draft-ietf-dnssd-srp-00.txt   draft-ietf-dnssd-srp-01.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: April 26, 2019 Nibbhaya Consulting Expires: September 12, 2019 Nibbhaya Consulting
October 23, 2018 March 11, 2019
Service Registration Protocol for DNS-Based Service Discovery Service Registration Protocol for DNS-Based Service Discovery
draft-ietf-dnssd-srp-00 draft-ietf-dnssd-srp-01
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 eliminates the dependency Discovery using only unicast packets. This makes it possible to
on Multicast DNS as the foundation layer, which greatly improves deploy DNS Service Discovery without multicast, which greatly
scalability and improves performance on networks where multicast improves scalability and improves performance on networks where
service is not an optimal choice, particularly 802.11 (Wi-Fi) and multicast service is not an optimal choice, particularly 802.11
802.15.4 (IoT) networks. DNS-SD Service registration uses public (Wi-Fi) and 802.15.4 (IoT) networks. DNS-SD Service registration
keys and SIG(0) to allow services to defend their registrations uses public keys and SIG(0) to allow services to defend their
against attack. registrations against attack.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 April 26, 2019. This Internet-Draft will expire on September 12, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 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
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Service Registration Protocol . . . . . . . . . . . . . . . . 4 2. Service Registration Protocol . . . . . . . . . . . . . . . . 4
2.1. What to publish . . . . . . . . . . . . . . . . . . . . . 5 2.1. What to publish . . . . . . . . . . . . . . . . . . . . . 5
2.2. Where to publish it . . . . . . . . . . . . . . . . . . . 6 2.2. Where to publish it . . . . . . . . . . . . . . . . . . . 6
2.3. How to publish it . . . . . . . . . . . . . . . . . . . . 6 2.3. How to publish it . . . . . . . . . . . . . . . . . . . . 6
2.3.1. How DNS-SD Service Registration differs from standard 2.3.1. How DNS-SD Service Registration differs from standard
RFC2136 DNS Update . . . . . . . . . . . . . . . . . 7 RFC2136 DNS Update . . . . . . . . . . . . . . . . . 7
2.3.2. Testing using standard RFC2136-compliant servers . . 7 2.3.2. Testing using standard RFC2136-compliant servers . . 7
2.3.3. How to allow services to update standard 2.3.3. How to allow services to update standard
RFC2136-compliant servers . . . . . . . . . . . . . . 7 RFC2136-compliant servers . . . . . . . . . . . . . . 8
2.4. How to secure it . . . . . . . . . . . . . . . . . . . . 8 2.4. How to secure it . . . . . . . . . . . . . . . . . . . . 8
2.4.1. First-Come First-Served Naming . . . . . . . . . . . 8 2.4.1. First-Come First-Served Naming . . . . . . . . . . . 9
2.4.2. SRP Server Behavior . . . . . . . . . . . . . . . . . 9 2.4.2. SRP Server Behavior . . . . . . . . . . . . . . . . . 10
2.5. TTL Consistency . . . . . . . . . . . . . . . . . . . . . 12 2.5. TTL Consistency . . . . . . . . . . . . . . . . . . . . . 12
2.6. Maintenance . . . . . . . . . . . . . . . . . . . . . . . 12 2.6. Maintenance . . . . . . . . . . . . . . . . . . . . . . . 13
2.6.1. Cleaning up stale data . . . . . . . . . . . . . . . 12 2.6.1. Cleaning up stale data . . . . . . . . . . . . . . . 13
2.6.2. Sleep Proxy . . . . . . . . . . . . . . . . . . . . . 13 2.6.2. Sleep Proxy . . . . . . . . . . . . . . . . . . . . . 14
3. Security Considerations . . . . . . . . . . . . . . . . . . . 14 3. Security Considerations . . . . . . . . . . . . . . . . . . . 15
4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 15 3.1. Source Validation . . . . . . . . . . . . . . . . . . . . 15
5. Delegation of 'services.arpa.' . . . . . . . . . . . . . . . 15 3.2. SIG(0) signature validation . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 3.3. Required Signature Algorithm . . . . . . . . . . . . . . 16
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 16
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 5. Delegation of 'services.arpa.' . . . . . . . . . . . . . . . 16
8.1. Normative References . . . . . . . . . . . . . . . . . . 16 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
8.2. Informative References . . . . . . . . . . . . . . . . . 17 6.1. Registration and Delegation of 'services.arpa' as a
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 Special-Use Domain Name . . . . . . . . . . . . . . . . . 17
6.2. 'dnssd-srp' Service Name . . . . . . . . . . . . . . . . 17
6.3. Anycast Address . . . . . . . . . . . . . . . . . . . . . 17
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Sample BIND9 configuration for
default.services.arpa. . . . . . . . . . . . . . . . 20
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
clients that can do service discovery using the DNS protocol. This clients that can discover services using the DNS protocol. This
extension makes it much easier to take advantage of this existing extension makes it much easier to take advantage of this existing
functionality. functionality.
