| HOMENET | D. Migault (Ed) |
| Internet-Draft | Orange |
| Intended status: Standards Track | W. Cloetens |
| Expires: March 23, 2015 | SoftAtHome |
| C. Griffiths | |
| Dyn | |
| R. Weber | |
| Nominum | |
| September 19, 2014 |
Outsourcing Home Network Authoritative Naming Service
draft-ietf-homenet-front-end-naming-delegation-00.txt
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.
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This Internet-Draft will expire on March 23, 2015.
Copyright (c) 2014 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.
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].
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, [I-D.ietf-homenet-arch] 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 two alternatives. Section 7 discusses the impact of multiple views and Section 8 discusses the case of the reverse zone.
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.
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. The content of the DNS(SEC) Homenet Zone is out of the scope of this document. The CPE may host and involve multiple services like a web GUI, DHCP [RFC6644] or mDNS [RFC6762]. These services may coexist and may be used to populate the DNS Homenet Zone. This document assumes the DNS(SEC) Homenet Zone has been populated with domain names that are intended to be publicly published and that are publicly reachable. More specifically, names associated to services or devices that are not expected to be reachable from outside the home network or names bound to non globally reachable IP addresses MUST NOT be part of the DNS(SEC) Homenet Zone.
Once the DNS(SEC) Homenet Zone has been built, the CPE does not host the authoritative naming service for it, but instead outsources it to the Public Authoritative Servers. The Public Authoritative Servers take the DNS(SEC) Homenet as an input and publishes the DNS(SEC) Public Zone. In fact the DNS(SEC) Homenet Zone and the DNS(SEC) Public Zone have different names as they may be different. If the CPE does not sign the DNS Homenet Zone, for example, the Public Authoritative Servers may instead sign it on behalf of the CPE. Figure 1 provides a more detailed description of the Public Authoritative Servers, but overall, it is expected that the CPE provides the DNS(SEC) Homenet Zone, the DNS(SEC) Public Zone is derived from the DNS(SEC) Homenet Zone and published on the Internet.
As a result, DNS(SEC) queries from the DNS(SEC) Resolvers on the Internet are answered by the Public Authoritative Server and do not reach the CPE. Figure 1 illustrates the case of the resolution of node1.example.com.
home network +-------------------+ Internet
| |
| CPE |
| | +----------------------+
+-------+ |+-----------------+| | Public Authoritative |
| | || DNS(SEC) Homenet|| | Servers |
| node1 | || Zone || |+--------------------+|
| | || || ||DNS(SEC) Public Zone||
+-------+ || Homenet Domain ||=========|| ||
|| Name || ^ || (example.com) ||
node1.\ || (example.com) || | |+--------------------+|
example.com |+-----------------+| | +----------------------+
+-------------------+ | ^ |
Synchronization | |
| |
DNSSEC resolution for node1.example.com | v
+----------------------+
| |
| DNSSEC Resolver |
| |
+----------------------+
Figure 1: Homenet Naming Architecture Description
The Public Authoritative Servers are described in Figure 2. The Public Authoritative Name Server Set receives the DNS(SEC) Homenet Zone as an input. The received zone may be transformed to output the DNS(SEC) Public Zone. Various operations may be performed here, however the one this document considers here is zone signing when the CPE outsources this operation. 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
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.
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]. 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.
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:
Setting the DNS(SEC) Homenet Zone requires the following information.
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.
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.
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:
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 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 [RFC5996] 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.
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.
[I-D.ietf-homenet-arch] 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.
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:
Reasons for signing the zone by the Public Authoritative Servers are:
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, [I-D.ietf-dnsop-delegation-trust-maintainance] may mitigate such issues.
The issue raised by handling different views of the DNS Homenet Zone or a DNS Homenet Zone that differs from the Public Zone is that a given DNS query may lead to different responses. The responses may be different values for the queried RRsets or different RCODE or different RRsets types in the responses for DNS/DNSSEC responses.
The document does not recommend the CPE manages different views, since devices may be connected to different networks at the same time or may flip / flop from one network to the other.
Most of the description considered the DNS Homenet Zone as the non-Reverse Zone. This section is focused on the Reverse Zone.
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.mglt-homenet-naming-architecture-dhc-options] describes how automatic configuration may be performed.
The Homenet Naming Architecture described in this document solves exposing the CPE's DNS service as a DoS attack vector.
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.
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.
This document has no actions for IANA.
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.
| [I-D.ietf-dnsop-delegation-trust-maintainance] | Kumari, W., Gudmundsson, O. and G. Barwood, "Automating DNSSEC Delegation Trust Maintenance", Internet-Draft draft-ietf-dnsop-delegation-trust-maintainance-14, June 2014. |
| [I-D.ietf-homenet-arch] | Chown, T., Arkko, J., Brandt, A., Troan, O. and J. Weil, "IPv6 Home Networking Architecture Principles", Internet-Draft draft-ietf-homenet-arch-16, June 2014. |
| [I-D.mglt-homenet-naming-architecture-dhc-options] | Migault, D., Cloetens, W., Griffiths, C. and R. Weber, "DHCP Options for Homenet Naming Architecture", Internet-Draft draft-mglt-homenet-naming-architecture-dhc-options-02, July 2014. |
| [RFC1033] | Lottor, M., "Domain administrators operations guide", RFC 1033, November 1987. |
[RFC Editor: This section is to be removed before publication]
-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
-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.