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USENIX 2002 Annual Conference - Technical Program Abstract
A Precise and Efficient Evaluation of the Proximity between Web Clients and their Local DNS Servers
Zhuoqing Morley Mao, Charles D. Cranor, Fred Douglis, Michael Rabinovich,
Oliver Spatscheck, and Jia Wang,
AT&T Labs/Research
Abstract
Content Distribution Networks (CDNs) attempt to improve Web performance by
delivering Web content to end-users from servers located at the edge of the
network. An important factor contributing to the performance improvement is
the ability of a CDN to select servers in
the proximity of the requesting clients. Most CDNs today use the Domain Name
System (DNS) to make such server selection decisions. However, DNS provides only
the IP address of the client's local DNS server to the CDN, rather than
the client's IP address. Therefore, CDNs using DNS-based server selection
assume that clients are ``close'' to their local DNS servers.
To quantify the proximity between clients and their local DNS
servers, we propose a novel, precise, and efficient technique for
finding the associations of client to local DNS servers. We collected
more than 4.2 million such unique associations
in three months. From this data, we study the impact of
proximity on DNS-based server selection using four different proximity
metrics. We conclude that DNS is good for very coarse-grained server
selection, since 64% of the associations belong to the same
Autonomous System.
DNS is less useful for finer-grained server selection, since only 16%
of the client and local DNS associations are in the same network-aware
cluster (based on BGP routing information from
a wide set of routers).
As an application of this methodology, we
evaluate DNS-based server selection in three of the largest commercially deployed
CDNs to study its accuracy.
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