draft-ietf-dnssd-hybrid-00.txt   draft-ietf-dnssd-hybrid-01.txt 
Internet Engineering Task Force S. Cheshire Internet Engineering Task Force S. Cheshire
Internet-Draft Apple Inc. Internet-Draft Apple Inc.
Intended status: Standards Track November 10, 2014 Intended status: Standards Track October 19, 2015
Expires: May 14, 2015 Expires: April 21, 2016
Hybrid Unicast/Multicast DNS-Based Service Discovery Hybrid Unicast/Multicast DNS-Based Service Discovery
draft-ietf-dnssd-hybrid-00 draft-ietf-dnssd-hybrid-01
Abstract Abstract
Performing DNS-Based Service Discovery using purely link-local Performing DNS-Based Service Discovery using purely link-local
Multicast DNS enables discovery of services that are on the local Multicast DNS enables discovery of services that are on the local
link, but not (without some kind of proxy or similar special support) link, but not (without some kind of proxy or similar special support)
of services that are outside the local link. Using a very large discovery of services that are outside the local link. Using a very
local link with thousands of hosts improves service discovery, but at large local link with thousands of hosts facilitates service
the cost of large amounts of multicast traffic. discovery, but at the cost of large amounts of multicast traffic.
Performing DNS-Based Service Discovery using purely Unicast DNS is Performing DNS-Based Service Discovery using purely Unicast DNS is
more efficient, but requires configuration of DNS Update keys on the more efficient and doesn't require excessively large multicast
devices offering the services, which can be onerous for simple domains, but requires that the relevant data be available in the
devices like printers and network cameras. Unicast DNS namespace. This can be achieved by manual DNS
configuration (as has been done for many years at IETF meetings to
advertise the IETF Terminal Room printer) but this is labor
intensive, error prone, and requires a reasonable degree of DNS
expertise. The Unicast DNS namespace can be populated with the
required data automatically by the devices themselves, but that
requires configuration of DNS Update keys on the devices offering the
services, which has proven onerous and impractical for simple devices
like printers and network cameras.
Hence a compromise is needed, that provides easy service discovery Hence a compromise is needed, that combines the ease-of-use of
without requiring either large amounts of multicast traffic or Multicast DNS with the efficiency and scalability of Unicast DNS.
onerous configuration.
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 http://datatracker.ietf.org/drafts/current/. Drafts is at http://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 21, 2016.
This Internet-Draft will expire on May 14, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Terminology Used in this Document . . . . . . 4 2. Conventions and Terminology Used in this Document . . . . . . 5
3. Hybrid Proxy Operation . . . . . . . . . . . . . . . . . . . . 5 3. Hybrid Proxy Operation . . . . . . . . . . . . . . . . . . . . 6
3.1. Domain Enumeration . . . . . . . . . . . . . . . . . . . . 6 3.1. Delegated Subdomain for Service Discovery Records . . . . 7
3.2. Delegated Subdomain for LDH Host Names . . . . . . . . . . 7 3.2. Domain Enumeration . . . . . . . . . . . . . . . . . . . . 8
3.3. Delegated Subdomain for Reverse Mapping . . . . . . . . . 9 3.2.1. Domain Enumeration via Unicast Queries . . . . . . . . 8
3.4. Data Translation . . . . . . . . . . . . . . . . . . . . . 10 3.2.2. Domain Enumeration via Multicast Queries . . . . . . . 9
3.4.1. DNS TTL limiting . . . . . . . . . . . . . . . . . . . 10 3.3. Delegated Subdomain for LDH Host Names . . . . . . . . . . 10
3.4.2. Suppressing Unusable Records . . . . . . . . . . . . . 10 3.4. Delegated Subdomain for Reverse Mapping . . . . . . . . . 12
3.4.3. Application-Specific Data Translation . . . . . . . . 11 3.5. Data Translation . . . . . . . . . . . . . . . . . . . . . 13
3.5. Answer Aggregation . . . . . . . . . . . . . . . . . . . . 12 3.5.1. DNS TTL limiting . . . . . . . . . . . . . . . . . . . 13
3.5.1. Discovery of LLQ Service . . . . . . . . . . . . . . . 14 3.5.2. Suppressing Unusable Records . . . . . . . . . . . . . 13
4. Implementation Status . . . . . . . . . . . . . . . . . . . . 15 3.5.3. Application-Specific Data Translation . . . . . . . . 14
4.1. Already Implemented and Deployed . . . . . . . . . . . . . 15 3.6. Answer Aggregation . . . . . . . . . . . . . . . . . . . . 15
4.2. Partially Implemented . . . . . . . . . . . . . . . . . . 15 3.6.1. Discovery of LLQ or PUSH Notification Service . . . . 17
4.3. Not Yet Implemented . . . . . . . . . . . . . . . . . . . 16 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 18
5. IPv6 Considerations . . . . . . . . . . . . . . . . . . . . . 16 4.1. Already Implemented and Deployed . . . . . . . . . . . . . 18
6. Security Considerations . . . . . . . . . . . . . . . . . . . 17 4.2. Partially Implemented . . . . . . . . . . . . . . . . . . 18
6.1. Authenticity . . . . . . . . . . . . . . . . . . . . . . . 17 4.3. Not Yet Implemented . . . . . . . . . . . . . . . . . . . 19
6.2. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 17 5. IPv6 Considerations . . . . . . . . . . . . . . . . . . . . . 19
6.3. Denial of Service . . . . . . . . . . . . . . . . . . . . 17 6. Security Considerations . . . . . . . . . . . . . . . . . . . 20
7. Intelectual Property Rights . . . . . . . . . . . . . . . . . 18 6.1. Authenticity . . . . . . . . . . . . . . . . . . . . . . . 20
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 6.2. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 20
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 6.3. Denial of Service . . . . . . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 7. Intelectual Property Rights . . . . . . . . . . . . . . . . . 21
10.1. Normative References . . . . . . . . . . . . . . . . . . . 18 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
10.2. Informative References . . . . . . . . . . . . . . . . . . 19 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 19 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
10.1. Normative References . . . . . . . . . . . . . . . . . . . 21
10.2. Informative References . . . . . . . . . . . . . . . . . . 22
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction 1. Introduction
Multicast DNS [RFC6762] and its companion technology DNS-based Multicast DNS [RFC6762] and its companion technology DNS-based
Service Discovery [RFC6763] were created to provide IP networking Service Discovery [RFC6763] were created to provide IP networking
with the ease-of-use and autoconfiguration for which AppleTalk was with the ease-of-use and autoconfiguration for which AppleTalk was
well known [RFC6760] [ZC]. well known [RFC6760] [ZC].
