wdiff rfc6760.original rfc6760.txt

Document: draft-cheshire-dnsext-nbp-10.txt Stuart
Internet Engineering Task Force (IETF) S. Cheshire
Internet-Draft Marc
Request for Comments: 6760 M. Krochmal
Category: Informational Apple Inc.
Expires: 16 July 2011 12 January 2011
ISSN: 2070-1721 February 2013

Requirements for a Protocol to Replace AppleTalk NBP

<draft-cheshire-dnsext-nbp-10.txt>

Status of this Memo

This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of
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This Internet-Draft will expire on 16th July 2011. AppleTalk Name Binding Protocol (NBP)

Abstract

One of the goals of the authors of Multicast DNS (mDNS) and DNS-Based
Service Discovery (DNS-SD) was the desire to retire AppleTalk and the AppleTalk
Name Binding Protocol, Protocol (NBP) and to replace them with an IP-based
solution. This document presents a brief overview of the
capabilities of AppleTalk NBP, NBP and outlines the properties required of
an IP-based replacement. The views expressed in this Informational

Status of This Memo

This document is not an Internet Standards Track specification; it is
published for informational purposes.

This document
represent is a product of the opinions Internet Engineering Task Force
(IETF). It represents the consensus of the authors, not IETF consensus. community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6760.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction...................................................3 Introduction ....................................................3
2. Zero Configuration Networking..................................4 Networking ...................................4
3. Requirements...................................................5
3.1 Requirements ....................................................4
3.1. Name-to-Address Mapping........................................5
3.2 Mapping ....................................5
3.2. Name Services, not Hardware....................................5
3.3 Not Hardware ................................5
3.3. Address Services, not Hardware.................................6
3.4 Not Hardware -- or -- Escape the
Tyranny of Well-Known Ports ................................6
3.4. Typed Name Space...............................................8
3.5 Space ...........................................8
3.5. User-Friendly Names............................................9
3.6 Names ........................................9
3.6. Zeroconf Operation.............................................9
3.7 Operation .........................................9
3.7. Name Space Management.........................................10
3.8 Management -- or -- Name Conflict Detection ....10
3.8. Late Binding..................................................11
3.9 Simplicity....................................................11
3.10 Binding ..............................................11
3.9. Simplicity ................................................11
3.10. Network Browsing..............................................11
3.11 Browsing .........................................11
3.11. Browsing and Registration Guidance............................12
3.12 Guidance .......................12
3.12. Power Management Support......................................12
3.13 Support .................................12
3.13. Protocol Agnostic.............................................13
3.14 Agnostic ........................................13
3.14. Distributed Cache Coherency Protocol..........................13
3.15 Protocol .....................13
3.15. Immediate and Ongoing Information Presentation................13 Presentation ...........13
4. Existing Protocols............................................14 Protocols .............................................14
5. IPv6 Considerations...........................................14 Considerations ............................................14
6. Security Considerations.......................................14 Considerations ........................................14
7. IANA Considerations...........................................15
8. Copyright Notice..............................................15
9. Informative References........................................15
10. Author's Address..............................................16 References .........................................15

1. Introduction

An important goal of the participants working on Zeroconf, Multicast
DNS, and DNS-Based Service Discovery was to provide a viable IP-based
replacement for AppleTalk and the AppleTalk Name Binding Protocol
(NBP).

There are many who are experts in the area of DNS Domain Name System (DNS) who
know nothing about NBP, and without the AppleTalk Name Binding Protocol (NBP).
Without some background on how AppleTalk and NBP worked, it may be
difficult to understand the reasoning and motivations that led to some of the
design decisions in Multicast
DNS, DNS and DNS-Based Service Discovery.

This document seeks to remedy this problem by clearly stating the
requirements for an IP-based replacement for AppleTalk and NBP.
Replacing NBP was not the sole goal of Multicast DNS, and therefore DNS; therefore,
these requirements are not the sole design considerations. However,
replacing NBP was a major motivation behind the work in Multicast
DNS.

