Measuring and Understanding TTL Violations in DNS Resolvers

The Domain Name System (DNS) is a scalable-distributed caching architecture where each DNS records are cached around several DNS servers distributed globally. DNS records include a time-to-live (TTL) value that dictates how long the record can be stored before it's evicted from the cache. TTL holds significant importance in aspects of DNS security, such as determining the caching period for DNSSEC-signed responses, as well as performance, like the responsiveness of CDN-managed domains. On a high level, TTL is crucial for ensuring efficient caching, load distribution, and network security in Domain Name System. Setting appropriate TTL values is a key aspect of DNS administration to ensure the reliable and efficient functioning of the Domain Name System. Therefore, it is crucial to measure how TTL violations occur in resolvers. But, assessing how DNS resolvers worldwide handle TTL is not easy and typically requires access to multiple nodes distributed globally. In this work, we introduce a novel methodology for measuring TTL violations in DNS resolvers leveraging a residential proxy service called Brightdata, enabling us to evaluate more than 27,000 resolvers across 9,500 Autonomous Systems (ASes). We found that 8.74% arbitrarily extends TTL among 8,524 resolvers that had atleast five distinct exit nodes. Additionally, we also find that the DNSSEC standard is being disregarded by 44.1% of DNSSEC-validating resolvers, as they continue to provide DNSSEC-signed responses even after the RRSIGs have expired.