  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.








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11.2.  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.

11.3.  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 11.3.1 considers the Hidden Primary,
   Section 11.3.2 the Synchronization Server, and Section 11.3.3 the
   Public Authoritative Server(s).

11.3.1.  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.





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   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 9,
   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 CPE 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 CPE 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 CPE resources.  If a flood lasts more than the expired time



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   defined by the SOA, it is RECOMMENDED to re-initiate a
   synchronization between the Hidden Primary and the secondaries.

11.3.2.  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 11.5.  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 CPE.

   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.

11.3.3.  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 CPE, as it is believed that the Public Authoritative
   Server(s) will be better able to defend itself.



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11.4.  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 CPE.  This is done by outsourcing the
   DNS service to the Public Authoritative Server(s).  By doing so, the
   CPE limits its DNS interactions between the Hidden Primary and the
   Synchronization Server.  This limits the number of entities the CPE
   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
   CPE and the Synchronization Server, enables detection of illegitimate
   DNS queries, so appropriate action may be taken - like dropping the
   queries.  If signatures are validated, then most likely, the CPE is
   under a replay attack, as detailed in Section 11.5

   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.

11.5.  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 11.3 details how to mitigate reflection attacks and
   Section 11.4 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



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   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.

12.  IANA Considerations

   This document has no actions for IANA.

13.  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
   CPE 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 CPE; Mark Andrew
   and Peter Koch for clarifying the renumbering.

14.  References

14.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC1995]  Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
              August 1996.

   [RFC1996]  Vixie, P., "A Mechanism for Prompt Notification of Zone
              Changes (DNS NOTIFY)", RFC 1996, August 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2136]  Vixie, P., Thomson, S., Rekhter, Y., and J. Bound,
              "Dynamic Updates in the Domain Name System (DNS UPDATE)",
              RFC 2136, April 1997.




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   [RFC2142]  Crocker, D., "MAILBOX NAMES FOR COMMON SERVICES, ROLES AND
              FUNCTIONS", RFC 2142, May 1997.

   [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS
              NCACHE)", RFC 2308, March 1998.

   [RFC2845]  Vixie, P., Gudmundsson, O., Eastlake, D., and B.
              Wellington, "Secret Key Transaction Authentication for DNS
              (TSIG)", RFC 2845, May 2000.

   [RFC2930]  Eastlake, D., "Secret Key Establishment for DNS (TKEY
              RR)", RFC 2930, September 2000.

   [RFC2931]  Eastlake, D., "DNS Request and Transaction Signatures (
              SIG(0)s )", RFC 2931, September 2000.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, March 2005.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC4555]  Eronen, P., "IKEv2 Mobility and Multihoming Protocol
              (MOBIKE)", RFC 4555, June 2006.

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol", RFC
              4960, September 2007.

   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
              Security (DNSSEC) Hashed Authenticated Denial of
              Existence", RFC 5155, March 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5936]  Lewis, E. and A. Hoenes, "DNS Zone Transfer Protocol
              (AXFR)", RFC 5936, June 2010.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

   [RFC6644]  Evans, D., Droms, R., and S. Jiang, "Rebind Capability in
              DHCPv6 Reconfigure Messages", RFC 6644, July 2012.

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              February 2013.




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   [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
              Discovery", RFC 6763, February 2013.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, October 2014.

14.2.  Informational 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-dnssd-requirements]
              Lynn, K., Cheshire, S., Blanchet, M., and D. Migault,
              "Requirements for Scalable DNS-SD/mDNS Extensions", draft-
              ietf-dnssd-requirements-06 (work in progress), March 2015.

   [I-D.ietf-homenet-naming-architecture-dhc-options]
              Migault, D., Cloetens, W., Griffiths, C., and R. Weber,
              "DHCP Options for Homenet Naming Architecture", draft-
              ietf-homenet-naming-architecture-dhc-options-02 (work in
              progress), May 2015.

   [I-D.ietf-opsec-ipv6-host-scanning]
              Gont, F. and T. Chown, "Network Reconnaissance in IPv6
              Networks", draft-ietf-opsec-ipv6-host-scanning-07 (work in
              progress), April 2015.

   [RFC1033]  Lottor, M., "Domain administrators operations guide", RFC
              1033, November 1987.

