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HOMENET D. Migault (Ed)
Internet-Draft Ericsson
Intended status: Standards Track R. Weber
Expires: January 3, 2016 Nominum
R. Hunter
Globis Consulting BV
C. Griffiths
W. Cloetens
SoftAtHome
July 2, 2015
Outsourcing Home Network Authoritative Naming Service
draft-ietf-homenet-front-end-naming-delegation-03.txt
Abstract
RFC7368 'IPv6 Home Networking Architecture Principles' section 3.7
describes architecture principles related to naming and service
discovery in residential home networks.
Customer Edge Routers and other Customer Premises Equipment (CPEs)
are designed to provide IP connectivity to home networks. Most CPEs
assign IP addresses to the nodes of the home network which makes them
good candidates for hosting the naming service. IPv6 provides global
connectivity, and nodes from the home network will be reachable from
the global Internet. As a result, the naming service is expected to
be exposed on the Internet.
However, CPEs have not been designed to host such a naming service
exposed on the Internet. Running a naming service visible on the
Internet may expose the CPEs to resource exhaustion and other
attacks, which could make the home network unreachable, and most
probably would also affect the internal communications of the home
network.
In addition, regular end users may not understand, or possess the
necessary skills to be able to perform, DNSSEC management and
configuration. Misconfiguration may also result in naming service
disruption, thus these end users may prefer to rely on third party
name service providers.
This document describes a homenet naming architecture, where the CPEs
manage the DNS zones associated with its own home network, and
outsource elements of the naming service (possibly including DNSSEC
management) to a third party running on the Internet.
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Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 3, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Architecture Description . . . . . . . . . . . . . . . . . . 6
4.1. Architecture Overview . . . . . . . . . . . . . . . . . . 6
4.2. Example: Homenet Zone . . . . . . . . . . . . . . . . . . 8
4.3. Example: CPE necessary parameters for outsourcing . . . . 10
5. Synchronization between CPE and the Synchronization Server . 11
5.1. Synchronization with a Hidden Primary . . . . . . . . . . 11
5.2. Securing Synchronization . . . . . . . . . . . . . . . . 12
5.3. CPE Security Policies . . . . . . . . . . . . . . . . . . 13
6. DNSSEC compliant Homenet Architecture . . . . . . . . . . . . 14
6.1. Zone Signing . . . . . . . . . . . . . . . . . . . . . . 14
6.2. Secure Delegation . . . . . . . . . . . . . . . . . . . . 16
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7. Handling Different Views . . . . . . . . . . . . . . . . . . 16
7.1. Misleading Reasons for Local Scope DNS Zone . . . . . . . 17
7.2. Consequences . . . . . . . . . . . . . . . . . . . . . . 17
7.3. Guidance and Recommendations . . . . . . . . . . . . . . 18
8. Homenet Reverse Zone . . . . . . . . . . . . . . . . . . . . 19
9. Renumbering . . . . . . . . . . . . . . . . . . . . . . . . . 19
9.1. Hidden Primary . . . . . . . . . . . . . . . . . . . . . 19
9.2. Synchronization Server . . . . . . . . . . . . . . . . . 21
10. Privacy Considerations . . . . . . . . . . . . . . . . . . . 21
11. Security Considerations . . . . . . . . . . . . . . . . . . . 22
11.1. Names are less secure than IP addresses . . . . . . . . 22
11.2. Names are less volatile than IP addresses . . . . . . . 23
11.3. DNS Reflection Attacks . . . . . . . . . . . . . . . . . 23
11.3.1. Reflection Attack involving the Hidden Primary . . . 23
11.3.2. Reflection Attacks involving the Synchronization
Server . . . . . . . . . . . . . . . . . . . . . . . 25
11.3.3. Reflection Attacks involving the Public
Authoritative Servers . . . . . . . . . . . . . . . 25
11.4. Flooding Attack . . . . . . . . . . . . . . . . . . . . 26
11.5. Replay Attack . . . . . . . . . . . . . . . . . . . . . 26
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
13. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . 27
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
14.1. Normative References . . . . . . . . . . . . . . . . . . 27
14.2. Informational References . . . . . . . . . . . . . . . . 29
Appendix A. Document Change Log . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32
1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Introduction
IPv6 provides global end to end IP reachability. End users prefer to
use names instead of long and complex IPv6 addresses when accessing
services hosted in the home network.
Customer Edge Routers and other Customer Premises Equipment (CPEs)
are already providing IPv6 connectivity to the home network, and
generally provide IPv6 addresses or prefixes to the nodes of the home
network. This makes CPEs good candidates to manage the binding
between names and IP addresses of nodes. In addition, [RFC7368]
recommends that home networks be resilient to connectivity disruption
from the ISP. This could be achieved by a dedicated device inside
the home network that builds the Homenet Zone, thus providing
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bindings between names and IP addresses. All this makes the CPE the
natural candidate for populating the Homenet zone.
CPEs are usually low powered devices designed for the home network,
but not for terminating heavy traffic. As a result, hosting an
authoritative DNS service on the Internet may expose the home network
to resource exhaustion and other attacks. This may isolate the home
network from the Internet and also impact the services hosted by the
CPEs, thus affecting overall home network communication.
In order to avoid resource exhaustion and other attacks, this
document describes an architecture that outsources the authoritative
naming service of the home network. More specifically, the Homenet
Zone built by the CPE is outsourced to an Outsourcing Infrastructure.
The Outsourcing Infrastructure publishes the corresponding Public
Homenet Zone on the Internet. Section 4.1 describes the
architecture. In order to keep the Public Homenet Zone up-to-date
Section 5 describes how the Homenet Zone and the Public Homenet Zone
can be synchronized. The proposed architecture aims at deploying
DNSSEC, and the Public Homenet Zone is expected to be signed with a
secure delegation. The zone signing and secure delegation may be
performed either by the CPE or by the Outsourcing Infrastructure.
Section 6 discusses these two alternatives. Section 7 discusses the
consequences of publishing multiple representations of the same zone
also commonly designated as views. This section provides guidance to
limit the risks associated with multiple views. Section 8 discusses
management of the reverse zone. Section 9 discusses how renumbering
should be handled. Finally, Section 10 and Section 11 respectively
discuss privacy and security considerations when outsourcing the
Homenet Zone.
3. Terminology
- Customer Premises Equipment: (CPE) is the router providing
connectivity to the home network. It might be configured and
managed by the end user. In this document, the CPE might also
host services such as DHCPv6. This device might be provided by
the ISP.
- Registered Homenet Domain: is the Domain Name associated to the
home network.
- Homenet Zone: is the DNS zone associated with the home network.
It is designated by its Registered Homenet Domain. This zone
is built by the CPE and contains the bindings between names and
IP addresses of the nodes in the home network. The CPE
synchronizes the Homenet Zone with the Synchronization Server
via a hidden primary / secondary architecture. The Outsourcing
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Infrastructure may process the Homenet Zone - for example
providing DNSSEC signing - to generate the Public Homenet Zone.
This Public Homenet Zone is then transmitted to the Public
Authoritative Server(s) that publish it on the Internet.
- Public Homenet Zone: is the public version of the Homenet Zone.
It is expected to be signed with DNSSEC. It is hosted by the
Public Authoritative Server(s), which are authoritative for
this zone. The Public Homenet Zone and the Homenet Zone might
be different. For example some names might not become
reachable from the Internet, and thus not be hosted in the
Public Homenet Zone. Another example of difference may also
occur when the Public Homenet Zone is signed whereas the
Homenet Zone is not signed.
