On the effectiveness of DNS-based server selection

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 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 reducing DNS TTL values on Web access latency and show that it 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.