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Versions: (draft-mglt-homenet-front-end-naming-delegation) 00 01 02 03 04 05 06 07 08 09

HOMENET                                                  D. Migault (Ed)
Internet-Draft                                                  Ericsson
Intended status: Standards Track                             W. Cloetens
Expires: November 5, 2015                                     SoftAtHome
                                                            C. Griffiths
                                                                     Dyn
                                                                R. Weber
                                                                 Nominum
                                                             May 4, 2015


         Outsourcing Home Network Authoritative Naming Service
         draft-ietf-homenet-front-end-naming-delegation-02.txt

Abstract

   CPEs are designed to provide IP connectivity to home networks.  Most
   CPEs assign IP addresses to the nodes of the home network which makes
   it a good candidate for hosting the naming service.  With IPv6, the
   naming service makes nodes reachable from the home network as well as
   from the Internet.

   However, CPEs have not been designed to host such a naming service
   exposed on the Internet.  This may expose the CPEs to resource
   exhaustion which would make the home network unreachable, and most
   probably would also affect the home network inner communications.

   In addition, DNSSEC management and configuration may not be well
   understood or mastered by regular end users.  Misconfiguration may
   also result in naming service disruption, thus these end users may
   prefer to rely on third party naming providers.

   This document describes a homenet naming architecture where the CPEs
   manage the DNS zone associated to its home network, and outsources
   the naming service and eventually the DNSSEC management on the
   Internet to a third party designated as the Public Authoritative
   Servers.

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
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 5, 2015.

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  . . . . . . . . . . . . . . . . . .   5
     4.1.  Architecture Overview . . . . . . . . . . . . . . . . . .   6
     4.2.  Example: DNS(SEC) Homenet Zone  . . . . . . . . . . . . .   8
     4.3.  Example: CPE necessary parameters for outsourcing . . . .  10
   5.  Synchronization between CPE and Public Authoritative Name
       Server Sets . . . . . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  Synchronization with a Hidden Primary . . . . . . . . . .  11
     5.2.  Securing Synchronization  . . . . . . . . . . . . . . . .  12
     5.3.  CPE Security Policies . . . . . . . . . . . . . . . . . .  14
   6.  DNSSEC compliant Homenet Architecture . . . . . . . . . . . .  14
     6.1.  Zone Signing  . . . . . . . . . . . . . . . . . . . . . .  14
     6.2.  Secure Delegation . . . . . . . . . . . . . . . . . . . .  16
   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.  Reverse Zone  . . . . . . . . . . . . . . . . . . . . . . . .  18
   9.  Renumbering . . . . . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  Hidden Primary  . . . . . . . . . . . . . . . . . . . . .  19
     9.2.  Public Authoritative Name Server Set  . . . . . . . . . .  21
   10. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  21



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   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 Public
                Authoritative Name Server Set  . . . . . . . . . . .  25
       11.3.3.  Reflection Attacks involving the Public
                Authoritative Primary  . . . . . . . . . . . . . . .  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.  To access services
   hosted in the home network with IPv6 addresses, end users prefer to
   use names instead of long and complex IPv6 addresses.

   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 the CPEs a good candidate to manage binding
   between names and IP addresses of the nodes.  In addition, [RFC7368]
   recommends that home networks be resilient to connectivity disruption
   from the ISP.  This requires that a dedicate device inside the home
   network manage bindings between names and IP addresses of the nodes
   and builds the DNS Homenet Zone.  All this makes the CPE the natural
   candidate for setting the DNS(SEC) zone file of the home network.

   CPEs are usually low powered devices designed for the home network,
   but not for heavy traffic.  As a result, hosting an authoritative DNS
   service on the Internet may expose the home network to resource
   exhaustion, which may isolate the home network from the Internet and
   affect the services hosted by the CPEs, thus affecting the overall
   home network communications.




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   In order to avoid resource exhaustion, this document describes an
   architecture that outsources the authoritative naming service of the
   home network.  More specifically, the DNS(SEC) Homenet Zone built by
   the CPE is outsourced to Public Authoritative Servers.  These servers
   publish the corresponding DN(SEC) Public Zone on the Internet.
   Section 4.1 describes the architecture.  In order to keep the
   DNS(SEC) Public Zone up-to-date Section 5 describes how the DNS(SEC)
   Homenet Zone and the DN(SEC) Public Zone can be synchronized.  The
   proposed architecture aims at deploying DNSSEC and the DNS(SEC)
   Public Zone is expected to be signed with a secure delegation.  The
   zone signing and secure delegation can be performed either by the CPE
   or by the Public Authoritative Servers.  Section 6 discusses these
   two alternatives.  Section 7 discusses multiple views aspects and
   provide guidance to avoid them.  Section 8 discusses the case 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 DNS Homenet Zone.