In most cases, the requirements presented in this document are simply
a restatement of what AppleTalk NBP currently does. However, this
document is not restricted to describing only what NBP currently
does. Achieving at least equivalent functionality to NBP is a
necessary but not sufficient condition for a viable replacement. In
some cases, the requirements for a viable IP-based replacement go
beyond NBP. For example, AppleTalk NBP uses Apple Extended ASCII for
its character set. It is clear that an IP-based replacement being
designed today should use Unicode, in the form of UTF-8 [RFC 3629]. [RFC3629].
AppleTalk NBP has a reputation, partially deserved, partially not, for being too
'chatty' on the network. An IP-based replacement should not have
this same failing. The intent is to learn from NBP and build a
superset of its functionality, not to replicate it precisely with all
the same flaws.

The protocols specified in "Multicast DNS" [mDNS] [RFC6762] and "DNS-Based
Service Discovery" [DNS-SD], [RFC6763], taken together, describe a solution
that meets these requirements. This document is written, in part, in
response to requests for more background information explaining the
rationale behind the design of those protocols.

The design principles and requirements outlined in this Informational
document represent the opinions of the authors, not IETF consensus.

2. Zero Configuration Networking

Historically

Historically, TCP/IP networking required configuration, either in the
form of manual configuration by a human operator, operator or in the form of
automated configuration provided by a DHCP server [RFC 2131]. [RFC2131].

One of the characteristics of AppleTalk was that it could operate
without any dependency on manual configuration of or a network service
to provide automated configuration. An AppleTalk network could be as
small as just two laptop computers connected via an Ethernet
cable, or wirelessly. cable
(or wirelessly).

IP now has self-assigned link-local addresses [RFC 3927] [RFC 4862], [RFC3927] [RFC4862],
which enable IP-based networking in the absence of external
configuration. What remains is the need for Zero Configuration
name-to-address name-
to-address translation and Zero Configuration service discovery, both
capabilities that AppleTalk NBP offered.

It is not necessarily the case that Zero Configuration Networking
protocols will always be used in all three areas (addressing, naming,
and service discovery) simultaneously on any given network. For
example, even on networks with a DHCP server to provide address
configuration, users may still use Zero Configuration protocols for
name-to-address translation and service discovery. Indeed, on a
single network, users may use conventional Unicast DNS for looking up
the addresses of Internet web sites while at the same time using
Multicast DNS for looking up the addresses of peers on the local
link. Therefore, Zero Configuration Networking protocols must
coexist peacefully with conventional configured IP networking when
used together on the same network.

Networks change state over time. Hosts and services may come and go.
Connectivity, addresses addresses, and names change. In a manually configured
network
network, a human operator can remedy errors when they arise. In a
Zero Configuration Network, no such human operator is available to
diagnose and troubleshoot problems, so Zero Configuration protocols
need to be self-correcting, automatically accommodating changing
network conditions. conditions, continually converging to correctness in the
absence of human intervention to manually rectify errors.

3. Requirements

This section lists the 15 requirements for an IP-based replacement
for AppleTalk NBP.

3.1

3.1. Name-to-Address Mapping

NBP's primary function is translating names to addresses.

NBP stands for Name Binding Protocol, not Network Browsing Protocol.
Many people know NBP only as "that thing that used to let you browse
the network in the old Macintosh Chooser". While browsing is an
important facility of NBP, it is secondary to NBP's primary function
of translating names to addresses.

Every time a user prints using AppleTalk, the printing software takes
the name of the currently selected printer, looks up the current
AppleTalk address associated with that named service, and establishes
a connection to that service on the network. The user may invoke
NBP's browsing capability once once, when first selecting the desired
printer in the Chooser, but then after that, every time something is
printed, it is a simple efficient name-to-address lookup that is
being performed, not a full-fledged browsing operation.

Any NBP replacement needs to support, as it's its primary function, an
efficient name-to-address lookup operation.

3.2

3.2. Name Services, not Not Hardware

The primary named entities in NBP are services, not "hosts",
"machines", "devices", or pieces of hardware of any kind. This
concept is more subtle than it may seem at first, so it bears some
discussion.

The AppleTalk NBP philosophy is that naming a piece of hardware on
the network is of little use if you can't communicate with that piece
of hardware. To communicate with a piece of hardware, there needs to
be a piece of software running on that hardware which that sends and
receives network packets conforming to some specific protocol. This
means that whenever you communicate with a machine, you are really
communicating with some piece of software on that machine. Even if
you just 'ping' a machine to see if it is responding, it is not
really the machine that you are 'pinging', it is the software on that
machine that generates ICMP Echo Responses [RFC 792]. [RFC792].

