HOMENET D. Migault (Ed)
Internet-Draft Ericsson
Intended status: Standards Track W. Cloetens
Expires: August 20, 2015 SoftAtHome
C. Griffiths
Dyn
R. Weber
Nominum
February 16, 2015
Outsourcing Home Network Authoritative Naming Service
draft-ietf-homenet-front-end-naming-delegation-01.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 results 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 associates 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
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This Internet-Draft will expire on August 20, 2015.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Architecture Description . . . . . . . . . . . . . . . . . . 5
4.1. Architecture Overview . . . . . . . . . . . . . . . . . . 5
4.2. Example: DNS(SEC) Homenet Zone . . . . . . . . . . . . . 7
4.3. Example: CPE necessary parameters for outsourcing . . . . 9
5. Synchronization between CPE and Public Authoritative Servers 10
5.1. Synchronization with a Hidden Master . . . . . . . . . . 10
5.2. Securing Synchronization . . . . . . . . . . . . . . . . 11
5.3. CPE Security Policies . . . . . . . . . . . . . . . . . . 13
6. DNSSEC compliant Homenet Architecture . . . . . . . . . . . . 13
6.1. Zone Signing . . . . . . . . . . . . . . . . . . . . . . 13
6.2. Secure Delegation . . . . . . . . . . . . . . . . . . . . 15
7. Handling Different Views . . . . . . . . . . . . . . . . . . 15
7.1. Motivations . . . . . . . . . . . . . . . . . . . . . . . 16
7.2. Consequences . . . . . . . . . . . . . . . . . . . . . . 16
7.3. Guidance and Recommendations . . . . . . . . . . . . . . 17
8. Reverse Zone . . . . . . . . . . . . . . . . . . . . . . . . 17
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18
10. Security Considerations . . . . . . . . . . . . . . . . . . . 19
10.1. Names are less secure than IP addresses . . . . . . . . 19
10.2. Names are less volatile than IP addresses . . . . . . . 19
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
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12. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . 20
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
13.1. Normative References . . . . . . . . . . . . . . . . . . 20
13.2. Informational References . . . . . . . . . . . . . . . . 21
Appendix A. Document Change Log . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
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 the 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.
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
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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 and Section 10 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 hosts
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 master / slave 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
the zone. In this document, the Public Authoritative Server
synchronizes the DNS Homenet Zone with the CPE via a hidden
master / slave architecture. The Public Authoritative Server
acts as a slave 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 Master(s).
- DNSSEC Public Zone: corresponds to the signed version of the DNS
Homenet Zone. It is hosted by the Public Authoritative Server,
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which is authoritative for this zone, and is reachable on the
Public Authoritative Master(s).
- Public Authoritative Master(s): 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
master for the zone.
- Public Authoritative Name Server Set: is the server the CPE
synchronizes the DNS Homenet Zone. It is configured as a slave
and the CPE acts as master. The CPE sends information so the
DNSSEC zone can be set and served.
- Reverse Public Authoritative Master(s): 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 master 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 slave and the CPE acts as master. 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
Master(s). 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.
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
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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.
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
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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 Master. Implications of such
policy are detailed in Section 6 and Section 7.
Internet
+--------------------------------------------------------+
| Public Authoritative Servers |
+--------------------------------------------------------+
+----------------------+ +----------------------+
| | | |
| Public Authoritative | | Public Authoritative |
| Name Server Set | | Masters |
| | | |
| +------------------+ | 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 Masters, 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 Masters. In other words "Homenet to Public
Zone transformation" is the identity.
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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 Masters. This is illustrated in Figure 3.
public.masters.example.net is the FQDN of the Public Authoritative
Masters, 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.
$ORIGIN example.com
$TTL 1h
@ IN SOA public.masters.example.net
hostmaster.example.com. (
2013120710 ; serial number of this zone file
1d ; slave refresh
2h ; slave retry time in case of a problem
4w ; slave expiration time
1h ; maximum caching time in case of failed
; lookups
)
@ NS public.authoritative.servers.example.net
public.masters.example.net A @IP1
public.masters.example.net A @IP2
public.masters.example.net AAAA @IP3
public.masters.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 Master and the Public Authoritative Name Server Set and
published on the DNS Public Authoritative Master.
- MNAME: indicates the primary master. In our case the zone is
published on the Public Authoritative Master, and its name MUST
be mentioned. If multiple Public Authoritative Masters are
involved, one of them MUST be chosen. More specifically, the
CPE MUST NOT place the name of the Hidden Master.
- 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
slaves need to check the master and the time between two
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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 Masters and the CPE are expected
to implement NOTIFY [RFC1996]. Then short values MAY increase
the bandwidth usage for slaves hosting large number of zones.
As a result, default values looks fine.
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 plug / 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 (1hour) 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 Master(s): The FQDN or IP addresses of the
Public Authoritative Master. It MAY correspond to the data
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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.
- Registered Homenet Domain: The domain name the Public
Authoritative is configured for DNS slave, 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 Server: The Public Authoritative Servers
associated to the Registered Homenet Domain. Multiple Public
Authoritative Server may be provided.
5. Synchronization between CPE and Public Authoritative Servers
The DNS(SEC) Homenet Reverse Zone and the DNS Homenet Zone can be
updated either with DNS update [RFC2136] or using a master / slave
synchronization. The master / slave mechanism is preferred as it
better scales and avoids DoS attacks: First the master notifies the
slave the zone must be updated, and leaves the slave to proceed to
the update when possible. Then, the NOTIFY message sent by the
master is a small packet that is less likely to load the slave. At
last, the AXFR query performed by the slave is a small packet sent
over TCP (section 4.2 [RFC5936]) which makes unlikely the slave 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 master / slave mechanism
instead of the use of nsupdates. This section details the master /
slave mechanism.