3.  Terminology

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

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

   - DNS Homenet Zone:   is the DNS zone associated to the home network.
         This zone is set by the CPE and essentially contains the
         bindings between names and IP addresses of the nodes of the
         home network.  In this document, the CPE does neither perform
         any DNSSEC management operations such as zone signing nor
         provide an authoritative service for the zone.  Both are
         delegated to the Public Authoritative Server.  The CPE
         synchronizes the DNS Homenet Zone with the Public Authoritative
         Server via a hidden primary / secondary architecture.  The
         Public Authoritative Server MAY use specific servers for the
         synchronization of the DNS Homenet Zone: the Public
         Authoritative Name Server Set as public available name servers
         for the Registered Homenet Domain.

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

   - Public Authoritative Server:   performs DNSSEC management
         operations as well as provides the authoritative service for



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         the zone.  In this document, the Public Authoritative Server
         synchronizes the DNS Homenet Zone with the CPE via a hidden
         primary / secondary architecture.  The Public Authoritative
         Server acts as a secondary and MAY use specific servers called
         Public Authoritative Name Server Set. Once the Public
         Authoritative Server synchronizes the DNS Homenet Zone, it
         signs the zone and generates the DNSSEC Public Zone.  Then the
         Public Authoritative Server hosts the zone as an authoritative
         server on the Public Authoritative Primary(ies).

   - DNSSEC Public Zone:   corresponds to the signed version of the DNS
         Homenet Zone.  It is hosted by the Public Authoritative Server,
         which is authoritative for this zone, and is reachable on the
         Public Authoritative Primary(ies).

   - Public Authoritative Primary(ies):   are the visible name server
         hosting the DNSSEC Public Zone.  End users' resolutions for the
         Homenet Domain are sent to this server, and this server is a
         primary for the zone.

   - Public Authoritative Name Server Set:   is the server the CPE
         synchronizes the DNS Homenet Zone.  It is configured as a
         secondary and the CPE acts as primary.  The CPE sends
         information so the DNSSEC zone can be set and served.

   - Reverse Public Authoritative Primary(ies):   are the visible name
         server hosting the DNS Homenet Reverse Zone.  End users'
         resolutions for the Homenet Domain are sent to this server, and
         this server is a primary for the zone.

   - Reverse Public Authoritative Name Server Set:   is the server the
         CPE synchronizes the DNS Homenet Reverse Zone.  It is
         configured as a secondary and the CPE acts as primary.  The CPE
         sends information so the DNSSEC zone can be set and served.

4.  Architecture Description

   This section describes the architecture for outsourcing the
   authoritative naming service from the CPE to the Public Authoritative
   Primary(ies).  Section 4.1 describes the architecture, Section 4.2
   and Section 4.3 illustrate this architecture and shows how the
   DNS(SEC) Homenet Zone should be built by the CPE, as well as lists
   the necessary parameters the CPE needs to outsource the authoritative
   naming service.  These two section are informational and non
   normative.






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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 DNS(SEC) Homenet Zone
   associated to the home network.  How the DNS(SEC) Homenet Zone is
   built is out of the scope of this document.  The CPE may host and
   involve multiple services like a web GUI, DHCP [RFC6644] or mDNS
   [RFC6762].  These services may coexist and may be used to populate
   the DNS Homenet Zone.  This document assumes the DNS(SEC) Homenet
   Zone has been populated with domain names that are intended to be
   publicly published and that are publicly reachable.  More
   specifically, names associated to 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
   DNS(SEC) Homenet Zone.

   Once the DNS(SEC) Homenet Zone has been built, the CPE does not host
   the authoritative naming service for it, but instead outsources it to
   the Public Authoritative Servers.  The Public Authoritative Servers
   take the DNS(SEC) Homenet as an input and publishes the DNS(SEC)
   Public Zone.  In fact the DNS(SEC) Homenet Zone and the DNS(SEC)
   Public Zone have different names as they may be different.  If the
   CPE does not sign the DNS Homenet Zone, for example, the Public
   Authoritative Servers may instead sign it on behalf of the CPE.
   Figure 1 provides a more detailed description of the Public
   Authoritative Servers, but overall, it is expected that the CPE
   provides the DNS(SEC) Homenet Zone, the DNS(SEC) Public Zone is
   derived from the DNS(SEC) Homenet Zone and published on the Internet.

   As a result, DNS(SEC) queries from the DNS(SEC) Resolvers on the
   Internet are answered by the Public Authoritative Server and do not
   reach the CPE.  Figure 1 illustrates the case of the resolution of
   node1.example.com.
















