wdiff draft-sctl-service-registration-01.txt draft-sctl-service-registration-02.txt

Internet Engineering Task Force S. Cheshire
Internet-Draft Apple Inc.
Intended status: Informational T. Lemon
Expires: January 3, 15, 2019 Nibbhaya Consulting
July 2, 14, 2018

Service Registration Protocol for DNS-Based Service Discovery
draft-sctl-service-registration-01
draft-sctl-service-registration-02

Abstract

The DNS-SD Service Registration Protocol uses the standard DNS Update
mechanism to enable DNS-Based Service Discovery using only unicast
packets. This eliminates the dependency on Multicast DNS as the
foundation layer, which greatly improves scalability and improves
performance on networks where multicast service is not an optimal
choice, particularly 802.11 (WiFi) (Wi-Fi) and 802.15 802.15.4 (IoT) networks.
DNS-SD Service registration uses public keys and SIG(0) to allow
services to defend their registrations against attack.

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 https://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, 15, 2019.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

1. Introduction

DNS-Based Service Discovery [RFC6763] is a component of Zero
Configuration Networking [RFC6760] [ZC] [I-D.cheshire-dnssd-roadmap].

This document describes an enhancement to DNS-Based Service Discovery
[RFC6763] that allows services to automatically register their
services using the DNS protocol rather than using mDNS. There is
already a large installed base of DNS-SD clients that can do service
discovery using the DNS protocol. This extension makes it much
easier to take advantage of this existing functionality.

This document is intended for three audiences: implementors of
software that provides services that should be advertised using DNS-
SD, implementors of DNS servers that will be used in contexts where
DNS-SD registration is needed, and administrators of networks where
DNS-SD service is required. The document is intended to provide
sufficient information to allow interoperable implementation of the
registration protocol.

DNS-Based Service Discovery (DNS-SD) allows services to advertise the
fact that they provide service, and to provide the information
required to access that service. Clients can then discover the set
of services of a particular type that are available. They can then
select a service from among those that are available and obtain the
information required to use it.

The DNS-SD Service Registration protocol, described in this document,
provides a reasonably secure mechanism for publishing this
information: what services are offered, and how to use them.
information. Once published, these services can be readily
discovered by clients using standard DNS lookups.

In the DNS-Based Service Discovery specification [RFC6763] Section 10
"Populating the DNS with Information" briefly discusses ways that
services can publish their information in the DNS namespace. In the
case of Multicast DNS [RFC6762], it allows clients to directly query services to publish their
information on the local link for link, using names in the ".local" namespace. namespace,
which makes their services directly discoverable by peers attached to
that same local link.

RFC6763 also allows clients to discover services using the DNS
protocol [RFC1035]; this is [RFC1035]. This can be done either by having a system
administrator manually configure service information in the DNS, or
by using a Discovery Proxy [I-D.ietf-dnssd-hybrid], which performs
mDNS queries on behalf clients issuing queries using DNS. This
eliminats the "link local" limitation of mDNS, but provides no
additional security, and still relies on multicast.

Manual configuration of
manually populating DNS servers authoritative server databases is costly and failure-prone,
potentially error-prone, and requires a knowledgable network
administrator. Consequently, although all DNS-SD client
implementations of which we are aware support it, DNS-SD using DNS
queries, in practice it is used much less frequently used than mDNS. The
Discovery Proxy [I-D.ietf-dnssd-hybrid] provides one way to
automatically populate the DNS namespace, but is only appropriate on
networks where services are already advertised using mDNS. This
document describes a
solution: a way to provide DNS-SD using DNS that can be as automatic
as solution more suitable for networks where
multicast DNS, but with better performance, scalability is inefficient, or undesirable for other reasons, by
supporting both offering of services, and
security. discovery of services,
using unicast.

2. Service Registration Protocol

Services using that implement the DNS-SD Service Registration Protocol use
DNS Update [RFC2136] [RFC3007] to publish service information in the
DNS.
We will discuss several parts to this process: how to know what to
publish, how to know where to publish it (under what name), how to
publish it, how to secure its publication, Two variants exist, one for full-featured devices, and how to maintain one for
devices designed for "Constrained-Node Networks" [RFC7228].

Full-featured devices are either configured manually, or use the
information once published.

