Internet Engineering Task Force Alain Durand INTERNET-DRAFT SUN Microsystems,inc. Oct, 28, 2002 Expires April, 29, 2003 IPv6 DNS transition issues <draft-ietf-dnsop-ipv6-dns-issues-00.txt. Status of this memo This memo provides information to the Internet community. It does not specify an Internet standard of any kind. This memo is in full conformance with all provisions of Section 10 of RFC2026 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 This memo summarizes DNS related issues when transitioning a network to IPv6. Consensus and open issues are presented. 1. Representing IPv6 addresses in DNS records In the direct zones, according to [RFC3363], IPv6 addresses are represented using AAAA records [RFC1886]. In the reverse zone, IPv6 addresses are represented using PTR records in nibble format under the ip6.arpa. tree [RFC3152]. 2. IPv4/IPv6 name space Keeping the Internet name space unfragmented is a critical thing for the operation of the Internet. This covers IPv4 and IPv6. It means that any record in the public Internet should be available unmodified to any nodes, IPv4 or IPv6, regardless of the transport being used. See [FRAGMENTATION] and [DNS-OPS-REQ] for details. The RECOMMENDED approach to maintain name space continuity is to use administrative procedures: - every recursive DNS server SHOULD be either IPv4-only or dual stack, - every single DNS zone SHOULD be served by at least an IPv4 reachable DNS server. This rules out IPv6-only recursive DNS servers and DNS zones served by IPv6-only DNS servers. This approach could be revisited if/when translation techniques between IPv4 and IPv6 were to be widely deployed. 3. Local Scope addresses. [IPv6ADDRARCH] define three scopes of addresses, link local, site local and global. 3.1 Link local addresses Local addresses SHOULD NOT be published in the DNS, neither in the forward tree nor in the reverse tree. 3.2 Site local addresses Note: There is an ongoing discussion in the IPv6 wg on the usefulness of site local addresses that may end up deprecating or limiting the use of Site Local addresses. Site local addresses are an evolution of private addresses [RFC1918] in IPv4. The main difference is that, within a site, nodes are expected to have several addresses with different scopes. [ADDRSELEC] recommends to use the lowest possible scope possible for communications. That is, if both site local & global addresses are published in the DNS for node B, and node A is configured also with both site local & global addresses, the communication between node A and B has to use site local addresses. For reasons illustrated in [DontPublish], site local addresses SHOULD NOT be published in the public DNS. They MAY be published in a site view of the DNS if two-face DNS is deployed. 3.3 Reverse path DNS for site local addresses. The main issue is that the view of a site may be different on a stub resolver and on a fully recursive resolver it points to. A simple scenario to illustrate the issue is a home network deploying site local addresses. Reverse DNS resolution for site local addresses has to be done within the home network and the stub resolver cannot simply point to the ISP DNS resolver. Site local addresses SHOULD NOT be populated in the public reverse tree. If two-face DNS is deployed, site local addresses MAY be populated in the local view of reverse tree. 4. Automatic population of the Reverse path DNS Getting the reverse tree DNS populated correctly in IPv4 is not an easy exercise and very often the records are not really up to date or simply are just not there. As IPv6 addresses are much longer than IPv4 addresses, the situation of the reverse tree DNS will probably be even worse. A fairly common practice from IPv4 ISP is to generate PTR records for home customers automatically from the IPv4 address itself. Something like: 220.127.116.11.in-addr.arpa. IN PTR 18.104.22.168.local-ISP.net It is not clear today if something similar need to be done in IPv6. As