This document is intended for three audiences: implementors of This document is intended for three audiences: implementors of
software that provides services that should be advertised using DNS- software that provides services that should be advertised using
SD, implementors of DNS servers that will be used in contexts where DNS-SD, implementors of DNS servers that will be used in contexts
DNS-SD registration is needed, and administrators of networks where where DNS-SD registration is needed, and administrators of networks
DNS-SD service is required. The document is intended to provide where DNS-SD service is required. The document is intended to
sufficient information to allow interoperable implementation of the provide sufficient information to allow interoperable implementation
registration protocol. of the registration protocol.
DNS-Based Service Discovery (DNS-SD) allows services to advertise the DNS-Based Service Discovery (DNS-SD) allows services to advertise the
fact that they provide service, and to provide the information fact that they provide service, and to provide the information
required to access that service. Clients can then discover the set required to access that service. Clients can then discover the set
of services of a particular type that are available. They can then of services of a particular type that are available. They can then
select a service from among those that are available and obtain the select a service from among those that are available and obtain the
information required to use it. information required to use it.
The Service Registration Protocol for DNS-SD (SRP), described in this The Service Registration Protocol for DNS-SD (SRP), described in this
document, provides a reasonably secure mechanism for publishing this document, provides a reasonably secure mechanism for publishing this
skipping to change at page 4, line 37 skipping to change at page 4, line 45
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.
For devices designed for Constrained-Node Networks [RFC7228] some For devices designed for Constrained-Node Networks [RFC7228] some
simplifications are used. 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] "services.arpa" is used. Instead of use domain name [RFC6761] "default.services.arpa" is used. Instead
learning the server to which they should send DNS updates, a fixed of learning the server to which they should send DNS updates, a fixed
IPv6 anycast address is used (value TBD). Anycasts are sent using IPv6 anycast address is used (value TBD). Anycasts are sent using
UDP unless TCP is required due to the size of the update. It is the UDP unless TCP is required due to the size of the update. It is the
responsibility of a Constrained-Node Network supporting SRP to 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 "services.arpa" zone, which has only local directly into a local "default.services.arpa" zone, which has only
visibility. In other network environments, updates for names ending local visibility. In other network environments, updates for names
in "services.arpa" may be rewritten internally to names with broader ending in "default.services.arpa" may be rewritten internally to
visibility. names 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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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] "services.arpa", and let the SRP server handle domain name [RFC6761] "default.services.arpa", and let the SRP server
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 if it
already exists, or creating one if it doesn't, and creating or already exists, or creating one if it doesn't, and creating or
updating the Service Instance Name and Host Description in a single updating the Service Instance Name and Host Description in a single
transaction. transaction.
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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 "services.arpa" to some other o It optionally performs rewriting of "default.services.arpa" to
domain. some 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 "services.arpa" address, for names ending in "default.services.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 _dnssd-srp._tcp SRV on the anycast address, or advertising it in the
record. It must be configured to be authoritative for _dnssd-srp._tcp.<zone> SRV record. It must be configured to be
"services.arpa", and to accept updates from hosts on local networks authoritative for "default.services.arpa", and to accept updates from
for names under "services.arpa" without authentication, since such hosts on local networks for names under "default.services.arpa"
servers will not have support for FCFS authentication Section 2.4.1. without authentication, since such servers 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 constraints will be applied, and this means that the test
server will accept internally inconsistent SRP updates, and will not server will accept internally inconsistent SRP updates, and will not
stop two SRP updates, sent by different services, that claim the same stop two SRP updates, sent by different services, that claim the same
name(s), from overwriting each other. name(s), from overwriting each other.