   [RFC4192]  Baker, F., Lear, E., and R. Droms, "Procedures for
              Renumbering an IPv6 Network without a Flag Day", RFC 4192,
              September 2005.

   [RFC7010]  Liu, B., Jiang, S., Carpenter, B., Venaas, S., and W.
              George, "IPv6 Site Renumbering Gap Analysis", RFC 7010,
              September 2013.

   [RFC7344]  Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
              DNSSEC Delegation Trust Maintenance", RFC 7344, September
              2014.

   [RFC7368]  Chown, T., Arkko, J., Brandt, A., Troan, O., and J. Weil,
              "IPv6 Home Networking Architecture Principles", RFC 7368,
              October 2014.



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Appendix A.  Document Change Log

   [RFC Editor: This section is to be removed before publication]

   -07:

   Ray Hunter is added as a co-author.

   -06:

   Ray Hunter is added in acknowledgment.

   Adding Renumbering section with comments from Dallas meeting

   Replacing Master / Primary - Slave / Secondary

   Security Consideration has been updated with Reflection attacks,
   flooding attacks, and replay attacks.

   -05:

   *Clarifying on handling different views:

   - 1:  How the CPE may be involved in the resolution and responds
         without necessarily requesting the Public Authoritative
         Server(s) (and eventually the Hidden Primary)

   - 2:  How to handle local scope resolution that is link-local, site-
         local and NAT IP addresses as well as Private domain names that
         the administrator does not want to publish outside the home
         network.

   Adding a Privacy Considerations Section

   Clarification on pro/cons outsourcing zone-signing

   Documenting how to handle reverse zones

   Adding reference to RFC 2308

   -04:

   *Clarifications on zone signing

   *Rewording

   *Adding section on different views




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   *architecture clarifications

   -03:

   *Simon's comments taken into consideration

   *Adding SOA, PTR considerations

   *Removing DNSSEC performance paragraphs on low power devices

   *Adding SIG(0) as a mechanism for authenticating the servers

   *Goals clarification: the architecture described in the document 1)
   does not describe new protocols, and 2) can be adapted to specific
   cases for advance users.

   -02:

   *remove interfaces: "Public Authoritative Server Naming Interface" is
   replaced by "Public Authoritative Server(s)y(ies)".  "Public
   Authoritative Server Management Interface" is replaced by
   "Synchronization Server".

   -01.3:

   *remove the authoritative / resolver services of the CPE.
   Implementation dependent

   *remove interactions with mdns and dhcp.  Implementation dependent.

   *remove considerations on low powered devices

   *remove position toward homenet arch

   *remove problem statement section

   -01.2:

   * add a CPE description to show that the architecture can fit CPEs

   * specification of the architecture for very low powered devices.

   * integrate mDNS and DHCP interactions with the Homenet Naming
   Architecture.

   * Restructuring the draft. 1) We start from the homenet-arch draft to
   derive a Naming Architecture, then 2) we show why CPE need mechanisms




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   that do not expose them to the Internet, 3) we describe the
   mechanisms.

   * I remove the terminology and expose it in the figures A and B.

   * remove the Front End Homenet Naming Architecture to Homenet Naming

   -01:

   * Added C.  Griffiths as co-author.

   * Updated section 5.4 and other sections of draft to update section
   on Hidden Primary / Slave functions with CPE as Hidden Primary/
   Homenet Server.

   * For next version, address functions of MDNS within Homenet Lan and
   publishing details northbound via Hidden Primary.

   -00: First version published.

Authors' Addresses

   Daniel Migault
   Ericsson
   8400 Boulevard Decarie
   Montreal, QC H4P 2N2
   Canada

   Phone: +1 (514) 452-2160
   Email: daniel.migault@ericsson.com


   Ralf Weber
   Nominum
   2000 Seaport Blvd #400
   Redwood City, CA  94063
   US

   Email: ralf.weber@nominum.com
   URI:   http://www.nominum.com











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   Ray Hunter
   Globis Consulting BV
   Weegschaalstraat 3
   5632CW Eindhoven
   The Netherlands

   Email: v6ops@globis.net
   URI:   http://www.globis.net


   Chris Griffiths

   Email: cgriffiths@gmail.com


   Wouter Cloetens
   SoftAtHome
   vaartdijk 3 701
   3018 Wijgmaal
   Belgium

   Email: wouter.cloetens@softathome.com





























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