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   home network +-------------------+ Internet
                |                   |
                |        CPE        |
                |                   |         +----------------------+
   +-------+    |+-----------------+|         | Public Authoritative |
   |       |    || DNS(SEC) Homenet||         | Servers              |
   | node1 |    || Zone            ||         |+--------------------+|
   |       |    ||                 ||         ||DNS(SEC) Public 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 Public Authoritative Servers are described in Figure 2.  The
   Public Authoritative Name Server Set receives the DNS(SEC) Homenet
   Zone as an input.  The received zone may be transformed to output the
   DNS(SEC) Public Zone.  Various operations may be performed here,
   however this document only considers zone signing as potential
   operation.  This could occur only when the CPE outsources this
   operation to the Public Authoritative Name Server Set. On the other
   hand, if the CPE signs the DNSSEC Homenet Zone itself, the zone it
   collected by the Public Authoritative Name Server Set and directly
   transferred to the Public Authoritative Primary.  Implications of
   such policy are detailed in Section 6 and Section 7.
















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                                      Internet

             +--------------------------------------------------------+
             |              Public Authoritative Servers              |
             +--------------------------------------------------------+

             +----------------------+         +----------------------+
             |                      |         |                      |
             | Public Authoritative |         | Public Authoritative |
             | Name Server Set      |         | Primaries            |
             |                      |         |                      |
             | +------------------+ |    X    | +------------------+ |
             | | DNS(SEC) Homenet | |    ^    | | DNS(SEC) Public  | |
   =========>| | Zone             | |    |    | | Zone             | |
       ^     | |                  | |    |    | |                  | |
       |     | | (example.com)    | |    |    | | (example.com)    | |
       |     | +------------------+ |    |    | +------------------+ |
       |     +----------------------+    |    +----------------------+
       |                         Homenet to Public Zone
   Synchronization                   transformation
   from the CPE

            Figure 2: Public Authoritative Servers Description

4.2.  Example: DNS(SEC) Homenet Zone

   This section is not normative and intends to illustrate how the CPE
   builds the DNS(SEC) Homenet Zone.

   As depicted in Figure 1 and Figure 2, the DNS(SEC) Public Zone is
   hosted on the Public Authoritative Primaries, whereas the DNS(SEC)
   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 Primaries.  In other words "Homenet to
   Public Zone transformation" is the identity.

   In that case, the DNS Homenet Zone should configure its Name Server
   RRset (NS) and Start of Authority (SOA) with the ones associated to
   the Public Authoritative Primaries.  This is illustrated in Figure 3.
   public.primary.example.net is the FQDN of the Public Authoritative
   Primaries, and IP1, IP2, IP3, IP4 are the associated IP addresses.
   Then the CPE should add the different new nodes that enter the home
   network, remove those that should be removed and sign the DNS 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: DNS 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 Public Authoritative Name Server Set and
   published on the DNS Public Authoritative Primary.

   - MNAME:   indicates the primary.  In our case the zone is published
         on the Public Authoritative Primary, and its name MUST be
         mentioned.  If multiple Public Authoritative Primaries are
         involved, one of them MUST be chosen.  More specifically, the
         CPE MUST NOT place the name of the Hidden Primary.

   - RNAME:   indicates the email address to reach the administrator.
         [RFC2142] recommends to use 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 value indicated by
         [RFC1033] are 3600 (1 hour) for refresh and 600 (10 minutes)
         for retry.  This value MAY be long for highly dynamic content.
         However, Public Authoritative Primaries and the CPE are
         expected to implement NOTIFY [RFC1996].  Then short values MAY
         increase the bandwidth usage for secondaries hosting large
         number of zones.  As a result, default values looks fine.





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   EXPIRE:   is the upper limit data SHOULD be kept in absence of
         refresh.  Default value indicated by [RFC1033] is 3600000 about
         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 large period.

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

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.

   Public Authoritative Name Server Set may be defined with the
   following parameters.  These parameters are necessary to establish a
   secure channel between the CPE and the Public Authoritative Name
   Server Set:

   - Public Authoritative Name Server Set:   The associated FQDNs or IP
         addresses of the Public Authoritative 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
         Public Server.  This MAY depend on the implementation but we
         should consider 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, files for the CPE private keys,
         certificates and certification authority should be specified.

   - Public Authoritative Primary(ies):   The FQDN or IP addresses of
         the Public Authoritative Primary.  It MAY correspond to the
         data that will be set in the NS RRsets and SOA of the DNS
         Homenet Zone.  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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   - Registered Homenet Domain:   The domain name the Public
         Authoritative is configured for DNS secondary, DNSSEC zone
         signing and DNSSEC zone hosting.