- Outsourcing Infrastructure: is the combination of the
Synchronization Server and the Public Authoritative Server(s).
- Public Authoritative Servers: are the authoritative name servers
hosting the Public Homenet Zone. Name resolution requests for
the Homenet Domain are sent to these servers. For resiliency
the Public Homenet Zone SHOULD be hosted on multiple servers.
- Synchronization Server: is the server with which the CPE
synchronizes the Homenet Zone. The Synchronization Server is
configured as a secondary and the CPE acts as primary. There
MAY be multiple Synchronization Servers, but the text assumes a
single server. In addition, the text assumes the
Synchronization Server is a separate entity. This is not a
requirement, and when the CPE signs the zone, the
synchronization function might also be operated by the Public
Authoritative Servers.
- Homenet Reverse Zone: The reverse zone file associated with the
Homenet Zone.
- Reverse Public Authoritative Servers: are the authoritative name
server(s) hosting the Public Homenet Reverse Zone. Queries for
reverse resolution of the Homenet Domain are sent to this
server. Similarly to Public Authoritative Servers, for
resiliency, the Homenet Reverse Zone SHOULD be hosted on
multiple servers.
- Reverse Synchronization Server: is the server with which the CPE
synchronizes the Homenet Reverse Zone. It is configured as a
secondary and the CPE acts as primary. There MAY be multiple
Reverse Synchronization Servers, but the text assumes a single
server. In addition, the text assumes the Reverse
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Synchronization Server is a separate entity. This is not a
requirement, and when the CPE signs the zone, the
synchronization function might also be operated by the Reverse
Public Authoritative Servers.
- Hidden Primary: designates the primary server of the CPE, that
synchronizes the Homenet Zone with the Synchronization Server.
A primary / secondary architecture is used between the CPE and
the Synchronization Server. The hidden primary is not expected
to serve end user queries for the Homenet Zone as a regular
primary server would. The hidden primary is only known to its
associated Synchronization Server.
4. Architecture Description
This section describes the architecture for outsourcing the
authoritative naming service from the CPE to the Outsourcing
Infrastructure. Section 4.1 describes the architecture, Section 4.2
and Section 4.3 illustrates this architecture and shows how the
Homenet Zone should be built by the CPE. It also lists the necessary
parameters the CPE needs to be able to outsource the authoritative
naming service. These two sections are informational and non-
normative.
4.1. Architecture Overview
Figure 1 provides an overview of the architecture.
The home network is designated by the Registered Homenet Domain Name
-- example.com in Figure 1. The CPE builds the Homenet Zone
associated with the home network. How the Homenet Zone is built is
out of the scope of this document. The CPE may host or interact with
multiple services to determine name-to-address mappings, such as a
web GUI, DHCP [RFC6644] or mDNS [RFC6762]. These services may
coexist and may be used to populate the Homenet Zone. This document
assumes the Homenet Zone has been populated with domain names that
are intended to be publicly published and that are publicly
reachable. More specifically, names associated with services or
devices that are not expected to be reachable from outside the home
network or names bound to non-globally reachable IP addresses MUST
NOT be part of the Homenet Zone.
Once the Homenet Zone has been built, the CPE does not host an
authoritative naming service, but instead outsources it to the
Outsourcing Infrastructure. The Outsourcing Infrastructure takes the
Homenet Zone as an input and publishes the Public Homenet Zone. If
the CPE does not sign the Homenet Zone, the Outsourcing
Infrastructure may instead sign it on behalf of the CPE. Figure 1
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provides a more detailed description of the Outsourcing
Infrastructure, but overall, it is expected that the CPE provides the
Homenet Zone. Then the Public Homenet Zone is derived from the
Homenet Zone and published on the Internet.
As a result, DNS queries from the DNS resolvers on the Internet are
answered by the Outsourcing Infrastructure and do not reach the CPE.
Figure 1 illustrates the case of the resolution of node1.example.com.
home network +-------------------+ Internet
| |
| CPE |
| | +-----------------------+
+-------+ |+-----------------+| | Public Authoritative |
| | || Homenet Zone || | Server(s) |
| node1 | || || |+---------------------+|
| | || || || Public Homenet Zone ||
+-------+ || Homenet Domain ||=========|| ||
|| Name || ^ || (example.com) ||
node1.\ || (example.com) || | |+---------------------+|
example.com |+-----------------+| | +-----------------------+
+-------------------+ | ^ |
Synchronization | |
| |
DNSSEC resolution for node1.example.com | v
+-----------------------+
| |
| DNSSEC Resolver |
| |
+-----------------------+
Figure 1: Homenet Naming Architecture Description
The Outsourcing Infrastructure is described in Figure 2. The
Synchronization Server receives the Homenet Zone as an input. The
received zone may be transformed to output the Public Homenet Zone.
Various operations may be performed here, however this document only
considers zone signing as a potential operation. This should occur
only when the CPE outsources this operation to the Synchronization
Server. On the other hand, if the CPE signs the Homenet Zone itself,
the zone would be collected by the Synchronization Server and
directly transferred to the Public Authoritative Server(s). These
policies are discussed and detailed in Section 6 and Section 7.
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Internet
+------------------------------------------------------+
| Outsourcing Infrastructure |
+------------------------------------------------------+
+----------------------+ +----------------------+
| | | |
| Synchronization | | Public Authoritative |
| Server | | Server(s) |
| | | |
| +------------------+ | X |+--------------------+|
| | Homenet Zone | | ^ || Public Homenet Zone||
=========>| | | | || ||
^ | | | | | || ||
| | | (example.com) | | | || (example.com) ||
| | +------------------+ | | |+--------------------+|
| +----------------------+ | +----------------------+
| Homenet to Public Zone
Synchronization transformation
from the CPE
Figure 2: Outsourcing Infrastructure Description
4.2. Example: Homenet Zone
This section is not normative and intends to illustrate how the CPE
builds the Homenet Zone.
As depicted in Figure 1 and Figure 2, the Public Homenet Zone is
hosted on the Public Authoritative Server(s), whereas the Homenet
Zone is hosted on the CPE. Motivations for keeping these two zones
identical are detailed in Section 7, and this section considers that
the CPE builds the zone that will be effectively published on the
Public Authoritative Server(s). In other words "Homenet to Public
Zone transformation" is the identity also commonly designated as "no
operation" (NOP).
In that case, the Homenet Zone should configure its Name Server RRset
(NS) and Start of Authority (SOA) with the values associated with the
Public Authoritative Server(s). This is illustrated in Figure 3.
public.primary.example.net is the FQDN of the Public Authoritative
Server(s), and IP1, IP2, IP3, IP4 are the associated IP addresses.
Then the CPE should add the additional new nodes that enter the home
network, remove those that should be removed, and sign the Homenet
Zone.
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$ORIGIN example.com
$TTL 1h
@ IN SOA public.primary.example.net
hostmaster.example.com. (
2013120710 ; serial number of this zone file
1d ; secondary refresh
2h ; secondary retry time in case of a problem
4w ; secondary expiration time
1h ; maximum caching time in case of failed
; lookups
)
@ NS public.authoritative.servers.example.net
public.primary.example.net A @IP1
public.primary.example.net A @IP2
public.primary.example.net AAAA @IP3
public.primary.example.net AAAA @IP4
Figure 3: Homenet Zone
The SOA RRset is defined in [RFC1033], [RFC1035] and [RFC2308]. This
SOA is specific, as it is used for the synchronization between the
Hidden Primary and the Synchronization Server and published on the
DNS Public Authoritative Server(s)..
