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
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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Local addresses SHOULD NOT be published in the DNS, neither in the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:
1.2.3.4.in-addr.arpa. IN PTR 4.3.2.1.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:
*.0.1.2.3.4.5.6.7.8.9.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 2.0.0.2.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.
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