For a small network consisting of just a single link (or several For a small network consisting of just a single link (or several
physical links bridged together to appear as a single logical link to physical links bridged together to appear as a single logical link to
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any device forwarding a packet modifies any part of the IP header or any device forwarding a packet modifies any part of the IP header or
IP payload then the packet is no longer considered to be on the same IP payload then the packet is no longer considered to be on the same
link. This means that the packet may pass through devices such as link. This means that the packet may pass through devices such as
repeaters, bridges, hubs or switches and still be considered to be on repeaters, bridges, hubs or switches and still be considered to be on
the same link for the purpose of this document, but not through a the same link for the purpose of this document, but not through a
device such as an IP router that decrements the IP TTL or otherwise device such as an IP router that decrements the IP TTL or otherwise
modifies the IP header. modifies the IP header.
3. Hybrid Proxy Operation 3. Hybrid Proxy Operation
In a typical configuration, a Hybrid Proxy is configured to be
authoritative for four DNS subdomains, and authority for these
subdomains is delegated to it via NS records:
A DNS subdomain for service discovery records.
This subdomain name may contain rich text, including spaces and
other punctuation. This is because this subdomain name is used
only in graphical user interfaces, where rich text is appropriate.
A DNS subdomain for host name records.
This subdomain name SHOULD be limited to letters, digits and
hyphens, to facilitate convenient use of host names in command-
line interfaces.
A DNS subdomain for IPv6 Reverse Mapping records.
This subdomain name will be a name that ends in "ip6.arpa."
A DNS subdomain for IPv4 Reverse Mapping records.
This subdomain name will be a name that ends in "in-addr.arpa."
These three varieties of delegated subdomains (service discovery,
host names, and reverse mapping) are described below.
3.1. Delegated Subdomain for Service Discovery Records
In its simplest form, each physical link in an organization is In its simplest form, each physical link in an organization is
assigned a unique Unicast DNS domain name, such as assigned a unique Unicast DNS domain name, such as
"Building 1.example.com" or "4th Floor.Building 1.example.com". "Building 1.example.com" or "4th Floor.Building 1.example.com".
Grouping multiple links under a single Unicast DNS domain name is to Grouping multiple links under a single Unicast DNS domain name is to
be specified in a future companion document, but for the purposes of be specified in a future companion document, but for the purposes of
this document, assume that each link has its own unique Unicast DNS this document, assume that each link has its own unique Unicast DNS
domain name. In a graphical user interface these names are not domain name. In a graphical user interface these names are not
displayed as strings with dots as shown above, but something more displayed as strings with dots as shown above, but something more
akin to a typical file browser graphical user interface (which is akin to a typical file browser graphical user interface (which is
harder to illustrate in a text-only document) showing folders, harder to illustrate in a text-only document) showing folders,
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case, "_printer._tcp.local. PTR ?"). Then, from the received case, "_printer._tcp.local. PTR ?"). Then, from the received
Multicast DNS data, the Hybrid Proxy synthesizes the appropriate Multicast DNS data, the Hybrid Proxy synthesizes the appropriate
Unicast DNS response. Unicast DNS response.
Naturally, the existing Multicast DNS caching mechanism is used to Naturally, the existing Multicast DNS caching mechanism is used to
avoid issuing unnecessary Multicast DNS queries on the wire. The avoid issuing unnecessary Multicast DNS queries on the wire. The
Hybrid Proxy is acting as a client of the underlying Multicast DNS Hybrid Proxy is acting as a client of the underlying Multicast DNS
subsystem, and benefits from the same caching and efficiency measures subsystem, and benefits from the same caching and efficiency measures
as any other client using that subsystem. as any other client using that subsystem.
3.1. Domain Enumeration 3.2. Domain Enumeration
An DNS-SD client performs Domain Enumeration [RFC6763] via certain
PTR queries. It issues unicast Domain Enumeration queries using its
"home" domain (typically learned learned via DHCP) and using its IPv6
prefix and IPv4 subnet address. These are described below in
Section 3.2.1. It also issues multicast Domain Enumeration queries
in the "local" domain [RFC6762]. These are described below in
Section 3.2.2. The results of all Domain Enumeration queries are
combined for Service Discovery purposes.
3.2.1. Domain Enumeration via Unicast Queries
The administrator creates Domain Enumeration PTR records [RFC6763] to The administrator creates Domain Enumeration PTR records [RFC6763] to
inform clients of available service discovery domains, e.g.,: inform clients of available service discovery domains, e.g.,:
b._dns-sd._udp.example.com. PTR Building 1.example.com. b._dns-sd._udp.example.com. PTR Building 1.example.com.
PTR Building 2.example.com. PTR Building 2.example.com.
PTR Building 3.example.com. PTR Building 3.example.com.
PTR Building 4.example.com. PTR Building 4.example.com.
db._dns-sd._udp.example.com. PTR Building 1.example.com. db._dns-sd._udp.example.com. PTR Building 1.example.com.
lb._dns-sd._udp.example.com. PTR Building 1.example.com. lb._dns-sd._udp.example.com. PTR Building 1.example.com.
The "b" ("browse") records tell the client device the list of The "b" ("browse") records tell the client device the list of
browsing domains to display for the user to select from and the "db" browsing domains to display for the user to select from and the "db"
("default browse") record tells the client device which domain in ("default browse") record tells the client device which domain in
that list should be selected by default. The "lb" ("legacy browse") that list should be selected by default. The "lb" ("legacy browse")
record tells the client device which domain to automatically browse record tells the client device which domain to automatically browse
on behalf of applications that don't implement UI for multi-domain on behalf of applications that don't implement UI for multi-domain
browsing (which is most of them, today). The "lb" domain is usually browsing (which is most of them, today). The "lb" domain is often
the same as the "db" domain. the same as the "db" domain, or sometimes the "db" domain plus one or
more others that should be included in the list of automatic browsing
domains for legacy clients.