   Setting the DNS(SEC) Homenet Zone requires the following information.

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

   - Public Authoritative Primaries:   The public authoritative servers
         associated to the Registered Homenet Domain.  Multiple public
         authoritative server may be provided.

5.  Synchronization between CPE and Public Authoritative Name Server
    Sets

   The DNS(SEC) Homenet Reverse Zone and the DNS Homenet Zone can be
   updated either with DNS update [RFC2136] or using a primary /
   secondary synchronization.  The primary / secondary mechanism is
   preferred as it better scales and avoids DoS attacks: First the
   primary notifies the secondary the zone must be updated, and leaves
   the secondary to proceed to the update when possible.  Then, the
   NOTIFY message sent by the primary is a small packet that is less
   likely to load the secondary.  At last, the AXFR query performed by
   the secondary is a small packet sent over TCP (section 4.2 [RFC5936])
   which makes unlikely the secondary to perform reflection attacks with
   a forged NOTIFY.  On the other hand, DNS updates can use UDP, packets
   require more processing then a NOTIFY, and they do not provide the
   server the opportunity to post-pone the update.

   This document recommends the use of a primary / secondary mechanism
   instead of the use of nsupdates.  This section details the primary /
   secondary mechanism.

5.1.  Synchronization with a Hidden Primary

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

   The Public Authoritative Name Server Set 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 Public
   Authoritative Name Server Sets.  In order to set the primary/
   secondary architecture, the CPE acts as a Hidden Primary Server,



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   which is a regular Authoritative DNS(SEC) Server listening on the WAN
   interface.

   The Hidden Primary Server is expected to accept SOA [RFC1033], AXFR
   [RFC1034], and IXFR [RFC1995] queries from its configured secondary
   DNS servers.  The Hidden Primary Server SHOULD send NOTIFY messages
   [RFC1996] in order to update Public DNS server zones as updates
   occur.  Because, DNS Homenet Zones are likely to be small, 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
         synchronizes with the Public Authoritative Name Server Set, not
         to serve zone.  As a result, exchanges are performed with
         specific nodes (the Public Authoritative Name Server Sets).
         Then exchange types are limited.  The only legitimate exchanges
         are: NOTIFY initiated by the Hidden Primary and IXFR or AXFR
         exchanges initiated by the Public Authoritative Name Server
         Set.  On the other hand regular authoritative servers would
         respond any hosts on the home network, and any DNS(SEC) query
         would be considered.  The CPE SHOULD filter IXFR/AXFR traffic
         and drop traffic not initiated by the Public Authoritative Name
         Server Set. The CPE MUST listen for DNS on TCP and UDP and at
         least allow SOA lookups to the DNS Homenet Zone.

5.2.  Securing Synchronization

   Exchange between the Public Authoritative Name Server Sets and the
   CPE MUST be secured, at least for integrity protection and for
   authentication.

   TSIG [RFC2845] or SIG(0) [RFC2931] can be used to secure the DNS
   communications between the CPE and the Public DNS(SEC) Servers.  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 to roll the keys 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
   ease testing and integration.  On the other hand, using TSIG, TKEY or
   SIG(0) requires these mechanisms to be implemented on the DNS(SEC)
   Server's implementation running on the CPE, which adds codes.




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   Another disadvantage is that TKEY does not provide authentication
   mechanism.

   Protocols like TLS [RFC5246] / DTLS [RFC6347] can be used to secure
   the transactions between the Public Authoritative Name Server Sets
   and the CPE.  The advantage of TLS/DTLS is that this technology is
   widely deployed, and most of the boxes already embeds a TLS/DTLS
   libraries, eventually taking advantage of hardware acceleration.
   Then TLS/DTLS provides authentication facilities and can use
   certificates to authenticate the Public Authoritative Name Server Set
   and the CPE.  On the other hand, using TLS/DTLS requires to integrate
   DNS exchange over TLS/DTLS, as well as a new service port.  This is
   why we do not recommend this option.

   IPsec [RFC4301] IKEv2 [RFC7296] can also be used to secure the
   transactions between the CPE and the Public Authoritative Servers.
   Similarly to TLS/DTLS, most CPE already embeds a IPsec stack, and
   IKEv2 provides multiple authentications possibilities with its EAP
   framework.  In addition, IPsec can be used to protect the DNS
   exchanges between the CPE and the Public Authoritative Servers
   without any modifications of the DNS Servers or client.  DNS
   integration over IPsec only requires an additional security policy in
   the Security Policy Database.  One disadvantage of IPsec is that it
   hardly goes through NATs and firewalls.  However, in our case, the
   CPE is connected to the Internet, and IPsec communication between the
   CPE and Public Authoritative Name Server Set 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 CPE MAY use PSK or certificate base
   authentication and that Public Authoritative Servers Servers MUST
   support PSK and certificate based authentication.

