draft-ietf-dnssd-srp-01.txt   draft-ietf-dnssd-srp-02.txt 
Internet Engineering Task Force S. Cheshire Internet Engineering Task Force S. Cheshire
Internet-Draft Apple Inc. Internet-Draft Apple Inc.
Intended status: Informational T. Lemon Intended status: Informational T. Lemon
Expires: September 12, 2019 Nibbhaya Consulting Expires: January 9, 2020 Nibbhaya Consulting
March 11, 2019 July 8, 2019
Service Registration Protocol for DNS-Based Service Discovery Service Registration Protocol for DNS-Based Service Discovery
draft-ietf-dnssd-srp-01 draft-ietf-dnssd-srp-02
Abstract Abstract
The Service Registration Protocol for DNS-Based Service Discovery The Service Registration Protocol for DNS-Based Service Discovery
uses the standard DNS Update mechanism to enable DNS-Based Service uses the standard DNS Update mechanism to enable DNS-Based Service
Discovery using only unicast packets. This makes it possible to Discovery using only unicast packets. This makes it possible to
deploy DNS Service Discovery without multicast, which greatly deploy DNS Service Discovery without multicast, which greatly
improves scalability and improves performance on networks where improves scalability and improves performance on networks where
multicast service is not an optimal choice, particularly 802.11 multicast service is not an optimal choice, particularly 802.11
(Wi-Fi) and 802.15.4 (IoT) networks. DNS-SD Service registration (Wi-Fi) and 802.15.4 (IoT) networks. DNS-SD Service registration
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 12, 2019. This Internet-Draft will expire on January 9, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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2.4.2. SRP Server Behavior . . . . . . . . . . . . . . . . . 10 2.4.2. SRP Server Behavior . . . . . . . . . . . . . . . . . 10
2.5. TTL Consistency . . . . . . . . . . . . . . . . . . . . . 12 2.5. TTL Consistency . . . . . . . . . . . . . . . . . . . . . 12
2.6. Maintenance . . . . . . . . . . . . . . . . . . . . . . . 13 2.6. Maintenance . . . . . . . . . . . . . . . . . . . . . . . 13
2.6.1. Cleaning up stale data . . . . . . . . . . . . . . . 13 2.6.1. Cleaning up stale data . . . . . . . . . . . . . . . 13
2.6.2. Sleep Proxy . . . . . . . . . . . . . . . . . . . . . 14 2.6.2. Sleep Proxy . . . . . . . . . . . . . . . . . . . . . 14
3. Security Considerations . . . . . . . . . . . . . . . . . . . 15 3. Security Considerations . . . . . . . . . . . . . . . . . . . 15
3.1. Source Validation . . . . . . . . . . . . . . . . . . . . 15 3.1. Source Validation . . . . . . . . . . . . . . . . . . . . 15
3.2. SIG(0) signature validation . . . . . . . . . . . . . . . 16 3.2. SIG(0) signature validation . . . . . . . . . . . . . . . 16
3.3. Required Signature Algorithm . . . . . . . . . . . . . . 16 3.3. Required Signature Algorithm . . . . . . . . . . . . . . 16
4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 16 4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 16
5. Delegation of 'services.arpa.' . . . . . . . . . . . . . . . 16 5. Delegation of 'service.arpa.' . . . . . . . . . . . . . . . . 17
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
6.1. Registration and Delegation of 'services.arpa' as a 6.1. Registration and Delegation of 'service.arpa' as a
Special-Use Domain Name . . . . . . . . . . . . . . . . . 17 Special-Use Domain Name . . . . . . . . . . . . . . . . . 17
6.2. 'dnssd-srp' Service Name . . . . . . . . . . . . . . . . 17 6.2. 'dnssd-srp' Service Name . . . . . . . . . . . . . . . . 17
6.3. Anycast Address . . . . . . . . . . . . . . . . . . . . . 17 6.3. 'dnssd-srp-tls' Service Name . . . . . . . . . . . . . . 18
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 6.4. Anycast Address . . . . . . . . . . . . . . . . . . . . . 18
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . . 18 8.1. Normative References . . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . . 19 8.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Sample BIND9 configuration for Appendix A. Sample BIND9 configuration for default.service.arpa. 21
default.services.arpa. . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction 1. Introduction
DNS-Based Service Discovery [RFC6763] is a component of Zero DNS-Based Service Discovery [RFC6763] is a component of Zero
Configuration Networking [RFC6760] [ZC] [I-D.cheshire-dnssd-roadmap]. Configuration Networking [RFC6760] [ZC] [I-D.cheshire-dnssd-roadmap].