- MNAME: indicates the primary. In our case the zone is published
on the Public Authoritative Server(s), and its name MUST be
included. If multiple Public Authoritative Server(s) are
involved, one of them MUST be chosen. More specifically, the
CPE MUST NOT include the name of the Hidden Primary.
- RNAME: indicates the email address to reach the administrator.
[RFC2142] recommends using hostmaster@domain and replacing the
'@' sign by '.'.
- REFRESH and RETRY: indicate respectively in seconds how often
secondaries need to check the primary, and the time between two
refresh when a refresh has failed. Default values indicated by
[RFC1033] are 3600 (1 hour) for refresh and 600 (10 minutes)
for retry. This value might be too long for highly dynamic
content. However, the Public Authoritative Server(s) and the
CPE are expected to implement NOTIFY [RFC1996]. So whilst
shorter refresh timers might increase the bandwidth usage for
secondaries hosting large number of zones, it will have little
practical impact on the elapsed time required to achieve
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synchronization between the Outsourcing Infrastructure and the
Hidden Master. As a result, the default values are acceptable.
EXPIRE: is the upper limit data SHOULD be kept in absence of
refresh. The default value indicated by [RFC1033] is 3600000
(approx. 42 days). In home network architectures, the CPE
provides both the DNS synchronization and the access to the
home network. This device may be plugged and unplugged by the
end user without notification, thus we recommend a long expiry
timer.
MINIMUM: indicates the minimum TTL. The default value indicated by
[RFC1033] is 86400 (1 day). For home network, this value MAY
be reduced, and 3600 (1 hour) seems more appropriate.
4.3. Example: CPE necessary parameters for outsourcing
This section specifies the various parameters required by the CPE to
configure the naming architecture of this document. This section is
informational, and is intended to clarify the information handled by
the CPE and the various settings to be done.
Synchronization Server may be configured with the following
parameters. These parameters are necessary to establish a secure
channel between the CPE and the Synchronization Server as well as to
specify the DNS zone that is in the scope of the communication:
- Synchronization Server: The associated FQDNs or IP addresses of
the Synchronization Server. IP addresses are optional and the
FQDN is sufficient. To secure the binding name and IP
addresses, a DNSSEC exchange is required. Otherwise, the IP
addresses should be entered manually.
- Authentication Method: How the CPE authenticates itself to the
Synchronization Server. This MAY depend on the implementation
but this should cover at least IPsec, DTLS and TSIG
- Authentication data: Associated Data. PSK only requires a single
argument. If other authentication mechanisms based on
certificates are used, then CPE private keys, certificates and
certification authority should be specified.
- Public Authoritative Server(s): The FQDN or IP addresses of the
Public Authoritative Server(s). It MAY correspond to the data
that will be set in the NS RRsets and SOA of the Homenet Zone.
IP addresses are optional and the FQDN is sufficient. To
secure the binding between name and IP addresses, a DNSSEC
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exchange is required. Otherwise, the IP addresses should be
entered manually.
- Registered Homenet Domain: The domain name used to establish the
secure channel. This name is used by the Synchronization
Server and the CPE for the primary / secondary configuration as
well as to index the NOTIFY queries of the CPE when the CPE has
been renumbered.
Setting the Homenet Zone requires the following information.
- Registered Homenet Domain: The Domain Name of the zone. Multiple
Registered Homenet Domains may be provided. This will generate
the creation of multiple Public Homenet Zones.
- Public Authoritative Server(s): The Public Authoritative
Server(s) associated with the Registered Homenet Domain.
Multiple Public Authoritative Server(s) may be provided.
5. Synchronization between CPE and the Synchronization Server
The Homenet Reverse Zone and the Homenet Zone MAY be updated either
with DNS UPDATE [RFC2136] or using a primary / secondary
synchronization. The primary / secondary mechanism is preferred as
it scales better and avoids DoS attacks: First the primary notifies
the secondary that the zone must be updated and leaves the secondary
to proceed with the update when possible. Then, a NOTIFY message is
sent by the primary, which is a small packet that is less likely to
load the secondary. Finally, the AXFR query performed by the
secondary is a small packet sent over TCP (section 4.2 [RFC5936]),
which mitigates reflection attacks using a forged NOTIFY. On the
other hand, DNS UPDATE (which can be transported over UDP), requires
more processing than a NOTIFY, and does not allow the server to
perform asynchronous updates.
This document RECOMMENDS use of a primary / secondary mechanism
instead of the use of DNS UPDATE. This section details the primary /
secondary mechanism.
5.1. Synchronization with a Hidden Primary
Uploading and dynamically updating the zone file on the
Synchronization Server can be seen as zone provisioning between the
CPE (Hidden Primary) and the Synchronization Server (Secondary
Server). This can be handled either in band or out of band.
The Synchronization Server is configured as a secondary for the
Homenet Domain Name. This secondary configuration has been
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previously agreed between the end user and the provider of the
Synchronization Server. In order to set the primary / secondary
architecture, the CPE acts as a Hidden Primary Server, which is a
regular authoritative DNS Server listening on the WAN interface.
The Hidden Primary Server SHOULD accept SOA [RFC1033], AXFR
[RFC1034], and IXFR [RFC1995] queries from its configured secondary
DNS server(s). The Hidden Primary Server SHOULD send NOTIFY messages
[RFC1996] in order to update Public DNS server zones as updates
occur. Because, the Homenet Zones are likely to be small, the CPE
MUST implement AXFR and SHOULD implement IXFR.
Hidden Primary Server differs from a regular authoritative server for
the home network by:
- Interface Binding: the Hidden Primary Server listens on the WAN
Interface, whereas a regular authoritative server for the home
network would listen on the home network interface.
- Limited exchanges: the purpose of the Hidden Primary Server is to
synchronize with the Synchronization Server, not to serve any
zones to end users. As a result, exchanges are performed with
specific nodes (the Synchronization Server). Further, exchange
types are limited. The only legitimate exchanges are: NOTIFY
initiated by the Hidden Primary and IXFR or AXFR exchanges
initiated by the Synchronization Server. On the other hand,
regular authoritative servers would respond to any hosts, and
any DNS query would be processed. The CPE SHOULD filter IXFR/
AXFR traffic and drop traffic not initiated by the
Synchronization Server. The CPE MUST listen for DNS on TCP and
UDP and MUST at least allow SOA lookups of the Homenet Zone.
5.2. Securing Synchronization
Exchange between the Synchronization Server and the CPE MUST be
secured, at least for integrity protection and for authentication.
TSIG [RFC2845] or SIG(0) [RFC2931] MAY be used to secure the DNS
communications between the CPE and the Synchronization Server. TSIG
uses a symmetric key which can be managed by TKEY [RFC2930].
Management of the key involved in SIG(0) is performed through zone
updates. How keys are rolled over with SIG(0) is out-of-scope of
this document. The advantage of these mechanisms is that they are
only associated with the DNS application. Not relying on shared
libraries eases testing and integration. On the other hand, using
TSIG, TKEY or SIG(0) requires these mechanisms to be implemented on
the CPE, which adds code and complexity. Another disadvantage is
that TKEY does not provide authentication mechanisms.
