Routing


30 October 2009
   CS5229 Semester 1, 2009/10
   1
Are Internet routes
                         stable? "
                      symmetric? "
                        efficient...
AS 1




                                                           AS 3


                   AS 2




30 October 2009
   ...
Intra-Domain Routing


30 October 2009
     CS5229 Semester 1, 2009/10
   4
ISPs are free to use own
            metrics to route "
            (e.g. hop count)

30 October 2009
   CS5229 Semester 1...
Inter-Domain Routing"
                   (using BGP)


30 October 2009
     CS5229 Semester 1, 2009/10
   6
Depends on policy:
                   business contract, "
                     load balancing"
                    qualit...
“early exit” routing"
              (or hot potato routing)


30 October 2009
      CS5229 Semester 1, 2009/10
   8
AS 1




                                                           AS 3


                   AS 2




30 October 2009
   ...
“End-to-End Routing
         Behavior in the Internet”"
                           V. Paxson"
                         SIG...
37"
                    hosts


30 October 2009
   CS5229 Semester 1, 2009/10
   11
mean inter-measurement
             interval of"
        2 hours & 2.75 days

30 October 2009
   CS5229 Semester 1, 2009/1...
traceroute


30 October 2009
    CS5229 Semester 1, 2009/10
   13
measure A to B
                   immediately after"
                       B to A

30 October 2009
        CS5229 Semeste...
~50% "
                       of ASs"
                   (weighted by their importance)




30 October 2009
       CS5229 ...
Routing Pathologies


30 October 2009
    CS5229 Semester 1, 2009/10
   16
Routing Loops


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   17
1 ir6gw.lbl.gov 1.853 ms 1.623 ms 2.358 ms
     2 er1gw.lbl.gov 7.165 ms 2.996 ms 3.098 ms
     3 ir2gw.lbl.gov 4.882 ms 3...
50"
               occurrences of loops                




30 October 2009
     CS5229 Semester 1, 2009/10
       19
loops can last for hours


30 October 2009
   CS5229 Semester 1, 2009/10
   20
clustered geographically
             and temporally


30 October 2009
   CS5229 Semester 1, 2009/10
   21
confined within one AS


30 October 2009
   CS5229 Semester 1, 2009/10
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Routing Error


30 October 2009
      CS5229 Semester 1, 2009/10
   23
1 mfd-01.rt.connix.net 8 ms 4 ms 3 ms
     2 sl-dc-5-s2/0-512k.sprintlink.net 39 ms 39 ms 39 ms 3 sl-dc-6-
     f0/0.sprin...
A route to London ends
                up in Israel?


30 October 2009
   CS5229 Semester 1, 2009/10
   25
Route Fluttering


30 October 2009
        CS5229 Semester 1, 2009/10
   26
1 fpls.postech.ac.kr 2 ms 2 ms 2 ms
     2 fddicc.postech.ac.kr 3 ms 2 ms 2 ms
     3 ktrc-postech.hana.nm.kr 57 ms 123 ms...
Taken from Paxson’s PhD Thesis: Alternate routes are taken
                      for packets from WUSTL to U Mannheim

30 ...
Are Routes Stable?


30 October 2009
         CS5229 Semester 1, 2009/10
   29
are network paths
                      predictable? 


30 October 2009
        CS5229 Semester 1, 2009/10
   30
end-to-end
                    measurement: "
                   the same path?

30 October 2009
       CS5229 Semester 1,...
prevalence"
        “given a route r observed at present, how
            likely to observe r again in future?”




30 Oct...
persistence"
          “given a route r observed at time t, how
           long before this route is likely to have
      ...
1, 1, 1, 1, 2, 1, 1, 1, 1


30 October 2009
           CS5229 Semester 1, 2009/10
   34
prevalence of r = k/n"

     we make n traceroute and k of them shows
                      route r "




30 October 2009
...
36
in one instance, two sites
          exhibit 9 diff routes


30 October 2009
   CS5229 Semester 1, 2009/10
   37
At UCL, the prevalence of
     dominant routes is below
                0.5

30 October 2009
   CS5229 Semester 1, 2009/10...
In general, paths are
             dominated by a single
                route, but there is
             significant site-...
persistence"
          “given a route r observed at time t, how
           long before this route is likely to have
      ...
Summary: occur over
                large time scale


30 October 2009
    CS5229 Semester 1, 2009/10
   41
seconds and minutes:
      flutter and tightly coupled
               routers

30 October 2009
   CS5229 Semester 1, 2009/1...
10s of minutes: "
                         9%


30 October 2009
       CS5229 Semester 1, 2009/10
   43
hours:"
             intra network changes"
                       (4%)

30 October 2009
    CS5229 Semester 1, 2009/10
  ...
6+ hours:"
             intra network changes"
                      (19%)

30 October 2009
    CS5229 Semester 1, 2009/10...
68% shows persistence
               over days


30 October 2009
   CS5229 Semester 1, 2009/10
   46
Are Routes Symmetric?


30 October 2009
   CS5229 Semester 1, 2009/10
   47
49%"
       of routes are asymmetric"
                   (>1 diff city)                




30 October 2009
   CS5229 Seme...
30%"
       of routes are asymmetric"
                   (>1 diff AS)                  




30 October 2009
   CS5229 Seme...
Are Routes Optimal?


30 October 2009
   CS5229 Semester 1, 2009/10
   50
“The End-to-End Effects of
         Internet Path Selection”"
                   S. Savage et al.


