"On the Effectiveness of DNS-based Server Selection"
Anees Shaikh, Renu Tewari, and Mukesh Agrawal
The rapid growth of the Internet in users and content has fueled extensive
efforts to improve the user's overall Internet experience. A growing number
of providers deliver content from multiple servers or proxies to reduce
response time by moving content closer to end users. An increasingly popular
mechanism to direct clients to the closest point of service is DNS-based
redirection, due to its transparency and generality. This paper studies
draws attention to two of the main issues in using DNS: 1) the negative
effects of reducing or eliminating the cache lifetimes of DNS information,
and 2) the implicit assumption that client nameservers are indicative of
actual client location and performance. We quantify the impact of
reduced DNS TTL values on web access latency and show that they can increase
name resolution latency by two orders of magnitude. Using HTTP and
DNS server logs, as well as a large number of dial-up ISP clients, we measure
client-nameserver proximity and show that a significant fraction are distant,
more than 8 hops apart. Finally, we suggest protocol modifications
to improve the accuracy of DNS-based redirection schemes.