Publications Technical Report

new technical report “T-DNS: Connection-Oriented DNS to Improve Privacy and Security (extended)”

We released a new technical report “T-DNS: Connection-Oriented DNS to Improve Privacy and Security (extended)”, ISI-TR-2014-693, available as

From the abstract:resp_cdf_diff_key_all

DNS is the canonical protocol for connectionless UDP. Yet DNS today is challenged by eavesdropping that compromises privacy, source-address spoofing that results in denial-of-service (DoS) attacks on the server and third parties, injection attacks that exploit fragmentation, and size limitations that constrain policy and operational choices. We propose T-DNS to address these problems. It uses TCP to smoothly support large payloads and to mitigate spoofing and amplification for DoS. T-DNS uses transport-layer security (TLS) to provide privacy from users to their DNS resolvers and optionally to authoritative servers. Expectations about DNS suggest connections will balloon client latency and overwhelm server with state, but our evaluation shows costs are modest: end-to-end latency from TLS to the recursive resolver is only about 9% slower when UDP is used to the authoritative server, and 22% slower with TCP to the authoritative. With diverse traces we show that frequent connection reuse is possible (60–95% for stub and recursive resolvers, although half that for authoritative servers), and after connection establishment, we show TCP and TLS latency is equivalent to UDP. With conservative timeouts (20 s at authoritative servers and 60 s elsewhere) and conservative estimates of connection state memory requirements, we show that server memory requirements match current hardware: a large recursive resolver may have 24k active connections requiring about 3.6 GB additional RAM. We identify the key design and implementation decisions needed to minimize overhead: query pipelining, out-of-order responses, TLS connection resumption, and plausible timeouts.

This paper is a major revision of the prior technical report ISI-TR-2014-688. Since that work we have improved our understanding of the availability of TCP fast open and TLS resumption, and we have tightened our estimates on memory based on external reports (section 5.2). This additional information has allowed us to conduct additional experiments, improve our modeling, and provide a more accurate view of what is possible today; our estimates of latency and memory consumption are both lower than in our prior technical report as a result. We have also added additional information about packet size limitations (Figure 2), experiments evaluating DNSCrypt/DNSCurve (section 6.1), analysis of DTLS, and covered a broader range of RTTs in our experiments. We believe these additions strengthen our central claims: that connectionless DNS causes multiple problems and that T-DNS addresses those problems with modest increase in latency and memory suitable for current hardware.