Document: draft-cheshire-dnsext-nbp-06.txt Stuart Cheshire Internet-Draft Marc Krochmal Category: Informational Apple Inc. Expires: 10 March 2009 10 September 2008 Requirements for Replacing AppleTalk Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. For the purposes of this document, the term "BCP 79" refers exclusively to RFC 3979, "Intellectual Property Rights in IETF Technology", published March 2005. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Abstract One of the important goals of the participants working on Zeroconf, Multicast DNS, and DNS-Based Service Discovery was the desire to retire AppleTalk and the AppleTalk Name Binding Protocol, and to replace them with an all-IP solution. This document outlines the specific requirements that IP-based protocol(s) need to meet to make that possible. Expires 10th March 2009 Cheshire [Page 1] Internet Draft Replacement of AppleTalk 10th September 2008 Table of Contents 1. Introduction...................................................3 2. Zero Configuration Networking..................................4 3. Requirements...................................................5 3.1 Name-to-Address Mapping........................................5 3.2 Name Services, not Hardware....................................5 3.3 Address Services, not Hardware.................................6 3.4 Typed Name Space...............................................8 3.5 User-Friendly Names............................................9 3.6 Zeroconf Operation.............................................9 3.7 Name Space Management.........................................10 3.8 Late Binding..................................................11 3.9 Simplicity....................................................11 3.10 Network Browsing..............................................11 3.11 Browsing and Registration Guidance............................12 3.12 Power Management Support......................................12 3.13 Protocol Agnostic.............................................13 3.14 Distributed Cache Coherency Protocol..........................13 3.15 Immediate and Ongoing Information Presentation................13 4. Existing Protocols............................................14 5. IPv6 Considerations...........................................14 6. Security Considerations.......................................14 7. IANA Considerations...........................................15 8. Copyright Notice..............................................15 9. Intellectual Property Notice..................................15 10. Informative References........................................16 11. Author's Address..............................................17 Expires 10th March 2009 Cheshire [Page 2] Internet Draft Replacement of AppleTalk 10th September 2008 1. Introduction A 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 who know nothing about NBP, and 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. This document seeks to remedy this problem by clearly stating the requirements for an IP-based replacement for AppleTalk and NBP. Replacing NBP is not the sole goal of Multicast DNS, and therefore these requirements are not the sole design considerations. However, replacing NBP is 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. AppleTalk NBP has no built-in security provisions; an IP-based replacement should not have that same error. 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] and "DNS-Based Service Discovery" [DNS-SD], 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. Expires 10th March 2009 Cheshire [Page 3] Internet Draft Replacement of AppleTalk 10th September 2008 2. Zero Configuration Networking Historically TCP/IP networking required configuration, either in the form of manual configuration by a human operator, or in the form of automated configuration provided by a DHCP server [RFC 2131]. One of the characteristics of AppleTalk was that it could operate without any dependency on manual configuration of 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. IP now has self-assigned link-local addresses [RFC 2462] [RFC 3927], which enable IP-based networking in the absence of external configuration. What remains is the need for Zero Configuration name-to-address translation and 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, 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 and names change. In a manually configured 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. Expires 10th March 2009 Cheshire [Page 4] Internet Draft Replacement of AppleTalk 10th September 2008 3. Requirements This section lists the 15 requirements for an IP-based replacement for AppleTalk NBP. 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 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 primary function, an efficient name-to-address lookup operation. 3.2 Name Services, 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 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]. Consequently, this means that the only thing worth naming is 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 Expires 10th March 2009 Cheshire [Page 5] Internet Draft Replacement of AppleTalk 10th September 2008 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 Address Services, not Hardware -or- Escape the Tyranny of 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." and "time.example.com.", we do not assume that each of those names refer to a different host. They are clearly intended to be logical service names, and could in fact all refer 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 TCP or UDP 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 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, Expires 10th March 2009 Cheshire [Page 6] Internet Draft Replacement of AppleTalk 10th September 2008 all three print queues are typically reached through the same well-known port number, 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 the same well-known port. A similar trick is used in HTTP 1.1, where the "Host" header is used to allow multiple logical http services to run at the same IP address. Again, this works for a single-vendor solution, but if you have an image server, a database program, an http email access gateway, and a regular http server, they can't all run on the same TCP port on the same machine. Yet another problem of well-known ports is that port numbers are a finite resource. Originally, port numbers 0-1023 were reserved for well-known services, and the remaining 98% of the port space was free for dynamic allocation. 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. 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. Expires 10th March 2009 Cheshire [Page 7] Internet Draft Replacement of AppleTalk 10th September 2008 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 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. "printing"), and for the typical 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, 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 over PAP/ATP/DDP (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. 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 like "Engineering", "Sales", and "Building 1, 3rd floor, North". The equivalent concept in DNS could be a subdomain such as "Engineering.company.com.", "Sales.company.com." or "Building 1, 3rd floor, North.company.