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Protocols like TLS [RFC5246] / DTLS [RFC6347] MAY be used to secure
the transactions between the Synchronization Server and the CPE. The
advantage of TLS/DTLS is that this technology is widely deployed, and
most of the devices already embed TLS/DTLS libraries, possibly also
taking advantage of hardware acceleration. Further, TLS/DTLS
provides authentication facilities and can use certificates to
authenticate the Synchronization Server and the CPE. On the other
hand, using TLS/DTLS requires implementing DNS exchanges over TLS/
DTLS, as well as a new service port. This document therefore does
NOT RECOMMEND this option.
IPsec [RFC4301] IKEv2 [RFC7296] MAY also be used to secure
transactions between the CPE and the Synchronization Server.
Similarly to TLS/DTLS, most CPEs already embed an IPsec stack, and
IKEv2 supports multiple authentication mechanisms via the EAP
framework. In addition, IPsec can be used to protect DNS exchanges
between the CPE and the Synchronization Server without any
modifications of the DNS server or client. DNS integration over
IPsec only requires an additional security policy in the Security
Policy Database (SPD). One disadvantage of IPsec is that NATs and
firewall traversal may be problematic. However, in our case, the CPE
is connected to the Internet, and IPsec communication between the CPE
and the Synchronization Server should not be impacted by middle
boxes.
How the PSK can be used by any of the TSIG, TLS/DTLS or IPsec
protocols: Authentication based on certificates implies a mutual
authentication and thus requires the CPE to manage a private key, a
public key, or certificates, as well as Certificate Authorities.
This adds complexity to the configuration especially on the CPE side.
For this reason, we RECOMMEND that the CPE MAY use PSK or certificate
base authentication, and that the Synchronization Server MUST support
PSK and certificate based authentication.
Note also that authentication of message exchanges between the CPE
and the Synchronization Server SHOULD NOT use the external IP address
of the CPE to index the appropriate keys. As detailed in Section 9,
the IP addresses of the Synchronization Server and the Hidden Primary
are subject to change, for example while the network is being
renumbered. This means that the necessary keys to authenticate
transaction SHOULD NOT be indexed using the IP address, and SHOULD be
resilient to IP address changes.
5.3. CPE Security Policies
This section details security policies related to the Hidden Primary
/ Secondary synchronization.
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The Hidden Primary, as described in this document SHOULD drop any
queries from the home network. This could be implemented via port
binding and/or firewall rules. The precise mechanism deployed is out
of scope of this document.
The Hidden Primary SHOULD drop any DNS queries arriving on the WAN
interface that are not issued from the Synchronization Server.
The Hidden Primary SHOULD drop any outgoing packets other than DNS
NOTIFY query, SOA response, IXFR response or AXFR responses.
The Hidden Primary SHOULD drop any incoming packets other than DNS
NOTIFY response, SOA query, IXFR query or AXFR query.
The Hidden Primary SHOULD drop any non protected IXFR or AXFR
exchange,depending on how the synchronization is secured.
6. DNSSEC compliant Homenet Architecture
[RFC7368] in Section 3.7.3 recommends DNSSEC to be deployed on both
the authoritative server and the resolver. The resolver side is out
of scope of this document, and only the authoritative part of the
server is considered.
Deploying DNSSEC requires signing the zone and configuring a secure
delegation. As described in Section 4.1, signing can be performed
either by the CPE or by the Outsourcing Infrastructure. Section 6.1
details the implications of these two alternatives. Similarly, the
secure delegation can be performed by the CPE or by the Outsourcing
Infrastructure. Section 6.2 discusses these two alternatives.
6.1. Zone Signing
This section discusses the pros and cons when zone signing is
performed by the CPE or by the Outsourcing Infrastructure. It is
RECOMMENDED that the CPE signs the zone unless there is a strong
argument against this, such as a CPE that is not capable of signing
the zone. In that case zone signing MAY be performed by the
Outsourcing Infrastructure on behalf of the CPE.
Reasons for signing the zone by the CPE are:
- 1: Keeping the Homenet Zone and the Public Homenet Zone equal to
securely optimize DNS resolution. As the Public Zone is signed
with DNSSEC, RRsets are authenticated, and thus DNS responses
can be validated even though they are not provided by the
authoritative server. This provides the CPE the ability to
respond on behalf of the Public Authoritative Server(s). This
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could be useful for example if, in the future, the CPE
announces to the home network that the CPE can act as a local
authoritative primary or equivalent for the Homenet Zone.
Currently the CPE is not expected to receive authoritative DNS
queries, as its IP address is not mentioned in the Public
Homenet Zone. On the other hand most CPEs host a resolving
function, and could be configured to perform a local lookup to
the Homenet Zone instead of initiating a DNS exchange with the
Public Authoritative Server(s). Note that outsourcing the zone
signing operation means that all DNSSEC queries SHOULD be
cached to perform a local lookup, otherwise a resolution with
the Public Authoritative Server(s) would be performed.
- 2: Keeping the Homenet Zone and the Public Homenet Zone equal to
securely address the connectivity disruption independence
detailed in [RFC7368] section 4.4.1 and 3.7.5. As local
lookups are possible in case of network disruption,
communications within the home network can still rely on the
DNSSEC service. Note that outsourcing the zone signing
operation does not address connectivity disruption independence
with DNSSEC. Instead local lookup would provide DNS as opposed
to DNSSEC responses provided by the Public Authoritative
Server(s).
- 3: Keeping the Homenet Zone and the Public Homenet Zone equal to
guarantee coherence between DNS responses. Using a unique zone
is one way to guarantee uniqueness of the responses among
servers and places. Issues generated by different views are
discussed in more details in Section 7.
- 2: Privacy and Integrity of the DNSSEC Homenet Zone are better
guaranteed. When the Zone is signed by the CPE, it makes
modification of the DNS data -- for example for flow
redirection -- impossible. As a result, signing the Homenet
Zone by the CPE provides better protection for end user
privacy.
Reasons for signing the zone by the Outsourcing Infrastructure are:
- 1: The CPE may not be capable of signing the zone, most likely
because its firmware does not support this function. However
this reason is expected to become less and less valid over
time.
- 2: Outsourcing DNSSEC management operations. Management
operations involve key roll-over, which can be performed
automatically by the CPE and transparently for the end user.
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Avoiding DNSSEC management is mostly motivated by bad software
implementations.
- 3: Reducing the impact of CPE replacement on the Public Homenet
Zone. Unless the CPE private keys can be extracted and stored
off-device, CPE hardware replacement will result in an
emergency key roll-over. This can be mitigated by using
relatively small TTLs.
- 4: Reducing configuration impact on the end user. Unless there
are zero configuration mechanisms in place to provide
credentials between the new CPE and the Synchronization Server,
authentication associations between the CPE and the
Synchronization Server would need to be re-configured. As CPE
replacement is not expected to happen regularly, end users may
not be at ease with such configuration settings. However,
mechanisms as described in
[I-D.ietf-homenet-naming-architecture-dhc-options] use DHCP
Options to outsource the configuration and avoid this issue.
- 5: The Outsourcing Infrastructure is more likely to handle private
keys more securely than the CPE. However, having all private
keys in one place may also nullify that benefit.