DNS responses are limited to a maximum size of 65535 bytes. This DNS responses are limited to a maximum size of 65535 bytes. This
limits the maximum number of domains that can be returned for a limits the maximum number of domains that can be returned for a
Domain Enumeration query, as follows: Domain Enumeration query, as follows:
A DNS response header is 12 bytes. That's typically followed by a A DNS response header is 12 bytes. That's typically followed by a
single qname (up to 256 bytes) plus qtype (2 bytes) and qclass single qname (up to 256 bytes) plus qtype (2 bytes) and qclass
(2 bytes), leaving 65275 for the Answer Section. (2 bytes), leaving 65275 for the Answer Section.
An Answer Section Resource Record consists of: An Answer Section Resource Record consists of:
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This means that each Resource Record in the Answer Section can take This means that each Resource Record in the Answer Section can take
up to 268 bytes total, which means that the Answer Section can up to 268 bytes total, which means that the Answer Section can
contain, in the worst case, no more than 243 domains. contain, in the worst case, no more than 243 domains.
In a more typical scenario, where the domain names are not all In a more typical scenario, where the domain names are not all
maximum-sized names, and there is some similarity between names so maximum-sized names, and there is some similarity between names so
that reasonable name compression is possible, each Answer Section that reasonable name compression is possible, each Answer Section
Resource Record may average 140 bytes, which means that the Answer Resource Record may average 140 bytes, which means that the Answer
Section can contain up to 466 domains. Section can contain up to 466 domains.
3.2. Delegated Subdomain for LDH Host Names 3.2.2. Domain Enumeration via Multicast Queries
The rules for DNS-SD service instance names and domains are more Since a Hybrid Proxy exists on many, if not all, the links in an
permissive than the traditional rules for host names. enterprise, it offers an additional way to provide Domain Enumeration
data for clients.
A Hybrid Proxy can be configured to generate Multicast DNS responses
for the following Multicast DNS Domain Enumeration queries issues by
clients:
b._dns-sd._udp.local. PTR ?
db._dns-sd._udp.local. PTR ?
lb._dns-sd._udp.local. PTR ?
This provides the ability for Hybrid Proxies to provide configuration
data on a per-link granularity to DNS-SD clients. In some
enterprises it may be preferable to provide this per-link
configuration data in the form of Hybrid Proxy configuration, rather
than populating the Unicast DNS servers with the same data (in the
"ip6.arpa" or "in-addr.arpa" domains).
3.3. Delegated Subdomain for LDH Host Names
The traditional rules for host names are more restrictive than those
for DNS-SD service instance names and domains.
Users typically interact with DNS-SD by viewing a list of discovered Users typically interact with DNS-SD by viewing a list of discovered
service instance names on the display and selecting one of them by service instance names on the display and selecting one of them by
pointing, touching, or clicking. Similarly, in software that pointing, touching, or clicking. Similarly, in software that
provides a multi-domain DNS-SD user interface, users view a list of provides a multi-domain DNS-SD user interface, users view a list of
offered domains on the display and select one of them by pointing, offered domains on the display and select one of them by pointing,
touching, or clicking. To use a service, users don't have to touching, or clicking. To use a service, users don't have to
remember domain or instance names, or type them; users just have to remember domain or instance names, or type them; users just have to
be able to recognize what they see on the display and click on the be able to recognize what they see on the display and click on the
thing they want. thing they want.
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names and domains, it is advisable, for maximum compatibility with names and domains, it is advisable, for maximum compatibility with
existing software, to restrict host names to the traditional letter- existing software, to restrict host names to the traditional letter-
digit-hyphen rules. This means that while a service name digit-hyphen rules. This means that while a service name
"My Printer._ipp._tcp.Building 1.example.com" is acceptable and "My Printer._ipp._tcp.Building 1.example.com" is acceptable and
desirable (it is displayed in a graphical user interface as an desirable (it is displayed in a graphical user interface as an
instance called "My Printer" in the domain "Building 1" at instance called "My Printer" in the domain "Building 1" at
"example.com"), a host name "My-Printer.Building 1.example.com" is "example.com"), a host name "My-Printer.Building 1.example.com" is
not advisable (because of the space in "Building 1"). not advisable (because of the space in "Building 1").
To accomodate this difference in allowable characters, a Hybrid Proxy To accomodate this difference in allowable characters, a Hybrid Proxy
MUST support having two subdomains delegated to it, one to be used MUST support having separate subdomains delegated to it, one to be
for host names (names of 'A' and 'AAAA' address records), which is used for host names (names of 'A' and 'AAAA' address records), which
restricted to the traditional letter-digit-hyphen rules, and another is restricted to the traditional letter-digit-hyphen rules, and
to be used for other records (including the PTR, SRV and TXT records another to be used for other records (including the PTR, SRV and TXT
used by DNS-SD), which is allowed to be arbitrary Net-Unicode text records used by DNS-SD), which is allowed to be arbitrary Net-Unicode
[RFC5198]. text [RFC5198].
For example, a Hybrid Proxy could have the two subdomains For example, a Hybrid Proxy could have the two subdomains
"Building 1.example.com" and "bldg1.example.com" delegated to it. "Building 1.example.com" and "bldg1.example.com" delegated to it.
The Hybrid Proxy would then translate these two Multicast DNS The Hybrid Proxy would then translate these two Multicast DNS
records: records:
My Printer._ipp._tcp.local. SRV 0 0 631 prnt.local. My Printer._ipp._tcp.local. SRV 0 0 631 prnt.local.
prnt.local. A 10.0.1.2 prnt.local. A 10.0.1.2
into Unicast DNS records as follows: into Unicast DNS records as follows:
My Printer._ipp._tcp.Building 1.example.com. My Printer._ipp._tcp.Building 1.example.com.
