cache me if you can effects of dns time to live
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Cache Me If You Can: Effects of DNS Time-to-Live Giovane C. M. Moura - PowerPoint PPT Presentation

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Cache Me If You Can: Effects of DNS Time-to-Live Giovane C. M. Moura 1 , 2 , John Heidemann 3 , Wes Hardaker 3 , Ricardo de O. Schmidt 4 RIPE 79 Rotterdam, The Netherlands 2019-10-15 1 SIDN Labs, 2 TU Delft, 3 USC/ISI, 4 UPF Outline

  1. Cache Me If You Can: Effects of DNS Time-to-Live Giovane C. M. Moura 1 , 2 , John Heidemann 3 , Wes Hardaker 3 , Ricardo de O. Schmidt 4 RIPE 79 Rotterdam, The Netherlands 2019-10-15 1 SIDN Labs, 2 TU Delft, 3 USC/ISI, 4 UPF

  2. Outline Introduction Parent vs Child Zone configurations and Effective TTL TTLs Use in the Wild Operators Notification Caching (Longer TTL) vs Anycast Shorter vs Longer TTLs Recommendation and Conclusions

  3. Our research on DNS over the last years Our rearch on DNS security/stability: • Anycast and DDoS : IMC 2016 [2] • Resolvers : IMC 2017 [5] • Anycast Engineering : IMC 2017 [1] • Caching and DDoS : IMC 2018 [4] • Caching and TTL, and performance: IMC 2019 [3] • (this paper) • IMC will be next week in Amsterdam 1

  4. Introduction

  5. The role of TTL authoritative user resolver server 1

  6. The role of TTL authoritative user resolver server Q: google.com? 1

  7. The role of TTL authoritative user resolver server Q: google.com? Q: google.com? 1

  8. The role of TTL authoritative user resolver server Q: google.com? Q: google.com? A: 10.10.10.10 A: 10.10.10.10 1

  9. The role of TTL authoritative user resolver server Q: google.com? Q: google.com? A: 10.10.10.10 A: 10.10.10.10 cache 1

  10. The role of TTL authoritative user resolver server Q: google.com? Q: google.com? A: 10.10.10.10 A: 10.10.10.10 ? m o c . e l g o cache o g : Q 1

  11. The role of TTL x authoritative user resolver server Q: google.com? Q: google.com? A: 10.10.10.10 A: 10.10.10.10 ? m o c . e 0 l g 1 o . cache 0 o 1 g . 0 : Q 1 . 0 1 : A cache hit! FASTER 1

  12. The role of TTL x ISP GOOGLE authoritative user resolver server Q: google.com? Q: google.com? A: 10.10.10.10 A: 10.10.10.10 ? m o BUT caching FOR c . e 0 l g 1 o . cache HOW LONG??? 0 o 1 g . 0 : Q 1 . 0 1 : A cache hit! FASTER 1

  13. The role of TTL x ISP GOOGLE authoritative user resolver server Q: google.com? Q: google.com? A: 10.10.10.10 A: 10.10.10.10 ? m o BUT caching FOR c . e 0 l g 1 o . cache HOW LONG??? 0 o 1 g . 0 : Q 1 . 0 1 TTL : A cache hit! FASTER 1

  14. The role of TTL x ISP GOOGLE authoritative user resolver server Q: google.com? Q: google.com? A: 10.10.10.10 A: 10.10.10.10 ? m o BUT caching FOR c . e 0 l g 1 o . cache HOW LONG??? 0 o 1 g . 0 : Q 1 . 0 1 TTL : A cache hit! FASTER • TTL controls caching • auth servers SIGNAL to resolvers how long (TTL) • Caching is VERY important for performance • improves user experience 2

  15. And you must set TTLs • Say you register cachetest.net 3

  16. What TTL values are good? Today it is unclear what an operator should do • DNS OPs folks on TTLs: “ if it ain’t broke don’t fix it ” We think we can help Figure 1: DNS ops chaging TTLs. src: trainworld.be 4

  17. Our contribution Because of conflicting and under-explained TTL advice, we show: 1. the effective TTL comes from multiple places • Parent and Child authoritative servers • NS and A records (sometimes) 2. TTLs are unnecesssarily short • a. because sometimes multiple places → one is shorter and wins • or operators don’t realize the cost 3. We show that longer TTLs are MUCH faster 4. Our results were adopted by 3 ccTLD for ∼ 20ms median latency improvement; 171ms 75%ile 5

  18. The rest of this talk 1. Parent vs Child: who really sets the TTL? 2. NS and A records: are they limited? And bailiwick? 3. Real-world variation exists 4. Longer TTLs are MUCH better 5. Our recommendations 6

  19. Parent vs Child

  20. Duplicate info: which one is chosen? • Parent and child TTLs may vary: dig NS cachetest.net ROOT . NS cachetest.net: .nl .org ... .net * ns1.cachetest.net * TTL: 172800s NS cachetest.net: * ns1.cachetest.net cachetest.net Resolver * TTL: 3600s Which TTL will Rembrandt use? Parent ( 172800s) or child ( TTL: 3600s) 7

  21. Are resolvers parent- or child-centric? Parent vs Child experiment • Test with experiment on .uy : (2019-02-14) • Parent : NS/A TTL: 172800s • Child : NS TTL: 300s ; A: 120s • We query with 15k VPs (Ripe Atlas) mutliple times, every 10min • We analyze TTL values received at VPs 8

