Homenet Naming and Service Discovery Architecture
draft-lemon-homenet-naming-architecture-00
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draft-lemon-homenet-naming-architecture-00
Network Working Group T. Lemon
Internet-Draft Nominum, Inc.
Intended status: Informational March 21, 2016
Expires: September 22, 2016
Homenet Naming and Service Discovery Architecture
draft-lemon-homenet-naming-architecture-00
Abstract
This document recommends a naming and service discovery resolution
architecture for homenets. This architecture covers the publication
and resolution of names of hosts on the homenet both within the
homenet and on the public internet, and the use of such names for
offering and discovering services that exist on the homenet both
within the homenet and on the public internet. Security and privacy
implications and techniques for automatically and administratively
setting security and privacy policies for such names are also
described.
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 22, 2016.
Copyright Notice
Copyright (c) 2016 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
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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. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Existing solutions . . . . . . . . . . . . . . . . . . . 4
2. Homenet Naming Database . . . . . . . . . . . . . . . . . . . 5
2.1. Global Name . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Local namespaces . . . . . . . . . . . . . . . . . . . . 7
2.3. Public namespaces . . . . . . . . . . . . . . . . . . . . 7
2.4. Adding Names . . . . . . . . . . . . . . . . . . . . . . 8
2.4.1. mDNS Snooping . . . . . . . . . . . . . . . . . . . . 8
2.4.2. DHCP DNS Update (stateful or stateless) . . . . . . . 9
2.4.3. DNS Update . . . . . . . . . . . . . . . . . . . . . 9
2.5. Removing Names . . . . . . . . . . . . . . . . . . . . . 9
2.6. Name Collisions . . . . . . . . . . . . . . . . . . . . . 10
2.7. Recovery from loss . . . . . . . . . . . . . . . . . . . 10
2.8. Persistence . . . . . . . . . . . . . . . . . . . . . . . 10
2.9. Well-known names . . . . . . . . . . . . . . . . . . . . 11
3. Name Resolution . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. Configuring Resolvers . . . . . . . . . . . . . . . . . . 11
3.2. Configuring Service Discovery . . . . . . . . . . . . . . 12
3.3. Resolution of local namespaces . . . . . . . . . . . . . 12
3.4. Local and Public Zones . . . . . . . . . . . . . . . . . 12
3.5. Legacy support . . . . . . . . . . . . . . . . . . . . . 13
3.6. DNSSEC Validation . . . . . . . . . . . . . . . . . . . . 13
3.7. Support for Multiple Provisioning Domains . . . . . . . . 14
3.8. Using the Local Namespace While Away From Home . . . . . 14
4. Publishing the Public Namespace . . . . . . . . . . . . . . . 15
4.1. Acquiring the Global Name . . . . . . . . . . . . . . . . 15
4.2. Hidden Primary/Public Secondaries . . . . . . . . . . . . 16
4.3. DNSSEC security . . . . . . . . . . . . . . . . . . . . . 17
4.4. PKI security . . . . . . . . . . . . . . . . . . . . . . 17
4.5. Renumbering . . . . . . . . . . . . . . . . . . . . . . . 18
4.6. ULA . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5. Management . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1. End-user management . . . . . . . . . . . . . . . . . . . 18
5.2. Central management . . . . . . . . . . . . . . . . . . . 19
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 19
9. Normative References . . . . . . . . . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
Associating domain names with hosts on the Internet is a key factor
in enabling communication with hosts, particularly service discovery.
In order to provide name service, several provisioning mechanisms
must be available:
o Provisioning of a namespace in which names can be published and
services advertised
o Associating a name within that namespace to the set of IP
addresses on which a host is reachable
o Advertising services available on the local network and
associating those services with names published in the namespace
o Distribution of names published in that namespace to servers that
can be queried in order to resolve names
o Correct advertisement of name servers that can be queried in order
to resolve names
o Timely removal of published names when they are no longer in use
Homenet adds the following considerations:
1. Some names may be published in a broader scope than others. For
example, it may be desirable to advertise some homenet services
to users who are not connected to the homenet. However, it is
unlikely that all services published on the home network would be
appropriate to publish outside of the home network. In many
cases, no services will be appropriate to publish outside of the
network, but the ability to do so is required.