SRV 0 0 631 prnt.bldg1.example.com. SRV 0 0 631 prnt.bldg1.example.com.
prnt.bldg1.example.com. A 10.0.1.2 prnt.bldg1.example.com. A 10.0.1.2
Note that the SRV record name is translated using the rich-text Note that the SRV record name is translated using the rich-text
domain name ("Building 1.example.com") and the address record name is domain name ("Building 1.example.com") and the address record name is
translated using the LDH domain ("bldg1.example.com"). translated using the LDH domain ("bldg1.example.com").
3.3. Delegated Subdomain for Reverse Mapping 3.4. Delegated Subdomain for Reverse Mapping
A Hybrid Proxy can facilitate easier management of reverse mapping A Hybrid Proxy can facilitate easier management of reverse mapping
domains, particularly for IPv6 addresses where manual management may domains, particularly for IPv6 addresses where manual management may
be more onerous than it is for IPv4 addresses. be more onerous than it is for IPv4 addresses.
To achieve this, in the parent domain, NS records are used to To achieve this, in the parent domain, NS records are used to
delegate ownership of the appropriate reverse mapping domain to the delegate ownership of the appropriate reverse mapping domain to the
Hybrid Proxy. In other words, the Hybrid Proxy becomes the Hybrid Proxy. In other words, the Hybrid Proxy becomes the
authoritative name server for the reverse mapping domain. authoritative name server for the reverse mapping domain.
For example, if a given link is using the IPv4 subnet 10.1/16, then For example, if a given link is using the IPv6 prefix 2001:0DB8/32,
the domain "1.10.in-addr.arpa" is delegated to the Hybrid Proxy for then the domain "8.b.d.0.1.0.0.2.ip6.arpa" is delegated to the Hybrid
that link. Proxy for that link.
If a given link is using the IPv6 prefix 2001:0DB8/32, then the If a given link is using the IPv4 subnet 10.1/16, then the domain
domain "8.b.d.0.1.0.0.2.ip6.arpa" is delegated to the Hybrid Proxy "1.10.in-addr.arpa" is delegated to the Hybrid Proxy for that link.
for that link.
When a reverse mapping query arrives at the Hybrid Proxy, it issues When a reverse mapping query arrives at the Hybrid Proxy, it issues
the identical query on its local link as a Multicast DNS query. the identical query on its local link as a Multicast DNS query.
(In the Apple "/usr/include/dns_sd.h" APIs, using ForceMulticast (In the Apple "/usr/include/dns_sd.h" APIs, using ForceMulticast
indicates that the DNSServiceQueryRecord() call should perform the indicates that the DNSServiceQueryRecord() call should perform the
query using Multicast DNS.) When the host owning that IPv4 or IPv6 query using Multicast DNS.) When the host owning that IPv6 or IPv4
address responds with a name of the form "something.local", the address responds with a name of the form "something.local", the
Hybrid Proxy rewrites that to use its configured LDH host name domain Hybrid Proxy rewrites that to use its configured LDH host name domain
instead of "local" and returns the response to the caller. instead of "local" and returns the response to the caller.
For example, a Hybrid Proxy with the two subdomains For example, a Hybrid Proxy with the two subdomains
"1.10.in-addr.arpa" and "bldg1.example.com" delegated to it would "1.10.in-addr.arpa" and "bldg1.example.com" delegated to it would
translate this Multicast DNS record: translate this Multicast DNS record:
3.2.1.10.in-addr.arpa. PTR prnt.local. 3.2.1.10.in-addr.arpa. PTR prnt.local.
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3.2.1.10.in-addr.arpa. PTR prnt.bldg1.example.com. 3.2.1.10.in-addr.arpa. PTR prnt.bldg1.example.com.
Subsequent queries for the prnt.bldg1.example.com address record, Subsequent queries for the prnt.bldg1.example.com address record,
falling as it does within the bldg1.example.com domain, which is falling as it does within the bldg1.example.com domain, which is
delegated to the Hybrid Proxy, will arrive at the Hybrid Proxy, where delegated to the Hybrid Proxy, will arrive at the Hybrid Proxy, where
they are answered by issuing Multicast DNS queries and using the they are answered by issuing Multicast DNS queries and using the
received Multicast DNS answers to synthesize Unicast DNS responses, received Multicast DNS answers to synthesize Unicast DNS responses,
as described above. as described above.
3.4. Data Translation 3.5. Data Translation
Generating the appropriate Multicast DNS queries involves, at the Generating the appropriate Multicast DNS queries involves, at the
very least, translating from the configured DNS domain very least, translating from the configured DNS domain
(e.g., "Building 1.example.com") on the Unicast DNS side to "local" (e.g., "Building 1.example.com") on the Unicast DNS side to "local"
on the Multicast DNS side. on the Multicast DNS side.
Generating the appropriate Unicast DNS responses involves translating Generating the appropriate Unicast DNS responses involves translating
back from "local" to the configured DNS Unicast domain. back from "local" to the configured DNS Unicast domain.
Other beneficial translation and filtering operations are described Other beneficial translation and filtering operations are described
below. below.
3.4.1. DNS TTL limiting 3.5.1. DNS TTL limiting
For efficiency, Multicast DNS typically uses moderately high DNS TTL For efficiency, Multicast DNS typically uses moderately high DNS TTL
values. For example, the typical TTL on DNS-SD PTR records is 75 values. For example, the typical TTL on DNS-SD PTR records is 75
minutes. What makes these moderately high TTLs acceptable is the minutes. What makes these moderately high TTLs acceptable is the
cache coherency mechanisms built in to the Multicast DNS protocol cache coherency mechanisms built in to the Multicast DNS protocol
which protect against stale data persisting for too long. When a which protect against stale data persisting for too long. When a
service shuts down gracefully, it sends goodbye packets to remove its service shuts down gracefully, it sends goodbye packets to remove its
PTR records immediately from neighbouring caches. If a service shuts PTR records immediately from neighbouring caches. If a service shuts
down abruptly without sending goodbye packets, the Passive down abruptly without sending goodbye packets, the Passive
Observation Of Failures (POOF) mechanism described in Section 10.5 of Observation Of Failures (POOF) mechanism described in Section 10.5 of
the Multicast DNS specification [RFC6762] comes into play to purge the Multicast DNS specification [RFC6762] comes into play to purge
the cache of stale data. the cache of stale data.
