INTERNET-DRAFT Local DNS Names March 1998 Expires September 1998 Local Domain (DNS) Names ----- ------ ----- ----- Donald E. Eastlake 3rd Status of This Document This draft, file name draft-ietf-dnsind-local-names-05.txt, is intended to be become an Experimental RFC. Distribution of this document is unlimited. Comments should be sent to the DNS mailing list or to the author. This document is an Internet-Draft. 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. Internet-Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet- Drafts as reference material or to cite them other than as a ``working draft'' or ``work in progress.'' To learn the current status of any Internet-Draft, please check the 1id-abstracts.txt listing contained in the Internet-Drafts Shadow Directories on ds.internic.net (East USA), ftp.isi.edu (West USA), ftp.nordu.net (North Europe), ftp.nis.garr.it (South Europe), munnari.oz.au (Pacific Rim), or ftp.is.co.za (Africa). Abstract A new top level domain (TLD) name is defined such that local private DNS zones can easily be maintained similar to the private IP addresses reserved in [RFC 1918]. These zones locally appear to be part of the global DNS name tree and can be locally resolved, even by "out of the box" resolvers starting at the global root zone, but are inaccessible outside their enclave. Additional second level domain names are reserved under this TLD for IPv6 link and site local addresses and loopback addresses. User confusion is reduced by grouping all non-global names under this new TLD so they are more easily recognizable. Donald E. Eastlake 3rd [Page 1] INTERNET-DRAFT Local DNS Names Acknowledgments The valuable contributions of the following persons are gratefully acknowledged: Dan Harrington Michael A. Patton Table of Contents Status of This Document....................................1 Abstract...................................................1 Acknowledgments............................................2 Table of Contents..........................................2 1. Introduction............................................3 2. Local Names Via The .local Top Level Domain.............4 2.1 Local DNS Server Specifics.............................6 2.2 Local in-addr.arpa Zones...............................6 2.3 Name Conflicts.........................................7 2.4 Nested Enclaves........................................8 3. Other Names in .local...................................8 4. Analysis of Alternatives................................8 4.1 Locally Configured .local..............................8 4.2 Local Delegations Anywhere.............................9 4.3 No Change..............................................9 5. Security Considerations.................................9 5.1 Strength of Privacy Offered............................9 5.2 Interaction with DNSSEC...............................10 5.3 Network Abuse.........................................10 References................................................11 Author's Address..........................................11 Expiration and File Name..................................11 Appendix A: the .local zone...............................12 Appendix B: the .in-addr.arpa zone.......................14 Donald E. Eastlake 3rd [Page 2] INTERNET-DRAFT Local DNS Names 1. Introduction The global Internet Domain Name System (DNS) is documented in [RFC 1034, 1035, 1591] and numerous additional Requests for Comment. It defines a tree of names starting with root, ".", immediately below which are top level domain names such as .com and .us. Below top level domain names there are normally additional levels of names. Generally the information in the DNS is public and intended to be globally accessible. Certainly, in the past, the model of the Internet was one of end-to-end openness [RFC 1958]. However, with increasing security threats and privacy concerns, firewalls and enclaves have appeared. In many cases, organizations have hosts or resources that they specifically want to reference with DNS names but which they also want to be walled off from global access and even from global knowledge of their DNS name. In the realm of IPv4 addresses, this has been accomplished by reserving three blocks of addresses as documented in [RFC 1918]. This designation of private IP addresses also helps conserve global IP addresses. Familiarity with the contents of [RFC 1918] is assumed. In the DNS area, [RFC 1918] recommends "splitting" DNS at the enclave boundary, giving different answers to resolvers depending or whether they are inside or outside of the enclave, using different servers for inside and outside, etc. Such relatively complex configuration diddling is at variance with the simple global tree structure envisaged in the original DNS design. It can cause the local names to be invisible to "out of the box" resolvers within the enclave if