This document describes an enhancement to DNS-Based Service Discovery This document describes an enhancement to DNS-Based Service Discovery
[RFC6763] that allows services to automatically register their [RFC6763] that allows services to automatically register their
services using the DNS protocol rather than using Multicast DNS services using the DNS protocol rather than using Multicast DNS
[RFC6762] (mDNS). There is already a large installed base of DNS-SD [RFC6762] (mDNS). There is already a large installed base of DNS-SD
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Manual configuration of the registraton domain can be done either by Manual configuration of the registraton domain can be done either by
querying the list of available registration zones ("r._dns-sd._udp") querying the list of available registration zones ("r._dns-sd._udp")
and allowing the user to select one from the UI, or by any other and allowing the user to select one from the UI, or by any other
means appropriate to the particular use case being addressed. Full- means appropriate to the particular use case being addressed. Full-
featured devices construct the names of the SRV, TXT, and PTR records featured devices construct the names of the SRV, TXT, and PTR records
describing their service(s) as subdomains of the chosen service describing their service(s) as subdomains of the chosen service
registration domain. For these names they then discover the zone registration domain. For these names they then discover the zone
apex of the closest enclosing DNS zone using SOA queries apex of the closest enclosing DNS zone using SOA queries
[I-D.ietf-dnssd-push]. Having discovered the enclosing DNS zone, [I-D.ietf-dnssd-push]. Having discovered the enclosing DNS zone,
they query for the "_dnssd-srp._tcp<zone>" SRV record to discover the they query for the "_dnssd-srp._tcp<zone>" SRV record to discover the
server to which they should send DNS updates. server to which they should send DNS updates. Hosts that support SRP
updates using TLS use the "_dnssd-srp-tls._tcp<zone>" SRV record
instead.
For devices designed for Constrained-Node Networks [RFC7228] some For devices designed for Constrained-Node Networks [RFC7228] some
simplifications are available. Instead of being configured with (or simplifications are available. Instead of being configured with (or
discovering) the service registration domain, the (proposed) special- discovering) the service registration domain, the (proposed) special-
use domain name [RFC6761] "default.services.arpa" is used. Instead use domain name (see [RFC6761]) "default.service.arpa" is used.
of learning the server to which they should send DNS updates, a fixed Instead of learning the server to which they should send DNS updates,
IPv6 anycast address is used (value TBD). Anycasts are sent using a fixed IPv6 anycast address is used (value TBD). Anycasts are sent
UDP unless TCP is required due to the size of the update. It is the using UDP unless TCP is required due to the size of the update. It
responsibility of a Constrained-Node Network supporting SRP to is the responsibility of a Constrained-Node Network supporting SRP to
provide appropriate anycast routing to deliver the DNS updates to the provide appropriate anycast routing to deliver the DNS updates to the
appropriate server. It is the responsibility of the SRP server appropriate server. It is the responsibility of the SRP server
supporting a Constrained-Node Network to handle the updates supporting a Constrained-Node Network to handle the updates
appropriately. In some network environments, updates may be accepted appropriately. In some network environments, updates may be accepted
directly into a local "default.services.arpa" zone, which has only directly into a local "default.service.arpa" zone, which has only
local visibility. In other network environments, updates for names local visibility. In other network environments, updates for names
ending in "default.services.arpa" may be rewritten internally to ending in "default.service.arpa" may be rewritten internally to names
names with broader visibility. with broader visibility.
The reason for these different assumptions is that Constrained-Node The reason for these different assumptions is that Constrained-Node
Networks generally require special egress support, and Anycast Networks generally require special egress support, and Anycast
packets captured at the Constrained-Node Network egress can be packets captured at the Constrained-Node Network egress can be
assumed to have originated locally. Low-power devices that typically assumed to have originated locally. Low-power devices that typically
use Constrained-Node Networks may have very limited battery power. use Constrained-Node Networks may have very limited battery power.
The additional DNS lookups required to discover an SRP server and The additional DNS lookups required to discover an SRP server and
then communicate with it will increase the power required to then communicate with it will increase the power required to
advertise a service; for low-power devices, the additional advertise a service; for low-power devices, the additional
flexibility this provides does not justify the additional use of flexibility this provides does not justify the additional use of
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We refer to the DNS Update message sent by services using SRP as an We refer to the DNS Update message sent by services using SRP as an
SRP update. Three types of updates appear in an SRP update: Service SRP update. Three types of updates appear in an SRP update: Service
Discovery records, Service Description records, and Host Description Discovery records, Service Description records, and Host Description
records. records.
o Service Discovery records are one or more PTR RRs, mapping from o Service Discovery records are one or more PTR RRs, mapping from
the generic service type (or subtype) to the specific Service the generic service type (or subtype) to the specific Service
Instance Name. Instance Name.
o Service Description records are exactly one SRV RR, exactly one o Service Description records are exactly one SRV RR, exactly one
KEY RR, and one or more TXT RRs, both with the same name, the KEY RR, and one or more TXT RRs, all with the same name, the
Service Instance Name ([RFC6763] section 4.1). In principle Service Instance Name ([RFC6763] section 4.1). In principle
Service Description records can include other record types, with Service Description records can include other record types, with
the same Service Instance Name, though in practice they rarely do. the same Service Instance Name, though in practice they rarely do.