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. Expires 10th March 2009 Cheshire [Page 8] Internet Draft Replacement of AppleTalk 10th September 2008 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 spaces or other unusual 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.ietf.org." Of course a user is free to restrict their Service Names to lower-case letters without 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, spaces, accented characters, and so on. The correct solution is likely to be UTF-8 Unicode. Note that this requirement for user-friendly rich-text names applies equally to the 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 and Zone strings are all allowed to contain almost any character, including ':' and '@'. The naming scheme provided by an NBP replacement must allow use of any desired characters in service names, including dots ('.'), spaces, percent signs, etc. 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 operate in the absence of external network infrastructure. It should also be possible to take advantage of appropriate external network infrastructure, where present, to perform queries via unicast instead of multicast. Expires 10th March 2009 Cheshire [Page 9] Internet Draft Replacement of AppleTalk 10th September 2008 3.7 Name Space Management -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 managed network 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 and freedom to choose any desired name means that 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 this is not a problem, but it could be 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 laptop computers, which have keyboards, screens, and human users, the software should display a message telling one or both users that they need to select a new name. In the case of the printers which 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. "Brother Printer 2". Note that although this 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. a Web Browser) depends on the ability to find the printer and connect to it in the first place. Hence the programmatically-derived unique name serves a vital bootstrapping role, even if its use in that role is short-lived. 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 verify uniqueness of names for a few seconds during the boot process and then assume that the names will remain unique indefinitely. Expires 10th March 2009 Cheshire [Page 10] Internet Draft Replacement of AppleTalk 10th September 2008 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, available for organizations to use locally without charge as they wish [RFC 1918]. 3.8 Late Binding When the user selects their default printer, the software should not store the IP address and port number, but just the name. 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] or self-assigned link-local addresses [RFC 2462] [RFC 3927], a device's IP address may change from day to day. By deferring binding of name to address until actual use, this 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 the correct port number at the time the service is used. 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 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 (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, or a file server client, to enumerate all the named instances of services in a specified zone (domain) which speak its protocol(s). Expires 10th March 2009 Cheshire [Page 11] Internet Draft Replacement of AppleTalk 10th September 2008 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 may be browsed. Note 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 Power Management Support Many modern network devices have the ability to go into a low-power 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 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 wake a device up when it is needed. Expires 10th March 2009 Cheshire [Page 12] Internet Draft Replacement of AppleTalk 10th September 2008 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 software to be written in a new computer language, or requires all the 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 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 a useful service discovery protocol needs to include cache coherency mechanisms. 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 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. Expires 10th March 2009 Cheshire [Page 13] Internet Draft Replacement of AppleTalk 10th September 2008 4. Existing Protocols The question has been asked, "Isn't SLP the IETF replacement for NBP?" SLP [RFC 2608] 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 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 SLP would have to depend on Multicast DNS or something similar to resolve names to addresses 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 3.10. 5. IPv6 Considerations An IP replacement for AppleTalk Name Binding Protocol needs to support IPv6 as well as IPv4. 6. Security Considerations AppleTalk Name Binding Protocol has no inherent security mechanism. This would not be acceptable in an IP replacement. It should be possible for a client to verify the authenticity of the information it is receiving. It may also be useful for a server to be able to verify that a client has authority to request that information, and it may be useful to have a way to encrypt the data in transit to protect it against eavesdropping. A solution based on or derived from DNS could use DNSSEC [RFC 2535] to meet these requirements. Expires 10th March 2009 Cheshire [Page 14] Internet Draft Replacement of AppleTalk 10th September 2008 7. IANA Considerations AppleTalk Name Binding Protocol defines a name space for Zones, a name space for service Types, and name spaces for named instances of those services. Each name space uses 32-character ASCII text strings, so the name space for Type names is sufficiently large and sufficiently sparsely used that Apple never bothered with maintaining an official registry of assigned NBP service Type names. IANA should probably manage the name space of service type names, to prevent unintended name collisions. However, the name space of textual names is large enough that type names would not be a precious resource, so they could be handed out freely to anyone who needs one, effectively without limit, on a First Come First Served basis [RFC 2434]. The name space of instance names is managed locally at each site. 8. Copyright Notice Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 9. Intellectual Property Notice The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this Expires 10th March 2009 Cheshire [Page 15] Internet Draft Replacement of AppleTalk 10th September 2008 specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. 10. Informative References [DNS-SD] Cheshire, S., and M. Krochmal, "DNS-Based Service Discovery", Internet-Draft (work in progress), draft-cheshire-dnsext-dns-sd-05.txt, September 2008. [mDNS] Cheshire, S., and M. Krochmal, "Multicast DNS", Internet-Draft (work in progress), draft-cheshire-dnsext-multicastdns-07.txt, September 2008. [RFC 792] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792,September 1981. [RFC 1918] Rekhter, Y., et al., "Address Allocation for Private Internets", RFC 1918, February 1996. [RFC 2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [RFC 2434] Narten, T., and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 2434, October 1998. [RFC 2535] Eastlake, D. "Domain Name System Security Extensions", RFC 2535, March 1999. [RFC 2462] S. Thomson and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. [RFC 2608] Guttman, Perkins, Veizades & Day, "Service Location Protocol, Version 2", RFC 2608, June 1999. [RFC 3927] Cheshire, S., B. Aboba, and E. Guttman, "Dynamic Configuration of IPv4 Link-Local Addresses", RFC 3927, May 2005. Expires 10th March 2009 Cheshire [Page 16] Internet Draft Replacement of AppleTalk 10th September 2008 11. Author's Address Stuart Cheshire Apple Inc. 1 Infinite Loop Cupertino California 95014 USA Phone: +1 408 974 3207 EMail: cheshire@apple.com Marc Krochmal Apple Inc. 1 Infinite Loop Cupertino California 95014 USA Phone: +1 408 974 4368 EMail: marc@apple.com Expires 10th March 2009 Cheshire [Page 17]