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Understanding DNSSEC Validation Measurement Techniques and Challenges

This document delves into the theory and reality of measuring DNSSEC validation, exploring the differences between DNSSEC validators and standard DNS resolvers. It discusses necessary records, such as DNSKEY and DS, and the complexities involved in measurement practices, including the impact of TTLs. The findings reveal significant insights into the behavior of validators, traffic patterns, and the need for refined measurement strategies. Key topics include validator types, measurement tools, and potential pitfalls when interpreting data, offering a comprehensive overview for researchers and network administrators.

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Understanding DNSSEC Validation Measurement Techniques and Challenges

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  1. Measuring DNSSEC validationi.e. how to do it Ólafur Guðmundsson Steve Crocker ogud, steve at shinkuro.com

  2. Outline • Theory of measurement • Reality of measurements • Results and questions

  3. Theory 101: Basics • Do DNSSEC validators behave differently from regular DNS resolvers? • Ask for DNSSEC records • DNSKEY • DS • Needs to refresh these records once in a while • DNSKEY about once every TTL • DS • Resolver needs to resolve RRset that is not in cache AND • If TTL’s on DNSKEY and DS have expired BUT • Not on NS

  4. Theory 201: Complications • Validators not only ones: • DNSSEC measurement tools • DNSSEC key mangers for trust anchors • “Rollover and Die” validators • DDoS tools • Need to exclude most of above. • Validator will ask for DNSKEY • Separated by at leastDNSKEY TTL • Asked for non-DNSSEC record just before • Cue on RRtype or name?

  5. Theory 202: Validator Draft rules • Asks for DNSKEY multiple times in a sample at least DNSKEY TTL apart • Asks for info, followed by DNSKEY query • Asks for multiple DS records • Rule 1 and 3 combined

  6. Measurements: ORG traffic • TTL’s: • 900 for SOA, NSEC3, DNSKEY • 84600 for NS and DS • By simple measure: • 10% of queries originate from suspected DNSSEC validators • BUT: • includes DNSKEY + DS traffic • Excludes: some only using dlv.isc.org

  7. Measurement Reality: • Saw traffic for some of DNS servers for ORG • 2/3 NS records, ~ 50% of traffic • Queries are scattered • Some resolvers ask a narrow band of servers • Busy ones • Some ask random ones and no subsequent questions to the same one. • Sporadic ones • Multiple validators/resolvers behind an address • All classified as one, • Traces • short < 1 hour • Time 2000-2050 UTZ

  8. How good are the samples • Are validators over/under represented? • Do the validators we see do more/less DNSSEC than others? • Do DNSSEC validators scatter queries different ? • DNSKEY set size > 1500 effects: • Validator tries multiple UDP servers before falling back on TCP  Overrepresented • Do measurement tools trick us ? • What to exclude in calculations? • DNSKEY ? • DS ? • DLV ? • SOA ?

  9. Discussion • How to measure • What to measure • Where to measure • How to tune TTL’s

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