they start at a global root zone. Furthermore, because local DNS names created in accordance with [RFC 1918] can be entirely arbitrary and unrecognizable as local, user confusion is increased. This document specifies an alternative approach to achieving the effect of local names that is more in tune with the concept of a single global DNS tree and reduces user confusion by making local names easily recognizable. Use of this approach by local DNS administrators is not required and older techniques will continue to work as well as they have in the past. [RFC 1918] requires that private IP addresses not be indirectly exposed to the general Internet via DNS records or otherwise. This RFC provides a recommended way to accomplish such private IP address hiding and carves out an exception thereto for the addresses of the servers for some zones which are children of the ".local" top level domain name. Donald E. Eastlake 3rd [Page 3] INTERNET-DRAFT Local DNS Names 2. Local Names Via The .local Top Level Domain The fundamental idea for providing local names, as described in more detail below, is to define second level domains under ".local" which are served by domain name system (DNS) name servers that have private IP addresses. These server's addresses would only be routed within the enclave to which the names are local. Thus the servers, and the names and resource records inside them, would, if the guidelines in this document are followed, be inaccessible outside the enclave. The following figure shows a highly simplified overview of an example configuration: +----------------------------+ | domain/enclave A | | | | #====================# | | H private IP addrs A H | | H H | +-----------------------O privhost1 H | | | H H | +-----+-----------------O privhost2 H | | | | H H | | | | #====================# | | | a | | | +--------------------O pubhost3 | .local | | | | | +----+ | | +----------------------------+ | | | | | | | | +----------------------------+ | | | | | domain/enclave B | (root) | | | | | | . ----+ | | | | #====================# | | | | | | H private IP addrs B H | | | | | | H H | | +--|--------------------O privhost2 H | | | | | H H | +-------+ +-----------------O privhost3 H | .com | | H : H | | | #====:===============# | | | : | | b +-------------O pubhost4 | +------+ | | | +-------------O pubhost5 | | | | | +----------------------------+ | | example +---------------------O pubhost6 Donald E. Eastlake 3rd [Page 4] INTERNET-DRAFT Local DNS Names Starting at the bottom, pubhost6 is intended to illustrate an ordinary host connected to the Internet with domain name pubhost6.example.com. Though not indicated in the above diagram, every DNS zone is in fact served by at least two hosts and some by substantially more than two. The addresses of the servers for the root ("."), ".com", and example.com zones would all be in the public portion of the IP address space, i.e., in the space of unicast IP addresses not reserved for private use so these servers are accessible to all. Moving to the top of the figure, enclave A represents some organization that wishes to have some hosts with publicly visible names and some with hidden names that are only visible locally. pubhost3.a.com is an example of a publicly visible host which would probably have a public IP address (although access to pubhost3 from outside the enclave might be filtered or even blocked by a firewall or the like). privhost1 and privhost2 are examples of hidden names. If a zone with privhost1 and privhost2 in it is served by DNS servers with private IP addresses ("private IP addresses A") such that the servers are accessible within enclave A but not from outside enclave A, then the information is that zone will only be locally visible. As show in the above figure, privhost1 and privhost2 have addresses that are also private IP addresses, making those hosts inaccessible outside enclave A, but it is the private addresses of the DNS servers, not of the hosts pointed to from within the private DNS zone, that provides the protection for the DNS names and other private DNS information. (From the above simplified diagram, it might appear that fully qualified domain names of these hosts would be privhost1.local and privhost2.local but the names are actually a little more complex as explained in Section 2.1.) Finally, in the middle, another enclave is shown with two hosts with visible names and public IP addresses, pubhost4.b.com and pubhost5.b.com. In addition, there are two private host names privhost2 and privhost3. The duplication of privhost2 between enclaves A and B would not be a problem as only DNS resolvers in enclave A can access the DNS servers with the zone having the enclave A version of privhost2 and only DNS resolvers in enclave B can access the DNS servers with the zone having the enclave B version of privhost2. Publicly visible host names are required by [RFC 1918] to have public (i.e., globally unique) IP addresses. Private DNS names would normally have private IP addresses, and all do in the figure above, but this is not required. A public IP address could be stored under a private name. And, of course, it is possible for the same physical host to have multiple IP addresses, including a mix of public and private addresses. The dotted line in the figure above is intended to indicate that privhost3 and pubhost4 are actually the same physical machine. The could also be accomplished by storing a single Donald E. Eastlake 3rd [Page 5] INTERNET-DRAFT Local DNS Names public address for that host under both the public and private names or by having the host answer to both a public IP address stored under the public name and a private IP address stored under the private name. In the later case you could even also store the public address along with the private address under the private name. 2.1 Local DNS Server Specifics A variety of second level names are provided in the ".local" zone each of which is a delegation point to a zone with some number of name servers in one of the private IP address space blocks. The multiple second level names permit choice between the different private IP blocks and different numbers of servers. Thus the actual fully qualified name for the private host examples in the figure above would be more like privhost1.a2.local, privhost2.a2.local, etc. (but see Section 2.3 below). Glue records are provided to give private IP addresses for initial name servers; however, it should be noted that the NS and A records in the local zones will dominate the information stored in the ".local" zone. This means that once a resolver has contacted a local server, the list of NS RRs in the local zone on that server will control and could contain more or different servers than were given at the chosen ".local" delegation point. Nevertheless, the glue A records in the global ".local" zone do place some constraints of the private IP address of the local DNS servers implementing zones which are children of ".local". It is only necessary for the local DNS servers to have private IP addresses to achieve the effect of local names. However, care MUST be taken that none of the local DNS servers or any server that might cache their output is accessible by any globally accessible network interface. Otherwise confusion could result if local names are resolved by a resolver outside a local enclave to private IP addresses which are meaningless or have a different meaning for that resolver. The Appendix A to this document gives an initial content of the ".local" zone. 2.2 Local in-addr.arpa Zones Inverse look up of local names corresponding to private IP addresses needs to be provided via the in-addr.arpa zone. Appendix B contains recommended additions to the in-addr.arpa domain to accomplish this. Because of the fixed naming within this zone, different names with Donald E. Eastlake 3rd [Page 6] INTERNET-DRAFT Local DNS Names different numbers of servers or different addresses can not be provided. As with the forward ".local" entries, the actual NS RRs in the servers serving the private portions of the inverse in-addr.arpa will dominate. When one of these is queried by a resolver, it can provide information on additional servers for that particular subzone in the private IP address portion of the in-addr.arpa tree. 2.3 Name Conflicts The intention is that local names would only be used in the enclave where the entities they refer to exist, and these names would not be exported. However, experience indicates that, despite best efforts to avoid it, some such names will occasionally leak out via email cc's, URL's in HTML, etc. This occurs currently with local names not following the design in this document. These leaked private names can cause confusion if they can conflict with global names or names local to other enclaves. Use of the ".local" top level domain assures no conflict with global names. To assure no conflict with different local fully qualified names, the domain name of the enclave SHOULD always be included in ".local" names. For example, a company might have host1.company.co.xy as a globally accessible host and host2.company.co.xy.b3.local as a host for internal use only. The global name could normally be resolvable anywhere on the Internet while the local name would be undefined anywhere except within the company.co.xy enclave. Note that different names were chosen for the initial label in the two names above, i.e., host1 and host2. The reason for this is that, in some environments, local hosts are referred to by an unqualified names, such as host3. For DNS look up purposes, such a name must be expanded into a fully qualified domain name and a "search list" of possible suffix qualifications is tried. If, for example, both host4.school.ac.xy and host4.school.ac.xy.b3.local