2. Users cannot be assumed to be skilled or knowledgeable in name
service operation, or even to have any sort of mental model of
how these functions work. With the possible exception of policy
decisions, all of the operations mentioned here must reliably
function automatically, without any user intervention or
debugging. Even to the extent that users may provide input on
policy, such as whether a service should or should not be
advertised outside of the home, the user must be able to safely
provide such input without having a correct mental model of how
naming and service discovery work, and without being able to
reason about security in a nuanced way.
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3. Because user intervention cannot be required, naming conflicts
must be resolved automatically, and, to the extent possible,
transparently.
4. Where services are advertised both on and off the home network,
differences in naming conventions that may vary depending on the
user's location must likewise be transparent to the end user.
5. Hosts that do not implement any homenet-specific capabilities
must still be able to discover and access services on the
homenet, to the extent possible.
6. Homenet explicitly supports multihoming--connecting to more than
one Internet Service Provider--and therefore support for multiple
provisioning domains [6] is required to deal with situations
where the DNS may give a different answer depending on whether
caching resolvers at one ISP or another are queried.
7. Multihomed homenets may treat all service provider links as
equivalent, or may treat some links as primary and some as
backup, either because of differing transit costs or differing
performance. Services advertised off-network may therefore be
advertised for some links and not others.
In addition to these considerations, there may be a need to provide
for secure communication between end users and the user interface of
the home network, as well as to provide secure name validation (e.g.,
DNSSEC). Secure communications require that the entity being secured
have a name that is unique and can be cryptographically authenticated
within the scope of use of all devices that must communicate with
that entity. Because it is very likely that devices connecting to
one homenet will be sufficiently portable that they may connect to
many homenets, the scope of use must be assumed to be global.
Therefore, each homenet must have a globally unique name.
1.1. Existing solutions
Previous attempts to automate naming and service discovery in the
context of a home network are able to function with varying degrees
of success depending on the topology of the home network. For
example, Multicast DNS [4] can provide naming and service discovery
[5], but only within a single multicast domain.
The Domain Name System provides a hierarchical namespace [1], a
mechanism for querying name servers to resolve names [2], a mechanism
for updating namespaces by adding and removing names [3], and a
mechanism for discovering services [5]. Unfortunately, DNS provides
no mechanism for automatically provisioning new namespaces, and
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secure updates to namespaces require pre-shared keys, which won't
work for an unmanaged network. DHCP can be used to populate names in
a DNS namespace; however at present DHCP cannot provision service
discovery information.
Hybrid Multicast DNS [7] proposes a mechanism for solving the single-
multicast-domain problem. However, it has serious shortcomings as a
solution to the Homenet naming problem. The most obvious shortcoming
is that it requires that every multicast domain have a separate name.
This then requires that the homenet generate names for every
multicast domain, and requires that the end user have a mental model
of the topology of the network in order to guess on which link a
given service may appear.
2. Homenet Naming Database
In order to resolve names, there must be a place where names are
stored. There are two ways to go about this: either names are stored
on the devices that own them, or they are stored in the network.
This isn't a clean dichotomy, however: it's possible for the source
of truth about a name to be owned by the device, while the resolution
of the name is owned by a service separate from the device.
Additionally, if names are owned by devices, conflicts can arise,
since two devices might present the same name by default or by
accident. Further, devices can be attached to more than one network,
in which case we want the same name to identify them on both
networks. Additionally, although homenets are self-configuring, user
customization is permitted and useful.
In order to achieve this, the Homenet Naming Database (HNDB) provides
a persistent central store into which names can be registered
2.1. Global Name
Every homenet must be able to have a name in the global DNS hierarchy
which serves as the root of the zone in which the homenet publishes
its public namespaces. Homenets that do not yet have a name in the
global namespace use the homenet special-use TLD [TBD1] as their
"global name" until they are configured with a global name.
[It's tempting to have the homenet generate a UUID-like name that can
be used as a global name, but we really don't want that, because it
will be quite ugly to the user, difficult to remember, and therefore
not protective against the kinds of mistakes we'd want such a name to
protect against. It's better as a security UI to have the user see a
name that is the same on all homenets. This will allow the user to
fairly easily notice that they see the same name on every homenet.
To present a name that isn't really unique and isn't easily
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identified as anything other than "random gibberish," may lull the
end user into a sense that they are talking to the right homenet when
they see the random gibberish, without realizing that actually it's
different gibberish and they aren't talking to their own homenet.]
A homenet's global name can be a name that the homenet user has
registered on their own in the DNS using a public DNS registrar.
However, this is not required and, indeed, presents some operational
challenges. It can also be a name under a domain owned by one of the
user's service providers, or managed by some service provider that
specifically provides homenet naming services.
