Week4:DNS Performance and the Effectiveness of Caching
This paper has presented a
detailed analysis of traces of DNS and associated TCP traffic collected on the
Internet based on the data form traced links of MIT Laboratory and KAIST, then discusses
trace-driven simulations to study the effectiveness of DNS caching as a function
of TTL and degree of cache sharing.
By analyse the collected data,
the authors have these results:
1. 1. Distribution of popular
names following the Zipf’s law fails to make use of caching with larger TTL
values.
2. 2. Sharing cache among groups
of clients has limited gain in terms of cache hit after the total member count
crosses 20-25.
3. 3. The client-perceived
latency is adversely affected by number of referrals, and caching NS records to
reduce the number of referrals will decrease latency as well as load on the
root servers.
4. 4. Distribution of names
causing negative responses follows a heavy tailed distribution as well. As a
result, hit rate of negative caching is also limited.
Using trace-driven simulations
algorithm, the author wants to find how useful to share DNS caches among many
client machines and what is the impact of choice of TTL on caching
effectiveness. The authors quantify two important statistics: the distribution of name popularity and TTL
values in the trace data. Both determine cache hit rates. And draw a conclusion
that for A-records, lower TTL seems won’t harm the hit rates, caching appears
to have limited effectiveness. But for NS-records, it
would increase the load on root server and harm DNS scalability.
At the end, the paper draw a
conclusion that the widespread use of
dynamic, lower-TTL A-record bindings should not harm DNS performance.
Such that the scalability of DNS are less dependent on the hierarchical design of its
name space or good A-record caching(originally believed).