   Note also that authentication of the messages exchanged between the
   CPE and the Public Authoritative Name Server Set should not involve
   the IP address to index the appropriated keys.  As detailed in
   Section 9, the IP addresses of the Public Authoritative Name Server
   Set 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 must not be indexed using the IP and be
   resilient to IP updates.






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5.3.  CPE 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 can be performed with port
   binding and/or firewall rules.

   The Hidden Primary SHOULD drop on the WAN interface any DNS queries
   that is not issued from the Public Authoritative Name Server Set.

   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.  This depends how the synchronization is secured.

6.  DNSSEC compliant Homenet Architecture

   [RFC7368] in Section 3.7.3 recommends DNSSEC to be deployed on the
   both the authoritative server and the resolver.  The resolver side is
   out of scope of this document, and only the authoritative part is
   considered.

   Deploying DNSSEC requires signing the zone and configuring a secure
   delegation.  As described in Section 4.1, signing can be performed by
   the CPE or by the Public Authoritative Name Server Sets.  Section 6.1
   details the implications of these two alternatives.  Similarly, the
   secure delegation can be performed by the CPE or by the Public
   Authoritative Servers.  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 Public Authoritative Name Servers Set.
   It is recommended the CPE signs the zone unless there is a strong
   argument against it, like a CPE that is not able to sign the zone.
   In that case zone signing may be performed by the Public
   Authoritative Name Servers Set on behalf of the CPE.

   Reasons for signing the zone by the CPE are:

   - 1:  Keeping the Homenet Zone and the Public Zone equals to securely
         optimize DNS resolution.  As the Public Zone is signed with



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         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 Primary.  This
         could be useful for example if, in the future, the CPE could
         announce to the home network that the CPE can act a 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 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 Primary.  Note that outsourcing the zone signing
         operation requires that all DNSSEC queries be cached to perform
         a local lookup, otherwise a resolution with the Public
         Authoritative Primary is performed.

   - 2:  Keeping the Homenet Zone and the Public Zone equals to securely
         address the connectivity disruption independence exposed 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 Primaries.

   - 3:  Keeping the Homenet Zone and the Public Zone equals to
         guarantee coherence between DNS(SEC) 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 DNS Zone are better guaranteed.
         When the Zone is signed by the CPE, it makes modification of
         the DNS data -- for example for flow redirection -- not
         possible.  As a result, signing the Homenet Zone by the CPE
         provides better protection for the end user privacy.

   Reasons for signing the zone by the Public Authoritative Servers are:

   - 1:  The CPE is not able to sign the zone, most likely because its
         firmware does not make it possible.  However the reason is
         expected to be less and less valid over time.

   - 2:  Outsourcing DNSSEC management operations.  Management
         operations involve key-roll over which can be done
         automatically by the CPE and transparently for the end user.



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         As result avoiding DNSSEC management is mostly motivated by bad
         software implementations.

   - 3:  Reducing the impact of CPE replacement on the Public Zone.
         Unless the CPE private keys are backuped, CPE replacement
         results in a emergency key roll over.  This can be mitigated
         also by using relatively small TTLs.

   - 4:  Reducing configuration impacts on the end user.  Unless there
         are some zero configuration mechanisms to provide credentials
         between the new CPE and the Public Authoritative Name Server
         Sets.  Authentications to Public Authoritative Name Server Set
         should 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:  Public Authoritative Servers are more likely to handle securely
         private keys than the CPE.  However, having all private
         information at one place may also balance that risk.

6.2.  Secure Delegation

   The secure delegation is set if the DS RRset is properly set in the
   parent zone.  Secure delegation can be performed by the CPE or the
   Public Authoritative Servers.

   The DS RRset can be updated manually by the CPE or the Public
   Authoritative Servers.  This can be used then with nsupdate for
   example but requires the CPE or the Public Authoritative Server to be
   authenticated by the Parent Zone Server.  Such a trust channel
   between the CPE and the Parent Zone server may be hard to maintain,
   and thus may be easier to establish with the Public Authoritative
   Server.  On the other hand, [RFC7344] may mitigate such issues.

7.  Handling Different Views

   The DNS Homenet Zone provides information about the home network and
   some user may be tempted to have different information regarding 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 wild Internet.
   Each view can be associated to a dedicated Homenet Zone.  Note that
   this document does not specify how DNS queries coming from the home
   network are addressed to the DNS(SEC) Homenet Zone.  This could be
   done via the DNS resolver hosted on the CPE for example.




