DNS

6 November 2009
   CS5229 Semester 1 2009/10
   1
root




     .com
              .org
                          .sg




yahoo
   google
        pbs
                    nu...
root
          server



.sg



.nus
                                local 
                                      DNS




...
uses UDP


6 November 2009
     CS5229 Semester 1 2009/10
   4
Resource Record"
                   (name, TTL, class, type, value)"

     ns1.nus.edu.sg.          6562          IN      ...
TTL-based Caching


6 November 2009
         CS5229 Semester 1 2009/10
   6
Resource Type"
                   A NS PTR MX CNAME …"

     ns1.nus.edu.sg.     6562          IN       A     137.132.123....
DNS-based "
                   Load Balancing

6 November 2009
       CS5229 Semester 1 2009/10
   8
DNS-based "
                   Server Selection

6 November 2009
        CS5229 Semester 1 2009/10
   9
how fast?"
                   how efficient? "
                is caching useful?"
              how big should TTL be?

6 ...
“DNS Performance and
      Effectiveness of Caching”"
                     J Jung et. al."
                   IEEE TON 200...
Logger




                   Internet
                                MIT Subnets




6 November 2009
               CS52...
3 traces"
                   1 week each
6 November 2009
      CS5229 Semester 1 2009/10
   13
DNS query/respose"
            TCP SYN/FIN/RST

6 November 2009
   CS5229 Semester 1 2009/10
   14
basic analysis


6 November 2009
       CS5229 Semester 1 2009/10
   15
DNS Query Types for mit-jan00

                          6.4
                   6.8
                                      ...
496,802"
                   lookups followed by TCP
                         connections"


                     3,619,173...
80-87%"
                   DNS cache hit ratio"
                     for A lookup

6 November 2009
         CS5229 Semeste...
not very high since it includes
            Web browser’s"
              caching too


6 November 2009
   CS5229 Semester ...
how fast is DNS lookup?



6 November 2009
     CS5229 Semester 1, 2009/10
   20
lookup latency ≈ "
              time between first query"
                 and last response


6 November 2009
      CS522...
mit



       kaist




                22
Number of referals per lookup

                  mit-jan00
               1.16
 0.15

      24.07

                       ...
0


     1

          2




               24
NS Cache"
    miss: 
first query to gTLD or
     
 
 
root servers"
    hit: 
 
otherwise

6 November 2009
   CS5229 Semest...
hit

       miss




               26
2,486,104"
                   iterative lookups"


                   6,039,582"
                    query packets
6 Novem...
significant number of
                      retransmissions



6 November 2009
         CS5229 Semester 1 2009/10
   28
~24%"
              of lookups are unanswered


6 November 2009
      CS5229 Semester 1 2009/10
   29
persistent retransmission"
                         referral loops



6 November 2009
           CS5229 Semester 1 2009/10...
answered




zero referral




                 31
no need to retransmit beyond
              2-3 retransmissions!



6 November 2009
    CS5229 Semester 1 2009/10
   32
loops




         33
each loop generated on average"
                           10"
                   query packets


6 November 2009
     CS5...
~60%"
          of all queries are generated by
                 unanswered lookup


6 November 2009
     CS5229 Semester ...
popularity of domain name
                         follows "

                       Zipf"
                      distribut...
Frequency of the x-th most
popular item is




                             37
popularity of web pages"
population of countries"
occurances of English words"
 :"
 :

                               38
39
40
41
long tail :"

    46%"
of domain names "
are accessed once
                

                    42
43
20%"
  DNS responses are "
from root/gTLD servers


                          44
without caching NS records:"

           5X"
loads on root/gTLD servers
                         


                      ...
kaist




         mit




                46
popular sites have shorter TTL"

    TLL reduces over time
                        


                                  47
6 November 2009
   CS5229 Semester 1 2009/10
   48
sharing cache does not help



                               49
50
large TTL does not help



                           51
“King: Estimating Latency
        between Arbitrary End
               Hosts”"
                   Gummadi et. al."
       ...
how to find alternate path "
   with lower latency?



                              54
need to find latency between
    pair of Internet hosts
                         



                              55
assume name server "
 is close to end host
                    



                        56
authorative
                                authorative
                       NS
                                        ...
how to find a name server
   close to an end host?"

look at domain name, IP prefix
                            


         ...
how likely does a name server
   allow recursive query?"

> 72% of name server tested


                                59
how accurate is the estimated
         latency? 



                                60
61
62
how close, really, is an end
host to its authorative NS? 



                                63
64
65
66
many diverged paths consist of
  routers that are physically
           adjacent 


                                 67
75-80% of the disjoint paths
have latency less than 10ms"
    in the Napster trace


                               68
Summary:"
 Measurement study of DNS"
Use DNS to do measurement  


                               69
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CS5229 09/10 Lecture 11: DNS

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CS5229 09/10 Lecture 11: DNS

