Measuring Update Performance and Consistency Anomalies in Managed DNS Services

Managed DNS (MDNS) services today excel at providing a simple and cost-effective way to outsource domain management and ensure rapid lookup times for geo-distributed users. The intense focus on optimizing lookup performance coupled with DNS’ inherent expectations of weak consistency has had unfortunate side effects: updates are inexplicably slow and MDNS providers pay scant attention to consistency correctness. We conduct an empirical measurement-driven study of 8 top-tier managed DNS providers and find that inter-nameserver update propagation delays commonly take tens of seconds with little improvement over the last several years. Client-perceived inconsistency is rampant with roughly a third of end-users being vulnerable to TTL abuse by local DNS resolvers. Furthermore, we find that 6 of the 8 MDNS providers violate monotonic read consistency under frequent updates and at least one large MDNS provider appears to violate even eventual consistency.

I. Introduction

The Internet’s Domain Name System (DNS) is widely presented as a textbook example of a distributed system with eventual consistency, a system that effectively trades off consistency to improve performance and reduce cost. DNS achieves this design goal through its liberal use of TTL-based caching, a design that also implicitly embeds the synergistic assumption of infrequent updates. Weakly consistent caching alongside hierarchical federation is key to DNS’ scalability.