2.1. What
"dr._dns-sd._udp" query [RFC6763] to publish

RFC 6763 describes learn the details of what is to be published. In
general terms, a service will have a name under which it offers
services ([RFC6763] section 4.1.1) and one or more default registration
domain from the network. Using the chosen service registration
domain, full-featured devices construct the names
under which that instance name appears ([RFC6763] section 4.1.2).
The full details of how this works are described in section 4 of that
document in its entirety. A service publishes its contact
information using an SRV record on the Service Instance Name. It can
also publish TXT SRV, TXT,
and PTR records with additional information about describing their service(s). For these names they
then discover the
service; this is discussed in section 6 zone apex of RFC 6763.

RFC 6763 is the definitive source for information about what to
publish; closest enclosing DNS zone using
SOA queries [I-D.ietf-dnssd-push]. Having discovered the reason enclosing
DNS zone, they query for mentioning it here is that the reader may
prefer "_dns-update._udp<zone>" SRV record to have an overview
discover the server to which they should send DNS updates.

For devices designed for "Constrained-Node Networks" [RFC7228] some
simplifications are used. Instead of being configured with (or
discovering) the whole service registration process
before digging into the details. Also, domain, the "Service Instance Name" (proposed) special
use domain name [RFC6761] "services.arpa" is an important aspect used. Instead of first-come, first-serve naming, which we
describe later on in this document.

2.2. Where
learning the server to publish it

Multicast which they should send DNS uses updates, a single namespace, ".local", which fixed
IPv6 anycast address is valid on
the local link. This convenience used (value TBD). It is not available for the responsibility
of a "Constrained-Node Network" supporting DNS-SD using Service
Registration Protocol to provide appropriate anycast routing to
deliver the DNS protocol: updates to the portion appropriate server. It is the
responsibility of the DNS namespace in which services DNS-SD Service Registration server on a
"Constrained-Node Network" to handle the local updates appropriately. In
some network are to be published must environments, updates may be discovered by accepted directly into a
local "services.arpa" zone, which has only local visibility. In
other network environments, updates for names ending in
"services.arpa" may be rewritten internally to names with broader
visibility.

The reason for these different assumptions is that "Constrained-Node
Networks" generally require special egress support, and Anycast
packets captured at the
service before it "Constrained-Node Network" egress can register itself.

Names published using DNS-SD service be
assumed to have originated locally. Low-power devices that typically
use "Constrained-Node Networks" may have very limited battery power.
The additional DNS lookups required to discover a registration server
and then communicate with it will increase the power required to
advertise a service; for low-power devices, the additional
flexibility this provides does not justify the additional use of
power.

General networks have the potential to have more complicated
topologies at the Internet layer, which makes anycast routing more
difficult. Such networks may or may not have the infrastructure
required to route anycast to a server that can process it. However,
they can be published
under assumed to be able to provide registration domain
discovery and routing. By requiring the use of TCP, the possibility
of off-network spoofing is eliminated.

We will discuss several parts to this process: how to know what to
publish, how to know where to publish it (under what name), how to
publish it, how to secure its publication, and how to maintain the
information once published.

2.1. What to publish

We refer to the message that services using the DNSSD Registration
Protocol send as a Registration. Three types of updates appear in a
Registration: Service Discovery records, Service Description records,
and Host Description records.

o Service Discovery records are one or more PTR RRs, mapping from
the generic service type (or subtype) to the specific Service
Instance Name.

o Service Description records are exactly one SRV RR, and one or
more TXT RRs, both with the same name, the Service Instance Name
([RFC6763] section 4.1). In principle Service Description records
can include other record types, with the same Service Instance
Name, though in practice they rarely do. The Service Instance
Name MUST be referenced by one or more Service Discovery PTR
records, unless it is a placeholder service registration for an
intentionally non-discoverable service name.

o The Host Description records for a service are a KEY RR, used to
claim exclusive ownership of the service registration, and one or
more RRs of type A or AAAA, giving the IPv4 or IPv6 address(es) of
the host where the service resides.

RFC 6763 describes the details of what each of these types of updates
contains and is the definitive source for information about what to
publish; the reason for mentioning it here is to provide the reader
with enough information about what will be published that the service
registration process can be understood at a high level without first
learning the full details of DNS-SD. Also, the "Service Instance
Name" is an important aspect of first-come, first-serve naming, which
we describe later on in this document.

