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Impact of Configuration Errors on DNS Robustness

This study examines the impact of configuration errors on DNS robustness and performance, highlighting issues such as lame delegation and diminished server redundancy. By analyzing error frequency and their effects, we aim to improve DNS reliability. The findings provide insights for enhancing system resilience and reducing downtime caused by misconfigurations.

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Impact of Configuration Errors on DNS Robustness

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  1. Impact of Configuration Errors on DNS Robustness V. Pappas * Z. Xu *, S. Lu *, D. Massey **, A. Terzis ***, L. Zhang * * UCLA, ** Colorado State, *** John Hopkins

  2. are they the same? Motivation • DNS: part of the Internet core infrastructure • Applications: web, e-mail, e164, CDNs … • DNS: considered as a very reliable system • Works almost always • Question: is DNS a robust system? • User-perceived robustness • System robustness

  3. Motivation Short Answer: “Microsoft's websites were offline for up to 23 hours -- the most dramatic snafu to date on the Internet --because of an equipment misconfiguration” -- Wired News, Jan 2001 • Thousands or even millions of users affected • All due to a singleDNS configuration error

  4. Related Work • Traffic & implementation errors studies: • Danzig et al. [SIGCOMM92]: bugs • CAIDA : traffic & bugs • Performance studies: • Jung et al. [IMW01]: caching • Cohen et al. [SAINT01]: proactive caching • Liston et al. [IMW02]: diversity • Server availability : • To appear [OSDI04, IMC04]

  5. Our Work: Study DNS Robustness • Classify DNS operational errors: • Study known errors • Identify new types of errors • Measure their pervasiveness • Quantify their impact on DNS • availability • performance

  6. Outline • DNS Overview • Measurement Methodology • DNS Configuration Errors • Example Cases • Measurement Results • Discussion & Summary

  7. jp net uk ca bar.foo.com. NS ns1.bar.foo.com. bar.foo.com. NS ns3.bar.foo.com. bar.foo.com. NS ns2.bar.foo.com. bar.foo.com. MX mail.bar.foo.com. www.bar.foo.com. A 10.10.10.10 Zone: Occupies a continues subspace Served by the same nameservers bar resource records name servers Background com foo buz bar bar1 bar2 bar3

  8. answer: www.bar.foo.com A 10.10.10.10 caching server referral: com NS RRs com A RRs root zone referral: foo NS RRs foo A RRs referral: bar NS RRs bar A RRs com zone foo zone bar zone asking for www.bar.foo.com client

  9. foo.com. NS ns1.foo.com. foo.com. NS ns2.foo.com. foo.com. NS ns3.foo.com. ns1.foo.com. A 1.1.1.1 ns2.foo.com. A 2.2.2.2 ns3.foo.com. A 3.3.3.3 foo.com. NS ns1.foo.com. foo.com. NS ns2.foo.com. foo.com. NS ns3.foo.com. ns1.foo.com. A 1.1.1.1 ns2.foo.com. A 2.2.2.2 ns3.foo.com. A 3.3.3.3 Infrastructure RRs • NS Resource Record: • Provides the names of a zone’s authoritative servers • Stored both at the parent and at the child zone com • A Resource Record • Associated with a NS resource record • Stored at the parent zone (glue A record) foo.com

  10. focus of our work What Affects DNS Availability • Name Servers: • Software failures • Network failures • Scheduled maintenance tasks • Infrastructure Resource Records: • Availability of these records • Configuration errors

  11. Lame Delegation Delegation Inconsistency Diminished Redundancy Cyclic Dependency The configuration of infrastructure RRs does not correspond to the actual authoritative name-servers. More than one name-servers share a common point of failure. Classification of Measured Errors Inconsistency Dependency

  12. What is Measured? • Frequency of configuration errors: • System parameters: TLDs , DNS level, zone size (i.e. the number of delegations) • Impact on availability: • Number of servers: lost due to these errors • Zone’s availability: probability of resolving a name • Impact on performance: • Total time to resolve a query • Starting from the query issuing time • Finishing at the query final answer time

