Abstract

DNS 1 latency is a concern for many service operators: CDNs exist to reduce service latency to end-users, but must rely on global DNS for reachability and load-balancing. Today, DNS latency is monitored by active probing from distributed platforms like RIPE Atlas or commercial services. While Atlas coverage is wide, its 10k sites see only a fraction of the Internet. In this paper we show that passive observation of TCP handshakes can measure live DNS latency, continuously, providing good coverage of current service clients. Estimating RTT from TCP is an old idea, but applying this approach to DNS has never scrutinized like this before. We show that there is sufficient TCP DNS traffic today to provide good operational coverage (particularly of IPv6), and very good temporal coverage (better than existing approaches), enabling near-real time evaluation of DNS latency. We also show that DNS servers can optionally solicit TCP to broaden coverage. We quantify coverage and show that estimates of DNS latency from TCP is consistent with UDP latency. Our approach finds previously unknown, real problems: DNS polarization is a new problem where a hypergiant sends global traffic to one anycast site rather than taking advantage of the global anycast deployment. Correcting polarization in Google DNS cut its latency from 100 ms to 10 ms; correcting polarization from Microsoft cut Azure latency from 90 ms to 20 ms. Finally, real-time use of our approach for a European country-level domain has helped detect and correct a BGP routing misconfiguration that detoured European traffic to Australia. We incorporated our approach into ENTRADA, our open …

Date

January 1, 1970

Authors

Giovane CM Moura, John Heidemann, Wes Hardaker, Pithayuth Charnsethikul, Jeroen Bulten, Joao Ceron, Cristian Hesselman

Journal

Update