2.2. Where to publish it

Multicast DNS uses a single namespace, ".local", which is valid on
the local link. This convenience is not available for DNS-SD using
the DNS protocol: services must exist in some specific unicast
namespace.

As described above, full-featured devices are responsible for knowing
in what domain they should register their services. Devices made for
"Constrained-Node Networks" register in the (proposed) special use
domain name [RFC6761] "services.arpa", and let the DNS-SD Service
Registration server handle rewriting that to a different domain if
necessary.

2.3. How to publish it

It is possible to issue a DNS Update that does several things at
once; this means that it's possible to do all the work of adding a
PTR resource record to the PTR RRset on the Service Name if it
already exists, or creating one if it doesn't, and creating or
updating the Service Instance Name and Host Description in a single
transaction.

A Registration is therefore implemented as a single DNS Update
message that contains a service's Service Discovery records, Service
Description records, and Host Description records.

Updates done according to this specification are somewhat different
than regular DNS Updates as defined in RFC2136. RFC2136 assumes that
updating is a fairly heavyweight process, so you might first attempt
to add a name if it doesn't exist, and then in a second message
update the name if it does exist but matches certain preconditions.
Because the registration protocol uses a single transaction, some of
this adaptability is lost.

In order to allow updates to happen in a single transaction,
Registrations do not include update constraints. The constraints
specified in Section 2.4.2 are implicit in the processing of
Registrations, and so there is no need for the service sending the
Registration to put in any explicit constraints.

2.3.1. How DNS-SD Service Registration differs from standard RFC2136
DNS Update

DNS-SD Service Registration is based on standard RFC2136 DNS Update,
with some differences:

o It implements first-come first-served name allocation, protected
using SIG(0).

o It enforces policy about what updates are allowed.

o It optionally performs rewriting of "services.arpa" to some other than .local. However, the process
domain.

o It optionally performs automatic population of
discovering what that name is the address-to-name
reverse mapping domains.

o A DNS-SD Service Registration server is complicated, and not required to implement
general DNS Update prerequsite processing.

o Simplified clients are allowed to send updates to an anycast
address, for any given
network it should always names ending in "services.arpa"

2.3.2. Testing using standard RFC2136-compliant servers

It may be the case useful to set up a DNS server for testing that there will does not
implement the Registration protocol. This can be just one
namespace done by configuring
the server to listen on the anycast address, or advertising it in which registered the
_dns-update._udp SRV record. It must be configured to be
authoritative for "services.arpa", and to accept updates from hosts
on local networks for names under "services.arpa" without
authentication.

A server configured in this way will be published. Rather than
requiring the service able to discover successfully accept
and process Registrations from services that send Registrations.
However, no constraints will be applied, and this name before issuing a
registration, the service SHOULD simply use the name ".local." The
DNS server means that receives the registration request test
server will rewrite all
instances of accept internally inconsistent Registrations, and will
not stop two Registrations, sent by different services, that claim
the terminal label ".local" same name(s), from overwriting each other.

2.3.3. How to use the local
registration domain name. The response allow services to update standard RFC2136-compliant
servers

Ordinarily Registrations will fail when sent to any non-Registration
Protocol server because the DNS Update zone being used updated is "services.arpa",
and no DNS server that is not a Registration Protocol server should
normally be configured to register the be authoritative for "services.arpa".
Therefore, a service will contain the rewritten names, instead of
".local". Subsequent updates should still use that sends a Registration can tell that the ".local" domain
and
receiving server does not support the registration domain, since Registration Protocol, but does
support RFC2136, because the registration domain may
change over time RCODE will either be NOTZONE, NOTAUTH or when the service
REFUSED, or because there is physically moved no response to the update request (when
using the anycast address)

In this case a new
network.

