CS5229 09/10 Lecture 11: DNS

•

1 gostou•420 visualizações

Wei Tsang Ooi

Tecnologia

DNS

6 November 2009
CS5229 Semester 1 2009/10
1

root

.com
.org
.sg

yahoo
google
pbs
nus
ntu

CS5229 Semester 1 2009/10
2

root
server

.sg

.nus
local
DNS

dig +trace www.nus.sg
CS5229 Semester 1 2009/10
3

uses UDP

6 November 2009
CS5229 Semester 1 2009/10
4

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

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 137.132.123.4

6 November 2009
CS5229 Semester 1 2009/10
7

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 November 2009
CS5229 Semester 1 2009/10
10

“DNS Performance and
Effectiveness of Caching”"
J Jung et. al."
IEEE TON 2002

6 November 2009
CS5229 Semester 1 2009/10
11

Logger

Internet
MIT Subnets

6 November 2009
CS5229 Semester 1 2009/10
12

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
A
PTR
MX
24.6
ANY
60.4
Others

6 November 2009
CS5229 Semester 1 2009/10
16

496,802"
lookups followed by TCP
connections"

3,619,173"
TCP connections
6 November 2009
CS5229 Semester 1 2009/10
17

80-87%"
DNS cache hit ratio"
for A lookup

6 November 2009
CS5229 Semester 1 2009/10
18

not very high since it includes
Web browser’s"
caching too

6 November 2009
CS5229 Semester 1 2009/10
19

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
CS5229 Semester 1 2009/10
21

Number of referals per lookup

mit-jan00
1.16
0.15

24.07

0
1
74.62
2
> 2

23

NS Cache"
miss:
ﬁrst query to gTLD or

root servers"
hit:

otherwise

6 November 2009
CS5229 Semester 1 2009/10
25

2,486,104"
iterative lookups"

6,039,582"
query packets
6 November 2009
CS5229 Semester 1 2009/10
27

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
30

no need to retransmit beyond
2-3 retransmissions!

6 November 2009
CS5229 Semester 1 2009/10
32

each loop generated on average"
10"
query packets

6 November 2009
CS5229 Semester 1 2009/10
34

~60%"
of all queries are generated by
unanswered lookup

6 November 2009
CS5229 Semester 1 2009/10
35

popularity of domain name
follows "

Zipf"
distribution

6 November 2009
CS5229 Semester 1 2009/10
36

Frequency of the x-th most
popular item is

37

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

38

long tail :"

46%"
of domain names "
are accessed once

42

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

44

without caching NS records:"

5X"
loads on root/gTLD servers

45

popular sites have shorter TTL"

TLL reduces over time

47

6 November 2009
CS5229 Semester 1 2009/10
48

“King: Estimating Latency
between Arbitrary End
Hosts”"
Gummadi et. al."
IMC 2002

6 November 2009
CS5229 Semester 1 2009/10
53

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
NS

6 November 2009
CS5229 Semester 1 2009/10
57

how to ﬁnd a name server
close to an end host?"

look at domain name, IP preﬁx

58

how likely does a name server
allow recursive query?"

> 72% of name server tested

59

how accurate is the estimated
latency?

60

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

63

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

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

2. root .com .org .sg yahoo google pbs nus ntu CS5229 Semester 1 2009/10 2

3. root server .sg .nus local DNS dig +trace www.nus.sg CS5229 Semester 1 2009/10 3

4. uses UDP 6 November 2009 CS5229 Semester 1 2009/10 4

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. TTL-based Caching 6 November 2009 CS5229 Semester 1 2009/10 6

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. DNS-based " Load Balancing 6 November 2009 CS5229 Semester 1 2009/10 8

9. DNS-based " Server Selection 6 November 2009 CS5229 Semester 1 2009/10 9

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

11. “DNS Performance and Effectiveness of Caching”" J Jung et. al." IEEE TON 2002 6 November 2009 CS5229 Semester 1 2009/10 11

