draft-ietf-dnssd-srp-02.txt   draft-ietf-dnssd-srp-03.txt 
Internet Engineering Task Force S. Cheshire Internet Engineering Task Force T. Lemon
Internet-Draft Apple Inc. Internet-Draft Nibbhaya Consulting
Intended status: Informational T. Lemon Intended status: Informational S. Cheshire
Expires: January 9, 2020 Nibbhaya Consulting Expires: January 14, 2021 Apple Inc.
July 8, 2019 July 13, 2020
Service Registration Protocol for DNS-Based Service Discovery Service Registration Protocol for DNS-Based Service Discovery
draft-ietf-dnssd-srp-02 draft-ietf-dnssd-srp-03
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 January 9, 2020. This Internet-Draft will expire on January 14, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 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 2.4. How to secure it . . . . . . . . . . . . . . . . . . . . 7
2.3.3. How to allow services to update standard 2.4.1. First-Come First-Served Naming . . . . . . . . . . . 8
RFC2136-compliant servers . . . . . . . . . . . . . . 8 2.4.2. Removing published services . . . . . . . . . . . . . 9
2.4. How to secure it . . . . . . . . . . . . . . . . . . . . 8 2.4.3. SRP Server Behavior . . . . . . . . . . . . . . . . . 9
2.4.1. First-Come First-Served Naming . . . . . . . . . . . 9
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 'service.arpa.' . . . . . . . . . . . . . . . . 17 5. Delegation of 'service.arpa.' . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
6.1. Registration and Delegation of 'service.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. 'dnssd-srp-tls' Service Name . . . . . . . . . . . . . . 18 6.3. 'dnssd-srp-tls' Service Name . . . . . . . . . . . . . . 17
6.4. Anycast Address . . . . . . . . . . . . . . . . . . . . . 18 6.4. Anycast Address . . . . . . . . . . . . . . . . . . . . . 17
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 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 default.service.arpa. 21 Appendix A. Testing using standard RFC2136-compliant servers . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 Appendix B. How to allow services to update standard
RFC2136-compliant servers . . . . . . . . . . . . . 21
Appendix C. Sample BIND9 configuration for default.service.arpa. 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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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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. Hosts that support SRP server to which they should send DNS updates. Hosts that support SRP
updates using TLS use the "_dnssd-srp-tls._tcp<zone>" SRV record updates using TLS use the "_dnssd-srp-tls._tcp<zone>" SRV record
instead. 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 (see [RFC6761]) "default.service.arpa" is used. use domain name (see [RFC6761]) "default.service.arpa" is used. The
Instead of learning the server to which they should send DNS updates, details of how SRP server(s) are discovered will be specific to the
a fixed IPv6 anycast address is used (value TBD). Anycasts are sent constrained network, and therefore we do not suggest a specific
using UDP unless TCP is required due to the size of the update. It mechanism here.
is the responsibility of a Constrained-Node Network supporting SRP to
provide appropriate anycast routing to deliver the DNS updates to the
appropriate server. It is the responsibility of the SRP server
supporting a Constrained-Node Network to handle the updates
appropriately. In some network environments, updates may be accepted
directly into a local "default.service.arpa" zone, which has only
local visibility. In other network environments, updates for names
ending in "default.service.arpa" may be rewritten internally to names
with broader visibility.
The reason for these different assumptions is that Constrained-Node SRP clients on constrained networks are expected to receive from the
Networks generally require special egress support, and Anycast network a list of SRP servers with which to register. It is the
packets captured at the Constrained-Node Network egress can be responsibility of a Constrained-Node Network supporting SRP to
assumed to have originated locally. Low-power devices that typically provide one or more SRP server addresses. It is the responsibility
use Constrained-Node Networks may have very limited battery power. of the SRP server supporting a Constrained-Node Network to handle the
The additional DNS lookups required to discover an SRP server and updates appropriately. In some network environments, updates may be
then communicate with it will increase the power required to accepted directly into a local "default.service.arpa" zone, which has
advertise a service; for low-power devices, the additional only local visibility. In other network environments, updates for
names ending in "default.service.arpa" may be rewritten internally to
names with broader visibility.
The reason for these different assumptions is that low-power devices
that typically use Constrained-Node Networks may have very limited
battery power. The series of DNS lookups required to discover an SRP
server and then communicate with it will increase the power required
to advertise a service; for low-power devices, the additional
flexibility this provides does not justify the additional use of flexibility this provides does not justify the additional use of
power. power. It is also fairly typical of such networks that some network
service information is obtained as part of the process of joining the
network, and so this can be relied upon to provide nodes with the
information they need.