Consequently, this means that the only thing things worth naming is are the
software entities with which you can communicate. A user who wants
to use a print server or a file server needn't care about what
hardware implements those services. There may be a single machine
hosting both services, or there may be two separate machines. The
end user doesn't need to care.

The one exception to this is network managers, who may want to name
physical hardware for the purpose of tracking physical inventory.
However, even this can be recast into a service-oriented view of the
world by saying that what you're naming is not the hardware, but the
ICMP Echo Responder that runs (or is assumed to be running) on every
piece of IP hardware.

3.3

3.3. Address Services, not Not Hardware
-or- -- or -- Escape the Tyranny of Well Known
Well-Known Ports

The reader may argue that DNS already supports the philosophy of
naming services instead of hosts. When we see names like
"www.example.com.", "pop.example.com.", "smtp.example.com.",
"news.example.com."
"news.example.com.", and "time.example.com.", we do not assume that
each of
those names necessarily refer to a different host. hosts. They are clearly
intended to be logical service names, names and could could, in fact fact, all refer resolve
to the same IP address.

The shortcoming here is that although the names are clearly logical
service names, the result today of doing a conventional ("A" or
"AAAA") DNS lookup for those names gives you only the IP address of
the hardware where the service is located. To communicate with the
desired service, you also need to know the port number at which the
service can be reached, not just the IP address.

This means that the port number has to be communicated out-of-band,
in some other way. One way is for the port number to be a specific
well-known constant for any given protocol. This makes it hard to
run more than one instance of a service on a single piece of
hardware. Another way is for the user to explicitly type in the port
number, for example, "www.example.com.:8080" instead of
"www.example.com.", but needing to know and type in a port number is
as ugly and fragile as needing to know and type in an IP address.

Another aspect of the difficulty of running more than one instance of
a service on a single piece of hardware is that it forces application
programmers to write their own demultiplexing capability. AppleTalk
did not suffer this limitation. If an AppleTalk print server offered
three print queues, each print queue ran as its own independent
service, listening on its own port number (called a socket number in
AppleTalk terminology), each advertised as a separate independent separate, independently
named NBP entity. When a client looks up the address of that named
NBP entity, the reply encodes not only on which net and subnet the
service resides, and on which host on that subnet (like an IP address
does), but also on which socket number (port number) within that
host. In contrast, if an lpr print server offers three print queues,
all three print queues are typically reached through the same
well-known well-
known port number (515), and then the lpr protocol has to use its own
demultiplexing capability (the print queue name) in order to
determine which print queue is sought. This makes it especially
difficult to run two different pieces of print queue software from
different vendors on the same machine, because they cannot both use
listen on the same well-known port.

A similar trick is used in HTTP 1.1, where the "Host" header line is
used to allow multiple logical http HTTP services to run at the same IP
address. Again, this works for a single-vendor solution, but if
you have a
user wishes to run multiple web servers (for example, an image
server, a database program, an http HTTP email access gateway, and a standard http server,
conventional HTTP server) on a single machine, they can't all run listen
on the same TCP port on 80, the same machine. traditional HTTP port.

Yet another problem of well-known ports is that port numbers are a
finite resource. Originally, port numbers 0-255 were reserved for
well-known services services, and the remaining 99.6% of the port space was
free for dynamic allocation [RFC 1122]. [RFC1122]. Since then, the range of
"Registered Ports" has crept upwards until today, ports 0-49151 are
reserved, and only 25% of the space remains available for dynamic
allocation. Even though 65535 may seem like a lot of available port
numbers, with the pace of software development today, if every new
protocol gets its own private port number, we will eventually run
out. To avoid having to do application-level demultiplexing,
protocols like the X Window System wisely use a range of port
numbers, and let TCP do the demultiplexing for them. The X Window
System uses 64 ports, in the range 6000-6063. If every new protocol
were to get its own chunk of 64 ports, we would run out even faster.