12. Logger Internet MIT Subnets 6 November 2009 CS5229 Semester 1 2009/10 12

13. 3 traces" 1 week each 6 November 2009 CS5229 Semester 1 2009/10 13

14. DNS query/respose" TCP SYN/FIN/RST 6 November 2009 CS5229 Semester 1 2009/10 14

15. basic analysis 6 November 2009 CS5229 Semester 1 2009/10 15

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. 496,802" lookups followed by TCP connections" 3,619,173" TCP connections 6 November 2009 CS5229 Semester 1 2009/10 17

18. 80-87%" DNS cache hit ratio" for A lookup 6 November 2009 CS5229 Semester 1 2009/10 18

19. not very high since it includes Web browser’s" caching too 6 November 2009 CS5229 Semester 1 2009/10 19

20. how fast is DNS lookup? 6 November 2009 CS5229 Semester 1, 2009/10 20

21. lookup latency ≈ " time between ﬁrst query" and last response 6 November 2009 CS5229 Semester 1 2009/10 21

22. mit kaist 22

23. Number of referals per lookup mit-jan00 1.16 0.15 24.07 0 1 74.62 2 > 2 23

24. 0 1 2 24

25. NS Cache" miss: ﬁrst query to gTLD or root servers" hit: otherwise 6 November 2009 CS5229 Semester 1 2009/10 25

26. hit miss 26

27. 2,486,104" iterative lookups" 6,039,582" query packets 6 November 2009 CS5229 Semester 1 2009/10 27

28. signiﬁcant number of retransmissions 6 November 2009 CS5229 Semester 1 2009/10 28

29. ~24%" of lookups are unanswered 6 November 2009 CS5229 Semester 1 2009/10 29

30. persistent retransmission" referral loops 6 November 2009 CS5229 Semester 1 2009/10 30

31. answered zero referral 31

32. no need to retransmit beyond 2-3 retransmissions! 6 November 2009 CS5229 Semester 1 2009/10 32

33. loops 33

34. each loop generated on average" 10" query packets 6 November 2009 CS5229 Semester 1 2009/10 34

35. ~60%" of all queries are generated by unanswered lookup 6 November 2009 CS5229 Semester 1 2009/10 35

36. popularity of domain name follows " Zipf" distribution 6 November 2009 CS5229 Semester 1 2009/10 36

37. Frequency of the x-th most popular item is 37

38. popularity of web pages" population of countries" occurances of English words" :" : 38

39. 39

40. 40

41. 41

42. long tail :" 46%" of domain names " are accessed once 42

43. 43

44. 20%" DNS responses are " from root/gTLD servers 44

45. without caching NS records:" 5X" loads on root/gTLD servers 45

46. kaist mit 46

47. popular sites have shorter TTL" TLL reduces over time 47

48. 6 November 2009 CS5229 Semester 1 2009/10 48

49. sharing cache does not help 49

50. 50

51. large TTL does not help 51

52. “King: Estimating Latency between Arbitrary End Hosts”" Gummadi et. al." IMC 2002 6 November 2009 CS5229 Semester 1 2009/10 53

53. how to ﬁnd alternate path " with lower latency? 54

54. need to ﬁnd latency between pair of Internet hosts 55

55. assume name server " is close to end host 56

56. authorative authorative NS NS 6 November 2009 CS5229 Semester 1 2009/10 57

57. how to ﬁnd a name server close to an end host?" look at domain name, IP preﬁx 58

58. how likely does a name server allow recursive query?" > 72% of name server tested 59

59. how accurate is the estimated latency? 60

60. 61

61. 62

62. how close, really, is an end host to its authorative NS? 63

63. 64

64. 65

65. 66

66. many diverged paths consist of routers that are physically adjacent 67

67. 75-80% of the disjoint paths have latency less than 10ms" in the Napster trace 68

68. Summary:" Measurement study of DNS" Use DNS to do measurement 69

CS5229 09/10 Lecture 11: DNS

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CS5229 09/10 Lecture 11: DNS