General networks have the potential to have more complicated Networks that are not constrained networks can more complicated
topologies at the Internet layer, which makes anycast routing more topologies at the Internet layer. Nodes connected to such networks
difficult. Such networks may or may not have the infrastructure can be assumed to be able to do DNSSD service registration domain
required to route anycast to a server that can process it. However, discovery. Such networks are generally able to provide registration
they can be assumed to be able to provide registration domain domain discovery and routing. By requiring the use of TCP, the
discovery and routing. By requiring the use of TCP, the possibility possibility of off-network spoofing is eliminated.
of off-network spoofing is eliminated.
We will discuss several parts to this process: how to know what to We will discuss several parts to this process: how to know what to
publish, how to know where to publish it (under what name), how to publish, how to know where to publish it (under what name), how to
publish it, how to secure its publication, and how to maintain the publish it, how to secure its publication, and how to maintain the
information once published. information once published.
2.1. What to publish 2.1. What to publish
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
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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, and PTR resource record to the PTR RRset on the Service Name, and
creating or updating the Service Instance Name and Host Description, creating or updating the Service Instance Name and Host Description,
in a single transaction. in a single transaction.
An SRP update takes advantage of this: it is implemented as a single An SRP update takes advantage of this: it is implemented as a single
DNS Update message that contains a service's Service Discovery DNS Update message that contains a service's Service Discovery
records, Service 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. The RFC2136 update
fairly heavyweight process for updating: you might first attempt to process can involve many update attempts: 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 prerequisites. The specified in updates do not include update prerequisites. The requirements
Section 2.4.2 are implicit in the processing of SRP updates, and so specified in Section 2.4.3 are implicit in the processing of SRP
there is no need for the service sending the SRP update to put in any updates, and so there is no need for the service sending the SRP
explicit prerequisites. update to put in any 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].
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o It optionally performs rewriting of "default.service.arpa" to some o It optionally performs rewriting of "default.service.arpa" to 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 Clients are allowed to send updates to the generic domain
address, for names ending in "default.service.arpa" "default.service.arpa"
2.3.2. Testing using standard RFC2136-compliant servers
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
on the anycast address, or advertising it in the
_dnssd-srp._tcp.<zone> SRV and _dnssd-srp-tls._tcp.<zone> record. It
must be configured to be authoritative for "default.service.arpa",
and to accept updates from hosts on local networks for names under
"default.service.arpa" 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
and process SRP updates from services that send SRP updates.
However, no prerequisites will be applied, and this means that the
test server will accept internally inconsistent SRP updates, and will
not stop two SRP updates, sent by different services, that claim the
same 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
servers
Ordinarily SRP updates will fail when sent to an RFC 2136-compliant
server that does not implement SRP because the zone being updated is
"default.service.arpa", and no DNS server that is not an SRP server
should normally be configured to be authoritative for
"default.service.arpa". Therefore, a service that sends an SRP
update can tell that the receiving server does not support SRP, but
does support RFC2136, because the RCODE will either be NOTZONE,
NOTAUTH or REFUSED, or because there is no response to the update
request (when using the anycast address)
In this case a service MAY attempt to register itself using regular
RFC2136 DNS updates. To do so, it must discover the default
registration zone and the DNS server designated to receive updates
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
to by the SRV record, and should use appropriate prerequisites to
avoid overwriting competing records. Such updates are out of scope
for SRP, and a service that implements SRP MUST first attempt to use
SRP to register itself, and should only attempt to use RFC2136
backwards compatibility if that fails. Although the owner name for
the SRV record specifies the UDP protocol for updates, it is also
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
registration has to be automatic. It is possible to layer more registration has to be automatic. It is possible to layer more
operational security on top of what we describe here, but what we operational security on top of what we describe here, but what we
describe here improves upon the security of mDNS. The goal is not to describe here is an improvement over the security of mDNS. The goal
provide the level of security of a network managed by a skilled is not to provide the level of security of a network managed by a
operator. skilled 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 the name 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
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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
days, it makes a claim on its name that lasts much longer. days, it makes a claim on its name that lasts much longer.
This means that even if a device is unplugged from the network for a This means that even if a device is unplugged from the network for a
few days, and its services are not available for that time, no other few days, and its services are not available for that time, no other
rogue device can come along and immediately claim its name the moment device can come along and claim its name the moment it disappears
it disappears from the network. In the event that a device is from the network. In the event that a device is unplugged from the
unplugged from the network and permanently discarded, then its name network and permanently discarded, then its name is eventually
is eventually cleaned up and made available for re-use. cleaned up and made available for re-use.
