Internet DRAFT - draft-durand-ngtrans-dns-issues
Internet Engineering Task Force Alain Durand
INTERNET-DRAFT SUN Microsystems,inc.
June, 23, 2002
Expires December, 24, 2002
IPv6 DNS transition issues
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
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This memo summarizes DNS related issues when transitioning a network
to IPv6. Those issues have been discussed in the NGtrans, IPv6,
DNSext and DNSop working group. Wherever consensus has been reached,
it is presented. When consensus has not yet been reached, a list of
open issues is presented.
1. DNS records
In the direct zones, the consensus is to use AAAA [RFC1886] records.
In the reverse zone, the consensus is to use PTR records in nibble
format under the ip6.arpa. tree.
2. IPv4/IPv6 name space
There is consensus that keeping the Internet name space unfragmented
is a good thing. This covers IPv4 and IPv6. It means that any record
in the public Internet should be available to any nodes, IPv4 or
IPv6. See [FRAGMENTATION] and [DNS-OPS-REQ] for details. One
possible approach is to maintain name space continuity with
administrative procedures: ask every full DNS resolver to be dual
stack and ask that every single DNS zone has to be served by at least
an IPv4 reachable DNS server. The other avenue to approach this
problem is to design a 'bridging system' enabling direct
communication between and IPv6 only DNS resolver and an IPv4 only DNS
server or an IPv4 only resolver talking to an IPv6 only DNS server.
NAT-PT [RFC2766] does not work for that purpose because of the DNS-
ALG built-in. Other issues surrounding NAT-PT are discussed in [NAT-
PTissues]. [NAT64] as a potential replacement for NAT-PT could be a
better fit, at least for the case of the IPv6 only DNS resolver
talking to an IPv4 only DNS server.
3. Local Scope addresses.
[IPv6ADDRARCH] define three scopes of addresses, link local, site
local and global.
3.1 Link local addresses
There is consensus not to publish link local addresses in the DNS.
3.2 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. This means that 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.
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.
4. Reverse 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
188.8.131.52.in-addr.arpa. IN PTR 184.108.40.206.local-ISP.net
Its 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:
*.0.1.2.3.220.127.116.11.8.9.a.b.c.ip6.arpa. IN PTR customer-42.local-ISP.net
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 18.104.22.168.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 Inernet. 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.
6. DNS resolver 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.
There is nothing specific to IPv6 or IPv4 in DNSsec.
8. Security considerations
A certain number of security considerations are not completely
- If a 'bridging system' based on translation is designed to
enable seamless interoperation between IPv4 & IPv6 DNS resolvers &
servers, this system should not introduce any new security issues.
- If DNS resolver discovery is done using the 'well known address'
approach, the stub resolver will not know exactly which resolver
it is talking to and thus may or may not be able establish a
cryptographically verified association with it.
9. Author addresses
SUN Microsystems, Inc
901 San Antonio Road MPK17-202
Palo Alto, CA 94303-4900
[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.
[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
[IPv6ADDRARCH] IP Version 6 Addressing Architecture, R. Hinden,
draft-ipngwg-addr-arch-v3-07.txt, work in progress.
[6to4ReverseDNS] 6to4 and DNS, K. Moore, draft-ietf-
ngtrans-6to4-dns-00.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-05.txt, work in progress.
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