Since SRP updates are signed with keys, validation of the SIG(0)
algorithm used by the client can be done by manually installing 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
can be used as a requirement for the update. An example
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
"services.arpa", and no DNS server that is not an SRP server should "default.services.arpa", and no DNS server that is not an SRP server
normally be configured to be authoritative for "services.arpa". should normally be configured to be authoritative for
Therefore, a service that sends an SRP update can tell that the "default.services.arpa". Therefore, a service that sends an SRP
receiving server does not support SRP, but does support RFC2136, update can tell that the receiving server does not support SRP, but
because the RCODE will either be NOTZONE, NOTAUTH or REFUSED, or does support RFC2136, because the RCODE will either be NOTZONE,
because there is no response to the update request (when using the NOTAUTH or REFUSED, or because there is no response to the update
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 constraints to avoid
overwriting competing records. Such updates are out of scope for overwriting competing records. Such updates are out of scope for
SRP, and a service that implements SRP MUST first attempt to use SRP SRP, and a service that implements SRP MUST first attempt to use SRP
to register itself, and should only attempt to use RFC2136 backwards to register itself, and should only attempt to use RFC2136 backwards
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describe here improves upon the security of mDNS. The goal is not to 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 provide the level of security of a network managed by a skilled
operator. operator.
2.4.1. First-Come First-Served Naming 2.4.1. First-Come First-Served Naming
First-Come First-Serve naming provides a limited degree of security: First-Come First-Serve naming provides a limited degree of security:
a service that registers its service using DNS-SD Registration a service that registers its service using DNS-SD Registration
protocol is given ownership of a name for an extended period of time 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 based on the key used to authenticate the DNS Update. As long as the
registration service remembers thename and the key used to register registration service remembers the name and the key used to register
that name, no other service can add or update the information that name, no other service can add or update the information
associated with that. FCFS naming is used to protect both the associated with that. FCFS naming is used to protect both the
Service Description and the Host Description. Service Description and the Host Description.
2.4.1.1. Service Behavior 2.4.1.1. Service Behavior
The service generates a public/private key pair. This key pair MUST The service generates a public/private key pair. This key pair MUST
be stored in stable storage; if there is no writable stable storage be stored in stable storage; if there is no writable stable storage
on the client, the client MUST be pre-configured with a public/ on the client, the client MUST be pre-configured with a public/
private key pair in read-only storage that can be used. This key private key pair in read-only storage that can be used. This key
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
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
each Service Description for which no KEY record is provided.
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.
The lifetime of the KEY records is set using the KEY-LEASE field of The lifetime of the KEY records is set using the KEY-LEASE field of
the Update Lease Option, and should be set to a much longer time, the Update Lease Option, and should be set to a much longer time,
typically 14 days. The result of this is that even though a device typically 14 days. The result of this is that even though a device
may be temporarily unplugged, disappearing from the network for a few may be temporarily unplugged, disappearing from the network for a few
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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
Service Instance Name, it contains Service Instance Name, it contains
o exactly one "Delete all RRsets from a name" update, o exactly one "Delete all RRsets from a name" update,
o exactly one SRV RRset update, o exactly one SRV RRset update,
o exactly one KEY RR update that adds a KEY RR that contains the o zero or one KEY RR update that adds a KEY RR that contains the
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 (if present, the KEY MUST match the KEY RR given in
the Host Description),
o one or more TXT RRset updates, o one or more TXT RRset updates,
o and the target of the SRV record update references a hostname for o and the target of the SRV record update references a hostname for
which there is a Host Description update in the SRP update. which there is a Host Description update in the SRP update.
o Service Descriptions do not update any other records. o Service Descriptions do not update any other records.
An update is a Host Description update if, for the appropriate An update is a Host Description update if, for the appropriate
hostname, it contains hostname, it contains
o exactly one "Delete all RRsets from a name" update, o exactly one "Delete all RRsets from a name" update,
o one or more A or AAAA RR update(s) o one or more A or AAAA RR update(s)
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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
conditions and is a valid SRP update, the server checks that the name conditions and is a valid SRP update, the server checks that the name
in the Host Description update exists. If so, then the server checks in the Host Description update exists. If so, then the server checks
to see if the KEY record on the name is the same as the KEY record in to see if the KEY record on the name is the same as the KEY record in
the update. The server performs the same check for the KEY records the update. The server performs the same check for the KEY records
in any Service Description update. If any existing KEY record in any Service Description update. For KEY records that were
corresponding to a KEY record in the SRP update does not match the omitted, the KEY from the Host Description update is used. If any
KEY record in the SRP update, then the server MUST reject the SRP existing KEY record corresponding to a KEY record in the SRP update
update with the YXDOMAIN RCODE. does not match the KEY record in the SRP update, then the server MUST
reject the SRP update with the YXDOMAIN RCODE.