For most end-users, the second or third options will be preferable.
It will allow them to choose an easily-remembered homenet domain name
under an easily-remembered service provider subdomain, and will not
require them to maintain a DNS registration.
[This doesn't belong in the arch document, at least not in this part,
but I'm writing it down because I think we should discuss it and
figure out exactly what we should recommend, and I do believe we
should recommend something here and not just hope for the best. I am
also hoping to stave off frivolous, privacy-harming patents by
publishing this now:]
Providers of either of these types of homenet naming service should
offer a selection of different provider TLDs rather than a flat
namespace, so as to avoid the exampleuser1997 problem. So for
example rather than having a single namespace "isp.example.com", the
provider should have a series of subdomains, like
"grapefruit.example.com", "warrior.example.com", "koala.example.com",
"rocket.example.com", and so forth.
Some small number of such subdomains should be presented to the user
when registering. Subdomains with more than perhaps 50,000 homenets
registered in them should never be presented for registration, to
avoid chosen name collisions. If the user is unable to find a
namespace they like, it may be beneficial to allow the user to cycle
through a larger set of namespaces. The user should wind up with a
global name like "hamburger.warrior.example.com".
This specification may seem frivolous or overly-prescriptive. The
reason for being this specific is that it is important for the user
to be able to quickly choose a memorable name that doesn't contain
personal identifying information. Getting this user interface right
has significant implications for the user's privacy and security.
Any user interface that meets the criterion that the user can quickly
choose a memorable name that doesn't contain personal information
will address this requirement. The user should be specifically told
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not to use personal information like birthdays or names of friends or
pets, and should be encouraged to write the chosen name down until
they have it memorized.
2.2. Local namespaces
Every homenet has two non-hierarchical local namespaces, one for
associating DNS RRs with names, and one for associating DNS RRs with
IP addresses. These namespaces are key-data stores, where for the
name mapping the primary key is a single DNS label, and for the IP
address mapping the primary key is an IP address. The secondary key
is an RRtype, so that there can be more than one RRset per IP
address, and each data element is an RRset of the corresponding
RRtype.
Each RRset in each local namespace is marked with a flag that
indicates whether it is to be public or private. Each RRset is also
marked with a flag that indicates whether its availability is
critical or best-effort. This flag only has meaning if the RRset is
marked public.
Each RR that contains a name (e.g, a CNAME or SRV record) either
contains a name in the local namespace or a global name. All global
names are references to external services, not to services on the
homenet. All local names are qualified with the homenet-specific
special-use TLD, [TBD1].
[Question: do we need RRset granularity for these flags?]
The local namespace is maintained as a distributed database with
copies on every homenet router. No copy is the master copy.
Although the local namespace is non-hierarchical, it is permissible
for it to contain RRtypes that contain delegations. However, from an
operational perspective is is most likely better for the local
namespace to be at the bottom of the delegation hierarchy, and so we
do not recommend the use of such delegations.
2.3. Public namespaces
Every homenet has two public namespaces. These are copies of the
private namespaces with four modifications:
1. Names with no public RRsets are not included in the public
namespace.
2. RRs that contain IP addresses in the homenet's ULA prefix are
omitted.
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3. By default, RRs that contain IPv4 addresses are omitted, because
IPv4 doesn't support renumbering. However, there should be a
whitelist of IPv4 addresses that may be published, so that if the
end user has static IPv4 addresses, those can be published.
4. If an RRset is marked best-effort rather than critical, RRs
containing IP addresses that match prefixes assigned by backup
links are omitted.
[Are there RRtypes or classes of DNSSD records that we want to always
omit?]
Because the public namespaces are copies of the private namespaces,
replication is not necessary: each homenet router automatically
produces public namespaces by deriving them from the private
namespaces using the above rules. The public namespaces can be
derived on demand, or maintained automatically as updates are made to
the private namespaces.
[Security/privacy considerations: It can be argued that public
namespaces provide a means for botnets to publish rendezvous
information. However, in fact this isn't really true because if
botnets did so, it would be very obvious, so would wind up being used
as a means of tracking and suppressing them. It's probably better to
encourage this mistake rather than trying to prevent it, since the
former benefits white hats, and the latter limits functionality.]
[Presumably we want it to be possible for devices that are meant to
be public servers to publish their names in the DNS, but how do we
automatically determine that a device is "meant" to be public? This
needs thought.]