2.4.2. SRP Server Behavior 2.4.2. Removing published services
The SRP server first validates that the SRP update is a syntactically To remove a service registration, the client retransmits its most
recent update with an Update Lease option that has a LEASE value of
zero. If the registration is to be permanently removed, KEY-LEASE
should also be zero. Otherwise, it should have the same value it had
previously; this holds the name in reserve for when the client is
once again able to provide the service.
SRP clients are normally expected to remove all service instances
when removing a host. However, in some cases a client may not have
retained sufficient state to know that some service instance is
pointing to a host that it is removing. Nevertheless, removing the
host can be assumed to mean that all service instances pointing to it
are no longer valid. Therefore, SRP servers MAY remove all service
instances pointing to a host when a host is removed, even if the
client doesn't remove them explicitly.
2.4.3. SRP Server Behavior
2.4.3.1. Validation of Adds
The SRP server first validates that the DNS Update is a syntactically
and semantically valid DNS Update according to the rules specified in and semantically valid DNS Update according to the rules specified in
RFC2136. RFC2136.
The SRP server checks each update in the SRP update to see that it SRP Updates consist of a set of Instructions that together add one or
contains a Service Discovery update, a Service Description update, more services. Each instruction consists either of a single add, or
and a Host Description update. Order matters in DNS updates. a delete followed by an add. When an instruction contains a delete
and an add, the delete MUST precede the add.
The SRP server checks each Instruction in the SRP update to see that
it is either a Service Discovery update, a Service Description
update, or 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 Because the SRP update is a DNS update, it MUST contain a single
question that indicates the zone to be updated. Every delete and 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 update in an SRP update MUST be within the zone that is specified for
the SRP Update. the SRP Update.
An update is a Service Discovery update if it contains An Instruction is a Service Discovery Instruction if it contains
o exactly one RRset update, o exactly one "Add to an RRSet" ([RFC2136] Section 2.5.1) RR,
o which is for a PTR RR, o which is 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 a Service Description Instruction is present in the SRP
o Service Discovery updates do not contain any deletes, and do not Update.
contain any other updates. o Service Discovery Instructions do not contain any deletes, and do
not contain any other adds.
An update is a Service Description update if, for the appropriate An Instruction is a Service Description Instruction if, for the
Service Instance Name, it contains appropriate 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 for the service
o exactly one SRV RRset update, instance name [RFC2136] Section 2.5.3,
o zero or one KEY RR update that adds a KEY RR that contains the o exactly one "Add to an RRset" SRV RR,
public key corresponding to the private key that was used to sign o zero or one "Add to an RRset" KEY RR that contains the public key
the message (if present, the KEY MUST match the KEY RR given in corresponding to the private key that was used to sign the message
the Host Description), (if present, the KEY MUST match the KEY RR given in the Host
o one or more TXT RRset updates, Description),
o and the target of the SRV record update references a hostname for o one or more "Add to an RRset" TXT RRs,
which there is a Host Description update in the SRP update. o and the target of the SRV RR Add points to a hostname for which
o Service Descriptions do not update any other records. there is a Host Description Instruction in the SRP Update.
o Service Descriptions Instructions do not modify any other RRs.
An update is a Host Description update if, for the appropriate An Instruction is a Host Description Instruction if, for the
hostname, it contains appropriate hostname, it contains
o exactly one "Delete all RRsets from a name" update, o exactly one "Delete all RRsets from a name" RR,
o one or more A or AAAA RR update(s) o one or more "Add to an RRset" RRs of type A and/or AAAA,
o exactly one KEY RR update that adds a KEY RR that contains the o exactly one "Add to an RRset" RR that adds a KEY RR that contains
public key corresponding to the private key that was used to sign the public key corresponding to the private key that was used to
the message, sign the message,
o there is a Service Instance Name update in the SRP update that o there is a Service Instance Name Instruction in the SRP update for
updates an SRV RR so that it points to the hostname being updated which the SRV RR that is added points to the hostname being
by this update. updated by this update.
o Host Description updates do not update any other records. o Host Description updates do not modify 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
least one Service Description update, and exactly one Host Instruction, at least one Service Description Instruction, and
Description update. An update message that does not is not an SRP exactly one Host Description Instruction. A DNS Update that does not
update. An update message that contains any other updates, any other is not an SRP update. A DNS Update that contains any other adds, any
deletes, or any update prerequisites, is not an SRP update. Such other deletes, or any prerequisites, is not an SRP update. Such
messages should either be processed as regular RFC2136 updates, messages should either be processed as regular RFC2136 updates,
including access control checks and constraint checks, if supported, including access control checks and constraint checks, if supported,
or else rejected 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 RRset Add to a Service Name and an RRset Add to a
Instance Name, where the Service Name does not reference the Service Service Instance Name, where the Service Name does not reference the
Instance Name, is not a valid SRP update message, but may be a valid Service Instance Name, is not a valid SRP update message, but may be
RFC2136 update. a valid RFC2136 update.