2.3. How service MAY attempt to publish it register itself using regular
RFC2136 DNS Updates are very flexible. As a consequence, it is possible to updates. To do the entire so, it must discover default registration in a single DNS message. The update
consists of two elements. The first updates
zone and the Service Name by
adding a PTR record pointing DNS server designated to the Service Instance Name. The
second updates the Service Instance Name. The second creates or receive updates for that zone,
as described earlier using the Service Instance Name update adds an _dns-update._udp SRV record and a KEY
record, and optionally adds a TXT record with extra information about
the service. The contents of the KEY record are described in record. It can
then make the
section on First-Come First-Served Naming (Section 2.4.1). The update is signed using the private key that corresponds port and host pointed to by the public
key in the KEY SRV
record, using the SIG(0) protocol [RFC2931].

The update may be rejected. If and should use appropriate constraints to avoid overwriting
competing records. Such updates are out of scope for the chosen DNSSD
Registration Protocol, and a service instance name is
not permitted, or is already taken, the update will be returned with that implements the error code YXDOMAIN. In this case, DNSSD
Registration Protocol MUST first attempt to use the service will need Registration
Protocol to
choose a new instance name register itself, and try again. should only attempt to use RFC2136
backwards compatibility if that fails.

2.4. How to secure it

Traditional DNS update is secured using the TSIG protocol, which uses
a secret key shared between the client (which issues the update) and
the server (which authenticates it). This model does not work for
automatic service registration.

The goal of securing the DNS-SD Registration Protocol is to provide
the best possible security given the constraint that service
registration has to be automatic. It is possible to layer more
operational security on top of what we describe here, but what we
describe here improves upon the security of mDNS. The goal is not to
provide the level of security of a network managed by a skilled
operator.

2.4.1. First-Come First-Served Naming

First-Come First-Serve naming provides a limited degree of security:
a service that registers its service using DNS-SD Registration
protocol is given ownership of a name for an extended period of time
based on the key used to authenticate the DNS Update. As long as the
registration service remembers the Service Instance Name and the key
used to register that Service Instance Name, no other service can add
or update the information associated with that Service Instance Name.

2.4.1.1. Service Behavior

The service generates a public/private key pair. This key pair MUST
be stored in stable storage; if there is no writable stable storage
on the client, the client MUST be pre-configured with a public/
private key pair that can be used.

When sending DNS updates, the service includes a KEY record
containing the public portion of the key, which is stored as an RRset
under the Service Instance Name. It is permissible for a device that
offers more than one service under more than one Service Instance
Name to use

When sending DNS updates, the same service includes a KEY on record
containing the public portion of the key in each such name. Host Description
update. The update is signed using SIG(0), using the private key
that corresponds to the public key in the KEY record. The lifetimes
of the records in the update is set using the EDNS(0) Update Lease
option.

The lifetime of the DNS-SD PTR, SRV SRV, A, AAAA and TXT records
[RFC6763] is typically set to two hours. This means that if a device
is disconnected from the network, it does not appear in the user
interfaces of devices looking for services of that type for too long.

However, the lifetime of its DNS SIG(0) public key KEY record should be set to a much
longer time, typically 14 days. The result of this is that even
though a device may be temporarily unplugged, disappearing from the
network for a few days, it makes a claim on its name that lasts much
longer.

This way, even if a device is unplugged from the network for a few
days, and its services are not available for that time, no other
rogue device can come along and immediately claim its name the moment
it disappears from the network, and yet network. In the event that a device is
unplugged from the network and permanently discarded, then its name
is eventually cleaned up and made available for re-use.

2.4.1.2.

2.4.2. Registration Server Behavior

The Registration server checks that the DNS update contains a Service
Instance Name. In principle, each name update in the update should be
evaluated as Registration to see
that it contains a candidate Service Instance Name. However, some names
will obviously be Discovery update, a Service Names, Description
update, and these can be skipped when
evaluating candidates. In order for a candidate to actually be Host Description update.

An update is a
service instance name, the following conditions must be true: Service Discovery update if it contains

o There is at least exactly one name that turns out NOT RRset update,
o which is for a PTR RR,
o which points to be a Service Instance Name
o for which there an update is a PTR RRset present in the Registration.

An update that includes is a record pointing to Service Description update if, for the candidate. appropriate
Service Instance Name, it contains

o The candidate includes an exactly one "Delete all RRsets from a name" update,
o exactly one SRV record RRset update,
o The candidate includes a KEY one or more TXT RRset updates,
o and the target of the SRV record

If an update does not contain references a valid Service Instance Name, or if hostname for
which there is a Host Description update in the Registration.