A Unicast DNS client on a remote link does not get to participate in A traditional Unicast DNS client on a remote link does not get to
these Multicast DNS cache coherency mechanisms on the local link. participate in these Multicast DNS cache coherency mechanisms on the
For Unicast DNS requests received without any LLQ option the DNS TTLs local link. For traditional Unicast DNS requests (those received
reported in the resulting Unicast DNS response SHOULD be capped to be without any Long-Lived Query [I-D.sekar-dns-llq] or DNS Push
no more than ten seconds. For received Unicast DNS requests that Notification [I-D.ietf-dnssd-push] option) the DNS TTLs reported in
contain an LLQ option, the Multicast DNS record's TTL SHOULD be the resulting Unicast DNS response SHOULD be capped to be no more
returned unmodified, because the LLQ notification channel exists to than ten seconds. For received Unicast DNS requests that contain an
inform the remote client as records come and go. For further details LLQ or DNS Push Notification option, the Multicast DNS record's TTL
about the LLQ option, see Section 3.5. SHOULD be returned unmodified, because the Push Notification channel
exists to inform the remote client as records come and go. For
further details about Long-Lived Queries, and its newer replacement,
DNS Push Notifications, see Section 3.6.
3.4.2. Suppressing Unusable Records 3.5.2. Suppressing Unusable Records
A Hybrid Proxy SHOULD suppress Unicast DNS answers for records that A Hybrid Proxy SHOULD suppress Unicast DNS answers for records that
are not useful outside the local link. For example, DNS A and AAAA are not useful outside the local link. For example, DNS A and AAAA
records for IPv4 link-local addresses [RFC3927] and IPv6 link-local records for IPv6 link-local addresses [RFC4862] and IPv4 link-local
addresses [RFC4862] should be suppressed. Similarly, for sites that addresses [RFC3927] should be suppressed. Similarly, for sites that
have multiple private address realms [RFC1918], private addresses have multiple private address realms [RFC1918], private addresses
from one private address realm should not be communicated to clients from one private address realm should not be communicated to clients
in a different private address realm. in a different private address realm.
By the same logic, DNS SRV records that reference target host names By the same logic, DNS SRV records that reference target host names
that have no addresses usable by the requester should be suppressed, that have no addresses usable by the requester should be suppressed,
and likewise, DNS PTR records that point to unusable SRV records and likewise, DNS PTR records that point to unusable SRV records
should be similarly be suppressed. should be similarly be suppressed.
3.4.3. Application-Specific Data Translation 3.5.3. Application-Specific Data Translation
There may be cases where Application-Specific Data Translation is There may be cases where Application-Specific Data Translation is
appropriate. appropriate.
For example, AirPrint printers tend to advertise fairly verbose For example, AirPrint printers tend to advertise fairly verbose
information about their capabilities in their DNS-SD TXT record. information about their capabilities in their DNS-SD TXT record.
This information is a legacy from LPR printing, because LPR does not This information is a legacy from LPR printing, because LPR does not
have in-band capability negotiation, so all of this information is have in-band capability negotiation, so all of this information is
conveyed using the DNS-SD TXT record instead. IPP printing does have conveyed using the DNS-SD TXT record instead. IPP printing does have
in-band capability negotiation, but for convenience printers tend to in-band capability negotiation, but for convenience printers tend to
include the same capability information in their IPP DNS-SD TXT include the same capability information in their IPP DNS-SD TXT
records as well. For local mDNS use this extra TXT record records as well. For local mDNS use this extra TXT record
information is inefficient, but not fatal. However, when a Hybrid information is inefficient, but not fatal. However, when a Hybrid
Proxy aggregates data from multiple printers on a link, and sends it Proxy aggregates data from multiple printers on a link, and sends it
via unicast (via UDP or TCP) this amount of unnecessary TXT record via unicast (via UDP or TCP) this amount of unnecessary TXT record
information can result in large responses. Therefore, a Hybrid Proxy information can result in large responses. Therefore, a Hybrid Proxy
that is aware of the specifics of an application-layer protocol such that is aware of the specifics of an application-layer protocol such
as Apple's AirPrint (which uses IPP) can elide unnecessary key/value as AirPrint (which uses IPP) can elide unnecessary key/value pairs
pairs from the DNS-SD TXT record for better network efficiency. from the DNS-SD TXT record for better network efficiency.
Note that this kind of Application-Specific Data Translation is Note that this kind of Application-Specific Data Translation is
expected to be very rare. It is the exception, rather than the rule. expected to be very rare. It is the exception, rather than the rule.
This is an example of a common theme in computing. It is frequently This is an example of a common theme in computing. It is frequently
the case that it is wise to start with a clean, layered design, with the case that it is wise to start with a clean, layered design, with
clear boundaries. Then, in certain special cases, those layer clear boundaries. Then, in certain special cases, those layer
boundaries may be violated, where the performance and efficiency boundaries may be violated, where the performance and efficiency
benefits outweigh the inelegance of the layer violation. benefits outweigh the inelegance of the layer violation.
As in other similar situations, these layer violations optional. As in other similar situations, these layer violations are optional.
They are done only for efficiency reasons, and are not required for They are done only for efficiency reasons, and are not required for
correct operation. A Hybrid Proxy can operate solely at the mDNS correct operation. A Hybrid Proxy can operate solely at the mDNS
layer, without any knowledge of semantics at the DNS-SD layer or layer, without any knowledge of semantics at the DNS-SD layer or
above. above.