Assuming that an update message has been validated with these Assuming that a DNS 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 Instruction exists. If so, then the server
to see if the KEY record on the name is the same as the KEY record in checks to see if the KEY record on that name is the same as the KEY
the update. The server performs the same check for the KEY records record in the Host Description Instruction. The server performs the
in any Service Description update. For KEY records that were same check for the KEY records in any Service Description
omitted, the KEY from the Host Description update is used. If any Instrructions. For KEY records that were omitted from Service
existing KEY record corresponding to a KEY record in the SRP update Description Instructions, the KEY from the Host Description
does not match the KEY record in the SRP update, then the server MUST Instruction is used. If any existing KEY record corresponding to a
reject the SRP update with the YXDOMAIN RCODE. KEY record in the SRP Update does not match the KEY same record in
the SRP Update (whether provided or taken from the Host Description
Instruction), 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. RFC2136.
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
skipping to change at page 19, line 34 skipping to change at page 19, line 15
[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
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>. November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", [RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997, RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>. <https://www.rfc-editor.org/info/rfc2131>.
[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)", "Dynamic Updates in the Domain Name System (DNS UPDATE)",
skipping to change at page 20, line 17 skipping to change at page 19, line 40
<https://www.rfc-editor.org/info/rfc2181>. <https://www.rfc-editor.org/info/rfc2181>.
[RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures [RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures
( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September ( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September
2000, <https://www.rfc-editor.org/info/rfc2931>. 2000, <https://www.rfc-editor.org/info/rfc2931>.
[RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic [RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic
Update", RFC 3007, DOI 10.17487/RFC3007, November 2000, Update", RFC 3007, DOI 10.17487/RFC3007, November 2000,
<https://www.rfc-editor.org/info/rfc3007>. <https://www.rfc-editor.org/info/rfc3007>.
[RFC3152] Bush, R., "Delegation of IP6.ARPA", BCP 49, RFC 3152,
DOI 10.17487/RFC3152, August 2001,
<https://www.rfc-editor.org/info/rfc3152>.
[RFC6760] Cheshire, S. and M. Krochmal, "Requirements for a Protocol [RFC6760] Cheshire, S. and M. Krochmal, "Requirements for a Protocol
to Replace the AppleTalk Name Binding Protocol (NBP)", to Replace the AppleTalk Name Binding Protocol (NBP)",
RFC 6760, DOI 10.17487/RFC6760, February 2013, RFC 6760, DOI 10.17487/RFC6760, February 2013,
<https://www.rfc-editor.org/info/rfc6760>. <https://www.rfc-editor.org/info/rfc6760>.
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names", [RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013, RFC 6761, DOI 10.17487/RFC6761, February 2013,
<https://www.rfc-editor.org/info/rfc6761>. <https://www.rfc-editor.org/info/rfc6761>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
skipping to change at page 21, line 7 skipping to change at page 20, line 27
DOI 10.17487/RFC8310, March 2018, DOI 10.17487/RFC8310, March 2018,
<https://www.rfc-editor.org/info/rfc8310>. <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-10 (work in Service Discovery", draft-ietf-dnssd-hybrid-10 (work in
progress), March 2019. 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-21 (work in progress), July 2019. draft-ietf-dnssd-push-25 (work in progress), October 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.service.arpa. Appendix A. Testing using standard RFC2136-compliant servers
zone "default.service.arpa." { It may be useful to set up a DNS server for testing that does not
type master; implement SRP. This can be done by configuring the server to listen
file "/etc/bind/master/service.db"; on the anycast address, or advertising it in the
allow-update { key demo.default.service.arpa.; }; _dnssd-srp._tcp.<zone> SRV and _dnssd-srp-tls._tcp.<zone> record. It
}; must be configured to be authoritative for "default.service.arpa",
and to accept updates from hosts on local networks for names under
"default.service.arpa" 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
and process SRP updates from services that send SRP updates.
However, no prerequisites will be applied, and this means that the
test server will accept internally inconsistent SRP updates, and will
not stop two SRP updates, sent by different services, that claim the
same 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 C.
