| Internet-Draft | 3901bis | October 2023 |
| Yamamoto & Fiebig | Expires 22 April 2024 | [Page] |
This memo provides guidelines and documents Best Current Practice for operating authoritative and recursive DNS servers given that queries and responses are carried in a mixed environment of IPv4 and IPv6 networks. It expands beyond [RFC3910] in so far that it now considers the reality of progressing IPv4 exhaustion, which will make IPv6-only resolvers necessary in the long-term.¶
This note is to be removed before publishing as an RFC.¶
Source for this draft and an issue tracker can be found at https://github.com/momoka0122y/draft-dnsop-3901bis.¶
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Despite IPv6 being first discussed in the mid 1990s [RFC1883], consistent deployment throughout the whole Internet has not yet been accomplished. Hence, today, the Internet is a mixture of IPv4, dual-stack (networks connected via both IP versions), and IPv6 networks.¶
This creates a complex landscape where authoritative name servers might be accessible only via specific network protocols [V6DNSRDY-23]. At the same time, DNS resolvers may only be able to access the Internet via either IPv4 or IPv6. This poses a challenge for such resolvers because they may encounter names for which queries must be directed to authoritative name servers with which they do not share an IP version during the name resolution process [draft-momoka-v6ops-ipv6-only-resolver-02].¶
In this document, we discuss:¶
IP version related namespace fragmentation and best-practices for avoiding it.¶
Guidelines for configuring authoritative name servers for zones.¶
Guidelines for operating recursive DNS resolvers.¶
While transitional technologies and dual-stack setups may mitigate some of the issues of DNS resolution in a mixed protocol-version Internet, making DNS data accessible over both IPv4 and IPv6 is the most robust and flexible approach, as it allows resolvers to reach the information they need without requiring intermediary translation or forwarding services which may introduce additional failure cases.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
This document uses DNS terminology as described in [RFC8499]. Furthermore, the following terms are used with a defined meaning:¶
A resolver that tries to look up a name starts out at the root, and follows referrals until it is referred to a name server that is authoritative for the name. If somewhere down the chain of referrals it is referred to a name server that is, based on the referral, only accessible over a transport which the resolver cannot use, the resolver is unable to continue DNS resolution.¶
If this occurs, the DNS has, effectively, fragmented based on the resolver's and authoritative's mismatching IP version support.¶
In a mixed IP Internet, fragmentation can occur for different reasons. One reason is that DNS zones are consistently configured to support only either IPv4 or IPv6. Another reason is due to misconfigurations that make a zone unresolvable by either IPv4 or IPv6-only resolvers. The latter cases are often hard to identify, as the impact of misconfigurations for only one IP version (IPv4 or IPv6) may be hidden in a dual-stack setting. In the worst case, a specific name may only be resolvable via dual-stack enabled resolvers.¶
With the final exhaustion of IPv4 pools in RIRs, e.g., [RIPEV4], and the progressing deployment of IPv6, there no longer is a "preferred" IP version. Yet, while we now observe the first zones becoming exclusively IPv6 resolvable, we also still see a major portion of zones solely relying on legacy IP [V6DNSRDY-23]. Hence, at the moment, dual stack connectivity is instrumental to be able to resolve zones and avoid name space fragmentation.¶
Having zones served only by name servers reachable via one IP version would fragment the DNS. Hence, we need to find a way to avoid this fragmentation.¶
The recommended approach to maintain name space continuity is to use administrative policies, as described in this section.¶
It is usually recommended that DNS zones contain at least two name servers, which are geographically diverse and operate under different routing policies [IANANS]. To reduce the chance of DNS name space fragmentation, it is RECOMMENDED that at least two NS for a zone are dual stack name servers. Specifically, this means that the following minimal requirements SHOULD be implemented for a zone:¶
Note: zone validation processes SHOULD ensure that there is at least one IPv4 address record and one IPv6 address record available for the name servers of any child delegations within the zone.¶
Every iterative name server SHOULD be dual stack.¶
While the zones that IPv6-only iterative resolvers can resolve are growing but do not yet cover all zones, they cannot fully resolve all zones. Hence, a recursive resolver MAY be IPv6-only, if it uses a transition mechanism for IPv4 reachability [draft-momoka-v6ops-ipv6-only-resolver-02] or use a configuration where such resolvers forward queries failing IPv6 only DNS resolution to a set of dual-stack recursive name servers that perform the actual recursive queries.¶
Similarly, a recursive resolver MAY be IPv4-only, if it use a configuration where such resolvers forward queries failing IPv4 only DNS resolution to a set of dual-stack recursive name servers that perform the actual recursive queries.¶
TODO: This requires some input as, e.g., dual-stack services have implications for ratelimiting etc.¶
The guidelines described in this memo introduce no new security considerations into the DNS protocol or associated operational scenarios.¶
This document asks IANA to update its technical requirements for authoritative name servers to require an IPv4 and an IPv6 address for each authoritative server [IANANS].¶
TODO: acknowledge people.¶
Thank you for reading this draft.¶