Authors: Fangfei Chen (Akamai Technologies), Ramesh K. Sitaraman (UMass, Amherst & Akamai Technologies), Marcelo Torres (Akamai Technologies)
Presenter: Fangfei Chen
Link to Public Review by Ethan Katz-Bassett
Summary:
Presenter: Fangfei Chen
Link to Public Review by Ethan Katz-Bassett
Summary:
A key component in a content delivery network (CDN) is the mapping system that routes a client’s request to a server. Traditionally, the mapping systems have used the local recursive domain name servers (LDNS) as a proxy for determining clients' path conditions (called NS-based mapping approach). However, in several cases the network conditions of the LDNS and the client may be different. This paper provides the first large-scale study of the limitations of NS-based mapping and the experience of deploying EDNS0 (client-subnet extension to the DNS protocol); a solution that uses the client’s prefix to infer information about the client (their resulting system is called end-user mapping).
They collected data from over 3.76 million IP blocks. They found that more than 50% of the clients were within 100miles of their LDNS. However, there was a lot of diversity across countries. For instance, the average distance between clients and LDNS in India and Brazil was large. The author conjectured that this was because there weren't many (or perhaps no) public DNS servers within these countries.
Fangfei then talked about the performance benefits of using end-user mapping as observed by Akamai. In particular, they found that the download times improved by approximately 100ms. This is significant because better download times for the end-users are correlated with revenue. However, a major challenge they ran into was scalability. As there are more clients than LDNS servers generally, using EDNS0 meant that there was increase in DNS query traffic. It is a significant problem which requires more attention.
They collected data from over 3.76 million IP blocks. They found that more than 50% of the clients were within 100miles of their LDNS. However, there was a lot of diversity across countries. For instance, the average distance between clients and LDNS in India and Brazil was large. The author conjectured that this was because there weren't many (or perhaps no) public DNS servers within these countries.
Fangfei then talked about the performance benefits of using end-user mapping as observed by Akamai. In particular, they found that the download times improved by approximately 100ms. This is significant because better download times for the end-users are correlated with revenue. However, a major challenge they ran into was scalability. As there are more clients than LDNS servers generally, using EDNS0 meant that there was increase in DNS query traffic. It is a significant problem which requires more attention.
Q/A (Paraphrased):
Q. Why did you report results in terms of miles as opposed to RTTs
A. It was tricky to report them in terms of RTTs. Reporting them in miles was more direct and also helped in geo-locating the IP addresses
Q. Did you look at the costs at the ISP side of scalability concerns
A. We didn't look at the costs but such an analysis could be carried out with our data.
Q. Did you measure EDNS0 adoption?
A. No but we are encouraging ISPs to adopt it.
Q. Was there a rollout of new cache servers while conducting this study?
A. We did not specifically restrict the rollout of new cache servers.
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