Appendix B. How to allow services to update standard RFC2136-compliant
servers
Ordinarily SRP updates will fail when sent to an RFC 2136-compliant
server that does not implement SRP because the zone being updated is
"default.service.arpa", and no DNS server that is not an SRP server
should normally be configured to be authoritative for
"default.service.arpa". Therefore, a service that sends an SRP
update can tell that the receiving server does not support SRP, but
does support RFC2136, because the RCODE will either be NOTZONE,
NOTAUTH or REFUSED, or because there is no response to the update
request (when using the anycast address)
In this case a service MAY attempt to register itself using regular
RFC2136 DNS updates. To do so, it must discover the default
registration zone and the DNS server designated to receive updates
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
to by the SRV record, and should use appropriate prerequisites to
avoid overwriting competing records. Such updates are out of scope
for SRP, and a service that implements SRP MUST first attempt to use
SRP to register itself, and should only attempt to use RFC2136
backwards compatibility if that fails. Although the owner name for
the SRV record specifies the UDP protocol for updates, it is also
possible to use TCP, and TCP should be required to prevent spoofing.
Appendix C. Sample BIND9 configuration for default.service.arpa.
zone "default.service.arpa." {
type master;
file "/etc/bind/master/service.db";
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.service.arpa IN SOA ns3.default.service.arpa. postmaster.default.service.arpa. ( default.service.arpa IN SOA ns3.default.service.arpa.
2951053287 ; serial postmaster.default.service.arpa. (
3600 ; refresh (1 hour) 2951053287 ; serial
1800 ; retry (30 minutes) 3600 ; refresh (1 hour)
604800 ; expire (1 week) 1800 ; retry (30 minutes)
3600 ; minimum (1 hour) 604800 ; expire (1 week)
) 3600 ; minimum (1 hour)
NS ns3.default.service.arpa. )
SRV 0 0 53 ns3.default.service.arpa. NS ns3.default.service.arpa.
$ORIGIN default.service.arpa. SRV 0 0 53 ns3.default.service.arpa.
$TTL 3600 ; 1 hour $ORIGIN default.service.arpa.
_ipps._tcp PTR demo._ipps._tcp $TTL 3600 ; 1 hour
$ORIGIN _ipps._tcp.default.service.arpa. _ipps._tcp PTR demo._ipps._tcp
demo TXT "0" $ORIGIN _ipps._tcp.default.service.arpa.
SRV 0 0 9992 demo.default.service.arpa. demo TXT "0"
$ORIGIN _udp.default.service.arpa. SRV 0 0 9992 demo.default.service.arpa.
$TTL 3600 ; 1 hour $ORIGIN _udp.default.service.arpa.
_dns-update PTR ns3.default.service.arpa. $TTL 3600 ; 1 hour
$ORIGIN _tcp.default.service.arpa. _dns-update PTR ns3.default.service.arpa.
_dnssd-srp PTR ns3.default.service.arpa. $ORIGIN _tcp.default.service.arpa.
$ORIGIN default.service.arpa. _dnssd-srp PTR ns3.default.service.arpa.
$TTL 300 ; 5 minutes $ORIGIN default.service.arpa.
ns3 AAAA 2001:db8:0:1::1 $TTL 300 ; 5 minutes
$TTL 3600 ; 1 hour ns3 AAAA 2001:db8:0:1::1
demo AAAA 2001:db8:0:2::1 $TTL 3600 ; 1 hour
KEY 513 3 13 ( demo AAAA 2001:db8:0:2::1
qweEmaaq0FAWok5//ftuQtZgiZoiFSUsm0srWREdywQU KEY 513 3 13 (
9dpvtOhrdKWUuPT3uEFF5TZU6B4q1z1I662GdaUwqg== qweEmaaq0FAWok5//ftuQtZgiZoiFSUsm0srWREdywQU
); alg = ECDSAP256SHA256 ; key id = 15008 9dpvtOhrdKWUuPT3uEFF5TZU6B4q1z1I662GdaUwqg==
AAAA ::1 ); alg = ECDSAP256SHA256 ; key id = 15008
AAAA ::1
Example Zone file Example Zone file
Authors' Addresses Authors' Addresses
Ted Lemon
Nibbhaya Consulting
P.O. Box 958
Brattleboro, Vermont 05302
United States of America
Email: mellon@fugue.com
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
Nibbhaya Consulting
P.O. Box 958
Brattleboro, Vermont 05302
United States of America
Email: mellon@fugue.com
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