existed, then a local reference to "host4" would be ambiguous and could lead to either machine depending on the order of qualifications tried. This order could even be different in different pieces of local software or on different local hosts, resulting in local confusion. For this reason, it is strongly recommended that fully qualified domain names be used wherever practical and that disjoint name sets be used for global and local entity unqualified domain names. Donald E. Eastlake 3rd [Page 7] INTERNET-DRAFT Local DNS Names 2.4 Nested Enclaves It is possible to have enclaves within enclaves. The best way to accomplish this is to use a different portion of the private IP address space at each nesting level of enclave. (Private IP address space can be reused in enclaves that are siblings or the like.) Then similar entries to those proposed here for ".local" can be made in the private zone referring to name servers with addresses in the next lower level nested enclave's private IP address space. 3. Other Names in .local Three additional second level domain names are assigned in the ".local" top level domain for other types of local names. In particular, link.local and site.local are reserved for use in qualifying IPv6 link local names and site local names and loopback.local is assigned and given the loopback address. 4. Analysis of Alternatives Possible alternatives to the scheme described in this document are (1) recommend that DNS administrators locally configure a ".local", (2) recommend that DNS administrators do a similar thing to ".local" somewhere in their current domain name tree, and (3) take no action leaving [RFC 1918] fully in effect. These alternatives are examined below. Only the scheme recommended in the sections of this document above always permit generic resolvers running within a enclave and starting at a global root zone to find private names and minimize user confusion. 4.1 Locally Configured .local It is possible for an enclave to locally configure its own version of the ".local" zone. This version could have whatever private addresses were desired for the name servers involved. However this generally requires that all of the resolvers within the enclave be configured to go through DNS servers that have this local variant of ".local" configured. Thus "out of the box" resolvers starting at a true root zone will not find the information. Furthermore, the probability is increased that some administrators will use a variant name increasing confusion. Donald E. Eastlake 3rd [Page 8] INTERNET-DRAFT Local DNS Names 4.2 Local Delegations Anywhere It would be possible to just recommend putting hidden names in a branch of the enclave's domain, like put them for the example company under local.example.com. If all these apexes of hidden name subtrees are visible in this way, then there would be a large number of different looking local domain names that could confuse users by not being globally resolvable. There would be a much greater chance of completely different names (private.example.com, hidden.example.com, net10.example.com, ...) being used increasing confusion.. However, generic resolvers starting from a global root inside an enclave would find private names configured in this way. 4.3 No Change Just banishing private IP addresses from the global DNS by fiat and having everyone who wants to use them run split DNS is the recommendation of RFC 1918. But as private IP addresses become more and more common, this restriction is increasingly overlooked. The private names leak out anyway. Browsers inside a enclave that started at a global root server are unable to find such hidden names. And there is be much less uniformity of naming resulting in more user confusion. 5. Security Considerations This section discusses the strength of the privacy offered by using subzones of ".local", interactions with DNS security, and possible interaction with network abuse. 5.1 Strength of Privacy Offered It should be noted that the privacy of the DNS information protected by storing it in servers with private IP addresses is relatively weak. It is dependent on the integrity of enclave perimeter routing to make these servers inaccessible. And the names may leak out in any case due to inclusion in email address fields, web pages, and the like; however, such leakage will be no worse than current split DNS implementations of DNS data hiding. Software should not depend on local names only existing within a particular enclave as someone could deliberately create the same names within a different enclave even if the names incorporate the name of the original enclave in an attempt to avoid such conflicts. Donald E. Eastlake 3rd [Page 9] INTERNET-DRAFT Local DNS Names 5.2 Interaction with DNSSEC Although an enclave may derive some amount of security by virtue of its isolation, it will normally be desirable to implement