2.4. Adding Names
Several mechanisms are available for updating the HNDB.
2.4.1. mDNS Snooping
Homenet snoops mDNS for device names. Homenet does not defend names.
If two devices with the same name appear on a link, mDNS handles
collision resolution. If two devices with the same name appear on
different links, homenet deterministically generates names for both
devices using the link-layer address of each device, plus the name
that device claimed. If a device that appears on two links is the
same device (presents the same link-layer address or DHCID) then it
is treated as a single device, with a single name. This whole
discussion probably belongs in a separate draft.
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2.4.2. DHCP DNS Update (stateful or stateless)
A and PTR records can be set up this way. Doesn't work (yet) for
service discovery. Should we write a draft, or just rely on:
2.4.3. DNS Update
DNS updates can be send to any resolver in the homenet to add names
to the local zone. If there is no conflict, the name is added;
otherwise the update is rejected.
[Really, what we ought to do is just allow devices to declare an ID
that is a public key, and then do DNS updates to the local service
zone signed with the corresponding private key. Devices would also
sign their mDNS claims with the same key, so that mDNS updates for
devices that support this functionality can be ignored by the mDNS
snooping agent.]
[Records added to the namespace that contain names are problematic:
the hostname label is obvious, but what about the domain name? I
think the answer is that these names shouldn't be qualified, and the
name server should qualify them appropriately. What does mDNS do?]
[Add something about [TBD1] versus global name. If there is a global
name, that is what we use for name resolution on the local network.
This is necessary because of the security implications, both for
DNSSEC and for PKI.]
2.5. Removing Names
mDNS: names time out
DHCP: names go away when lease expires, or, for stateless, when
refresh timer expires
DNS Update: names have to have a lifetime, determined by the DNS
server, and DNSSD devices that do DNS Update have to keep sending
updates at appropriate intervals to reset the timer. If the lifetime
of a name expires, the name is deleted. Names can also be deleted by
a new update, which must either be signed with SIG(0) using a key
published on the name, or else must come from an IP address published
in the name if no key is published on the name (what if there's no IP
address?)
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2.6. Name Collisions
Covered under adding names. Say more?
2.7. Recovery from loss
In principle the names in the zone aren't precious. If there are
multiple HNRs and one is replaced, the replacement recovers by
copying the local namespaces and other info from the others. If all
are lost, there are a few pieces of persistent data that need to be
recovered:
o The global name
o The ZSK for both local namespaces
o Names configured statically through the UI
All other names were acquired dynamically, and recovery is simply a
matter of waiting for the device to re-announce its name. We should
have a protocol for informing devices that they should do this,
either using an ND option or a DHCP message, or else devices should
know to do a fresh announcement whenever the link goes away (but that
doesn't work if the device is connected to the nearest router through
a separate switch, so ND option is better).
There should be some way (ideally) for the global name to be
recovered. How? This will cause problems with DNSSEC, because the
private ZSK is lost, and we don't expect the user to be smart about
keys. ZSK or KSK could be stored encrypted at the SP. Subject to
brute force attacks if so, probably not a good idea. Better to just
have a flag day? One answer is the end-user management RESTful API:
if the end-user has a phone, the ZSK and other static info can be
maintained in an app on the phone; this app can then be in touch with
the homenet, and if the homenet finds that it is amnesiac, the app
can notify the user. Of course, this is a potential attack--we don't
want some other network the phone connects to to be able to steal the
ZSK just by telling the app it's amnesiac.
2.8. Persistence
When the whole homenet goes away, can we recover the zone? Step 1:
figure out what name we had: how? Then, if we have off-site
secondaries that have copies of the private zone, we can poll for the
highest serial number and copy the contents of that zone. If we only
have secondaries for the public part of the zone, we can recover
that; should we?
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2.9. Well-known names
Homenets serve a zone under the special-use TLD [TBD2], that answers
queries for local configuration information and can be used to
advertise services provided by the homenet (as opposed to services
present on the homenet). This provides a standard means for querying
the homenet that can be assumed by management functions and homenet
clients. A registry of well-known names for this zone is defined in
IANA considerations (Section 8). Names and RRs in this zone are only
ever provided by the homenet--this is not a general purpose service
discovery zone.
All resolvers on the homenet will answer questions about names in
this zone; entries in the zone are guaranteed not to be globally
unique. Hosts and services that use the special names under this TLD
are assumed to be aware that it is a special TLD. If such hosts
cache DNS entries, DNS entries under this TLD are discarded whenever
the host detects a network reattachment.