6.2. Secure Delegation
Secure delegation is achieved only if the DS RRset is properly set in
the parent zone. Secure delegation can be performed by the CPE or
the Outsourcing Infrastructures (that is the Synchronization Server
or the Public Authoritative Server(s)).
The DS RRset can be updated manually with nsupdate for example. This
requires the CPE or the Outsourcing Infrastructure to be
authenticated by the DNS server hosting the parent of the Public
Homenet Zone. Such a trust channel between the CPE and the parent
DNS server may be hard to maintain with CPEs, and thus may be easier
to establish with the Outsourcing Infrastructure. In fact, the
Public Authoritative Server(s) may use Automating DNSSEC Delegation
Trust Maintenance [RFC7344].
7. Handling Different Views
The Homenet Zone provides information about the home network. Some
users may be tempted to have provide responses dependent on the
origin of the DNS query. More specifically, some users may be
tempted to provide a different view for DNS queries originating from
the home network and for DNS queries coming from the Internet. Each
view could then be associated with a dedicated Homenet Zone. Note
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that this document does not specify how DNS queries originating from
the home network are addressed to the Homenet Zone. This could be
done via hosting the DNS resolver on the CPE for example.
This section is not normative. Section 7.1 details why some nodes
may only be reachable from the home network and not from the global
Internet. Section 7.2 briefly describes the consequences of having
distinct views such as a "home network view" and an "Internet view".
Finally, Section 7.3 provides guidance on how to resolve names that
are only significant in the home network, without creating different
views.
7.1. Misleading Reasons for Local Scope DNS Zone
The motivation for supporting different views is to provide different
answers dependent on the origin of the DNS query, for reasons such
as:
- 1: An end user may want to have services not published on the
Internet. Services like the CPE administration interface that
provides the GUI to administer your CPE might not seem
advisable to publish on the Internet. Similarly, services like
the mapper that registers the devices of your home network may
also not be desirable to be published on the Internet. In both
cases, these services should only be known or used by the
network administrator. To restrict the access of such
services, the home network administrator may choose to publish
these pieces of information only within the home network, where
it might be assumed that the users are more trusted than on the
Internet. Even though this assumption may not be valid, at
least this may reduce the surface of any attack.
- 2: Services within the home network may be reachable using non
global IP addresses. IPv4 and NAT may be one reason. On the
other hand IPv6 may favor link-local or site-local IP
addresses. These IP addresses are not significant outside the
boundaries of the home network. As a result, they MAY be
published in the home network view, and SHOULD NOT be published
in the Public Homenet Zone.
7.2. Consequences
Enabling different views leads to a non-coherent naming system.
Depending on where resolution is performed, some services will not be
available. This may be especially inconvenient with devices with
multiple interfaces that are attached both to the Internet via a
3G/4G interface and to the home network via a WLAN interface.
Devices may also cache the results of name resolution, and these
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cached entries may no longer be valid if a mobile device moves
between a homenet connection and an internet connection e.g. a device
temporarily loses wifi signal and switches to 3G.
Regarding local-scope IP addresses, such devices may end up with poor
connectivity. Suppose, for example, that DNS resolution is performed
via the WLAN interface attached to the CPE, and the response provides
local-scope IP addresses, but the communication is initiated on the
3G/4G interface. Communications with local-scope addresses will be
unreachable on the Internet, thus aborting the communication. The
same situation occurs if a device is flip / flopping between various
WLAN networks.
Regarding DNSSEC, if the CPE does not sign the Homenet Zone and
outsources the signing process, the two views are different, because
one is protected with DNSSEC whereas the other is not. Devices with
multiple interfaces will have difficulty securing the naming
resolution, as responses originating from the home network may not be
signed.
For devices with all its interfaces attached to a single
administrative domain, that is to say the home network, or the
Internet. Incoherence between DNS responses may still also occur if
the device is able to perform DNS resolutions both using the DNS
resolving server of the home network, or one of the ISP. DNS
resolution performed via the CPE or the ISP resolver may be different
than those performed over the Internet.
7.3. Guidance and Recommendations
As documented in Section 7.2, it is RECOMMENDED to avoid different
views. If network administrators choose to implement multiple views,
impacts on devices' resolution SHOULD be evaluated.
As a consequence, the Homenet Zone is expected to be an exact copy of
the Public Homenet Zone. As a result, services that are not expected
to be published on the Internet SHOULD NOT be part of the Homenet
Zone, local-scope addresses SHOULD NOT be part of the Homenet Zone,
and when possible, the CPE SHOULD sign the Homenet Zone.
The Homenet Zone is expected to host public information only. It is
not the scope of the DNS service to define local home network
boundaries. Instead, local scope information is expected to be
provided to the home network using local scope naming services. mDNS
[RFC6762] DNS-SD [RFC6763] are two examples of these services.
Currently mDNS is limited to a single link network. However, future
protocols are expected to leverage this constraint as pointed out in
[I-D.ietf-dnssd-requirements].
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8. Homenet Reverse Zone
This section is focused on the Homenet Reverse Zone.
Firstly, all considerations for the Homenet Zone apply to the Homenet
Reverse Zone. The main difference between the Homenet Reverse Zone
and the Homenet Zone is that the parent zone of the Homenet Reverse
Zone is most likely managed by the ISP. As the ISP also provides the
IP prefix to the CPE, it may be able to authenticate the CPE using
mechanisms outside the scope of this document e.g. the physical
attachment point to the ISP network. If the Reverse Synchronization
Server is managed by the ISP, credentials to authenticate the CPE for
the zone synchronization may be set automatically and transparently
to the end user. [I-D.ietf-homenet-naming-architecture-dhc-options]
describes how automatic configuration may be performed.
With IPv6, the domain space for IP addresses is so large that reverse
zone may be confronted with scalability issues. How the reverse zone
is generated is out of scope of this document.
[I-D.howard-dnsop-ip6rdns] provides guidance on how to address
scalability issues.
9. Renumbering
This section details how renumbering is handled by the Hidden Primary
server or the Synchronization Server. Both types of renumbering are
discussed i.e. "make-before-break" and "break-before-make".
In the make-before-break renumbering scenario, the new prefix is
advertised, the network is configured to prepare the transition to
the new prefix. During a period of time, the two prefixes old and
new coexist, before the old prefix is completely removed. In the
break-before-make renumbering scenario, the new prefix is advertised
making the old prefix obsolete.
Renumbering has been extensively described in [RFC4192] and analyzed
in [RFC7010] and the reader is expected to be familiar with them
before reading this section.
9.1. Hidden Primary
In a renumbering scenario, the Hidden Primary is informed it is being
renumbered. In most cases, this occurs because the whole home
network is being renumbered. As a result, the Homenet Zone will also
be updated. Although the new and old IP addresses may be stored in
the Homenet Zone, we recommend that only the newly reachable IP
addresses be published.
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To avoid reachability disruption, IP connectivity information
provided by the DNS SHOULD be coherent with the IP plane. In our
case, this means the old IP address SHOULD NOT be provided via the
DNS when it is not reachable anymore. Let for example TTL be the TTL
associated with a RRset of the Homenet Zone, it may be cached for TTL
seconds. Let T_NEW be the time the new IP address replaces the old
IP address in the Homenet Zone, and T_OLD_UNREACHABLE the time the
old IP is not reachable anymore. In the case of the make-before-
break, seamless reachability is provided as long as T_OLD_UNREACHABLE
- T_NEW > 2 * TTL. If this is not satisfied, then devices associated
with the old IP address in the home network may become unreachable
for 2 * TTL - (T_OLD_UNREACHABLE - T_NEW). In the case of a break-
before-make, T_OLD_UNREACHABLE = T_NEW, and the device may become
unreachable up to 2 * TTL.