The Service Instance Name MUST be referenced by one or more The Service Instance Name MUST be referenced by one or more
Service Discovery PTR records, unless it is a placeholder service Service Discovery PTR records, unless it is a placeholder service
registration for an intentionally non-discoverable service name. registration for an intentionally non-discoverable service name.
o The Host Description records for a service are a KEY RR, used to o The Host Description records for a service are a KEY RR, used to
claim exclusive ownership of the service registration, and one or 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 more RRs of type A or AAAA, giving the IPv4 or IPv6 address(es) of
the host where the service resides. the host where the service resides.
RFC 6763 describes the details of what each of these types of updates RFC 6763 describes the details of what each of these types of updates
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2.2. Where to publish it 2.2. Where to publish it
Multicast DNS uses a single namespace, ".local", which is valid on Multicast DNS uses a single namespace, ".local", which is valid on
the local link. This convenience is not available for DNS-SD using the local link. This convenience is not available for DNS-SD using
the DNS protocol: services must exist in some specific unicast the DNS protocol: services must exist in some specific unicast
namespace. namespace.
As described above, full-featured devices are responsible for knowing As described above, full-featured devices are responsible for knowing
in what domain they should register their services. Devices made for in what domain they should register their services. Devices made for
Constrained-Node Networks register in the (proposed) special use Constrained-Node Networks register in the (proposed) special use
domain name [RFC6761] "default.services.arpa", and let the SRP server domain name [RFC6761] "default.service.arpa", and let the SRP server
handle rewriting that to a different domain if necessary. handle rewriting that to a different domain if necessary.
2.3. How to publish it 2.3. How to publish it
It is possible to issue a DNS Update that does several things at 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 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 PTR resource record to the PTR RRset on the Service Name, and
already exists, or creating one if it doesn't, and creating or creating or updating the Service Instance Name and Host Description,
updating the Service Instance Name and Host Description in a single in a single transaction.
transaction.
An SRP update is therefore implemented as a single DNS Update message An SRP update takes advantage of this: it is implemented as a single
that contains a service's Service Discovery records, Service DNS Update message that contains a service's Service Discovery
Description records, and Host Description records. records, Service Description records, and Host Description records.
Updates done according to this specification are somewhat different Updates done according to this specification are somewhat different
than regular DNS Updates as defined in RFC2136. RFC2136 uses a than regular DNS Updates as defined in RFC2136. RFC2136 uses a
fairly heavyweight process for updating: you might first attempt to fairly heavyweight process for updating: you might first attempt to
add a name if it doesn't exist; if that fails, then in a second add a name if it doesn't exist; if that fails, then in a second
message you might update the name if it does exist but matches message you might update the name if it does exist but matches
certain preconditions. Because the registration protocol uses a certain preconditions. Because the registration protocol uses a
single transaction, some of this adaptability is lost. single transaction, some of this adaptability is lost.
In order to allow updates to happen in a single transaction, SRP In order to allow updates to happen in a single transaction, SRP
updates do not include update constraints. The constraints specified updates do not include update prerequisites. The specified in
in Section 2.4.2 are implicit in the processing of SRP updates, and Section 2.4.2 are implicit in the processing of SRP updates, and so
so there is no need for the service sending the SRP update to put in there is no need for the service sending the SRP update to put in any
any explicit constraints. explicit prerequisites.
2.3.1. How DNS-SD Service Registration differs from standard RFC2136 2.3.1. How DNS-SD Service Registration differs from standard RFC2136
DNS Update DNS Update
DNS-SD Service Registration is based on standard RFC2136 DNS Update, DNS-SD Service Registration is based on standard RFC2136 DNS Update,
with some differences: with some differences:
o It implements first-come first-served name allocation, protected o It implements first-come first-served name allocation, protected
using SIG(0) [RFC2931]. using SIG(0) [RFC2931].
o It enforces policy about what updates are allowed. o It enforces policy about what updates are allowed.
o It optionally performs rewriting of "default.services.arpa" to o It optionally performs rewriting of "default.service.arpa" to some
some other domain. other domain.
o It optionally performs automatic population of the address-to-name o It optionally performs automatic population of the address-to-name
reverse mapping domains. reverse mapping domains.
o An SRP server is not required to implement general DNS Update o An SRP server is not required to implement general DNS Update
prerequsite processing. prerequsite processing.
o Simplified clients are allowed to send updates to an anycast o Simplified clients are allowed to send updates to an anycast
address, for names ending in "default.services.arpa" address, for names ending in "default.service.arpa"
2.3.2. Testing using standard RFC2136-compliant servers 2.3.2. Testing using standard RFC2136-compliant servers
It may be useful to set up a DNS server for testing that does not It may be useful to set up a DNS server for testing that does not
implement SRP. This can be done by configuring the server to listen implement SRP. This can be done by configuring the server to listen
on the anycast address, or advertising it in the on the anycast address, or advertising it in the
_dnssd-srp._tcp.<zone> SRV record. It must be configured to be _dnssd-srp._tcp.<zone> SRV and _dnssd-srp-tls._tcp.<zone> record. It
authoritative for "default.services.arpa", and to accept updates from must be configured to be authoritative for "default.service.arpa",
hosts on local networks for names under "default.services.arpa" and to accept updates from hosts on local networks for names under
without authentication, since such servers will not have support for "default.service.arpa" without authentication, since such servers
FCFS authentication Section 2.4.1. will not have support for FCFS authentication Section 2.4.1.