The uuid.[TBD2] name contains a TXT RR that contains the UUID of the
homenet. Each homenet generates its own distinct UUID; homenet
routers on any particular homenet all use the same UUID, which is
agreed upon using HNCP. If the homenet has not yet generated a UUID,
queries against this name will return NXDOMAIN.
The global-name.[TBD2] name contains a PTR record that contains the
global name of the homenet. If the homenet does not have a global
name, queries against this name will return NXDOMAIN.
The global-name-register.[TBD2] name contains one or more A and/or
AAAA records referencing hosts that provide a RESTful API over HTTP
that can be used to register the global name of the homenet, once
that name has been configured.
3. Name Resolution
3.1. Configuring Resolvers
Hosts on the homenet receive a set of resolver IP addresses using
either DHCP or RA. IPv4-only hosts will receive IPv4 addresses of
resolvers, if available, over DHCP. IPv6-only hosts will receive
resolver IPv6 addresses using either stateful (if available) or
stateless DHCPv6, or through the domain name option in router
advertisements. All homenet routers provide resolver information
using both stateless DHCPv6 and RA; support for stateful DHCPv6 and
DHCPv4 is optional (right?).
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3.2. Configuring Service Discovery
DNS-SD uses several default domains for advertising local zones that
are available for service discovery. These include the ".local"
domain, which is searched using mDNS, and also the IPv4 and IPv6
reverse zone corresponding to the prefixes in use on the local
network. For the homenet, queries against the ".local" zone are
supported, as well as queries against every IPv4 address prefix
advertised on a homenet link, and every IPv6 address prefix
advertised on a homenet link, including prefixes derived from the
homenet's ULA(s). In addition, the [TBD2] domain can be used, and is
preferred. Whenever the "<domain>" sequence appears in this section,
it references each of the domains mentioned in this paragraph.
Homenets advertise the availability of several browsing zones in the
"b._dns_sd.<domain>" subdomain. The zones advertised are the "well
known" zone (TBD2) and the zone containing the local namespace. If
the global name is available, only that name is advertised for the
local namespace; otherwise [TBD1] is advertised. Similarly, if the
global name is available, it is advertised as the default browsing
and service registration domain under "db._dns_sd.<domain>",
"r._dns_sd.<domain>", "dr._dns_sd.<domain>" and
"lb._dns_sd.<domain>"; otherwise, the name [TBD1] is advertised as
the default.
3.3. Resolution of local namespaces
The local namespace appears in two places, under [TBD1] and, if the
homenet has a global name, under the global name. Resolution from
inside the homenet yields the contents of the local namespaces;
resolution outside of the homenet yields the contents of the public
namespaces. If there is a global name for the homenet, RRs
containing names in both instances of the local namespace are
qualified with the global name; otherwise they are qualified with
[TBD1].
3.4. Local and Public Zones
The homenet's global name serves both as a unique identifier for the
homenet and as a delegation point in the DNS for the zone containing
the homenet's forward namespace. There are two versions of the
forward namespace: the public version and the private version. Both
of these versions of the namespace appear under the global name
delegation, depending on which resolver a host is querying.
The homenet provides two versions of the zone. One is the public
version, and one is the local version. The public version is never
visible on the homenet (could be an exception for a guest net). The
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public version is available outside of the homenet. The local
version is visible on the homenet. Whenever the zone is updated, it
is signed with the ZSK. Both versions of the zone are signed; the
local signed version always has a serial number greater than the
public signed version. [we want to not re-sign the public zone if no
public names in the private zone changed.]
This dual publication model relies on hosts connected to the homenet
using the local resolver and not some external resolver. Hosts that
use an external resolver will see the public version of the
namespace. From a security UI design perspective, allowing queries
from hosts on the homenet to resolvers off the homenet is risky, and
should be prevented by default. This is because if the user sees
inconsistent behavior on hosts that have external resolvers
configured, they may attempt to fix this by making all local names
public. If an alternate external resolver is to be used, it should
be configured on the homenet, not on the individual host.
One way to make this work is to intercept all DNS queries to non-
homenet IP addresses, check to see if they reference the local
namespace, and if so resolve them locally, answering as if from the
remote cache. If the query does not reference a local namespace, and
is listed as "do not forward" in RFC 6761 or elsewhere, it can be
sent to the intended cache server for resolution without any special
handling for the response. This functionality is not required for
homenet routers, but is likely to present a better user experience.