Any NBP replacement needs to provide, not just the network number,
subnet number, and host number within that subnet (i.e. (i.e., the IP
address) but also the port number within that host where the service
is located. Furthermore, since many existing IP services such as lpr
*do* already use additional application-layer demultiplexing
information such as a print queue name, an NBP replacement needs to
support this too by including this information as part of the
complete package of addressing information provided to the client to
enable it to use the service. The NBP replacement needs to name
individual print queues as first-class entities in their own right.
It is not sufficient merely to name a print server, within which
separate print queues can then be found by some other mechanism.

One possible answer here is that an IP-based NBP replacement could
use a solution derived from DNS SRV records instead of "A" records,
since SRV records *do* provide a port number. However, this alone is
not a complete solution, because SRV records cannot tell you an lpr
print queue name.

3.4

3.4. Typed Name Space

AppleTalk NBP names are structured names, generally written as:

Name : Type @ Zone

Name: The Name is the user-visible name of the service.

Type: The Type is an opaque identifier which that identifies the service
protocol and semantics. The user may think of the Type as
identifying the end-user function that the device performs (e.g. (e.g.,
"printing"), and for the typical end-user end-user, this may be an adequate
mental model, but strictly speaking, from a protocol-design
perspective, the Type identifies the semantic application protocol
the service speaks, speaks: no more, no less. For convenience, the opaque
Type identifier is generally constructed using descriptive ASCII
text, but this text has no meaning to the protocol, and care should
be taken in inferring too much meaning from it. For example, the NBP
Service Type "LaserWriter" means "any service that speaks PostScript
PS/PAP/ATP/DDP (PostScript over PAP/ATP/DDP (AppleTalk AppleTalk Printer Access Protocol
over AppleTalk Transaction Protocol over AppleTalk Datagram Delivery
Protocol)". It does not necessarily mean an Apple-branded
"LaserWriter" printer; nor does the service even have to be a
printer. A device that archives documents to digital media could
advertise itself as a "LaserWriter", meaning that it speaks
PostScript over PAP, not necessarily that it prints that document on
paper when it gets it. The end-user never directly sees the Service
Type. It is implicit in the user's action; e.g. for example, when
printing, the printing software knows what protocol(s) it speaks and
consequently what Service Type(s) it should be looking for -- the
user doesn't have to tell it.

Zone: The Zone is an organizational or geographical grouping of named
services. Typical AppleTalk Zone Names are things Zones were typically given names like
"Engineering", "Sales", and or "Building 1, 3rd floor, North". The
equivalent concept in DNS could be a subdomain such as
"Engineering.example.com.",
"Sales.example.com." "Sales.example.com.", or "Building 1, 3rd
floor, North.example.com."

Each {Type,Zone} pair defines a name space in which service names can
be registered. It is not a name conflict to have a printer called
"Sales" and a file server called "Sales", because one is
"Sales:LaserWriter@Zone" and the other is "Sales:AFPServer@Zone".

Any NBP replacement needs to provide a mechanism that allows names to
be grouped into organizational or geographical "zones", and within
each "zone", to provide an independent name space for each service
type.

3.5

3.5. User-Friendly Names

When repeatedly typing in names on command-line systems, it is
helpful to have names that are short, all lower-case, with no lowercase, without spaces
or other unusual hard-to-type characters.

Since Service Names are intended to be selected from a list, not
repeatedly typed in on a keyboard, there is no reason for them to be
restricted so. Users should be able to give their printers names
like "Sales", "Marketing", and "3rd Floor Copy Room", not just
"printer1.example.com."
"printer1.example.com.". Of course course, a user is free to name a
particular service using only lower-case lowercase letters and no spaces if they
wish, but they should not be forced to do that.

Any NBP replacement needs to support a full range of rich text
characters, including upper case, lower case, uppercase, lowercase, spaces, accented
characters, and so on. The correct solution is likely to be UTF-8
Unicode [RFC 3629]. [RFC3629].

Note that this requirement for user-friendly rich-text names applies
equally to the Zones/domains zones (domains) in which services are registered and
discovered.