DNS security [RFC 2065, draft-ietf-dnssec-secext-*.txt] within the enclave. The enclave owner should generate their own keys and sign their subzone of ".local". However, a signed copy of their public key can not be included in the ".local" zone as it is different for every enclave. Thus, to authenticate the ".local" subzone contents, it will be necessary to staticly configure the public key for the ".local" subzone in local resolvers or sign the KEY RR at the apex of the local subzone of ".local" with another key that is trusted by local resolvers such as the enclave domain name zone key or the ".local" zone key. 5.3 Network Abuse The existence of local IP addresses as provided in [RFC 1918] provides another way for network abusers to create confusion to cover their tracks and make abuse hard to trace. Use of ".local" does not change this but will reduce confusion by providing clearer notice that an address is not globally meaningful. Donald E. Eastlake 3rd [Page 10] INTERNET-DRAFT Local DNS Names References RFC 1033 - M. Lottor, "Domain Administrators Operations Guide", November 1987. RFC 1034 - P. Mockapetris, "Domain Names - Concepts and Facilities", STD 13, November 1987. RFC 1035 - P. Mockapetris, "Domain Names - Implementation and Specifications", STD 13, November 1987. RFC 1591 - J. Postel, "Domain Name System Structure and Delegation", 03/03/1994. RFC 1918 - Y. Rekhter, R. Moskowitz, D. Karrenberg, G. de Groot, E. Lear, "Address Allocation for Private Internets", 02/29/1996. RFC 1958 - B. Carpenter, "Architectural Principles of the Internet", 06/06/1996. RFC 2065 - D. Eastlake, C. Kaufman, "Domain Name System Security Extensions", 01/03/1997. draft-ietf-dnssec-secext2-*.txt - Author's Address Donald E. Eastlake 3rd CyberCash, Inc. 318 Acton Street Carlisle, MA 01741 USA Telephone: +1 978 287 4877 +1 703 620-4200 (main office, Reston, VA) FAX: +1 978 371 7148 EMail: dee@cybercash.com Expiration and File Name This draft expires September 1998. Its file name is draft-ietf-dnsind-local-names-05.txt. Donald E. Eastlake 3rd [Page 11] INTERNET-DRAFT Local DNS Names Appendix A: the .local zone ===== The .local zone suggested initial contents ==== local. IN SOA ... ... ( .... ; serial ..... ; refresh ..... ; retry ....... ; expiry ..... ) ; minimum NS ... ; actual servers for .local zone NS ... ... loopback A 127.0.0.1 AAAA 0::1 MX 100 loopback.local. link TXT "Reserved. See RFC xxxx." [the rfc this draft becomes] site TXT "Reserved. See RFC xxxx." [the rfc this draft becomes] a2.local. NS ns1.a2.local. NS ns2.a2.local. ns1.a2.local. A 10.1.1.2 ns2.a2.local. A 10.1.2.2 a3.local. NS ns1.a3.local. NS ns2.a3.local. NS ns3.a3.local. ns1.a3.local. A 10.1.1.2 ns2.a3.local. A 10.1.2.2 ns3.a3.local. A 10.2.1.2 a4.local. NS ns1.a4.local. NS ns2.a4.local. NS ns3.a4.local. NS ns4.a4.local. ns1.a4.local. A 10.1.1.2 ns2.a4.local. A 10.1.2.2 ns3.a4.local. A 10.2.1.2 ns4.a4.local. A 10.128.1.2 b2.local. NS ns1.b2.local. NS ns2.b2.local. ns1.b2.local. A 172.16.1.2 ns2.b2.local. A 172.16.2.2 b3.local. NS ns1.b3.local. NS ns2.b3.local. Donald E. Eastlake 3rd [Page 12] INTERNET-DRAFT Local DNS Names NS ns3.b3.local. ns1.b3.local. A 172.16.1.2 ns2.b3.local. A 172.16.2.2 ns3.b3.local. A 172.16.128.2 c2.local. NS ns1.c2.local. NS ns2.c2.local. ns1.c2.local. A 192.168.1.2 ns2.c2.local. A 192.168.2.2 c3.local. NS ns1.c3.local. NS ns2.c3.local. NS ns3.c3.local. ns1.c3.local. A 192.168.1.2 ns2.c3.local. A 192.168.2.2 ns3.c3.local. A 192.168.128.2 Donald E. Eastlake 3rd [Page 13] INTERNET-DRAFT Local DNS Names Appendix B: the .in-addr.arpa zone ===== Suggested additional entries in the in-addr.arpa zone ==== 10.in-addr.arpa. NS ns1.a2.local. NS ns2.a2.local. ns1.a2.local. A 10.1.1.2 ns2.a2.local. A 10.1.2.2 16.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. ns1.b2.local. A 172.16.1.2 ; one set of glue records ns2.b2.local. A 172.16.2.2 ; for all the b2 cases 17.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 18.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 19.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 20.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 21.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 22.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 23.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 24.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 25.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 26.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 27.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 28.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 29.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 30.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 31.172.in-addr.arpa. NS ns1.b2.local. NS ns2.b2.local. 168.192.in-addr.arpa. NS ns1.c2.local. NS ns2.c2.local. ns1.c2.local. A 192.168.1.2 ns2.c2.local. A 102.168.2.2 Donald E. Eastlake 3rd [Page 14]