Once the Homenet Zone file has been updated on the Hidden Primary,
the Hidden Primary needs to inform the Outsourcing Infrastructure
that the Homenet Zone has been updated and that the IP address to use
to retrieve the updated zone has also been updated. Both
notifications are performed using regular DNS exchanges. Mechanisms
to update an IP address provided by lower layers with protocols like
SCTP [RFC4960], MOBIKE [RFC4555] are not considered in this document.
The Hidden Primary SHOULD inform the Synchronization Server that the
Homenet Zone has been updated by sending a NOTIFY payload with the
new IP address. In addition, this NOTIFY payload SHOULD be
authenticated using SIG(0) or TSIG. When the Synchronization Server
receives the NOTIFY payload, it MUST authenticate it. Note that the
cryptographic key used for the authentication SHOULD be indexed by
the Registered Homenet Domain contained in the NOTIFY payload as well
as the RRSIG. In other words, the IP address SHOULD NOT be used as
an index. If authentication succeeds, the Synchronization Server
MUST also notice the IP address has been modified and perform a
reachability check before updating its primary configuration. The
routability check MAY performed by sending a SOA request to the
Hidden Primary using the source IP address of the NOTIFY. This
exchange is also secured, and if an authenticated response is
received from the Hidden Primary with the new IP address, the
Synchronization Server SHOULD update its configuration file and
retrieve the Homenet Zone using an AXFR or a IXFR exchange.
Note that the primary reason for providing the IP address is that the
Hidden Primary is not publicly announced in the DNS. If the Hidden
Primary were publicly announced in the DNS, then the IP address
update could have been performed using the DNS as described in
Section 9.2.
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9.2. Synchronization Server
Renumbering of the Synchronization Server results in the
Synchronization Server changing its IP address. The Synchronization
Server is a secondary, so its renumbering does not impact the Homenet
Zone. In fact, exchanges to the Synchronization Server are
restricted to the Homenet Zone synchronization. In our case, the
Hidden Primary MUST be able to send NOTIFY payloads to the
Synchronization Server.
If the Synchronization Server is configured in the Hidden Primary
configuration file using a FQDN, then the update of the IP address is
performed by DNS. More specifically, before sending the NOTIFY, the
Hidden Primary performs a DNS resolution to retrieve the IP address
of the secondary.
As described in Section 9.1, the Synchronization Server DNS
information SHOULD be coherent with the IP plane. Let TTL be the TTL
associated with the Synchronization Server FQDN, T_NEW the time the
new IP address replaces the old one and T_OLD_UNREACHABLE the time
the Synchronization Server is not reachable anymore with its old IP
address. Seamless reachability is provided as long as
T_OLD_UNREACHABLE - T_NEW > 2 * TTL. If this condition is not met,
the Synchronization Server may be unreachable during 2 * TTL -
(T_OLD_UNREACHABLE - T_NEW). In the case of a break-before-make,
T_OLD_UNREACHABLE = T_NEW, and it may become unreachable up to 2 *
TTL.
Some DNS infrastructure uses the IP address to designate the
secondary, in which case, other mechanisms must be found. The reason
for using IP addresses instead of names is generally to reach an
internal interface that is not designated by a FQDN, and to avoid
potential bootstrap problems. Such scenarios are considered as out
of scope in the case of home networks.
10. Privacy Considerations
Outsourcing the DNS Authoritative service from the CPE to a third
party raises a few privacy related concerns.
The Homenet Zone contains a full description of the services hosted
in the network. These services may not be expected to be publicly
shared although their names remain accessible through the Internet.
Even though DNS makes information public, the DNS does not expect to
make the complete list of services public. In fact, making
information public still requires the key (or FQDN) of each service
to be known by the resolver in order to retrieve information about
the services. More specifically, making mywebsite.example.com public
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in the DNS, is not sufficient to make resolvers aware of the
existence web site. However, an attacker may walk the reverse DNS
zone, or use other reconnaissance techniques to learn this
information as described in [I-D.ietf-opsec-ipv6-host-scanning].
In order to prevent the complete Homenet Zone being published on the
Internet, AXFR queries SHOULD be blocked on the Public Authoritative
Server(s). Similarly, to avoid zone-walking NSEC3 [RFC5155] SHOULD
be preferred over NSEC [RFC4034].
When the Homenet Zone is outsourced, the end user should be aware
that it provides a complete description of the services available on
the home network. More specifically, names usually provides a clear
indication of the service and possibly even the device type, and as
the Homenet Zone contains the IP addresses associated with the
service, they also limit the scope of the scan space.
In addition to the Homenet Zone, the third party can also monitor the
traffic associated with the Homenet Zone. This traffic may provide
an indication of the services an end user accesses, plus how and when
they use these services. Although, caching may obfuscate this
information inside the home network, it is likely that outside your
home network this information will not be cached.
11. Security Considerations
The Homenet Naming Architecture described in this document solves
exposing the CPE's DNS service as a DoS attack vector.
11.1. Names are less secure than IP addresses
This document describes how an end user can make their services and
devices from his home network reachable on the Internet by using
names rather than IP addresses. This exposes the home network to
attackers, since names are expected to include less entropy than IP
addresses. In fact, with IP addresses, the Interface Identifier is
64 bits long leading to up to 2^64 possibilities for a given
subnetwork. This is not to mention that the subnet prefix is also of
64 bits long, thus providing up to 2^64 possibilities. On the other
hand, names used either for the home network domain or for the
devices present less entropy (livebox, router, printer, nicolas,
jennifer, ...) and thus potentially exposes the devices to dictionary
attacks.
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11.2. Names are less volatile than IP addresses
IP addresses may be used to locate a device, a host or a service.
However, home networks are not expected to be assigned a time
invariant prefix by ISPs. As a result, observing IP addresses only
provides some ephemeral information about who is accessing the
service. On the other hand, names are not expected to be as volatile
as IP addresses. As a result, logging names over time may be more
valuable than logging IP addresses, especially to profile an end
user's characteristics.
PTR provides a way to bind an IP address to a name. In that sense,
responding to PTR DNS queries may affect the end user's privacy. For
that reason end users may choose not to respond to PTR DNS queries
and MAY instead return a NXDOMAIN response.
11.3. DNS Reflection Attacks
An attacker performs a reflection attack when it sends traffic to one
or more intermediary nodes (reflectors), that in turn send back
response traffic to the victim. Motivations for using an
intermediary node might be anonymity of the attacker, as well as
amplification of the traffic. Typically, when the intermediary node
is a DNSSEC server, the attacker sends a DNSSEC query and the victim
is likely to receive a DNSSEC response. This section analyzes how
the different components may be involved as a reflector in a
reflection attack. Section 11.3.1 considers the Hidden Primary,
Section 11.3.2 the Synchronization Server, and Section 11.3.3 the
Public Authoritative Server(s).