  13. Measurement Methodology • Error frequency and availability impact: • 3 sets of active measurements • Random set of 50K zones • 20K zones that allow zone transfers • 500 popular zones • Performance impact: • 2 sets of passive measurements:1-week DNS packet traces

  14. Lame Delegation foo.com. NS A.foo.com. foo.com. NS B.foo.com. A.foo.com. A 1.1.1.1 B.foo.com. A 2.2.2.2 com 1) Non-existing server -- 3 seconds perf. penalty foo 2) DNS error code -- 1 RTT perf. penalty 3) Useless referral -- 1 RTT perf. penalty 4) Non-authoritative answer (cached) A.foo.com B.foo.com

  15. Lame Delegation Results

  16. 50% 0.06 sec 3 sec 0.4 sec Lame Delegation Results

  17. Lame Delegation Results • Error Frequency: • 15% of the zones • 8% for the 500 most popular zones • independent of the zone’s size, varies a lot per TLD • Impact: • 70% of the zones with errors lose half or more of the authoritative servers • 8% of the queries experience increased response times (up to an order of magnitude) due to lame delegation

  18. Diminished Server Redundancy foo.com. NS A.foo.com. foo.com. NS B.foo.com. A.foo.com. A 1.1.1.1 B.foo.com. A 2.2.2.2 com A) Network level: - belong to the same subnet foo B) Autonomous system level: - belong to the same AS C) Geographic location level: - belong to the same city A.foo.com B.foo.com

  19. Diminished Server Redundancy Results • Error Frequency: • 45% of all zones have all servers in the same /24 subnet • 75% of all zones have servers in the same AS • large & popular zones: better AS and geo diversity • Impact: • less than 99.9% availability: all servers in the same /24 subnet • more than 99.99% availability: 3 servers at different ASs or different cities

  20. B.foo.com. A 2.2.2.2 The A glue RR for B.foo.com missing B.foo.com depends on A.foo.com If A.foo.com is unavailable then B.foo.com is too Cyclic Zone Dependency (1) foo.com. NS A.foo.com. foo.com. NS B.foo.com. A.foo.com. A 1.1.1.1 com foo A.foo.com B.foo.com

  21. bar.com. NS A.bar.com. bar.com. NS B.foo.com. A.bar.com. A 2.2.2.2 If A.foo and A.bar are unavailable, B addr. are unresolvable The B servers depend on A servers bar The foo.com zone seems correctly configured B.foo.com A.bar.com Cyclic Zone Dependency (2) foo.com. NS A.foo.com. foo.com. NS B.bar.com. A.foo.com. A 1.1.1.1 com The combination of foo.com and bar.com zones is wrongly configured foo B.bar.com A.foo.com

  22. Cyclic Zone Dependency Results • Error Frequency: • 2% of the zones • None of the 500 most popular zones • Impact: • 90% of the zones with cyclic dependency errors lose 25% (or even more) of their servers • 2 or 4 zones are involved in most errors

  23. Discussion: User-Perceived != System Robustness • User-perceived robustness: • Data replication: only one server is needed • Data caching: temporarymasks infrastructure failures • Popular zones: fewer configuration errors • System robustness: • Fewer available servers: due to inconsistency errors • Fewer redundant servers: due to dependency errors

  24. Discussion: Why so many errors? • Superficially: are due to operators: • Unaware of these errors • Lack of coordination • parent-child zone, secondary servers hosting • Fundamentally: are due to protocol design: • Lack of mechanisms to handle these errors • proactively or reactively • Design choices that embrace some of them: • Name-servers are recognized with names • Glue NS & A records necessary to set up the DNS tree

  25. Summary • DNS operational errors are widespread • DNS operational errors affect availability: • 50% of the servers lost • less than 99.9% availability • DNS operational errors affect performance: • 1 or even 2 orders of magnitude • DNS system robustness lower than user perception • Due to protocol design, not just due to operator errors

  26. Ongoing Work • Reactive mechanisms: • DNS Troubleshooting [NetTs 04] • Proactive mechanisms: • Enhancing DNS replication & caching

  27. Thank You!!!

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