the number of possible PTR records would be huge (2^80) for a /48 prefix, a possible solution would be to use wildcards entries like: *.0.1.2.3.22.214.171.124.8.9.a.b.c.ip6.arpa. IN PTR customer-42.local-ISP.net There is no consensus on using wildcards on this topic. Other solutions like dynamic generation of PTR records or allowing Dynamic DNS updates have been suggested. A more radical approach would be not to pre-populate the reverse tree at all. 5. Privacy extension addresses [RFC3041] defines privacy extensions for IPv6 stateless autoconfiguration where the interface ID is a random number. As those addresses are designed to provide privacy by making it more difficult to log and trace back to the user, it makes no sense to populate the reverse tree DNS with them. [RFC3041] type addresses SHOULD NOT be published in the reverse tree DNS. 6. 6to4 6to4 addresses can be published in the forward DNS, however special care is needed in the reverse tree. See [6to4ReverseDNS] for details. Delegations in the reverse zone under 126.96.36.199.ip6.arpa are the core of the problem. Delegating the next 32 bits of the IPv4 address used in the 6to4 domain won't scale and delegating on less may require cooperation from the upstream IPSs. Another problem with reverse DNS for 6to4 addresses is that the 6to4 prefix may be transient. One of the usage scenario of 6to4 is to have PCs connected via dial-up use 6to4 to connect to the IPv6 Internet. In such a scenario, the lifetime of the 6to4 prefix is the same as the DHCP lease of the IPv4 address it is derived from. It means that the reverse DNS delegation is only valid for the same duration. A possible approach is not to populate the reverse tree DNS for 6to4 addresses. 7. recursive DNS server discovery [DNSdiscovery] has been proposed to reserved a well known site local unicast address to configure the DNS resolver as a last resort mechanism, when no other information is available. Another approach is to use DHCPv6 extensions. 8. DNSsec There is nothing specific to IPv6 or IPv4 in DNSsec. 9. Security considerations Using wildcard DNS records in the reverse path tree may have some implication when used in conjunction with DNSsec. 10. Author addresses Alain Durand SUN Microsystems, Inc 25 Network circle UMPK17-202 Menlo Park, CA, 94025 USA Mail: Alain.Durand@sun.com 11. References [RFC1918] Address Allocation for Private Internets. Y. Rekhter, B. Moskowitz, D. Karrenberg, G. J. de Groot, E. Lear. February 1996. [RFC2766] Network Address Translation - Protocol Translation (NAT- PT). G. Tsirtsis, P. Srisuresh. February 2000. [RFC3041] Privacy Extensions for Stateless Address Autoconfiguration in IPv6, T. Narten, R. Draves, January 2001. [RFC3152] Delegation of ip6.arpa, R. Bush, August 2001. [RFC3363] Representing Internet Protocol version 6 (IPv6) Addresses in the Domain Name System (DNS), R. Bush, A. Durand, B. Fink, O. Gudmundsson, T. Hain. August 2002. [NAT-PTissues] Issues with NAT-PT DNS ALG in RFC2766, A. Durand, draft-durand-natpt-dns-alg-issues-00.txt, work in progress. [NAT64] NAT64 - NAT46, A. Durand, draft-durand-ngtrans- nat64-nat46-00.txt, work in progress. [FRAGMENTATION] IPv4-to-IPv6 migration and DNS namespace fragmentation, J. Ihren, draft-ietf-dnsop-v6-name-space- fragmentation-01.txt, work in progress. [DNS-OPS-REQ] NGtrans IPv6 DNS operational requirements and roadmap, A. Durand, J. Ihren, draft-ietf-ngtrans-dns-ops-req-04.txt, work in progress. [IPv6ADDRARCH] IP Version 6 Addressing Architecture, R. Hinden, draft-ipngwg-addr-arch-v3-09.txt, work in progress. [6to4ReverseDNS] 6to4 and DNS, K. Moore, draft-moore-6to4-dns-03.txt, work in progress. [DNSdiscovery] Well known site local unicast addresses for DNS resolver, A. Durand, J. hagano, D. Thaler, draft-ietf-ipv6-dns- discovery-07.txt, work in progress. 12. Full Copyright Statement "Copyright (C) The Internet Society (2001). All Rights Reserved. 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