  22. Most Atlas VPs resolvers are child-centric Figure 2: Observed TTLs from Atlas VPs for .uy-NS and a.nic.uy-A queries. Spike at Child TTL A (120s) : most resolvers are child centric 1 0.8 CDF TTL Answers 0.6 0.4 A queries 0.2 NS queries 0 5 10 50 120 300 1000 Answers TTL(s) Spike at Child TTL NS (300s): child centric 9 • Remember: TTL parents: 2 days

  23. Most Atlas VPs resolvers are child-centric Figure 2: Observed TTLs from Atlas VPs for .uy-NS and a.nic.uy-A queries. Spike at Child TTL A (120s) : most resolvers are child centric 1 0.8 CDF TTL Answers 0.6 0.4 A queries 0.2 NS queries 0 5 10 50 120 300 1000 Answers TTL(s) Spike at Child TTL NS (300s): child centric 9 • Remember: TTL parents: 2 days

  24. Most Atlas VPs resolvers are child-centric Figure 2: Observed TTLs from Atlas VPs for .uy-NS and a.nic.uy-A queries. Spike at Child TTL A (120s) : most resolvers are child centric 1 0.8 CDF TTL Answers 0.6 0.4 A queries 0.2 NS queries 0 5 10 50 120 300 1000 Answers TTL(s) Spike at Child TTL NS (300s): child centric 9 • Remember: TTL parents: 2 days

  25. Is centricity true for TLDs and SLDs? • Test with .nl TLD A records (ns*.dns.nl) • TTLs are 3600s (child) vs. 17800s (parent) Figure 3: Minimum interarrival time of A queries for TLD 1 0.8 0.6 CDF TTL 173800s TTL 3600s 0.4 0.2 0 1 2 5 10 20 50 Interarrival time (h) Spike at Child TTL A (3600s): confirm child centric for TLD We confirmed this with a second-level domain ( paper) 10

  26. Is centricity true for TLDs and SLDs? • Test with .nl TLD A records (ns*.dns.nl) • TTLs are 3600s (child) vs. 17800s (parent) Figure 3: Minimum interarrival time of A queries for TLD 1 0.8 0.6 CDF TTL 173800s TTL 3600s 0.4 0.2 0 1 2 5 10 20 50 Interarrival time (h) Spike at Child TTL A (3600s): confirm child centric for TLD We confirmed this with a second-level domain ( paper) 10

  27. Is centricity true for TLDs and SLDs? • Test with .nl TLD A records (ns*.dns.nl) • TTLs are 3600s (child) vs. 17800s (parent) Figure 3: Minimum interarrival time of A queries for TLD 1 0.8 0.6 CDF TTL 173800s TTL 3600s 0.4 0.2 0 1 2 5 10 20 50 Interarrival time (h) Spike at Child TTL A (3600s): confirm child centric for TLD We confirmed this with a second-level domain ( paper) 10

  28. Most resolvers wil use child TTLs • Rembrant (and users) mostly use child TTLs • Child TTL controls caching (most times) ROOT . NS cachetest.net: .nl .org ... .net * ns1.cachetest.net * TTL: 172800s NS cachetest.net: * ns1.cachetest.net Resolver cachetest.net * TTL: 3600s Which TTL will Rembrandt use? Parent ( 172800s) or child ( TTL: 3600s) 11

  29. Outline Introduction Parent vs Child Zone configurations and Effective TTL TTLs Use in the Wild Operators Notification Caching (Longer TTL) vs Anycast Shorter vs Longer TTLs Recommendation and Conclusions

  30. Zone configurations and Effective TTL

  31. Are there dependencies between A and NS TTLs? sub.cachetest.net In zone Out of zone NS : ns1.sub.cachetest.net 3600 NS : ns1.zurrundeddu.com 3600 A :10.10.10.10 7200 A :10.10.10.10 7200 To resolve *.sub.cachetest.net, you need both NS and A Are NS and A cached independently? 1. t=0 : all Atlas VPs query (fills cache with NS and A) 2. t=4800 : what happens ? NS is expired; A is still in cache: do resolvers use the “cached A” or refresh it again? trick: at t=540 , we renumber A to 10.10.10.2 (diff answer) Will Marcus Aurelius receive cached or new answer? 12

  32. Are there dependencies between A and NS TTLs? sub.cachetest.net In zone Out of zone NS : ns1.sub.cachetest.net 3600 NS : ns1.zurrundeddu.com 3600 A :10.10.10.10 7200 A :10.10.10.10 7200 To resolve *.sub.cachetest.net, you need both NS and A Are NS and A cached independently? 1. t=0 : all Atlas VPs query (fills cache with NS and A) 2. t=4800 : what happens ? NS is expired; A is still in cache: do resolvers use the “cached A” or refresh it again? trick: at t=540 , we renumber A to 10.10.10.2 (diff answer) Will Marcus Aurelius receive cached or new answer? 12

  33. Are there dependencies between A and NS TTLs? sub.cachetest.net In zone Out of zone NS : ns1.sub.cachetest.net 3600 NS : ns1.zurrundeddu.com 3600 A :10.10.10.10 7200 A :10.10.10.10 7200 To resolve *.sub.cachetest.net, you need both NS and A Are NS and A cached independently? 1. t=0 : all Atlas VPs query (fills cache with NS and A) 2. t=4800 : what happens ? NS is expired; A is still in cache: do resolvers use the “cached A” or refresh it again? trick: at t=540 , we renumber A to 10.10.10.2 (diff answer) Will Marcus Aurelius receive cached or new answer? 12

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