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   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 a "Internet view".
   Finally, Section 7.3 provides guidance to 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 main motivation to handle different views is to provide different
   information depending on the location the DNS query is emitted.  Here
   are a few motivations for doing so:

   - 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 administrate your CPE may not be published
         on the Internet.  Similarly services like the mapper that
         registers the devices of your home network may not be published
         on the Internet.  In both case, these services should only be
         known/used by the network administrator.  To restrict the
         access of such services, the home network administrator may
         chose to publish these information only within the home
         network, where it may suppose users are more trustable then on
         the Internet.  Even though, this assumption may not be valid,
         at least, this reduces the surface of 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 Internet.

   - 3:  If the CPE does not sign the Homenet Zone and outsource the
         signing process, the two views are at least different since,
         one is protected with DNSSEC whereas the other is not.

7.2.  Consequences

   Enabling different views leads to a non-coherent naming system.
   Basically, 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.




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   Regarding local-scope IP addresses, such device may end up with poor
   connectivity.  Suppose, for example, the DNS resolution is performed
   via the WLAN interface attached to the CPE, the response provides
   local-scope IP addresses and 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, devices with multiple interfaces will have
   difficulties to secure the naming resolution as responses emitted
   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 also happen if the
   device is able to perform DNS resolutions.  DNS resolutions performed
   via the CPE resolver may be different then those performed over the
   Internet.

7.3.  Guidance and Recommendations

   As exposed in Section 7.2, it is recommended to avoid different
   views.  If network administrators chose to implement multiple views,
   impacts on devices' resolution should be evaluated.

   A consequence the DNS(SEC) Homenet Zone is expected to be the exact
   copy of the DNS(SEC) Public Zone.  As a result, services that are not
   expected to be published on the Internet should not be part of the
   DNS(SEC) Homenet Zone, local-scope address should not be part of the
   DNS(SEC) Homenet Zone, and when possible, the CPE should sign the
   DNS(SEC) Homenet Zone.

   The DNS(SEC) Homenet Zone is expected to host public information.  It
   is not to the DNS service to define local home networks 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 one 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].

8.  Reverse Zone

   Most of the description considered the DNS Homenet Zone as the non-
   Reverse Zone.  This section is focused on the Reverse Zone.





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   First, all considerations for the DNS Homenet Zone apply to the
   Reverse Homenet Zone.  The main difference between the Reverse DNS
   Homenet Zone and the DNS Homenet Zone is that the parent zone of the
   Reverse Homenet 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.  If the Reverse Public Authoritative Name
   Server Set 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 address is so large, that reverse
   zone may be confronted to a scalability issue.  How to reverse zone
   is generated is out of scope of this document.
   [I-D.howard-dnsop-ip6rdns] provides guidance on how to address the
   scalability issue.

9.  Renumbering

   This section details how renumbering is handled by the Hidden Primary
   server or the Public Authoritative Name Server Set which acts as a
   secondary server.  Both types of renumbering also designated as
   "make-before-break" or "break-before-make" are discussed.

   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 become familiar with them.

9.1.  Hidden Primary

   In a renumbering scenario, the Hidden Primary is informed it is being
   renumbered.  In most cases, it occurs as the whole home network is
   being renumbered.  As a result, the DNS(SEC) Homenet Zone will also
   be updated.  Although the new and old IP addresses may be stored in
   the DNS(SEC) Homenet Zone, we recommend that only the newly reachable
   IP addresses be mentioned.

   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



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   TTL associate to a RRset of the Homenet Zone, it may be cache during
   TTL seconds.  Let T_NEW be the time the new IP address replaces the
   old IP address in the DNS, 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
   to 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 non
   reachable up to 2 * TTL.

   Once the DNS(SEC) Homenet Zone file has been updated on the Hidden
   Primary, the Hidden Primary needs to inform the Public Authoritative
   Naming Server Set that the DNS(SEC) Homenet Zone has been updated and
   that the IP address to use to retrieve the updated zone has also been
   updated.  Both information are updated using the regular DNS
   exchanges.  More specifically, mechanisms to update a IP address
   provided by lower layers with for protocols like SCTP [RFC4960],
   MOBIKE [RFC4555] are not considered in this document.