Note that although the characters ':' and '@' are used when writing
AppleTalk NBP names, they are simply a notational convenience in
written text. In the on-the-wire protocol and in the software data
structures, NBP Name, Type Type, and Zone strings are all allowed to
contain almost any character, including ':' and '@'. The naming
scheme provided by an NBP replacement must allow the use of any
desired characters in service names, including dots ('.'), spaces,
percent signs, etc.

3.6

3.6. Zeroconf Operation

AppleTalk NBP is self-configuring. On a network of just two hosts,
they communicate peer-to-peer using multicast. On a large managed
network, AppleTalk routers automatically perform an aggregation
function, allowing name lookups to be performed via unicast to a
service running on the router, instead of by flooding the entire
network with multicast packets to every host.

Any NBP replacement needs to be able to operate in the absence of
external network infrastructure. However, this should not be the
only mode of operation. In larger managed networks, it should also
be possible to take advantage of appropriate external network
infrastructure when present, to perform queries via unicast instead
of multicast.

3.7

3.7. Name Space Management
-or- -- or -- Name Conflict Detection

Because an NBP replacement needs to operate in a Zeroconf
environment, it cannot be assumed that a central network
administrator is managing the network. In a Unlike managed network networks where
normal administrative controls may apply, but in the Zeroconf case an NBP
replacement must make it easy for users to name their devices as they
wish, without the inconvenience or expense of having to seek
permission or pay some organization like a domain name registry for
the privilege. However, this ease of naming naming, and freedom to choose
any desired name, may lead to name means that two conflicts. Two users may
independently decide to run a personal file server on their laptop
computers, and (unimaginatively) name it "My Computer". When these
two users later attend the next IETF meeting and find themselves part
of the same wireless network, there may be problems.

Similarly, every Brother network printer may ship from the factory
with its Service Name set to "Brother Printer". On a typical small
home network where there is only one printer printer, this is not a problem,
but problem;
however, it could be become a problem if two or more such printers are
connected to the same network.

Any NBP replacement needs to detect such conflicts, and handle them
appropriately. In the case of the a laptop computers, computer, which have
keyboards, screens, has a
keyboard, screen, and a human users, user, the software should display a
message telling one or both users the user that they need to select a new name.

In the case of the printers printers, which typically have no keyboard or screen,
the software should automatically select a new unique name, perhaps
by appending an integer to the end of the existing name, e.g. e.g.,
"Brother Printer 2". Note that that, although this programmatically-derived programmatically
derived name should be recorded persistently for use next time the
device is powered on, the user is not forced to use that name as the
long-term name for the service/device. In a network with more than
one printer, the typical user will assign human-meaningful names to
those printers, such as "Upstairs Printer" and "Downstairs Printer",
but the ability to rename the printer using some configuration tool (e.g.
(e.g., a Web Browser) web browser) depends on the ability to find the printer and
connect to it in the first place. Hence Hence, the programmatically-derived programmatically
derived unique name serves a vital bootstrapping role, even if its
use in that role is short-lived. temporary.

Because of the potentially transient nature of connectivity on small
portable devices that are becoming more and more common (especially
when used with wireless networks), this name conflict detection needs
to be an ongoing process. It is not sufficient to simply to verify
uniqueness of names for a few seconds during the boot process and
then assume that the names will remain unique indefinitely.

If the Zeroconf naming mechanism is integrated with the existing
global DNS naming mechanism, then it would be beneficial for a sub-
tree of that global namespace to be designated as having only local
significance, for use without charge by cooperating peers, much as
portions of the IPv4 address space are already designated as
local-significance-only, local-
significance-only, available for organizations to use locally without
charge as they wish [RFC 1918].

3.8 [RFC1918].

3.8. Late Binding

When the user selects their default printer, the software should not
store only the name, not the IP address and port number, but just the name. number. Then, every
time the user prints, the software should look up the name to find
the current IP address and port number for that service. This allows
a named logical service to be moved from one piece of hardware to
another without disrupting the user's ability to print to that named
print service.

On a network using DHCP [RFC 2131] [RFC2131] or self-assigned link-local
addresses [RFC 3927] [RFC 4862], [RFC3927] [RFC4862], a device's IP address may change from
day to day. By deferring Deferring binding of name to address until actual
use, this use
allows the client to get the correct IP address at the time the
service is used.