A server configured in this way will be able to successfully accept A server configured in this way will be able to successfully accept
and process SRP updates from services that send SRP updates. and process SRP updates from services that send SRP updates.
However, no constraints will be applied, and this means that the test However, no prerequisites will be applied, and this means that the
server will accept internally inconsistent SRP updates, and will not test server will accept internally inconsistent SRP updates, and will
stop two SRP updates, sent by different services, that claim the same not stop two SRP updates, sent by different services, that claim the
name(s), from overwriting each other. same name(s), from overwriting each other.
Since SRP updates are signed with keys, validation of the SIG(0) Since SRP updates are signed with keys, validation of the SIG(0)
algorithm used by the client can be done by manually installing the algorithm used by the client can be done by manually installing the
client public key on the DNS server that will be receiving the client public key on the DNS server that will be receiving the
updates. The key can then be used to authenticate the client, and updates. The key can then be used to authenticate the client, and
can be used as a requirement for the update. An example can be used as a requirement for the update. An example
configuration for testing SRP using BIND 9 is given in Appendix A. configuration for testing SRP using BIND 9 is given in Appendix A.
2.3.3. How to allow services to update standard RFC2136-compliant 2.3.3. How to allow services to update standard RFC2136-compliant
servers servers
Ordinarily SRP updates will fail when sent to an RFC 2136-compliant Ordinarily SRP updates will fail when sent to an RFC 2136-compliant
server that does not implement SRP because the zone being updated is server that does not implement SRP because the zone being updated is
"default.services.arpa", and no DNS server that is not an SRP server "default.service.arpa", and no DNS server that is not an SRP server
should normally be configured to be authoritative for should normally be configured to be authoritative for
"default.services.arpa". Therefore, a service that sends an SRP "default.service.arpa". Therefore, a service that sends an SRP
update can tell that the receiving server does not support SRP, but update can tell that the receiving server does not support SRP, but
does support RFC2136, because the RCODE will either be NOTZONE, does support RFC2136, because the RCODE will either be NOTZONE,
NOTAUTH or REFUSED, or because there is no response to the update NOTAUTH or REFUSED, or because there is no response to the update
request (when using the anycast address) request (when using the anycast address)
In this case a service MAY attempt to register itself using regular In this case a service MAY attempt to register itself using regular
RFC2136 DNS updates. To do so, it must discover the default RFC2136 DNS updates. To do so, it must discover the default
registration zone and the DNS server designated to receive updates registration zone and the DNS server designated to receive updates
for that zone, as described earlier using the _dns-update._udp SRV for that zone, as described earlier, using the _dns-update._udp SRV
record. It can then make the update using the port and host pointed record. It can then make the update using the port and host pointed
to by the SRV record, and should use appropriate constraints to avoid to by the SRV record, and should use appropriate prerequisites to
overwriting competing records. Such updates are out of scope for avoid overwriting competing records. Such updates are out of scope
SRP, and a service that implements SRP MUST first attempt to use SRP for SRP, and a service that implements SRP MUST first attempt to use
to register itself, and should only attempt to use RFC2136 backwards SRP to register itself, and should only attempt to use RFC2136
compatibility if that fails. Although the owner name for the SRV backwards compatibility if that fails. Although the owner name for
record specifies the UDP protocol for updates, it is also possible to the SRV record specifies the UDP protocol for updates, it is also
use TCP, when the update is too large. possible to use TCP, and TCP should be required to prevent spoofing.
2.4. How to secure it 2.4. How to secure it
Traditional DNS update is secured using the TSIG protocol, which uses Traditional DNS update is secured using the TSIG protocol, which uses
a secret key shared between the client (which issues the update) and a secret key shared between the client (which issues the update) and
the server (which authenticates it). This model does not work for the server (which authenticates it). This model does not work for
automatic service registration. automatic service registration.
The goal of securing the DNS-SD Registration Protocol is to provide The goal of securing the DNS-SD Registration Protocol is to provide
the best possible security given the constraint that service the best possible security given the constraint that service
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pair MUST be unique to the device. pair MUST be unique to the device.
When sending DNS updates, the service includes a KEY record When sending DNS updates, the service includes a KEY record
containing the public portion of the key in each Host Description containing the public portion of the key in each Host Description
update and each Service Description update. Each KEY record MUST update and each Service Description update. Each KEY record MUST
contain the same public key. The update is signed using SIG(0), contain the same public key. The update is signed using SIG(0),
using the private key that corresponds to the public key in the KEY 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 record. The lifetimes of the records in the update is set using the
EDNS(0) Update Lease option [I-D.sekar-dns-ul]. EDNS(0) Update Lease option [I-D.sekar-dns-ul].