Otherwise, the server validates the SRP update using SIG(0) on the Otherwise, the server validates the SRP update using SIG(0) on the
public key in the KEY record of the Host Description update. If the public key in the KEY record of the Host Description update. If the
validation fails, the server MUST reject the SRP Update with the validation fails, the server MUST reject the SRP Update with the
REFUSED RCODE. Otherwise, the SRP update is considered valid and REFUSED RCODE. Otherwise, the SRP update is considered valid and
authentic, and is processed according to the method described in authentic, and is processed according to the method described in
RFC2136. The status that is returned depends on the result of RFC2136.
processing the update.
KEY record updates omitted from Service Description update are
processed as if they had been explicitly present: every Service
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
Description to which the Service Description refers.
The status that is returned depends on the result of processing the
update, and can be either SUCCESS or SERVFAIL: all other possible
outcomes should already have been accounted for when applying the
constraints.
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.
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
skipping to change at page 14, line 49 skipping to change at page 15, line 37
dealing with sleep and wakeup. An SRP registration for such a device dealing with sleep and wakeup. An SRP registration for such a device
will be useful regardless of the mechanism whereby messages are will be useful regardless of the mechanism whereby messages are
delivered to the sleepy end device. For example, the message might delivered to the sleepy end device. For example, the message might
be held in a buffer for an extended period of time by an intermediate be held in a buffer for an extended period of time by an intermediate
device on a mesh network, and then delivered to the device when it device on a mesh network, and then delivered to the device when it
wakes up. The exact details of such behaviors are out of scope for wakes up. The exact details of such behaviors are out of scope for
this document. this document.
3. Security Considerations 3. Security Considerations
3.1. Source Validation
SRP updates have no authorization semantics other than first-come, SRP updates have no authorization semantics other than first-come,
first-served. This means that if an attacker from outside of the first-served. This means that if an attacker from outside of the
administrative domain of the server knows the server's IP address, it administrative domain of the server knows the server's IP address, it
can in principle send updates to the server that will be processed can in principle send updates to the server that will be processed
successfully. Servers should therefore be configured to reject successfully. Servers should therefore be configured to reject
updates from source addresses outside of the administrative domain of updates from source addresses outside of the administrative domain of
the server. the server.
For Anycast updates, this validation must be enforced by every router For Anycast updates, this validation must be enforced by every router
that connects the Constrained-Device Network to the unconstrained that connects the Constrained-Device Network to the unconstrained
skipping to change at page 15, line 32 skipping to change at page 16, line 22
For example, a normal, authenticated RFC2136 update to any RR that For example, a normal, authenticated RFC2136 update to any RR that
was added using SRP, but that is authenticated using a different key, was added using SRP, but that is authenticated using a different key,
could be used to override a promise made by the registration could be used to override a promise made by the registration
protocol, by replacing all or part of the service registration protocol, by replacing all or part of the service registration
information with information provided by a different client. An information with information provided by a different client. An
implementation that allows both kinds of updates should not allow implementation that allows both kinds of updates should not allow
updates to records added by SRP updates using different updates to records added by SRP updates using different
authentication and authorization credentials. authentication and authorization credentials.
3.2. SIG(0) signature validation
This specification does not provide a mechanism for validating
responses from DNS servers to SRP clients. In the case of
Constrained Network/Constrained Node clients, such validation isn't
practical because there's no way to establish trust. In principle, a
KEY RR could be used by a non-constrained SRP client to validate
responses from the server, but this is not required, nor do we
specify a mechanism for determining which key to use.
3.3. Required Signature Algorithm
For validation, SRP Servers MUST implement the ECDSAP256SHA256
signature algorithm. SRP servers SHOULD implement the algorithms
specified in [I-D.ietf-dnsop-algorithm-update] section 3.1, in the
validation column of the table, starting with algorithm number 13.
SRP clients MUST NOT assume that any algorithm numbered lower than 13
is available for use in validating SIG(0) signatures.