Similarly, with a service using a dynamic port number instead of a
fixed well-known port, the service may not get the same port number
every time it is started or restarted. By deferring binding of name
to port number until actual use, this allows the client to get gets the correct port
number at the time the service is used.

3.9

3.9. Simplicity

Any NBP replacement needs to be simple enough that vendors of even a
low-cost network ink-jet printer can afford to implement it in the
device's limited firmware.

3.10

3.10. Network Browsing

AppleTalk NBP offers certain limited wild-card functionality. For
example, the service name "=" means "any name". This allows a client
to perform an NBP lookup such as "=:LaserWriter@My Zone" and receive
back in response a list of all the PAP PS/PAP (AppleTalk Printer Access
Protocol) printers in the Zone called "My Zone".

Any NBP replacement needs to allow a piece of software, such as a
printing client, client or a file server client, to enumerate all the named
instances of services in a specified zone (domain) which that speak its
protocol(s).

3.11

3.11. Browsing and Registration Guidance

AppleTalk NBP provides certain meta-information to the client.

On a network with multiple AppleTalk Zones, the AppleTalk network
infrastructure informs the client of the list of Zones that are
available for browsing. It also informs the client of the default
Zone, which defines the client's logical "home" location. This is
the Zone that is selected by default when the Macintosh Chooser is
opened, and is usually the Zone where the user is most likely to find
services like printers that are physically nearby, but the user is
still free to browse any Zone in the offered list that they wish.

A Brother printer may be pre-configured at the factory with the
Service Name "Brother Printer", but they do not know on which network
the printer will eventually be installed, so the printer will have to
learn this from the network on arrival. On a network with multiple
AppleTalk Zones, the AppleTalk network infrastructure informs the
client of a single default Zone within which it may register Service
Names. In the case of a device with a human user, the AppleTalk
network infrastructure may also inform the client of a list of Zones
within which the client may register Service Names, and the user may
choose to register Service Names in any one of those Zones instead of
in the suggested default Zone.

Any NBP replacement needs to provide the following information to the
client:

* The suggested zone (domain) in which to register Service Names.

* A list of recommended available zones (domains) in which Service
Names may be optionally registered.

* The suggested default zone (domain) for network browsing.

* A list of available zones (domains) which that may be browsed.

Note that that, because the domains used in this context are intended for
service browsing in a graphical user interface, they should be
permitted to be full user-friendly rich text, just like the rest of a
service name.

3.12

3.12. Power Management Support

Many modern network devices have the ability to go into a low-power
mode
mode, where only a small part of the Ethernet hardware remains
powered, and the device can be woken up by sending a specially
formatted Ethernet frame which that the device's power-management hardware
recognizes. A modern service discovery protocol should provide
facilities to enable this low-power mode to be used effectively
without sacrificing network functionality, such as the ability to
discover services on sleeping devices, and wake up a sleeping device up
when it is needed.

3.13

3.13. Protocol Agnostic

Fashions come and go in the computer industry, but a service
discovery protocol, being one of the foundation components on which
everything else rests, has to be able to outlive these swings of
fashion. A useful service discovery protocol should be agnostic to
the protocols being used by the higher-layer software it serves. If
a service discovery protocol requires all the higher layer higher-layer software
to be written in a new computer language, or requires all the higher higher-
layer protocols to embrace some trendy new data representation format
that is currently in vogue, then that service discovery protocol is
likely to have limited utility after the fashion changes and computer
industry moves on to its next infatuation.

3.14

3.14. Distributed Cache Coherency Protocol

Any modern service discovery protocol must use some kind of caching
for efficiency. Any time a distributed cache is maintained, a cache
coherency protocol is required to control the effects of stale data.
Thus
Thus, a useful service discovery protocol needs to include cache
coherency mechanisms.

3.15

3.15. Immediate and Ongoing Information Presentation

Many current discovery mechanisms display an hourglass or a "Please
Wait" message for five or ten seconds, and then present a list of
results to the user. At this point, the list of results is static,
and does not update in response to changes in the environment. To
see current information information, the user is forced to click a "Refresh"
button repeatedly, waiting another five to ten seconds each time.