An update is a Host Description update if, for the appropriate
hostname, it contains an

o exactly one "Delete all RRsets from a name" update,
o A or AAAA RR update(s)
o a KEY RR update to that adds a PTR RRset KEY RR that references contains the public key
corresponding to the private key that was used to sign the
message,
o there is a name Service Instance Name update in the Registration that
updates an SRV RR so that is not it points to the hostname being updated
by this update.

A Registration MUST include at least one Service Instance Name being updated, the update, at
least one Service Description update, and exactly one Host
Description update. An update message that does not is rejected with
the NOTAUTH RCODE.

If an not a
Registration. An update contains an SRV record message that contains an IP address any other
than the IP address from which the update was recieved, the updates, or
any update constraints, is not a Registration. Such messages should
either be processed as regular RFC2136 updates, including access
control checks and constraint checks, if supported, or else rejected
with RCODE=REFUSED.

Note that if the NOTAUTH RCODE.

Once definitions of each name for which there of these update types are updates in the DNS Update has been
considered as
followed carefully, this means that many things that look very much
like Registrations nevertheless are not. For example, a candidate, it should be the case Registration
that only one name
is actually contains an update to a possible Service Instance Name. If more than one name
is still Name and an update to a possible candidate, then Service
Instance Name, where the DNS Update Service Name does not reference the Service
Instance Name, is rejected not a valid Registration message, but may be a
valid RFC2136 update.

Assuming that an update message has been validated with
the FORMERR RCODE.

If there these
conditions and is only one candidate, then a valid Registration, the server checks to see if that the
name already in the Host Description update exists. If it does already exist, so, then the server
checks to see if the KEY record on the name is the same as the one KEY
record in the update for that name. update. If it is not, then the DNS Update is
rejected server MUST reject the
Registration with the YXDOMAIN RCODE.

Otherwise, the server validates the update using SIG(0). SIG(0) on the public
key in the KEY record of the Host Description update. If the
validation fails, the update is server MUST reject the rejectration rejected
with NOTAUTH. the REFUSED RCODE. Otherwise, the update is evaluated considered valid
and authentic, and is processed according to the rules method described in RFC2136
for
RFC2136. The status that is returned depends on the result of
processing DNS updates, and whatever the correct result is update.

The server MAY add a Reverse Mapping that corresponds to the Host
Description. This is
returned. not required because the Reverse Mapping serves
no protocol function, but it may be useful for debugging, e.g. in
annotating network packet traces or logs.

The server MAY apply additional criteria when accepting updates. In
some networks, it may be possible to do out-of-band registration of
keys, and only accept updates from pre-registered keys. In this
case, an update for a key that has not been registered should be
rejected using NOTAUTH. with the REFUSED RCODE.

There are at least two benefits to doing this rather than simply
using normal SIG(0) DNS updates. First, the same registration
protocol can be used in both cases, so both use cases can be
addressed by the same service implementation. Second, the
registration protocol includes maintenance functionality not present
with normal DNS updates.

Note that the semantics of using the Registration Protocol in this
way are different than for typical RFC2136 implementations: the KEY
used to sign the update in the Registration Protocol only allows the
client to update records that refer to its Host Description. RFC2136
implementations do not normally provide a way to enforce a constraint
of this type.

The server may also have a dictionary of names or name patterns that
are not permitted. If such a list is used, updates for Service
Instance Names that match entries in the dictionary are rejected with
YXDOMAIN.

2.5. TTL Consistency

All RRs within an RRset are required to have the same TTL
(Clarifications to the DNS Specification [RFC2181], Section 5.2). In
order to avoid inconsistencies, the Registration Protocol places
restrictions on TTLs sent by services and requires that Registration
Protocol Servers enforce consistency.

Services sending Registrations MUST use consistent TTLs in all RRs
within the Registration.

Registration Protocol servers MUST check that the TTLs for all RRs
within the Registration are the same. If they are not, the
Registration MUST be rejected with a REFUSED RCODE.

Additionally, when adding RRs to an RRset, for example when
processing Service Discovery records, the server MUST use the same
TTL on all RRs in the RRset. How this consistency is enforced is up
to the implementation.

