Afnic launches IBDNS, the “intentionally broken” DNS server

On the Internet, applications using the DNS (Domain Name System) generally follow the protocol’s technical specifications. But when developing a testing tool or a resolver, it can be useful to verify its behaviour compared when faced with DNS servers that do not comply with these specifications. After all, a good DNS client must be able to handle poorly formed messages or incorrect behaviour of name servers without malfunctioning.

This is where IBDNS comes into play. IBDNS fills a gap in the universe of DNS test tools by offering the possibility of deviating intentionally and on demand from the DNS specifications, and thus simulating incorrect behaviour of authoritative name servers.

Afnic had initially developed IBDNS to cater to the needs of Zonemaster, its DNS zone health assessment tool designed in collaboration with their Swedish counterpart Internetstiftelsen. This begs the question: how to ensure that Zonemaster gives the right diagnosis in all circumstances. The test suite accompanying Zonemaster to this end relied on zones that were intentionally misconfigured, but hosted on standard servers. The method worked well for 90% of the anomalies detected, but the remaining 10% needed a more specific tool. By allowing the anomalies observed on the Internet to be faithfully replicated, which a standard DNS server cannot do, IBDNS further improves the reliability and accuracy of Zonemaster’s diagnostics.

In its initial use case as a testing tool for testing tools, IBDNS aims to comfort Zonemaster in its position as the benchmark DNS testing tool. Its release as free software reflects the determination to shift gears and have Zonemaster’s unit tests reach a coverage as close as possible to 100%.

Afnic invites anyone who’s interested – be they developers of DNS resolvers, DNS testing tools and more generally tools that interact with authoritative name servers, security auditors for this same category of software applications, researchers interested in the DNS and its implementation, or just people curious about the workings of the DNS – to discover the IBDNS source code on Afnic Labs’ Gitlab server.