Neither limitation is acceptable in a protocol that is to replace
NBP. When a user initiates a browsing operation, the user interface
should take at most one second to present the list of results. In
addition, the list should update in response to changes in the
environment as they happen. If the user is waiting for a particular
service to become available, they should be able simply to watch
until it appears, with no "Refresh" button that they need to keep
clicking. A protocol to replace AppleTalk NBP must be able to meet
these requirement for timeliness of information discovery, and
liveness of information updating, without placing undue burden on the
network.

4. Existing Protocols

The

Ever since this work began with Stuart Cheshire's email to the net-
thinkers@thumper.vmeng.com mailing list in July 1997, the question
has been asked, "Isn't SLP the IETF replacement for AppleTalk NBP?"

SLP [RFC 2608]

The Service Location Protocol (SLP) [RFC2608] provides extremely rich
and flexible facilities in the area of Requirement 10, "Network
Browsing". However, SLP provides none of the service naming,
automatic name conflict detection, or efficient name-to-address
lookup which that form the majority of what AppleTalk NBP does.

SLP returns results in the form of URLs. In the absence of DNS, URLs
cannot usefully contain DNS names. Discovering a list of service
URLs of the form "ipp://169.254.17.202/" is not particularly
informative to the user. Discovering a list of service URLs of the
form "ipp://epson-stylus-900n.local./" is slightly less opaque
(though still not very user-friendly), but to do even this this, SLP would
have to depend on Multicast DNS or something similar to resolve names
to addresses in the absence of a conventional DNS server.

SLP provides fine-grained query capabilities, such as the ability to
prune a long list of printers to show only those that have blue paper
in the top tray, which could be useful on extremely large networks
with very many printers, but are certainly unnecessary for a typical
home or small office with only one or two printers.

In summary, SLP alone fails to meet most of the requirements, and
provides vastly more mechanism than necessary in the area of
Requirement 10.

5. IPv6 Considerations

An IP replacement for the AppleTalk Name Binding Protocol needs to
support IPv6 as well as IPv4.

6. Security Considerations

The AppleTalk Name Binding Protocol was developed in an era where when
little consideration was given to security issues. In today's world world,
this would no longer be appropriate. Any modern replacement for
AppleTalk NBP should have security measures appropriate to the
environment in which it will be used. Given that this document is a
broad historical overview of how AppleTalk NBP worked, and does not
specify any new protocol(s), it is beyond the scope of this document
to provide detailed discussion of possible network environments, what
protocols would be appropriate in each, and what security measures
would be expected of each such protocol, is beyond the scope
of this document. protocol.

7. IANA Considerations

No IANA actions are required by this document.

8. Copyright Notice

9. Informative References

[DNS-SD] Cheshire, S., and M. Krochmal, "DNS-Based Service
Discovery", Internet-Draft (work in progress),
draft-cheshire-dnsext-dns-sd-08.txt, January 2011.

[mDNS] Cheshire, S., and M. Krochmal, "Multicast DNS",
Internet-Draft (work in progress),
draft-cheshire-dnsext-multicastdns-13.txt, January 2011.

[RFC 792]

[RFC792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792,September 792, September 1981.

[RFC 1122]

[RFC1122] Braden, R. (Editor), R., Ed., "Requirements for Internet Hosts -- -
Communication Layers", STD 3, RFC 1122, October 1989.

[RFC 1918]

[RFC1918] Rekhter, Y., et al., Moskowitz, B., Karrenberg, D., de Groot, G.,
and E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.

[RFC 2131]

[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.

[RFC 2608]

[RFC2608] Guttman, E., Perkins, Veizades & C., Veizades, J., and M. Day,
"Service Location Protocol, Version 2", RFC 2608, June
1999.

[RFC 3629]

[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.

[RFC 3927]

[RFC3927] Cheshire, S., B. Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927, May
2005.

[RFC 4862]

[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.

10. Author's Address

[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
February 2013.

[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, February 2013.

Authors' Addresses

Stuart Cheshire
Apple Inc.
1 Infinite Loop
Cupertino
California
Cupertino, CA 95014
USA

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

Marc Krochmal
Apple Inc.
1 Infinite Loop
Cupertino
California
Cupertino, CA 95014
USA

Phone: +1 408 974 4368
EMail: marc@apple.com