11.3.1. Reflection Attack involving the Hidden Primary
With the specified architecture, the Hidden Primary is only expected
to receive DNS queries of type SOA, AXFR or IXFR. This section
analyzes how these DNS queries may be used by an attacker to perform
a reflection attack.
DNS queries of type AXFR and IXFR use TCP and as such are less
subject to reflection attacks. This makes SOA queries the only
remaining practical vector of attacks for reflection attacks, based
on UDP.
SOA queries are not associated with a large amplification factor
compared to queries of type "ANY" or to query of non existing FQDNs.
This reduces the probability a DNS query of type SOA will be involved
in a DDoS attack.
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SOA queries are expected to follow a very specific pattern, which
makes rate limiting techniques an efficient way to limit such
attacks, and associated impact on the naming service of the home
network.
Motivations for such a flood might be a reflection attack, but could
also be a resource exhaustion attack performed against the Hidden
Primary. The Hidden Primary only expects to exchange traffic with
the Synchronization Server, that is its associated secondary. Even
though secondary servers may be renumbered as mentioned in Section 9,
the Hidden Primary is likely to perform a DNSSEC resolution and find
out the associated secondary's IP addresses in use. As a result, the
Hidden Primary is likely to limit the origin of its incoming traffic
based on the origin IP address.
With filtering rules based on IP address, SOA flooding attacks are
limited to forged packets with the IP address of the secondary
server. In other words, the only victims are the Hidden Primary
itself or the secondary. There is a need for the Hidden Primary to
limit that flood to limit the impact of the reflection attack on the
secondary, and to limit the resource needed to carry on the traffic
by the CPE hosting the Hidden Primary. On the other hand, mitigation
should be performed appropriately, so as to limit the impact on the
legitimate SOA sent by the secondary.
The main reason for the Synchronization Server sending a SOA query is
to update the SOA RRset after the TTL expires, to check the serial
number upon the receipt of a NOTIFY query from the Hidden Primary, or
to re-send the SOA request when the response has not been received.
When a flood of SOA queries is received by the Hidden Primary, the
Hidden Primary may assume it is involved in an attack.
There are few legitimate time slots when the secondary is expected to
send a SOA query. Suppose T_NOTIFY is the time a NOTIFY is sent by
the Hidden Primary, T_SOA the last time the SOA has been queried, TTL
the TTL associated to the SOA, and T_REFRESH the refresh time defined
in the SOA RRset. The specific time SOA queries are expected can be
for example T_NOTIFY, T_SOA + 2/3 TTL, T_SOA + TTL, T_SOA +
T_REFRESH., and. Outside a few minutes following these specific time
slots, the probability that the CPE discards a legitimate SOA query
is very low. Within these time slots, the probability the secondary
may have its legitimate query rejected is higher. If a legitimate
SOA is discarded, the secondary will re-send SOA query every "retry
time" second until "expire time" seconds occurs, where "retry time"
and "expire time" have been defined in the SOA.
As a result, it is RECOMMENDED to set rate limiting policies to
protect CPE resources. If a flood lasts more than the expired time
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defined by the SOA, it is RECOMMENDED to re-initiate a
synchronization between the Hidden Primary and the secondaries.
11.3.2. Reflection Attacks involving the Synchronization Server
The Synchronization Server acts as a secondary coupled with the
Hidden Primary. The secondary expects to receive NOTIFY query, SOA
responses, AXFR and IXFR responses from the Hidden Primary.
Sending a NOTIFY query to the secondary generates a NOTIFY response
as well as initiating an SOA query exchange from the secondary to the
Hidden Primary. As mentioned in [RFC1996], this is a known "benign
denial of service attack". As a result, the Synchronization Server
SHOULD enforce rate limiting on sending SOA queries and NOTIFY
responses to the Hidden Primary. Most likely, when the secondary is
flooded with valid and signed NOTIFY queries, it is under a replay
attack which is discussed in Section 11.5. The key thing here is
that the secondary is likely to be designed to be able to process
much more traffic than the Hidden Primary hosted on a CPE.
This paragraph details how the secondary may limit the NOTIFY
queries. Because the Hidden Primary may be renumbered, the secondary
SHOULD NOT perform permanent IP filtering based on IP addresses. In
addition, a given secondary may be shared among multiple Hidden
Primaries which make filtering rules based on IP harder to set. The
time at which a NOTIFY is sent by the Hidden Primary is not
predictable. However, a flood of NOTIFY messages may be easily
detected, as a NOTIFY originated from a given Homenet Zone is
expected to have a very limited number of unique source IP addresses,
even when renumbering is occurring. As a result, the secondary, MAY
rate limit incoming NOTIFY queries.
On the Hidden Primary side, it is recommended that the Hidden Primary
sends a NOTIFY as long as the zone has not been updated by the
secondary. Multiple SOA queries may indicate the secondary is under
attack.
11.3.3. Reflection Attacks involving the Public Authoritative Servers
Reflection attacks involving the Public Authoritative Server(s) are
similar to attacks on any Outsourcing Infrastructure. This is not
specific to the architecture described in this document, and thus are
considered as out of scope.
In fact, one motivation of the architecture described in this
document is to expose the Public Authoritative Server(s) to attacks
instead of the CPE, as it is believed that the Public Authoritative
Server(s) will be better able to defend itself.
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11.4. Flooding Attack
The purpose of flooding attacks is mostly resource exhaustion, where
the resource can be bandwidth, memory, or CPU for example.
One goal of the architecture described in this document is to limit
the surface of attack on the CPE. This is done by outsourcing the
DNS service to the Public Authoritative Server(s). By doing so, the
CPE limits its DNS interactions between the Hidden Primary and the
Synchronization Server. This limits the number of entities the CPE
interacts with as well as the scope of DNS exchanges - NOTIFY, SOA,
AXFR, IXFR.
The use of an authenticated channel with SIG(0) or TSIG between the
CPE and the Synchronization Server, enables detection of illegitimate
DNS queries, so appropriate action may be taken - like dropping the
queries. If signatures are validated, then most likely, the CPE is
under a replay attack, as detailed in Section 11.5
In order to limit the resource required for authentication, it is
recommended to use TSIG that uses symmetric cryptography over SIG(0)
that uses asymmetric cryptography.
11.5. Replay Attack
Replay attacks consist of an attacker either resending or delaying a
legitimate message that has been sent by an authorized user or
process. As the Hidden Primary and the Synchronization Server use an
authenticated channel, replay attacks are mostly expected to use
forged DNS queries in order to provide valid traffic.
From the perspective of an attacker, using a correctly authenticated
DNS query may not be detected as an attack and thus may generate a
response. Generating and sending a response consumes more resources
than either dropping the query by the defender, or generating the
query by the attacker, and thus could be used for resource exhaustion
attacks. In addition, as the authentication is performed at the DNS
layer, the source IP address could be impersonated in order to
perform a reflection attack.
Section 11.3 details how to mitigate reflection attacks and
Section 11.4 details how to mitigate resource exhaustion. Both
sections assume a context of DoS with a flood of DNS queries. This
section suggests a way to limit the attack surface of replay attacks.
As SIG(0) and TSIG use inception and expiration time, the time frame
for replay attack is limited. SIG(0) and TSIG recommends a fudge
value of 5 minutes. This value has been set as a compromise between
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possibly loose time synchronization between devices and the valid
lifetime of the message. As a result, better time synchronization
policies could reduce the time window of the attack.