2.6. Maintenance

2.5.1.

2.6.1. Cleaning up stale data

Because the DNS-SD registration protocol is automatic, and not
managed by humans, some additional bookkeeping is required. When an
update is constructed by the client, it MUST include include an
EDNS(0) Update Lease option Option [I-D.sekar-dns-ul]. The Update Lease
Option contains two lease times: the Update Lease Time and an EDNS(0) the
Instance Lease option. Time.

These leases are promises, similar to DHCP leases [RFC2131], from the
client that it will send a new update for the service registration
before the lease time expires. The Update Lease time is chosen to
represent the time after the update during which the registered
records other than the KEY record should be assumed to be valid. The
Instance Lease time represents the time after the update during which
the KEY record should be assumed to be valid.

The reasoning behind the different lease times is discussed in the
section on first-come, first-served naming Section 2.4.1. DNS-SD
Registration Protocol servers may be configured with limits for these
values. A default limit of two hours for the Update Lease and 30 14
days for the Instance Lease SIG(0) KEY are currently thought to be good choices.
Clients that are going to continue to use names on which they hold
leases should update well before the lease ends, in case the
registration service is unavailable or under heavy load.

The Registration Protocol server MUST include an EDNS(0) Update Lease
option in the response if the lease time proposed by the service has
been shortened. The service MUST check for the EDNS(0) Update Lease
option in the response and MUST use the lease times from that option
in place of the options that it sent to the server when deciding when
to update its registration.

Clients should assume that each lease ends N seconds after the update
was first transmitted, where N is the number included in the option. lease duration. Servers should
assume that each lease ends N seconds after the update that was
successfully processed was received. Because the server will always
receive the update after the client sent it, this avoids the
possibility of misunderstandings.

DNS-SD Registration Protocol servers SHOULD MUST reject updates that do not
include a DNS update lease time. an EDNS(0) Update Lease option. Dual-use servers may MAY accept
updates that don't include leases, but SHOULD differentiate between
DNS-SD registration protocol updates and other updates, and SHOULD MUST
reject updates that are known to be DNS-SD registration protocol Registration Protocol
updates if they do not include leases.

2.5.2.

2.6.2. Sleep Proxy

Another use of Service Registration Protocol is for devices that
sleep to reduce power consumption.

In this case, in addition to the DNS Update Lease option
[I-D.sekar-dns-ul] described above, the device includes an EDNS(0)
OWNER Option [I-D.cheshire-edns0-owner-option].

The DNS EDNS(0) Update Lease option constitutes a promise by the device
that it will wake up before this time elapses, to renew its records
registration and thereby demonstrate that it is still attached to the
network. If it fails to renew the records registration by this time, that
indicates that it is no longer attached to the network, and its records
registration (except for the KEY in the Host Description) should be
deleted.

The EDNS(0) OWNER Option indicates that the device will be asleep,
and will not be receptive to normal network traffic. When a DNS
server receives a DNS Update with an EDNS(0) OWNER Option, that
signifies that the DNS Registration Protocol server should act as set up a proxy
for any IPv4 or IPv6 address records in the DNS Update message. This means that the
DNS server
proxy should send ARP or ND messages claiming ownership of the IPv4
and/or IPv6 addresses in the records in question. In addition,
the DNS server proxy
should answer future ARP or ND requests for those IPv4 and/or IPv6
addresses, claiming ownership of them. When the DNS server receives
a TCP SYN or UDP packet addressed to one of the IPv4 or IPv6
addresses for which it proxying, it should then wake up the sleeping
device using the information in the EDNS(0) OWNER Option. At present
version 0 of the OWNER Option specifies the "Wake-on-LAN Magic
Packet" that needs to be sent; future versions could be extended to
specify other wakeup mechanisms.

Note that although the authoritative DNS server that implements the
DNSSD Service Registration Protocol function need not be on the same
link as the sleeping host, the Sleep Proxy must be on the same link.

3. Security Considerations

DNS-SD Service Registration Protocol updates have no authorization
semantics other than first-come, first-served. This means that if an
attacker from outside of the administrative domain of the server
knows the server's IP address, it can in principle send updates to
the server that will be processed successfully. Servers should
therefore be configured to reject updates from source addresses
outside of the administrative domain of the server.

