DNS Performance and the Effectiveness of Caching

This paper analyzes DNS performance using traces collected in 2000 at MIT and Korea of client DNS queries.

Summary

The paper explores two key questions:

What is the latency of DNS requests and how often do they fail?
How does varying the TTL and caching sharing impact caching effectiveness?

The authors use data collected over three months at two different sites to answer these questions. The data consists of 60% lookups for A records and between 24% and 31% reverse lookups from addresses to host names. They found that around 20% of queries were not answered and had to be retransmitted. The average number of query packets sent for a successful reply was 1.27.

The median latency was 42ms with 35% of the responses taking less than 10ms. They found that caching NS records substantially reduces lookup latency.

Curiously they found that the hit rate of the cache does not increase substantially with additional clients beyond 10. They explain this by noticing that most DNS queries are for a very small but popular set of addresses. They also notice that increasing the TTL beyond several minutes has very little additional benefit.

Thoughts

This is an interesting study of how DNS works in real life. Particularly the statistics about the number of clients needed to have useful caching is very practical.