3.5. Legacy support
In principle, devices that support DNSSD should be able to do service
discovery using DNS without any special help. Devices that only
support mDNS should be able to get a complete list of services from a
combination of names published by devices on the same link and by the
homenet router that serves that link (what if there's more than
one?). In cases where the homenet router has an off-link entry that
has the same claimed name as an on-link service, the homenet router
does not advertise the off-link service.
3.6. DNSSEC Validation
The [TBD1] zone is not validated. We could define a special rule,
such that any particular local zone publishes a unique identifier for
that zone and signs itself with a ZSK; a homenet-aware host could to
TOFU on the id/ZSK, and could keep a list of id/ZSKs it has seen, and
then do DNSSEC validation on names in the local zone that way, but
it's a bit rickety and nonstandard, so I don't know if there's enough
benefit to justify the cost. Worth thinking about, though--could be
the keystone of a homenet security model if done right.
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3.7. Support for Multiple Provisioning Domains
Homenets must support the Multiple Provisioning Domain Architecture
[6]. In order to support this architecture, each homenet router that
provides name resolution must provide one resolver for each
provisioning domain (PvD). Each homenet router will advertise one
resolver IP address for each PvD. DNS requests to the resolver
associated with a particular PvD, e.g. using RA options [8] will be
resolved using the external resolver(s) provisioned by the service
provider responsible for that PvD.
The homenet is a separate provisioning domain from any of the service
providers. The global name of the homenet can be used as a
provisioning domain identifier, if one is configured. Homenets
should allow the name of the local provisioning domain to be
configured; otherwise by default it should be "Home Network xxx",
where xxx is the generated portion of the homenet's ULA prefix,
represented as a base64 string.
The resolver for the homenet PvD is offered as the primary resolver
in RAs and through DHCPv4 and DHCPv6. When queries are made to the
homenet-PvD-specific resolver for names that are not local to the
homenet, the resolver will use a round-robin technique, alternating
between service providers with each step in the round-robin process,
and then also between external resolvers at a particular service
provider if a service provider provides more than one. The round-
robining should be done in such a way that no service provider is
preferred, so if service provider A provides one caching resolver
(A), and service provider B provides two (B1, B2), the round robin
order will be (A, B1, A, B2), not (A, B1, B2).
Every resolver provided by the homenet, regardless of which
provisioning domain it is intended to serve, will accept updates for
services in the local service namespace.
3.8. Using the Local Namespace While Away From Home
Homenet routers do not answer unauthenticated DNS queries from off
the local network. However, some applications may benefit from the
ability to resolve names in the local namespace while off-network.
Therefore hosts connected to the homenet can register keys in the
same way that services are registered, and the homenet will cache
such keys. Such keys must be validated by the end user before
queries against the local namespace that have been authenticated with
that key are permitted. A host that will make remote queries to the
local namespace caches the names of all DNS servers on the homenet by
querying all-resolver-names.[TBD2]. If the local zone is not signed
using DNSSEC, the host also caches each server's SIG(0) key.
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Hosts that require name resolution from the local network must have a
stub resolver configured to contact the dns server on one or more
routers in the homenet when resolving names in the local namespace.
To do this, resolvers must know the global name of the local
namespace, which they can retain from previous connections to the
homenet. The homenet may not have a stable IP address, so such
resolvers cannot merely cache the IP address of the homenet routers.
Instead, they cache the names of the homenet routers that provide DNS
service and use those names to determine the IP addresses of the
homenet routers at the time of resolution. Such IP addresses can be
safely cached for the duration of the TTL of the A or AAAA record
that contained them. The names of the homenet router DNS servers
should be randomly generated so that they can't be guessed by off-
network attackers. [?]
To make a homenet DNS query, the host signs the request using SIG(0)
with the key that they registered to the homenet. The homenet router
first checks the question in the query for validity: it must be a
subdomain of the global name. The homenet router then checks the
name of the signing key against the list of cached, validated keys;
if that key is cached and validated, then the homenet router attempts
to validate the SIG(0) signature using that key. If the signature is
valid, then the homenet router answers the query. If the zone is not
signed, or doesn't have a trust anchor in the parent zone, the
responding server signs the answer with its own SIG(0) key. The
resolver that sent the query validates the response using DNSSEC if
possible, and otherwise using the SIG(0) key.
[it can be argued that this isn't necessary for the base spec, and it
obviously requires some additional protocol work, so may want to
leave it out of the base architecture. It may also make more sense
to serve queries using DNS-over-TLS (dprive) rather than SIG(0).]