12. IANA Considerations
This document has no actions for IANA.
13. Acknowledgment
The authors wish to thank Philippe Lemordant for its contributions on
the early versions of the draft; Ole Troan for pointing out issues
with the IPv6 routed home concept and placing the scope of this
document in a wider picture; Mark Townsley for encouragement and
injecting a healthy debate on the merits of the idea; Ulrik de Bie
for providing alternative solutions; Paul Mockapetris, Christian
Jacquenet, Francis Dupont and Ludovic Eschard for their remarks on
CPE and low power devices; Olafur Gudmundsson for clarifying DNSSEC
capabilities of small devices; Simon Kelley for its feedback as
dnsmasq implementer; Andrew Sullivan, Mark Andrew, Ted Lemon, Mikael
Abrahamson, Michael Richardson and Ray Bellis for their feedback on
handling different views as well as clarifying the impact of
outsourcing the zone signing operation outside the CPE; Mark Andrew
and Peter Koch for clarifying the renumbering.
14. References
14.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
August 1996.
[RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
Changes (DNS NOTIFY)", RFC 1996, August 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)",
RFC 2136, April 1997.
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[RFC2142] Crocker, D., "MAILBOX NAMES FOR COMMON SERVICES, ROLES AND
FUNCTIONS", RFC 2142, May 1997.
[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, March 1998.
[RFC2845] Vixie, P., Gudmundsson, O., Eastlake, D., and B.
Wellington, "Secret Key Transaction Authentication for DNS
(TSIG)", RFC 2845, May 2000.
[RFC2930] Eastlake, D., "Secret Key Establishment for DNS (TKEY
RR)", RFC 2930, September 2000.
[RFC2931] Eastlake, D., "DNS Request and Transaction Signatures (
SIG(0)s )", RFC 2931, September 2000.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, March 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol
(MOBIKE)", RFC 4555, June 2006.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC
4960, September 2007.
[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, March 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5936] Lewis, E. and A. Hoenes, "DNS Zone Transfer Protocol
(AXFR)", RFC 5936, June 2010.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
[RFC6644] Evans, D., Droms, R., and S. Jiang, "Rebind Capability in
DHCPv6 Reconfigure Messages", RFC 6644, July 2012.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
February 2013.
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[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, February 2013.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, October 2014.
14.2. Informational References
[I-D.howard-dnsop-ip6rdns]
Howard, L., "Reverse DNS in IPv6 for Internet Service
Providers", draft-howard-dnsop-ip6rdns-00 (work in
progress), June 2014.
[I-D.ietf-dnssd-requirements]
Lynn, K., Cheshire, S., Blanchet, M., and D. Migault,
"Requirements for Scalable DNS-SD/mDNS Extensions", draft-
ietf-dnssd-requirements-06 (work in progress), March 2015.
[I-D.ietf-homenet-naming-architecture-dhc-options]
Migault, D., Cloetens, W., Griffiths, C., and R. Weber,
"DHCP Options for Homenet Naming Architecture", draft-
ietf-homenet-naming-architecture-dhc-options-02 (work in
progress), May 2015.
[I-D.ietf-opsec-ipv6-host-scanning]
Gont, F. and T. Chown, "Network Reconnaissance in IPv6
Networks", draft-ietf-opsec-ipv6-host-scanning-07 (work in
progress), April 2015.
[RFC1033] Lottor, M., "Domain administrators operations guide", RFC
1033, November 1987.
[RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for
Renumbering an IPv6 Network without a Flag Day", RFC 4192,
September 2005.
[RFC7010] Liu, B., Jiang, S., Carpenter, B., Venaas, S., and W.
George, "IPv6 Site Renumbering Gap Analysis", RFC 7010,
September 2013.
[RFC7344] Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
DNSSEC Delegation Trust Maintenance", RFC 7344, September
2014.
[RFC7368] Chown, T., Arkko, J., Brandt, A., Troan, O., and J. Weil,
"IPv6 Home Networking Architecture Principles", RFC 7368,
October 2014.
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Appendix A. Document Change Log
[RFC Editor: This section is to be removed before publication]
-07:
Ray Hunter is added as a co-author.
-06:
Ray Hunter is added in acknowledgment.
Adding Renumbering section with comments from Dallas meeting
Replacing Master / Primary - Slave / Secondary
Security Consideration has been updated with Reflection attacks,
flooding attacks, and replay attacks.
-05:
*Clarifying on handling different views:
- 1: How the CPE may be involved in the resolution and responds
without necessarily requesting the Public Authoritative
Server(s) (and eventually the Hidden Primary)
- 2: How to handle local scope resolution that is link-local, site-
local and NAT IP addresses as well as Private domain names that
the administrator does not want to publish outside the home
network.
Adding a Privacy Considerations Section
Clarification on pro/cons outsourcing zone-signing
Documenting how to handle reverse zones
Adding reference to RFC 2308
-04:
*Clarifications on zone signing
*Rewording
*Adding section on different views
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*architecture clarifications
-03:
*Simon's comments taken into consideration
*Adding SOA, PTR considerations
*Removing DNSSEC performance paragraphs on low power devices
*Adding SIG(0) as a mechanism for authenticating the servers
*Goals clarification: the architecture described in the document 1)
does not describe new protocols, and 2) can be adapted to specific
cases for advance users.
-02:
*remove interfaces: "Public Authoritative Server Naming Interface" is
replaced by "Public Authoritative Server(s)y(ies)". "Public
Authoritative Server Management Interface" is replaced by
"Synchronization Server".
-01.3:
*remove the authoritative / resolver services of the CPE.
Implementation dependent
*remove interactions with mdns and dhcp. Implementation dependent.
*remove considerations on low powered devices
*remove position toward homenet arch
*remove problem statement section
-01.2:
* add a CPE description to show that the architecture can fit CPEs
* specification of the architecture for very low powered devices.
* integrate mDNS and DHCP interactions with the Homenet Naming
Architecture.
* Restructuring the draft. 1) We start from the homenet-arch draft to
derive a Naming Architecture, then 2) we show why CPE need mechanisms
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that do not expose them to the Internet, 3) we describe the
mechanisms.
* I remove the terminology and expose it in the figures A and B.
* remove the Front End Homenet Naming Architecture to Homenet Naming
-01:
* Added C. Griffiths as co-author.
* Updated section 5.4 and other sections of draft to update section
on Hidden Primary / Slave functions with CPE as Hidden Primary/
Homenet Server.
* For next version, address functions of MDNS within Homenet Lan and
publishing details northbound via Hidden Primary.
-00: First version published.
Authors' Addresses
Daniel Migault
Ericsson
8400 Boulevard Decarie
Montreal, QC H4P 2N2
Canada
Phone: +1 (514) 452-2160
Email: daniel.migault@ericsson.com
Ralf Weber
Nominum
2000 Seaport Blvd #400
Redwood City, CA 94063
US
Email: ralf.weber@nominum.com
URI: http://www.nominum.com
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Ray Hunter
Globis Consulting BV
Weegschaalstraat 3
5632CW Eindhoven
The Netherlands
Email: v6ops@globis.net
URI: http://www.globis.net
Chris Griffiths
Email: cgriffiths@gmail.com
Wouter Cloetens
SoftAtHome
vaartdijk 3 701
3018 Wijgmaal
Belgium
Email: wouter.cloetens@softathome.com
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