   The Hidden Primary informs the Public Authoritative Name Server Set
   the DNS(SEC) Homenet Zone has been updated by sending a NOTIFY
   payload with the new IP address.  In addition, this NOTIFY payload is
   authenticated using SIG(0) or TSIG.  When the Public Authoritative
   Name Server Set receives the NOTIFY payload, it MUST authenticate it.
   Note that the cryptographic key used for the authentication should be
   indexed by the Homenet Domain Name 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 Public Authoritative
   Name Server Set MUST also notice the IP address has been modified and
   perform a reachability check before updating its primary
   configuration.  The routability check is 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 Public Authoritative Name Server Set updates its configuration
   file and retrieve the DNS(SEC) 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.  Public Authoritative Name Server Set

   Renumbering of the Public Authoritative Name Server Set results in
   the Public Authoritative Name Server Set to change its IP address.
   The Public Authoritative Name Server Set is a secondary, so its
   renumbering does not impact the DNS(SEC) Homenet Zone.  In fact,
   exchanges to the Public Authoritative Name Server Set are restricted
   to the DNS(SEC) Homenet Zone synchronization.  In our case, the
   Hidden Primary MUST be able to send NOTIFY payloads to the Public
   Authoritative Name Server Set.

   If the Public Authoritative Name Server Set is configured in Hidden
   Primary configuration file with a FQDN, then the update of the IP
   address is performed by the DNS(SEC).  More specifically, before
   sending the NOTIFY, the Hidden Primary performs a DNS(SEC) resolution
   to retrieve the IP address of the secondary.

   As described in Section 9.1, the Public Authoritative Name Server Set
   DNS information should be coherent with the IP plane.  Let TTL be the
   TTL associated to the Public Authoritative Name Server Set FQDN,
   T_NEW the time the new IP address replaces the old one and
   T_OLD_UNREACHABLE the time the Public Authoritative Name Server Set
   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 Public Authoritative Name
   Server Set 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 non reachable 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.  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
   entity comes with a few privacy related concerns.

   First the DNS 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 remains accessible though
   the Internet.  Even though DNS makes information public, the DNS does
   not expect to make the complete list of service 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
   of the services.  More specifically, making mywebsite.example.com



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   public in the DNS, is not sufficient to make resolvers aware of the
   existence web site.

   In order to prevent the complete DN(SEC) Homenet Zone to be published
   on the Internet, one should prevent AXFR queries on the Public
   Authoritative Primaries.  Similarly, to avoid zone-walking one should
   prefer NSEC3 [RFC5155] over NSEC [RFC4034].

   When the DNS Homenet Zone is outsourced the end user must 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 eventually the device, by as the DNS
   Homenet Zone contains the IP addresses associated to the service,
   they limit the scope of the scan.

   In addition to the DNS Homenet Zone, the third party can also monitor
   the traffic associated to the DNS Homenet Zone.  This traffic may
   provide indication of the services you use, how and when you use
   these services.  Although, cache may alter 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 his services and
   devices from his home network reachable on the Internet with Names
   rather than IP addresses.  This exposes the home network to attackers
   since names are expected to provide less randomness than IP
   addresses.  The naming delegation protects the End User's privacy by
   not providing the complete zone of the home network to the ISP.
   However, using the DNS with names for the home network exposes the
   home network and its components to dictionary attacks.  In fact, with
   IP addresses, the Interface Identifier is 64 bit length leading to
   2^64 possibilities for a given subnetwork.  This is not to mention
   that the subnet prefix is also of 64 bit length, thus providing
   another 2^64 possibilities.  On the other hand, names used either for
   the home network domain or for the devices present less randomness
   (livebox, router, printer, nicolas, jennifer, ...) and thus 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 the same
   Prefix over time.  As a result observing IP addresses 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 that
   logging IP addresses, especially to profile 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 we recommend that End Users may choose to respond or not
   to PTR DNS queries and may return a NXDOMAIN response.

11.3.  DNS Reflection Attacks

   An attacker uses a reflection attack when it sends traffic to an
   intermediary node that in turn sends back some traffic to the victim.
   Motivations for using an intermediary node might be anonymity of the
   attacker as wells 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 in a
   reflection attack.  Section 11.3.1 considers the Hidden Primary,
   Section 11.3.2 the Public Authoritative Name Server Set, and
   Section 11.3.3 the Public Authoritative Primary.

11.3.1.  Reflection Attack involving the Hidden Primary

   With the current 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.

   At first, DNS queries of type AXFR and IXFR uses TCP and as such a
   less subject to reflection attacks.  This makes SOA query the only
   remaining vector of attacks for reflection based on UDP.

   Firstly, 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 is
   involved in a DDoS attack.  In addition, SOA queries are expected to
   follow a very specific pattern which makes rate limiting techniques
   an efficient way to limit such attacks, with a limited impact on the
   naming service of the home network.




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   This paragraph analyzes how a Hidden Primary could mitigate a flood
   of SOA requests.  Motivations for such flood might be a reflection
   attack, but could be also an attack performed against the Hidden
   Primary for resource exhaustion.  At first, the Hidden Primary only
   expects traffic from the Public Authoritative Name Server Set that is
   its associated secondary.  Even though secondary servers may be
   renumbered, as exposed 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 base on the 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 appropriately done, as to limit the impact on the
   legitimate SOA sent by the secondary.