4. Publishing the Public Namespace
4.1. Acquiring the Global Name
There are two ways to acquire a global name: the end-user can
register a domain name using a public domain name registry, or the
end-user can be assigned a subdomain of a registered domain by a
homenet global name service provider. We will refer to this as the
Global Name Registration Provider [GNRP]. In either case, the
registration process can either be manual or automatic. Homenet
routers support automatic registration regardless of the source of
the homenet's global name, using a RESTful API.
The RESTful API provides a method for generating a unique URL which
can be used for a limited time by the GNRP to register the global
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name once the end user has chosen one and made payment arrangements
(if necessary). When the GNRP is ready to convey the global name to
the homenet, it uses the specified URL to submit (POST) the name.
The URL will be https, but the certificate will not be valid; its
purpose is to provide privacy, not authenticity.
In response, the homenet server either rejects the POST, if the URL
has expired or is invalid, or else returns a text response containing
a single label, '@', representing the local namespace. Under that
label, the homenet will include one or more DNSKEY records for zone
signing keys, one of which is required, and key signing keys, which
are not required.
The returned zone will also include a TLSA record. The record has a
Usage field value of 0 (PKI Cert), a Selector value of 1 (just the
public key), and a matching type of 0 (exact match). The Certificate
Association data field contains a public key generated by the homenet
for use in authenticating local web traffic.
The returned zone may include NS records; if it does, the GNRP is
expected to use those NS records in the delegation for the global
name. Otherwise, it provides the NS records for its own
authoritative servers.
The GNRP then sets up a secure delegation using the currently-valid
ZSKs included in the zone. The GNRP also signs the public key
provided in the TLSA record using a PKI cert owned by the GNRP that
can be validated by web browsers, and posts it back to the homenet
using the RESTful API URL.
More detail on this process will be provided in a future document.
[or really, how much detail should there be here?]
4.2. Hidden Primary/Public Secondaries
The default configuration for a homenet's external name service is
that the primary server for the zone is not published in an NS record
in the zone's delegation. Instead, the GNRP provides authoritative
name service for the zone. Whenever the public zone is updated, the
hidden primary sends NOTIFY messages to all the secondaries, using
the zone's ZSK (or?) to sign the message.
When any of the GNRP secondary servers receives a notify for the
zone, it checks to see that the notify is signed with a valid ZSK for
that zone. If so, it contacts the IP address from which the NOTIFY
was send and initiates a zone transfer. Using this IP address avoids
renumbering issues. Upon finishing the zone transfer, the zone is
validated using each ZSK used to sign it. If any validation fails,
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the new version of the zone is discarded. If updates have been
recevied, but no valid updates received, over a user-settable
interval defaulting to a day (or?), the GNRP will communicate to the
registered user that there is a problem.
The reverse zone for any prefix delegated by an ISP should be
delegated by that ISP to the home gateway to which the delegation was
sent. The list of secondaries for that zone is sent to the home
gateway using DHCPv6 prefix delegation (or?). The ZSK is announced
to the ISP in each DHCP PD message sent by the home gateway.
Whenever an update is made to this zone, the home gateway sends a
NOTIFY to each of the listed secondaries for the delegation, and
updates occur as described above.
4.3. DNSSEC security
All zones published by the homenet are signed. Internal zones cannot
have secure delegations, however. Hosts that are aware of homenets
can do TOFU authentication of a particular instance of the homenet
zones [TBD1] or [TBD2]. To do this, the host queries the uuid.[TBD2]
name. The homenet always publishes this name with a single TXT RR
containing a UUID, which is expected to be unique and stable. The
homenet will also publish a name, rev.[TBD2] which contains a PTR
RRset that enumerates the outer delegations of all reverse zones
operated by the homenet at the time of the query that are in private
address spaces.
The homenet-aware host can then query and cache the ZSKs of the
[TBD2] domain on that homenet, using the UUID to identify it. The
homenet uses the same ZSK for all zones that it publishes. Homenet-
aware hosts can validate any record in the [TBD1] and [TBD2] zones
and in reverse zones for private and ULA number spaces using the
stashed ZSK for the homenet UUID to which the host is currently
connected (may be different on different interfaces). Names in non-
private, non-ULA number spaces are validated using secure
delegations, not homenet TOFU trust anchors, as are all other zones
other than [TBD1] and [TBD2].