For Anycast updates, this validation must be enforced by every router
that connects the CDN to the unconstrained portion of the network.
For TCP updates, the initial SYN-SYN+ACK handshake prevents updates
being forged from off-network. In order to ensure that this
handshake happens, Service Discovery Protocol servers MUST NOT accept
0-RTT TCP payloads.

Note that these rules only apply to the validation of DNS-SD
registration protocol updates. A server that accepts updates from
DNS-SD registration protocol clients may also accept other DNS
updates, and those DNS updates may be validated using different
rules. However, in the case of a DNS service that accepts automatic
updates, the intersection of the DNS-SD service registration update
rules and whatever other update rules are present must be considered
very carefully.

For example, a normal, authenticated RFC2136 update to any RR that
was added using the Registration protocol, but that is authenticated
using a different key, could be used to override a promise made by
the registration protocol, by replacing all or part of the service
registration information with information provided by a different
client. An implementation that allows both kinds of updates should
not allow updates to records added by Registrations using different
authentication and authorization credentials.

4. Privacy Considerations

5. Acknowledgments

Thanks to Toke Hoeiland-Joergensen for a thorough technical review,
to Tamara Kemper for doing a nice developmental edit, Tim Wattenberg
for doing a service implementation at the Montreal Hackathon at IETF
102, and [...] more reviewers to come, hopefully.

6. References
5.1.

6.1. Normative References

[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/info/rfc6763>.

5.2.

[I-D.sekar-dns-ul]
Sekar, K., "Dynamic DNS Update Leases", draft-sekar-dns-
ul-01 (work in progress), August 2006.

6.2. Informative References

[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.

[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.

[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.

[RFC2136] 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,
<https://www.rfc-editor.org/info/rfc2136>.

[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
<https://www.rfc-editor.org/info/rfc2181>.

[RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures
( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September
2000, <https://www.rfc-editor.org/info/rfc2931>.

[RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic
Update", RFC 3007, DOI 10.17487/RFC3007, November 2000,
<https://www.rfc-editor.org/info/rfc3007>.

[RFC3152] Bush, R., "Delegation of IP6.ARPA", BCP 49, RFC 3152,
DOI 10.17487/RFC3152, August 2001,
<https://www.rfc-editor.org/info/rfc3152>.

[RFC6760] Cheshire, S. and M. Krochmal, "Requirements for a Protocol
to Replace the AppleTalk Name Binding Protocol (NBP)",
RFC 6760, DOI 10.17487/RFC6760, February 2013,
<https://www.rfc-editor.org/info/rfc6760>.

[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
<https://www.rfc-editor.org/info/rfc6761>.

[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/info/rfc6762>.

[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.

[I-D.ietf-dnssd-hybrid]
Cheshire, S., "Discovery Proxy for Multicast DNS-Based
Service Discovery", draft-ietf-dnssd-hybrid-08 (work in
progress), March 2018.

[I-D.sekar-dns-ul]
Sekar, K., "Dynamic DNS Update Leases", draft-sekar-dns-
ul-01

[I-D.ietf-dnssd-push]
Pusateri, T. and S. Cheshire, "DNS Push Notifications",
draft-ietf-dnssd-push-14 (work in progress), August 2006. March 2018.

[I-D.cheshire-dnssd-roadmap]
Cheshire, S., "Service Discovery Road Map", draft-
cheshire-dnssd-roadmap-01 (work in progress), March 2018.

[I-D.cheshire-edns0-owner-option]
Cheshire, S. and M. Krochmal, "EDNS0 OWNER Option", draft-
cheshire-edns0-owner-option-01 (work in progress), July
2017.

[ZC] Cheshire, S. and D. Steinberg, "Zero Configuration
Networking: The Definitive Guide", O'Reilly Media, Inc. ,
ISBN 0-596-10100-7, December 2005.

Authors' Addresses
Stuart Cheshire
Apple Inc.
1 Infinite Loop
One Apple Park Way
Cupertino, California 95014
USA

Phone: +1 408 974 3207
Email: cheshire@apple.com

Ted Lemon
Nibbhaya Consulting
P.O. Box 958
Brattleboro, Vermont 05302
United States of America

Email: mellon@fugue.com