3.5. Answer Aggregation 3.6. Answer Aggregation
In a simple analysis, simply gathering multicast answers and In a simple analysis, simply gathering multicast answers and
forwarding them in a unicast response seems adequate, but it raises forwarding them in a unicast response seems adequate, but it raises
the question of how long the Hybrid Proxy should wait to be sure that the question of how long the Hybrid Proxy should wait to be sure that
it has received all the Multicast DNS answers it needs to form a it has received all the Multicast DNS answers it needs to form a
complete Unicast DNS response. If it waits too little time, then it complete Unicast DNS response. If it waits too little time, then it
risks its Unicast DNS response being incomplete. If it waits too risks its Unicast DNS response being incomplete. If it waits too
long, then it creates a poor user experience at the client end. In long, then it creates a poor user experience at the client end. In
fact, there may no time which is both short enough to produce a good fact, there may no time which is both short enough to produce a good
user experience and at the same time long enough to reliably produce user experience and at the same time long enough to reliably produce
skipping to change at page 12, line 27 skipping to change at page 15, line 27
Similarly, the Hybrid Proxy -- the authoritative name server for the Similarly, the Hybrid Proxy -- the authoritative name server for the
subdomain in question -- needs to decide what DNS TTL to report for subdomain in question -- needs to decide what DNS TTL to report for
these records. If the TTL is too long then the recursive (caching) these records. If the TTL is too long then the recursive (caching)
name servers issuing queries on behalf of their clients risk caching name servers issuing queries on behalf of their clients risk caching
stale data for too long. If the TTL is too short then the amount of stale data for too long. If the TTL is too short then the amount of
network traffic will be more than necessary. In fact, there may no network traffic will be more than necessary. In fact, there may no
TTL which is both short enough to avoid undesirable stale data and at TTL which is both short enough to avoid undesirable stale data and at
the same time long enough to be efficient on the network. the same time long enough to be efficient on the network.
These dilemmas are solved by use of DNS Long-Lived Queries (DNS LLQ) Both these dilemmas are solved by use of DNS Long-Lived Queries (DNS
[I-D.sekar-dns-llq]. The Hybrid Proxy responds immediately to the LLQ) [I-D.sekar-dns-llq] or its newer replacement, DNS Push
Unicast DNS query using the Multicast DNS records it already has in Notifications [I-D.ietf-dnssd-push]. When a Hybrid Proxy recieves a
its cache (if any). This provides a good client user experience by query containing a DNS LLQ or DNS Push Notification option, it
providing a near-instantaneous response. Simultaneously, the Hybrid responds immediately using the Multicast DNS records it already has
Proxy issues a Multicast DNS query on the local link to discover if in its cache (if any). This provides a good client user experience
there are any additional Multicast DNS records it did not already by providing a near-instantaneous response. Simultaneously, the
know about. Should additional Multicast DNS responses be received, Hybrid Proxy issues a Multicast DNS query on the local link to
these are then delivered to the client using DNS LLQ update messages. discover if there are any additional Multicast DNS records it did not
The timeliness of such LLQ updates is limited only by the timeliness already know about. Should additional Multicast DNS responses be
of the device responding to the Multicast DNS query. If the received, these are then delivered to the client using DNS LLQ or DNS
Multicast DNS device responds quickly, then the LLQ update is Push Notification update messages. The timeliness of such update
delivered quickly. If the Multicast DNS device responds slowly, then messages is limited only by the timeliness of the device responding
the LLQ update is delivered slowly. The benefit of using LLQ is that to the Multicast DNS query. If the Multicast DNS device responds
the Hybrid Proxy can respond promptly because it doesn't have to quickly, then the update message is delivered quickly. If the
delay its unicast response to allow for the expected worst-case delay Multicast DNS device responds slowly, then the update message is
for receiving all the Multicast DNS responses. Even if a proxy were delivered slowly. The benefit of using update messages is that the
to try to provide reliability by assuming an excessively pessimistic Hybrid Proxy can respond promptly because it doesn't have to delay
its unicast response to allow for the expected worst-case delay for
receiving all the Multicast DNS responses. Even if a proxy were to
try to provide reliability by assuming an excessively pessimistic
worst-case time (thereby giving a very poor user experience) there worst-case time (thereby giving a very poor user experience) there
would still be the risk of a slow Multicast DNS device taking even would still be the risk of a slow Multicast DNS device taking even
longer than that (e.g, a device that is not even powered on until ten longer than that (e.g, a device that is not even powered on until ten
seconds after the initial query is received) resulting in incomplete seconds after the initial query is received) resulting in incomplete
responses. Using LLQs solves this dilemma: even very late responses responses. Using update message solves this dilemma: even very late
are not lost; they are delivered in subsequent LLQ update messages. responses are not lost; they are delivered in subsequent update
messages.
There are two factors that determine specifically how responses are There are two factors that determine specifically how responses are
generated: generated:
The first factor is whether the query from the client included the The first factor is whether the query from the client included an LLQ
LLQ option (typical with long-lived service browsing PTR queries) or or DNS Push Notification option (typical with long-lived service
not (typical with one-shot operations like SRV or address record browsing PTR queries) or not (typical with one-shot operations like
queries). Note that queries containing the LLQ option are received SRV or address record queries). Note that queries containing the
directly from the client (see Section 3.5.1). Queries containing no LLQ/PUSH option are received directly from the client (see
LLQ option are generally received via the client's configured Section 3.6.1). Queries containing no LLQ/PUSH option are generally
recursive (caching) name server. received via the client's configured recursive (caching) name server.
The second factor is whether the Hybrid Proxy already has at least The second factor is whether the Hybrid Proxy already has at least
one record in its cache that positively answers the question. one record in its cache that positively answers the question.
o No LLQ option; no answer in cache: o No LLQ/PUSH option; no answer in cache:
Do local mDNS query up to three times, return answers if received, Do local mDNS query up to three times, return answers if received,
otherwise return negative response if no answer after three tries. otherwise return negative response if no answer after three tries.
DNS TTLs in responses are capped to at most ten seconds. DNS TTLs in responses are capped to at most ten seconds.
o No LLQ option; at least one answer in cache: o No LLQ/PUSH option; at least one answer in cache:
Send response right away to minimise delay. Send response right away to minimise delay.
DNS TTLs in responses are capped to at most ten seconds. DNS TTLs in responses are capped to at most ten seconds.
No local mDNS queries are performed. No local mDNS queries are performed.