  1. 1. DNS 6 November 2009 CS5229 Semester 1 2009/10 1
  2. 2. root .com .org .sg yahoo google pbs nus ntu CS5229 Semester 1 2009/10 2
  3. 3. root server .sg .nus local DNS dig +trace www.nus.sg CS5229 Semester 1 2009/10 3
  4. 4. uses UDP 6 November 2009 CS5229 Semester 1 2009/10 4
  5. 5. Resource Record" (name, TTL, class, type, value)" ns1.nus.edu.sg. 6562 IN A 137.132.123.4 6 November 2009 CS5229 Semester 1 2009/10 5
  6. 6. TTL-based Caching 6 November 2009 CS5229 Semester 1 2009/10 6
  7. 7. Resource Type" A NS PTR MX CNAME …" ns1.nus.edu.sg. 6562 IN A 137.132.123.4 6 November 2009 CS5229 Semester 1 2009/10 7
  8. 8. DNS-based " Load Balancing 6 November 2009 CS5229 Semester 1 2009/10 8
  9. 9. DNS-based " Server Selection 6 November 2009 CS5229 Semester 1 2009/10 9
  10. 10. how fast?" how efficient? " is caching useful?" how big should TTL be? 6 November 2009 CS5229 Semester 1 2009/10 10
  11. 11. “DNS Performance and Effectiveness of Caching”" J Jung et. al." IEEE TON 2002 6 November 2009 CS5229 Semester 1 2009/10 11
  12. 12. Logger Internet MIT Subnets 6 November 2009 CS5229 Semester 1 2009/10 12
  13. 13. 3 traces" 1 week each 6 November 2009 CS5229 Semester 1 2009/10 13
  14. 14. DNS query/respose" TCP SYN/FIN/RST 6 November 2009 CS5229 Semester 1 2009/10 14
  15. 15. basic analysis 6 November 2009 CS5229 Semester 1 2009/10 15
  16. 16. DNS Query Types for mit-jan00 6.4 6.8 A PTR MX 24.6 ANY 60.4 Others 6 November 2009 CS5229 Semester 1 2009/10 16
  17. 17. 496,802" lookups followed by TCP connections" 3,619,173" TCP connections 6 November 2009 CS5229 Semester 1 2009/10 17
  18. 18. 80-87%" DNS cache hit ratio" for A lookup 6 November 2009 CS5229 Semester 1 2009/10 18
  19. 19. not very high since it includes Web browser’s" caching too 6 November 2009 CS5229 Semester 1 2009/10 19
  20. 20. how fast is DNS lookup? 6 November 2009 CS5229 Semester 1, 2009/10 20
  21. 21. lookup latency ≈ " time between first query" and last response 6 November 2009 CS5229 Semester 1 2009/10 21
  22. 22. mit kaist 22
  23. 23. Number of referals per lookup mit-jan00 1.16 0.15 24.07 0 1 74.62 2 > 2 23
  24. 24. 0 1 2 24
  25. 25. NS Cache" miss: first query to gTLD or root servers" hit: otherwise 6 November 2009 CS5229 Semester 1 2009/10 25
  26. 26. hit miss 26
  27. 27. 2,486,104" iterative lookups" 6,039,582" query packets 6 November 2009 CS5229 Semester 1 2009/10 27
  28. 28. significant number of retransmissions 6 November 2009 CS5229 Semester 1 2009/10 28
  29. 29. ~24%" of lookups are unanswered 6 November 2009 CS5229 Semester 1 2009/10 29
  30. 30. persistent retransmission" referral loops 6 November 2009 CS5229 Semester 1 2009/10 30
  31. 31. answered zero referral 31
  32. 32. no need to retransmit beyond 2-3 retransmissions! 6 November 2009 CS5229 Semester 1 2009/10 32
  33. 33. loops 33
  34. 34. each loop generated on average" 10" query packets 6 November 2009 CS5229 Semester 1 2009/10 34
  35. 35. ~60%" of all queries are generated by unanswered lookup 6 November 2009 CS5229 Semester 1 2009/10 35
  36. 36. popularity of domain name follows " Zipf" distribution 6 November 2009 CS5229 Semester 1 2009/10 36
  37. 37. Frequency of the x-th most popular item is 37
  38. 38. popularity of web pages" population of countries" occurances of English words" :" : 38
  39. 39. 39
  40. 40. 40
  41. 41. 41
  42. 42. long tail :" 46%" of domain names " are accessed once 42
  43. 43. 43
  44. 44. 20%" DNS responses are " from root/gTLD servers 44
  45. 45. without caching NS records:" 5X" loads on root/gTLD servers 45
  46. 46. kaist mit 46
  47. 47. popular sites have shorter TTL" TLL reduces over time 47
  48. 48. 6 November 2009 CS5229 Semester 1 2009/10 48
  49. 49. sharing cache does not help 49
  50. 50. 50
  51. 51. large TTL does not help 51
  52. 52. “King: Estimating Latency between Arbitrary End Hosts”" Gummadi et. al." IMC 2002 6 November 2009 CS5229 Semester 1 2009/10 53
  53. 53. how to find alternate path " with lower latency? 54
  54. 54. need to find latency between pair of Internet hosts 55
  55. 55. assume name server " is close to end host 56
  56. 56. authorative authorative NS NS 6 November 2009 CS5229 Semester 1 2009/10 57
  57. 57. how to find a name server close to an end host?" look at domain name, IP prefix 58
  58. 58. how likely does a name server allow recursive query?" > 72% of name server tested 59
  59. 59. how accurate is the estimated latency? 60
  60. 60. 61
  61. 61. 62
  62. 62. how close, really, is an end host to its authorative NS? 63
  63. 63. 64
  64. 64. 65
  65. 65. 66
  66. 66. many diverged paths consist of routers that are physically adjacent 67
  67. 67. 75-80% of the disjoint paths have latency less than 10ms" in the Napster trace 68
  68. 68. Summary:" Measurement study of DNS" Use DNS to do measurement 69
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