This paper presents findings about DNS regarding its performance and effectiveness of caching. Studying traces from MIT and KAIST, the authors show the breakdown of DNS query types; they found that around 60% were name-to-address queries, with another 25-30% being reverse address-to-name queries. However, they say they excluded DNS lookups not associated with TCP connections from these statistics and then revealed that 50% of MIT lookups fall into this category. How much does this class of lookups change their results?
It sounds like a lot of DNS traffic is somewhat gratuitous, for example with systems doing reverse lookups and then verifying that result by doing an A lookup on it. Surprisingly, nearly 1/4th of all DNS lookups go unanswered, with at least another 10% receiving a negative answer. The authors also chart latency of lookups based on number of referrals in the process. Not surprisingly, 2 or more referrals can cause a a tenfold increase in latency. Also not surprising is that caching can bring this latency down significantly, as well as easing the load at the root servers.
The authors further study caching through a trace-based simulation which looks at cached IP address hits. They find that a small number of names are very frequently accessed, allowing cache rates for small size caches to be high, and that increasing TTL increases cache hits only to a certain degree, as web pages with a given name are often accessed in small, successive bursts. I liked this paper because it actually took a look at what all those DNS lookups are running around the net doing.
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