5.1. Synchronization with a Hidden Master
Uploading and dynamically updating the zone file on the Public
Authoritative Name Server Set can be seen as zone provisioning
between the CPE (Hidden Master) and the Public Authoritative Name
Server Set (Slave Server). This can be handled either in band or out
of band.
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The Public Authoritative Name Server Set is configured as a slave for
the Homenet Domain Name. This slave configuration has been
previously agreed between the end user and the provider of the Public
Authoritative Servers. In order to set the master/ slave
architecture, the CPE acts as a Hidden Master Server, which is a
regular Authoritative DNS(SEC) Server listening on the WAN interface.
The Hidden Master Server is expected to accept SOA [RFC1033], AXFR
[RFC1034], and IXFR [RFC1995] queries from its configured slave DNS
servers. The Hidden Master 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 Master Server differs from a regular authoritative server for
the home network by:
- Interface Binding: the Hidden Master 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 Master 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 Servers). Then
exchange types are limited. The only legitimate exchanges are:
NOTIFY initiated by the Hidden Master 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
Server. 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 Servers and the CPE MUST be secured, at
least for integrity protection and for authentication. This is the
case whatever mechanism is used between the CPE and the Public
Authoritative Name Server Set.
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
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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 that these mechanisms to be implemented on the
DNS(SEC) Server's implementation running on the CPE, which adds
codes. Another disadvantage is that TKEY does not provides
authentication mechanism.
Protocols like TLS [RFC5246] / DTLS [RFC6347] can be used to secure
the transactions between the Public Authoritative Servers 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 Server 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 Server SHOULD NOT be impacted by middle
boxes.
As mentioned above, TSIG, IPsec and TLS/DTLS may be used to secure
transactions between the CPE and the Public Authentication Servers.
The CPE and Public Authoritative Server SHOULD implement TSIG and
IPsec.
How the PSK can be used by any of the TSIG, TLS/DTLS or IPsec
protocols. Authentication based on certificates implies a mutual
authentication and thus requires the 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 Authentication Servers MUST support
PSK and certificate based authentication.
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5.3. CPE Security Policies
This section details security policies related to the Hidden Master /
Slave synchronization.
The Hidden Master, 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 Master SHOULD drop on the WAN interface any DNS queries
that is not issued from the Public Authoritative Server Name Server
Set.
The Hidden Master SHOULD drop any outgoing packets other than DNS
NOTIFY query, SOA response, IXFR response or AXFR responses.
The Hidden Master SHOULD drop any incoming packets other than DNS
NOTIFY response, SOA query, IXFR query or AXFR query.
The Hidden Master 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 Servers. 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 Servers. It is
recommended to sign the zone by the CPE 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 Servers on behalf of the CPE.
Reasons for signing the zone by the CPE are:
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- 1: Keeping the Homenet Zone and the Public Zone equals 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 Master. 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 master 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 CPE 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 Master. 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 Master 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 lookup is
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 a
fall back to DNS resolution occurs as the local Homenet Zone is
not signed.
- 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.
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- 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.
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 bu 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
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network are addressed to the DNS(SEC) Homenet Zone. This could be
done via the DNS resolver hosted on the CPE for example.
This section is not normative. Section 7.1 expose different reasons
that result in different views, Section 7.2 briefly describes the
consequences of having distinct views, and Section 7.3 provides
guidance to avoid this situation.
7.1. Motivations
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 you are 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(SE) Homenet Zone, and when possible, the CPE should sign the
DNSSEC 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. Privacy Considerations
Outsourcing the DNS Authoritative service from the CPE to a third
entity comes with a 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
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 Masters. 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
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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.
10. Security Considerations
The Homenet Naming Architecture described in this document solves
exposing the CPE's DNS service as a DoS attack vector.
10.1. Names are less secure than IP addresses
This document describes how an End User can make 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.
10.2. Names are less volatile than IP addresses
IP addresses may be used to locate a device, a host or a Service.
However, home networks are not expected to be assigned 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.
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11. IANA Considerations
This document has no actions for IANA.
12. Acknowledgment
The authors wish to thank Philippe Lemordant for its contributions on
the early versions of the draft, Ole Troan for pointing out issues
with the IPv6 routed home concept and placing the scope of this
document in a wider picture, Mark Townsley for encouragement and
injecting a healthy debate on the merits of the idea, Ulrik de Bie
for providing alternative solutions, Paul Mockapetris, Christian
Jacquenet, Francis Dupont and Ludovic Eschard for their remarks on
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 and Michael Richardson, 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.
13. References
13.1. 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.
[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.
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[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.
[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.
[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.
13.2. Informational References
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[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-04 (work in progress), October
2014.
[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-00 (work in
progress), September 2014.
[RFC1033] Lottor, M., "Domain administrators operations guide", RFC
1033, November 1987.
[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.
Appendix A. Document Change Log
[RFC Editor: This section is to be removed before publication]
-05:
*Clarifying on handling different views:
- 1: How the CPE may be involved in the resolution and responds
without necessarily requesting the Public Masters (and
eventually the Hidden Master)
- 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
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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:
*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 Master(s)". "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
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-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.
* 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 Master / Slave functions with CPE as Hidden Master/Homenet
Server.
* For next version, address functions of MDNS within Homenet Lan and
publishing details northbound via Hidden Master.
-00: First version published.
Authors' Addresses
Daniel Migault
Ericsson
8400 boulevard Decarie
Montreal, QC H4P 2N2
Canada
Email: mglt.ietf@gmail.com
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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
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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