The KEY record in service description updates MAY be omitted for The KEY record in Service Description updates MAY be omitted for
brevity; if it is omitted, the SRP server MUST behave as if the same brevity; if it is omitted, the SRP server MUST behave as if the same
KEY record that is given for the Host Description is also given for KEY record that is given for the Host Description is also given for
each Service Description for which no KEY record is provided. each Service Description for which no KEY record is provided.
Omitted KEY records are not used when computing the SIG(0) signature. Omitted KEY records are not used when computing the SIG(0) signature.
The lifetime of the DNS-SD PTR, SRV, A, AAAA and TXT records The lifetime of the DNS-SD PTR, SRV, A, AAAA and TXT records
[RFC6763] uses the LEASE field of the Update Lease option, and is [RFC6763] uses the LEASE field of the Update Lease option, and is
typically set to two hours. This means that if a device is typically set to two hours. This means that if a device is
disconnected from the network, it does not appear in the user disconnected from the network, it does not appear in the user
interfaces of devices looking for services of that type for too long. interfaces of devices looking for services of that type for too long.
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RFC2136. RFC2136.
The SRP server checks each update in the SRP update to see that it The SRP server checks each update in the SRP update to see that it
contains a Service Discovery update, a Service Description update, contains a Service Discovery update, a Service Description update,
and a Host Description update. Order matters in DNS updates. and a Host Description update. Order matters in DNS updates.
Specifically, deletes must precede adds for records that the deletes Specifically, deletes must precede adds for records that the deletes
would affect; otherwise the add will have no effect. This is the would affect; otherwise the add will have no effect. This is the
only ordering constraint; aside from this constraint, updates may only ordering constraint; aside from this constraint, updates may
appear in whatever order is convenient when constructing the update. appear in whatever order is convenient when constructing the update.
Because the SRP update is a DNS update, it MUST contain a single
question that indicates the zone to be updated. Every delete and
update in an SRP update MUST be within the zone that is specified for
the SRP Update.
An update is a Service Discovery update if it contains An update is a Service Discovery update if it contains
o exactly one RRset update, o exactly one RRset update,
o which is for a PTR RR, o which is for a PTR RR,
o which points to a Service Instance Name o which points to a Service Instance Name
o for which an update is present in the SRP update. o for which an update is present in the SRP update.
o Service Discovery updates do not contain any deletes, and do not o Service Discovery updates do not contain any deletes, and do not
contain any other updates. contain any other updates.
An update is a Service Description update if, for the appropriate An update is a Service Description update if, for the appropriate
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public key corresponding to the private key that was used to sign public key corresponding to the private key that was used to sign
the message, the message,
o there is a Service Instance Name update in the SRP update that o there is a Service Instance Name update in the SRP update that
updates an SRV RR so that it points to the hostname being updated updates an SRV RR so that it points to the hostname being updated
by this update. by this update.
o Host Description updates do not update any other records. o Host Description updates do not update any other records.
An SRP update MUST include at least one Service Discovery update, at An SRP update MUST include at least one Service Discovery update, at
least one Service Description update, and exactly one Host least one Service Description update, and exactly one Host
Description update. An update message that does not is not an SRP Description update. An update message that does not is not an SRP
update. An update message that contains any other updates, or any update. An update message that contains any other updates, any other
update constraints, is not an SRP update. Such messages should deletes, or any update prerequisites, is not an SRP update. Such
either be processed as regular RFC2136 updates, including access messages should either be processed as regular RFC2136 updates,
control checks and constraint checks, if supported, or else rejected including access control checks and constraint checks, if supported,
with RCODE=REFUSED. or else rejected with RCODE=REFUSED.
Note that if the definitions of each of these update types are Note that if the definitions of each of these update types are
followed carefully, this means that many things that look very much followed carefully, this means that many things that look very much
like SRP updates nevertheless are not. For example, a DNS update like SRP updates nevertheless are not. For example, a DNS update
that contains an update to a Service Name and an update to a Service that contains an update to a Service Name and an update to a Service
Instance Name, where the Service Name does not reference the Service Instance Name, where the Service Name does not reference the Service
Instance Name, is not a valid SRP update message, but may be a valid Instance Name, is not a valid SRP update message, but may be a valid
RFC2136 update. RFC2136 update.
Assuming that an update message has been validated with these Assuming that an update message has been validated with these
skipping to change at page 12, line 10 skipping to change at page 12, line 14
KEY record updates omitted from Service Description update are KEY record updates omitted from Service Description update are
processed as if they had been explicitly present: every Service processed as if they had been explicitly present: every Service
Description that is updated MUST, after the update, have a KEY RR, Description that is updated MUST, after the update, have a KEY RR,
and it must be the same KEY RR that is present in the Host and it must be the same KEY RR that is present in the Host
Description to which the Service Description refers. Description to which the Service Description refers.