4. Privacy Considerations 4. Privacy Considerations
5. Delegation of 'services.arpa.' 5. Delegation of 'services.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 'services.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
Domain Name
IANA is requested to record the domain name 'services.arpa.' in the IANA is requested to record the domain name 'services.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 of for Served DNS Zones" registry[LSDZ]. The entry will be for the domain
'services.arpa.' with the description "DNS-SD Registration Protocol 'services.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
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 "_dnssd- Service for a given domain is advertised using the
srp._tcp.<domain>." SRV record gives the target host and port where "_dnssd-srp._tcp.<domain>." SRV record gives the target host and
DNSSD Service Registration Service is provided for the named domain. port where DNSSD Service Registration Service is provided for the
named domain.
6.3. Anycast Address
IANA is requested to allocate an IPv6 Anycast address from the IPv6
Special-Purpose Address Registry, similar to the Port Control
Protocol anycast address, 2001:1::1. This address is referred to
within the document as TBD1, and the document should be updated to
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,
to Tamara Kemper for doing a nice developmental edit, Tim Wattenberg to Tamara Kemper for doing a nice developmental edit, Tim Wattenberg
for doing a service implementation at the Montreal Hackathon at IETF for doing a service implementation at the Montreal Hackathon at IETF
102, Tom Pusateri for reviewing during the hackathon and afterwards, 102, Tom Pusateri for reviewing during the hackathon and afterwards,
and [...] more reviewers to come, hopefully. and [...] more reviewers to come, hopefully.
8. References 8. References
skipping to change at page 17, line 9 skipping to change at page 18, line 35
[RFC8106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, [RFC8106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
"IPv6 Router Advertisement Options for DNS Configuration", "IPv6 Router Advertisement Options for DNS Configuration",
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]
Wouters, P. and O. Sury, "Algorithm Implementation
Requirements and Usage Guidance for DNSSEC", draft-ietf-
dnsop-algorithm-update-06 (work in progress), February
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 18, line 30 skipping to change at page 20, line 17
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>.
[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-08 (work in
progress), March 2018. progress), March 2018.
[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-15 (work in progress), September draft-ietf-dnssd-push-17 (work in progress), March 2019.
2018.
[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-02 (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.
zone "default.services.arpa." {
type master;
file "/etc/bind/master/service.db";
allow-update { key demo.default.services.arpa.; };
};
Zone Configuration in named.conf
$ORIGIN .
$TTL 57600 ; 16 hours
default.services.arpa IN SOA ns3.default.services.arpa. postmaster.default.services.arpa. (
2951053287 ; serial
3600 ; refresh (1 hour)
1800 ; retry (30 minutes)
604800 ; expire (1 week)
3600 ; minimum (1 hour)
)
NS ns3.default.services.arpa.
SRV 0 0 53 ns3.default.services.arpa.
$ORIGIN default.services.arpa.
$TTL 3600 ; 1 hour
_ipps._tcp PTR demo._ipps._tcp
$ORIGIN _ipps._tcp.default.services.arpa.
demo TXT "0"
SRV 0 0 9992 demo.default.services.arpa.
$ORIGIN _udp.default.services.arpa.
$TTL 3600 ; 1 hour
_dns-update PTR ns3.default.services.arpa.
$ORIGIN _tcp.default.services.arpa.
_dnssd-srp PTR ns3.default.services.arpa.
$ORIGIN default.services.arpa.
$TTL 300 ; 5 minutes
ns3 AAAA 2001:db8:0:1::1
$TTL 3600 ; 1 hour
demo AAAA 2001:db8:0:2::1
KEY 513 3 13 (
qweEmaaq0FAWok5//ftuQtZgiZoiFSUsm0srWREdywQU
9dpvtOhrdKWUuPT3uEFF5TZU6B4q1z1I662GdaUwqg==
); alg = ECDSAP256SHA256 ; key id = 15008
AAAA ::1
Example Zone file
Authors' Addresses Authors' Addresses
Stuart Cheshire Stuart Cheshire
Apple Inc. Apple Inc.
One Apple Park Way One Apple Park Way
Cupertino, California 95014 Cupertino, California 95014
USA USA
Phone: +1 408 974 3207 Phone: +1 408 974 3207
Email: cheshire@apple.com Email: cheshire@apple.com
Ted Lemon Ted Lemon
Nibbhaya Consulting Nibbhaya Consulting
P.O. Box 958 P.O. Box 958
Brattleboro, Vermont 05302 Brattleboro, Vermont 05302
United States of America United States of America
Email: mellon@fugue.com Email: mellon@fugue.com
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