   The main reason for the Public Authoritative Name Server Set to send
   a SOA query is to update the SOA RRset after the TTL expires, to
   check 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 can assume it is involved in an
   attack.  There are a few legitimate time slot the secondary is
   expected to send a SOA query.  These times may be specific times like
   T_NOTIFY the emission of a NOTIFY query, T_SOA + 2/3 TTL, T_SOA +
   TTL, T_SOA + T_REFRESH where TTL designates the SOA TTL value,
   T_REFRESH the refresh time defined in the SOA RRset, and T_SOA the
   last time the SOA has been queried.  Outside a few minutes following
   these specific time, the probability the CPE discard 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
   preserve the CPE resource.  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.






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11.3.2.  Reflection Attacks involving the Public Authoritative Name
         Server Set

   The Public Authoritative Name Server Set acts as a secondary toward
   the Hidden Primary.  The secondary expects to receive NOTIFY query,
   SOA responses, AXFR and IXFR responses from the Hidden Primary.

   Sending NOTIFY query to the secondary generates a NOTIFY response as
   well as an SOA query to the Hidden Primary.  As mentioned in
   [RFC1996], this is a "known benign denial of service attack".  As a
   result, the Public Authoritative Name Server Set should enforce rate
   limiting on the SOA queries and NOTIFY responses that are sent 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 address much 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
   may not proceed to IP filtering based on the IP address.  In
   addition, a given secondary may be shared among multiple Hidden
   Primaries which makes filtering rules based on IP harder to set.  At
   last, time at which a NOTIFY is sent by the Hidden Primary is not
   predictable.  However, a flood of NOTIFY may be easily detected as a
   NOTIFY for a given DNS Homenet Zone is expected to have a very
   limited number of different IP addresses even though renumbering
   occurs.  As a result, the secondary, can rate limit incoming NOTIFY
   queries.

   It is recommended the Hidden Primary sends 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 Primary

   The Public Authoritative Primary implication of reflection attacks is
   similar as any public authoritative server.  These is not specific to
   the architecture described in this document, and thus considered as
   out of scope.

   In fact, one of the motivation of the architecture described in this
   document was to expose the Public Authoritative Primary to attacks
   instead of the CPE.







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11.4.  Flooding Attack

   The purpose of flooding attacks is mostly resource exhaustion where
   the resource can be bandwidth or CPU for example.

   One of the goal of the architecture described in the document is to
   limit the surface of attack for the CPE.  This is done, by
   outsourcing the DNS service to the Public Authoritative Primaries.
   By doing so, the CPE limits its DNS interactions between the Hidden
   Primary and the Public Authoritative Name Server Set. This limits the
   number of entity the CPE interacts with as well as the scope of DNS
   exchanges - basically NOTIFY, SOA, AXFR, IXFR.

   The use of an authenticated channel with SIG(0) or TSIG between the
   CPE and the Public Authoritative Name Server Set, enables to detect
   illegitimate DNS queries, and take appropriated actions - 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 in sending a message that has already been
   sent.  As the Hidden Primary and the Public Authoritative Name Server
   Set use an authenticated channel, replay attacks are mostly expected
   to used over forged DNS queries in order to provide valid traffic.

   On an attacker points of view, using a correctly authenticated DNS
   query, may not be detected as an attack, and thus may generate the
   corresponding response.  Generating and sending a response consumes
   more resources then dropping the query and thus could be used for
   resource exhaustion attacks.  In addition, as the authentication is
   performed at the DNS layer, the 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
   section assumes a context of DoS with a flood of DNS queries.  This
   section address replay attack as a way to limit the surface of these
   attacks.

   As SIG(0) and TSIG uses 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
   loose time synchronization of the devices and short live time for the



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   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 feed backs on
   handling different views as well as clarifying the impact of
   outsourcing the zone signing operation outside the CPE; Ray Hunter,
   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-01 (work in
              progress), February 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]

   -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 Primaries (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

   *architecture clarifications

   -03:




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   *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 Primary(ies)".  "Public
   Authoritative Server Management Interface" is replaced by "Public
   Authoritative Name Server Set".

   -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
   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.




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   * 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

   Email: mglt.ietf@gmail.com


   Wouter Cloetens
   SoftAtHome
   vaartdijk 3 701
   3018 Wijgmaal
   Belgium

   Email: wouter.cloetens@softathome.com


   Chris Griffiths
   Dyn
   150 Dow Street
   Manchester, NH  03101
   US

   Email: cgriffiths@dyn.com
   URI:   http://dyn.com








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   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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