(Reasoning: Given RRSet TTL harmonisation, if the proxy has one (Reasoning: Given RRSet TTL harmonisation, if the proxy has one
Multicast DNS answer in its cache, it can reasonably assume that Multicast DNS answer in its cache, it can reasonably assume that
it has all of them.) it has all of them.)
o Query contains LLQ option; no answer in cache: o Query contains LLQ/PUSH option; no answer in cache:
As above, do local mDNS query up to three times, and return As above, do local mDNS query up to three times, and return
answers if received. answers if received.
If no answer after three tries, return negative response. If no answer after three tries, return negative response.
(Reasoning: We don't need to rush to send an empty answer.) (Reasoning: We don't need to rush to send an empty answer.)
In both cases the query remains active for as long as the client In both cases the query remains active for as long as the client
maintains the LLQ state, and if mDNS answers are received later, maintains the LLQ/PUSH state, and if mDNS answers are received
LLQ update messages are sent. later, LLQ/PUSH update messages are sent.
DNS TTLs in responses are returned unmodified. DNS TTLs in responses are returned unmodified.
o Query contains LLQ option; at least one answer in cache: o Query contains LLQ/PUSH option; at least one answer in cache:
As above, send response right away to minimise delay. As above, send response right away to minimise delay.
The query remains active for as long as the client maintains the The query remains active for as long as the client maintains the
LLQ state, and if additional mDNS answers are received later, LLQ LLQ/PUSH state, and if additional mDNS answers are received later,
update messages are sent. LLQ/PUSH update messages are sent.
(Reasoning: We want UI that is displayed very rapidly, yet (Reasoning: We want UI that is displayed very rapidly, yet
continues to remain accurate even as the network environment continues to remain accurate even as the network environment
changes.) changes.)
DNS TTLs in responses are returned unmodified. DNS TTLs in responses are returned unmodified.
Note that the "negative responses" referred to above are "no error no Note that the "negative responses" referred to above are "no error no
answer" negative responses, not NXDOMAIN. This is because the Hybrid answer" negative responses, not NXDOMAIN. This is because the Hybrid
Proxy cannot know all the Multicast DNS domain names that may exist Proxy cannot know all the Multicast DNS domain names that may exist
on a link at any given time, so any name with no answers may have on a link at any given time, so any name with no answers may have
child names that do exist, making it an "empty nonterminal" name. child names that do exist, making it an "empty nonterminal" name.
3.5.1. Discovery of LLQ Service 3.6.1. Discovery of LLQ or PUSH Notification Service
To issue LLQ queries, clients need to communicate directly with the To issue LLQ/PUSH queries, clients need to communicate directly with
authoritative Hybrid Proxy. The procedure by which the client the authoritative Hybrid Proxy. The procedure by which the client
locates the authoritative Hybrid Proxy is described in the LLQ locates the authoritative Hybrid Proxy is described in the LLQ
specification [I-D.sekar-dns-llq]. specification [I-D.sekar-dns-llq] and the DNS Push Notifications
specification [I-D.ietf-dnssd-push].
Briefly, the procedure is as follows: To discover the LLQ service for Briefly, the procedure is as follows:
a given domain name, a client first performs DNS zone apex discovery,
and then, having discovered <apex>, the client then issues a DNS To discover the LLQ service for a given domain name, a client first
query for the SRV record with the name _dns-llq._udp.<apex> to find performs DNS zone apex discovery, and then, having discovered <apex>,
the target host and port for the LLQ service for that zone. By the client then issues a DNS query for the SRV record with the name
default LLQ service runs on port 5352, but since SRV records are _dns-llq._udp.<apex> to find the target host and port for the LLQ
used, the LLQ service can be offered on any port. service for that zone. By default LLQ service runs on UDP port 5352,
but since SRV records are used, the LLQ service can be offered on any
port.
To discover the DNS Push Notification service for a given domain
name, a client first performs DNS zone apex discovery, and then,
having discovered <apex>, the client then issues a DNS query for the
SRV record with the name _dns-push-tls._tcp.<apex> to find the target
host and port for the DNS Push Notification service for that zone.
By default DNS Push Notification service runs on TCP port 5352, but
since SRV records are used, the DNS Push Notification service can be
offered on any port.
A client performs DNS zone apex discovery using the procedure below: A client performs DNS zone apex discovery using the procedure below:
1. The client issues a DNS query for the SOA record with the given 1. The client issues a DNS query for the SOA record with the given
domain name. domain name.
2. A conformant recursive (caching) name server will either send a 2. A conformant recursive (caching) name server will either send a
positive response, or a negative response containing the SOA positive response, or a negative response containing the SOA
record of the zone apex in the Authority Section. record of the zone apex in the Authority Section.
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flat list. This is largely a chicken-and-egg problem. Application flat list. This is largely a chicken-and-egg problem. Application
writers were naturally reluctant to spend time writing domain-aware writers were naturally reluctant to spend time writing domain-aware
UI code when few customers today would benefit from it. If Hybrid UI code when few customers today would benefit from it. If Hybrid
Proxy deployment becomes common, then application writers will have a Proxy deployment becomes common, then application writers will have a
reason to provide better UI. Existing applications will work with reason to provide better UI. Existing applications will work with
the Hybrid Proxy, but will show all services in a single flat list. the Hybrid Proxy, but will show all services in a single flat list.
Applications with improved UI will group services by domain. Applications with improved UI will group services by domain.
The Long-Lived Query mechanism [I-D.sekar-dns-llq] referred to in The Long-Lived Query mechanism [I-D.sekar-dns-llq] referred to in
this specification exists and is deployed, but has not been this specification exists and is deployed, but has not been
standardized by the IETF. It is possible that the IETF may choose to standardized by the IETF. The IETF is considering standardizing a
standardize a different or better Long-Lived Query mechanism. In superior Long-Lived Query mechanism called DNS Push Notifications
that case, the pragmatic deployment approach would be for vendors to [I-D.ietf-dnssd-push]. The pragmatic short-term deployment approach
produce Hybrid Proxies that implement both the deployed Long-Lived is for vendors to produce Hybrid Proxies that implement both the
Query mechanism [I-D.sekar-dns-llq] (for today's clients) and a new deployed Long-Lived Query mechanism [I-D.sekar-dns-llq] (for today's
IETF Standard Long-Lived Query mechanism (as the future long-term clients) and the new DNS Push Notifications mechanism
direction). [I-D.ietf-dnssd-push] as the preferred long-term direction.