4.4. PKI security
PKI security is only possible if the homenet has a global name. The
homenet should not use TLS unless it has a certificate that will be
successfully validated by web servers; otherwise, the homenet will be
training end-users to click through certificate warnings, and will be
inoperable to web browsers with correct security user interfaces
(which never present such warnings). If the homenet has a global
name, it should also have gotten a valid PKI certificate as part of
the process of acquiring the global name.
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The homenet tracks the expiration date of the TLS certificate. One
month before expiration, the homenet will send a renewal request to
the GNRP using the URL provided by the GNRP during registration. The
GNRP will then provide a new certificate and a new URL, which the
homenet will record for the next renewal (the URL is not required to
change). Because the key to be signed is published in the public
namespace of the homenet, there is no need for a secondary
authentication path for the key.
4.5. Renumbering
The homenet may renumber at any time. IP address RRs published in
either namespace must never have a TTL that is longer than the valid
lifetime for the prefix from which the IP address was allocated. If
a particular ISP has deprecated a prefix (its preferred lifetime is
zero), IP addresses derived from that prefix are not published in the
DNS. If more than one prefix is provided by the same ISP and some
have different valid lifetimes, only IP addresses in the prefix or
prefixes with the longest valid lifetime are.
4.6. ULA
Question: If the homenet has one or more ULAs, should we only publish
the ULAs and not the global addresses in the local namespace? This
would prevent renumbering events from having any impact on local
communication. Any reason not to do this? Would require some
rewording of the local/global namespace text.
5. Management
5.1. End-user management
Need to have well-known name with RESTful API that apps can connect
to, so that you can have an app on your phone, laptop or whatever
that operates the network. This is a model that seems popular and
accepted by end-users; having a well-defined API allows us to avoid a
million different undocumented vendor-specific management APIs. Web
API would also be nice, but we can't specify that, so better to
specify the RESTful API and let vendors decide what sort of frock to
put on it.
This API should provide a means for notifying end-users of issues on
the home network, using whatever app they have installed. The API
must provide a mechanism for registering end-users or devices that
are permitted to manage the homenet, and a way to recover if all such
devices are lost.
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5.2. Central management
Possibly can be done mostly through RESTful API, but might want
Netconf/Yang as well. Should be possible to have the local namespace
mastered on an external DNS auth server, e.g. in case a bunch of HNRs
are actually set up in an org, or in case an ISP wants to provide a
service package for users who would rather not have an entirely self-
operating network.
6. Privacy Considerations
Private information must not leak out as a result of publishing the
public namespace. We believe the current provisions adequately
address this concern. (right?)
7. Security Considerations
Need someone with security fu to review the registration model, etc.,
once we have it.
8. IANA considerations
IANA will add a new registry titled Homenet Management Well-Known
Names, which initially contains:
uuid Universally Unique Identifier--TXT record containing, in base64
encoding, a stable, randomly generated identifier for the homenet
that is statistically unlikely to be shared by any other homenet.
global-name The homenet's global name, represented as a PTR record
to that name.
global-name-register The hostname of the homenet's global name
registry service, with A and/or AAAA records.
all-resolver-names A list of all the names of the homenet's
resolvers for the homenet PvD, represented as an RRset containing
one or more PTR records.
The IANA will allocate two names out of the Special-use TLD names
registry:
TBD1 Suggested value: "homenet"
TBD2 Suggested value: "_hnsd"
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9. Normative References
[1] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.
[2] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>.
[3] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)",
RFC 2136, DOI 10.17487/RFC2136, April 1997,
<http://www.rfc-editor.org/info/rfc2136>.
[4] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<http://www.rfc-editor.org/info/rfc6762>.
[5] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<http://www.rfc-editor.org/info/rfc6763>.
[6] Anipko, D., Ed., "Multiple Provisioning Domain
Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
<http://www.rfc-editor.org/info/rfc7556>.
[7] Cheshire, S., "Hybrid Unicast/Multicast DNS-Based Service
Discovery", draft-ietf-dnssd-hybrid-03 (work in progress),
February 2016.
[8] Korhonen, J., Krishnan, S., and S. Gundavelli, "Support
for multiple provisioning domains in IPv6 Neighbor
Discovery Protocol", draft-ietf-mif-mpvd-ndp-support-03
(work in progress), February 2016.
Author's Address
Ted Lemon
Nominum, Inc.
800 Bridge Parkway
Redwood City, California 94065
United States of America
Phone: +1 650 381 6000
Email: ted.lemon@nominum.com
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