The status that is returned depends on the result of processing the The status that is returned depends on the result of processing the
update, and can be either SUCCESS or SERVFAIL: all other possible update, and can be either SUCCESS or SERVFAIL: all other possible
outcomes should already have been accounted for when applying the outcomes should already have been accounted for when applying the
constraints. constraints that qualify the update as an SRP Update.
The server MAY add a Reverse Mapping that corresponds to the Host The server MAY add a Reverse Mapping that corresponds to the Host
Description. This is not required because the Reverse Mapping serves Description. This is not required because the Reverse Mapping serves
no protocol function, but it may be useful for debugging, e.g. in no protocol function, but it may be useful for debugging, e.g. in
annotating network packet traces or logs. annotating network packet traces or logs. In order for the server to
add a reverse mapping update, it must be authoritative for the zone
or have credentials to do the update. The client MAY also do a
reverse mapping update if it has credentials to do so.
The server MAY apply additional criteria when accepting updates. In The server MAY apply additional criteria when accepting updates. In
some networks, it may be possible to do out-of-band registration of some networks, it may be possible to do out-of-band registration of
keys, and only accept updates from pre-registered keys. In this keys, and only accept updates from pre-registered keys. In this
case, an update for a key that has not been registered should be case, an update for a key that has not been registered should be
rejected with the REFUSED RCODE. rejected with the REFUSED RCODE.
There are at least two benefits to doing this rather than simply There are at least two benefits to doing this rather than simply
using normal SIG(0) DNS updates. First, the same registration using normal SIG(0) DNS updates. First, the same registration
protocol can be used in both cases, so both use cases can be protocol can be used in both cases, so both use cases can be
skipping to change at page 16, line 43 skipping to change at page 16, line 50
For validation, SRP Servers MUST implement the ECDSAP256SHA256 For validation, SRP Servers MUST implement the ECDSAP256SHA256
signature algorithm. SRP servers SHOULD implement the algorithms signature algorithm. SRP servers SHOULD implement the algorithms
specified in [I-D.ietf-dnsop-algorithm-update] section 3.1, in the specified in [I-D.ietf-dnsop-algorithm-update] section 3.1, in the
validation column of the table, starting with algorithm number 13. validation column of the table, starting with algorithm number 13.
SRP clients MUST NOT assume that any algorithm numbered lower than 13 SRP clients MUST NOT assume that any algorithm numbered lower than 13
is available for use in validating SIG(0) signatures. is available for use in validating SIG(0) signatures.
4. Privacy Considerations 4. Privacy Considerations
5. Delegation of 'services.arpa.' Because DNSSD SRP updates can be sent off-link, the privacy
implications of SRP are different than for multicast DNS responses.
Host implementations that are using TCP SHOULD also use TLS if
available. Server implementations MUST offer TLS support. The use
of TLS with DNS is described in [RFC7858] and [RFC8310].
Hosts that implement TLS support SHOULD NOT fall back to TCP; since
servers are required to support TLS, it is entirely up to the host
implementation whether to use it.
5. Delegation of 'service.arpa.'
In order to be fully functional, there must be a delegation of In order to be fully functional, there must be a delegation of
'services.arpa.' in the '.arpa.' zone [RFC3172]. This delegation 'service.arpa.' in the '.arpa.' zone [RFC3172]. This delegation
should be set up as was done for 'home.arpa', as a result of the should be set up as was done for 'home.arpa', as a result of the
specification in [RFC8375]Section 7. specification in [RFC8375]Section 7.
6. IANA Considerations 6. IANA Considerations
6.1. Registration and Delegation of 'services.arpa' as a Special-Use 6.1. Registration and Delegation of 'service.arpa' as a Special-Use
Domain Name Domain Name
IANA is requested to record the domain name 'services.arpa.' in the IANA is requested to record the domain name 'service.arpa.' in the
Special-Use Domain Names registry [SUDN]. IANA is requested, with Special-Use Domain Names registry [SUDN]. IANA is requested, with
the approval of IAB, to implement the delegation requested in the approval of IAB, to implement the delegation requested in
Section 5. Section 5.
IANA is further requested to add a new entry to the "Transport- IANA is further requested to add a new entry to the "Transport-
Independent Locally-Served Zones" subregistry of the the "Locally- Independent Locally-Served Zones" subregistry of the the "Locally-
Served DNS Zones" registry[LSDZ]. The entry will be for the domain Served DNS Zones" registry[LSDZ]. The entry will be for the domain
'services.arpa.' with the description "DNS-SD Registration Protocol 'service.arpa.' with the description "DNS-SD Registration Protocol
Special-Use Domain", listing this document as the reference. Special-Use Domain", listing this document as the reference.