The translating/filtering Hybrid Proxy specified in this document. The translating/filtering Hybrid Proxy specified in this document.
Implementations are under development, and operational experience Implementations are under development, and operational experience
with these implementations has guided updates to this document. with these implementations has guided updates to this document.
4.3. Not Yet Implemented 4.3. Not Yet Implemented
Client implementations of the new DNS Push Notifications mechanism
[I-D.ietf-dnssd-push] are currently underway.
A mechanism to 'stitch' together multiple ".local." zones so that A mechanism to 'stitch' together multiple ".local." zones so that
they appear as one. Such a mechanism will be specified in a future they appear as one. Such a mechanism will be specified in a future
companion document. companion document.
5. IPv6 Considerations 5. IPv6 Considerations
An IPv4-only host and an IPv6-only host behave as "ships that pass in An IPv6-only host and an IPv4-only host behave as "ships that pass in
the night". Even if they are on the same Ethernet, neither is aware the night". Even if they are on the same Ethernet, neither is aware
of the other's traffic. For this reason, each physical link may have of the other's traffic. For this reason, each physical link may have
*two* unrelated ".local." zones, one for IPv4 and one for IPv6. *two* unrelated ".local." zones, one for IPv6 and one for IPv4.
Since for practical purposes, a group of IPv4-only hosts and a group Since for practical purposes, a group of IPv6-only hosts and a group
of IPv6-only hosts on the same Ethernet act as if they were on two of IPv4-only hosts on the same Ethernet act as if they were on two
entirely separate Ethernet segments, it is unsurprising that their entirely separate Ethernet segments, it is unsurprising that their
use of the ".local." zone should occur exactly as it would if they use of the ".local." zone should occur exactly as it would if they
really were on two entirely separate Ethernet segments. really were on two entirely separate Ethernet segments.
It will be desirable to have a mechanism to 'stitch' together these It will be desirable to have a mechanism to 'stitch' together these
two unrelated ".local." zones so that they appear as one. Such two unrelated ".local." zones so that they appear as one. Such
mechanism will need to be able to differentiate between a dual-stack mechanism will need to be able to differentiate between a dual-stack
(v4/v6) host participating in both ".local." zones, and two different (v4/v6) host participating in both ".local." zones, and two different
hosts, one IPv4-only and the other IPv6-only, which are both trying hosts, one IPv6-only and the other IPv4-only, which are both trying
to use the same name(s). Such a mechanism will be specified in a to use the same name(s). Such a mechanism will be specified in a
future companion document. future companion document.
6. Security Considerations 6. Security Considerations
6.1. Authenticity 6.1. Authenticity
A service proves its presence on a link by its ability to answer A service proves its presence on a link by its ability to answer
link-local multicast queries on that link. If greater security is link-local multicast queries on that link. If greater security is
desired, then the Hybrid Proxy mechanism should not be used, and desired, then the Hybrid Proxy mechanism should not be used, and
skipping to change at page 18, line 28 skipping to change at page 21, line 28
the four styles of unicast response according to what data is the four styles of unicast response according to what data is
immediately available in the cache. Thanks to Andrew Yourtchenko for immediately available in the cache. Thanks to Andrew Yourtchenko for
comments about privacy issues. [Partial list; more names to be comments about privacy issues. [Partial list; more names to be
added.] added.]
10. References 10. References
10.1. Normative References 10.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987. STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://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, November 1987. specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and [RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., J. de Groot,
E. Lear, "Address Allocation for Private Internets", G., and E. Lear, "Address Allocation for Private
BCP 5, RFC 1918, February 1996. Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
February 1996, <http://www.rfc-editor.org/info/rfc1918>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic [RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927, Configuration of IPv4 Link-Local Addresses", RFC 3927,
May 2005. DOI 10.17487/RFC3927, May 2005,
<http://www.rfc-editor.org/info/rfc3927>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007. Address Autoconfiguration", RFC 4862, DOI 10.17487/
RFC4862, September 2007,
<http://www.rfc-editor.org/info/rfc4862>.
[RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
Interchange", RFC 5198, March 2008. Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
<http://www.rfc-editor.org/info/rfc5198>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762, [RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
December 2012. December 2012.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, December 2012. Discovery", RFC 6763, December 2012.
[I-D.sekar-dns-llq] [I-D.sekar-dns-llq]
Sekar, K., "DNS Long-Lived Queries", Sekar, K., "DNS Long-Lived Queries",
draft-sekar-dns-llq-01 (work in progress), August 2006. draft-sekar-dns-llq-01 (work in progress), August 2006.
[I-D.ietf-dnssd-push]
Pusateri, T. and S. Cheshire, "DNS Push Notifications",
draft-ietf-dnssd-push-02 (work in progress), October 2015.
10.2. Informative References 10.2. Informative References
[HOME] Cheshire, S., "Special Use Top Level Domain 'home'", [HOME] Cheshire, S., "Special Use Top Level Domain 'home'",
draft-cheshire-homenet-dot-home (work in progress), draft-cheshire-homenet-dot-home (work in progress),
November 2014. November 2014.
[IPR2119] "Apple Inc.'s Statement about IPR related to Hybrid [IPR2119] "Apple Inc.'s Statement about IPR related to Hybrid
Unicast/Multicast DNS-Based Service Discovery", Unicast/Multicast DNS-Based Service Discovery",
<https://datatracker.ietf.org/ipr/2119/>. <https://datatracker.ietf.org/ipr/2119/>.
[RFC2136] Vixie, P., 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)",
RFC 2136, April 1997. RFC 2136, DOI 10.17487/RFC2136, April 1997,
<http://www.rfc-editor.org/info/rfc2136>.
[RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic [RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic
Update", RFC 3007, November 2000. Update", RFC 3007, DOI 10.17487/RFC3007, November 2000,
<http://www.rfc-editor.org/info/rfc3007>.
[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, December 2012. RFC 6760, December 2012.
[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.
Author's Address Author's Address
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