6.2. 'dnssd-srp' Service Name 6.2. 'dnssd-srp' Service Name
IANA is also requested to add a new entry to the Service Names and IANA is also requested to add a new entry to the Service Names and
Port Numbers registry for dnssd-srp with a transport type of tcp. No Port Numbers registry for dnssd-srp with a transport type of tcp. No
port number is to be assigned. The reference should be to this port number is to be assigned. The reference should be to this
document, and the Assignee and Contact information should reference document, and the Assignee and Contact information should reference
the authors of this document. The Description should be as follows: the authors of this document. The Description should be as follows:
Availability of DNS Service Discovery Service Registration Protocol Availability of DNS Service Discovery Service Registration Protocol
Service for a given domain is advertised using the Service for a given domain is advertised using the
"_dnssd-srp._tcp.<domain>." SRV record gives the target host and "_dnssd-srp._tcp.<domain>." SRV record gives the target host and
port where DNSSD Service Registration Service is provided for the port where DNSSD Service Registration Service is provided for the
named domain. named domain.
6.3. Anycast Address 6.3. 'dnssd-srp-tls' Service Name
IANA is also requested to add a new entry to the Service Names and
Port Numbers registry for dnssd-srp with a transport type of tcp. No
port number is to be assigned. The reference should be to this
document, and the Assignee and Contact information should reference
the authors of this document. The Description should be as follows:
Availability of DNS Service Discovery Service Registration Protocol
Service for a given domain over TLS is advertised using the
"_dnssd-srp-tls._tcp.<domain>." SRV record gives the target host and
port where DNSSD Service Registration Service is provided for the
named domain.
6.4. Anycast Address
IANA is requested to allocate an IPv6 Anycast address from the IPv6 IANA is requested to allocate an IPv6 Anycast address from the IPv6
Special-Purpose Address Registry, similar to the Port Control Special-Purpose Address Registry, similar to the Port Control
Protocol anycast address, 2001:1::1. This address is referred to Protocol anycast address, 2001:1::1. This address is referred to
within the document as TBD1, and the document should be updated to within the document as TBD1, and the document should be updated to
reflect the address that was allocated. reflect the address that was allocated.
7. Acknowledgments 7. Acknowledgments
Thanks to Toke Hoeiland-Joergensen for a thorough technical review, Thanks to Toke Hoeiland-Joergensen for a thorough technical review,
skipping to change at page 18, line 38 skipping to change at page 19, line 22
RFC 8106, DOI 10.17487/RFC8106, March 2017, RFC 8106, DOI 10.17487/RFC8106, March 2017,
<https://www.rfc-editor.org/info/rfc8106>. <https://www.rfc-editor.org/info/rfc8106>.
[RFC8375] Pfister, P. and T. Lemon, "Special-Use Domain [RFC8375] Pfister, P. and T. Lemon, "Special-Use Domain
'home.arpa.'", RFC 8375, DOI 10.17487/RFC8375, May 2018, 'home.arpa.'", RFC 8375, DOI 10.17487/RFC8375, May 2018,
<https://www.rfc-editor.org/info/rfc8375>. <https://www.rfc-editor.org/info/rfc8375>.
[I-D.ietf-dnsop-algorithm-update] [I-D.ietf-dnsop-algorithm-update]
Wouters, P. and O. Sury, "Algorithm Implementation Wouters, P. and O. Sury, "Algorithm Implementation
Requirements and Usage Guidance for DNSSEC", draft-ietf- Requirements and Usage Guidance for DNSSEC", draft-ietf-
dnsop-algorithm-update-06 (work in progress), February dnsop-algorithm-update-10 (work in progress), April 2019.
2019.
[SUDN] "Special-Use Domain Names Registry", July 2012, [SUDN] "Special-Use Domain Names Registry", July 2012,
<https://www.iana.org/assignments/special-use-domain- <https://www.iana.org/assignments/special-use-domain-
names/special-use-domain-names.xhtml>. names/special-use-domain-names.xhtml>.
[LSDZ] "Locally-Served DNS Zones Registry", July 2011, [LSDZ] "Locally-Served DNS Zones Registry", July 2011,
<https://www.iana.org/assignments/locally-served-dns- <https://www.iana.org/assignments/locally-served-dns-
zones/locally-served-dns-zones.xhtml>. zones/locally-served-dns-zones.xhtml>.
8.2. Informative References 8.2. Informative References
skipping to change at page 20, line 10 skipping to change at page 20, line 39
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013, DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/info/rfc6762>. <https://www.rfc-editor.org/info/rfc6762>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228, Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014, DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>. <https://www.rfc-editor.org/info/rfc7228>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
for DNS over TLS and DNS over DTLS", RFC 8310,
DOI 10.17487/RFC8310, March 2018,
<https://www.rfc-editor.org/info/rfc8310>.
[I-D.ietf-dnssd-hybrid] [I-D.ietf-dnssd-hybrid]
Cheshire, S., "Discovery Proxy for Multicast DNS-Based Cheshire, S., "Discovery Proxy for Multicast DNS-Based
Service Discovery", draft-ietf-dnssd-hybrid-08 (work in Service Discovery", draft-ietf-dnssd-hybrid-10 (work in
progress), March 2018. progress), March 2019.
[I-D.ietf-dnssd-push] [I-D.ietf-dnssd-push]
Pusateri, T. and S. Cheshire, "DNS Push Notifications", Pusateri, T. and S. Cheshire, "DNS Push Notifications",
draft-ietf-dnssd-push-17 (work in progress), March 2019. draft-ietf-dnssd-push-21 (work in progress), July 2019.
[I-D.cheshire-dnssd-roadmap] [I-D.cheshire-dnssd-roadmap]
Cheshire, S., "Service Discovery Road Map", draft- Cheshire, S., "Service Discovery Road Map", draft-
cheshire-dnssd-roadmap-03 (work in progress), October cheshire-dnssd-roadmap-03 (work in progress), October
2018. 2018.
[I-D.cheshire-edns0-owner-option] [I-D.cheshire-edns0-owner-option]
Cheshire, S. and M. Krochmal, "EDNS0 OWNER Option", draft- Cheshire, S. and M. Krochmal, "EDNS0 OWNER Option", draft-
cheshire-edns0-owner-option-01 (work in progress), July cheshire-edns0-owner-option-01 (work in progress), July
2017. 2017.
[ZC] Cheshire, S. and D. Steinberg, "Zero Configuration [ZC] Cheshire, S. and D. Steinberg, "Zero Configuration
Networking: The Definitive Guide", O'Reilly Media, Inc. , Networking: The Definitive Guide", O'Reilly Media, Inc. ,
ISBN 0-596-10100-7, December 2005. ISBN 0-596-10100-7, December 2005.
Appendix A. Sample BIND9 configuration for default.services.arpa. Appendix A. Sample BIND9 configuration for default.service.arpa.
zone "default.services.arpa." { zone "default.service.arpa." {
type master; type master;
file "/etc/bind/master/service.db"; file "/etc/bind/master/service.db";
allow-update { key demo.default.services.arpa.; }; allow-update { key demo.default.service.arpa.; };
}; };
Zone Configuration in named.conf Zone Configuration in named.conf
$ORIGIN . $ORIGIN .
$TTL 57600 ; 16 hours $TTL 57600 ; 16 hours
default.services.arpa IN SOA ns3.default.services.arpa. postmaster.default.services.arpa. ( default.service.arpa IN SOA ns3.default.service.arpa. postmaster.default.service.arpa. (
2951053287 ; serial 2951053287 ; serial
3600 ; refresh (1 hour) 3600 ; refresh (1 hour)
1800 ; retry (30 minutes) 1800 ; retry (30 minutes)
604800 ; expire (1 week) 604800 ; expire (1 week)
3600 ; minimum (1 hour) 3600 ; minimum (1 hour)
) )
NS ns3.default.services.arpa. NS ns3.default.service.arpa.
SRV 0 0 53 ns3.default.services.arpa. SRV 0 0 53 ns3.default.service.arpa.
$ORIGIN default.services.arpa. $ORIGIN default.service.arpa.
$TTL 3600 ; 1 hour $TTL 3600 ; 1 hour
_ipps._tcp PTR demo._ipps._tcp _ipps._tcp PTR demo._ipps._tcp
$ORIGIN _ipps._tcp.default.services.arpa. $ORIGIN _ipps._tcp.default.service.arpa.
demo TXT "0" demo TXT "0"
SRV 0 0 9992 demo.default.services.arpa. SRV 0 0 9992 demo.default.service.arpa.
$ORIGIN _udp.default.services.arpa. $ORIGIN _udp.default.service.arpa.
$TTL 3600 ; 1 hour $TTL 3600 ; 1 hour
_dns-update PTR ns3.default.services.arpa. _dns-update PTR ns3.default.service.arpa.
$ORIGIN _tcp.default.services.arpa. $ORIGIN _tcp.default.service.arpa.
_dnssd-srp PTR ns3.default.services.arpa. _dnssd-srp PTR ns3.default.service.arpa.
$ORIGIN default.services.arpa. $ORIGIN default.service.arpa.
$TTL 300 ; 5 minutes $TTL 300 ; 5 minutes
ns3 AAAA 2001:db8:0:1::1 ns3 AAAA 2001:db8:0:1::1
$TTL 3600 ; 1 hour $TTL 3600 ; 1 hour
demo AAAA 2001:db8:0:2::1 demo AAAA 2001:db8:0:2::1
KEY 513 3 13 ( KEY 513 3 13 (
qweEmaaq0FAWok5//ftuQtZgiZoiFSUsm0srWREdywQU qweEmaaq0FAWok5//ftuQtZgiZoiFSUsm0srWREdywQU
9dpvtOhrdKWUuPT3uEFF5TZU6B4q1z1I662GdaUwqg== 9dpvtOhrdKWUuPT3uEFF5TZU6B4q1z1I662GdaUwqg==
); alg = ECDSAP256SHA256 ; key id = 15008 ); alg = ECDSAP256SHA256 ; key id = 15008
AAAA ::1 AAAA ::1
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