30 October 2009
      ...
host

        default
        path




                   52
path metrics
                        (delay, loss rate,
                        bandwidth)

  120
           35

         ...
Uses Paxson’s Dataset
            + 3 New Sets "
          (UW1, UW3, UW4)

30 October 2009
   CS5229 Semester 1, 2009/10
...
Can we find alt path with
            shorter RTT?


30 October 2009
   CS5229 Semester 1, 2009/10
   55
A
     120
              35

            10
C
                      50
                              B
              20
30...
57
Can we find alt path with
           lower loss rate?


30 October 2009
   CS5229 Semester 1, 2009/10
   58
Assuming that losses are uncorrelated




                    A
          0.3
            0.03

                 0.1
     ...
60
Can we find alt path with
         higher bandwidth?


30 October 2009
   CS5229 Semester 1, 2009/10
   61
A
  100kbps
                    256kbps


     C
 340kbps
    10kbps
                               B
           1Mbps
128...
optimistic model


                 A
   120,0.3
                  35,0.03

              10,0.1
   C
                    ...
pessimistic model


                 A
   120,0.3
               35,0.03

              10,0.1
   C
                      ...
65
66
Are these better alt paths
       due to a small set of hosts?


30 October 2009
   CS5229 Semester 1, 2009/10
   67
For each node, remove from graph, repeat experiments.
Find 10 nodes which affected the results the most.

                ...
69
For each node, find how many times it appears as an 
intermediate host in some superior alternate path.


      A
         ...
71
Are these better alt path due
       to a small set of ASes?


30 October 2009
   CS5229 Semester 1, 2009/10
   72
Alt




       Direct


                 73
74
Are shorter alt path due to
               less congestion?


30 October 2009
   CS5229 Semester 1, 2009/10
   75
Estimate prop delay as the
         10%-tile delay on a path


30 October 2009
   CS5229 Semester 1, 2009/10
   76
77
Prop Delay

                                                    2
                        3


                            ...
79
Conclusion:"
           Can often find better path by
           routing through another host


30 October 2009
     CS5229...
Impact:"
             Inspired overlay networks"
                (Skype, PPLive, etc.)


30 October 2009
      CS5229 Seme...
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CS5229 09/10 Lecture 10: Internet Routing

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CS5229 09/10 Lecture 10: Internet Routing

  1. 1. Routing 30 October 2009 CS5229 Semester 1, 2009/10 1
  2. 2. Are Internet routes stable? " symmetric? " efficient? 30 October 2009 CS5229 Semester 1, 2009/10 2
  3. 3. AS 1 AS 3 AS 2 30 October 2009 CS5229 Semester 1, 2009/10 3
  4. 4. Intra-Domain Routing 30 October 2009 CS5229 Semester 1, 2009/10 4
  5. 5. ISPs are free to use own metrics to route " (e.g. hop count) 30 October 2009 CS5229 Semester 1, 2009/10 5
  6. 6. Inter-Domain Routing" (using BGP) 30 October 2009 CS5229 Semester 1, 2009/10 6
  7. 7. Depends on policy: business contract, " load balancing" quality of routes 30 October 2009 CS5229 Semester 1, 2009/10 7
  8. 8. “early exit” routing" (or hot potato routing) 30 October 2009 CS5229 Semester 1, 2009/10 8
  9. 9. AS 1 AS 3 AS 2 30 October 2009 CS5229 Semester 1, 2009/10 9
  10. 10. “End-to-End Routing Behavior in the Internet”" V. Paxson" SIGCOMM 96" (2006 SIGCOMM Test of Time Award) 30 October 2009 CS5229 Semester 1, 2009/10 10
  11. 11. 37" hosts 30 October 2009 CS5229 Semester 1, 2009/10 11
  12. 12. mean inter-measurement interval of" 2 hours & 2.75 days 30 October 2009 CS5229 Semester 1, 2009/10 12
  13. 13. traceroute 30 October 2009 CS5229 Semester 1, 2009/10 13
  14. 14. measure A to B immediately after" B to A 30 October 2009 CS5229 Semester 1, 2009/10 14
  15. 15. ~50% " of ASs" (weighted by their importance) 30 October 2009 CS5229 Semester 1, 2009/10 15
  16. 16. Routing Pathologies 30 October 2009 CS5229 Semester 1, 2009/10 16
  17. 17. Routing Loops 30 October 2009 CS5229 Semester 1, 2009/10 17
  18. 18. 1 ir6gw.lbl.gov 1.853 ms 1.623 ms 2.358 ms 2 er1gw.lbl.gov 7.165 ms 2.996 ms 3.098 ms 3 ir2gw.lbl.gov 4.882 ms 3.516 ms 8.371 ms 4 isdn1gw.lbl.gov 7.98 ms 4.393 ms 4.311 ms 5 ascend49.lbl.gov 36.833 ms 32.772 ms 31.428 ms 6 isdn1gw.lbl.gov 30.428 ms 30.502 ms 33.528 ms 7 ascend49.lbl.gov 69.006 ms 59.429 ms 58.82 ms 8 isdn1gw.lbl.gov 59.358 ms 63.734 ms 61.775 ms 9 ascend49.lbl.gov 85.629 ms 84.168 ms 83.397 ms 10 isdn1gw.lbl.gov 83.374 ms 83.201 ms 83.349 ms 11 ascend49.lbl.gov 110.316 ms 120.243 ms 116.84 ms 12 isdn1gw.lbl.gov 109.221 ms 108.97 ms 109.242 ms 13 ascend49.lbl.gov 135.867 ms 136.797 ms 140.849 ms : : 30 October 2009 CS5229 Semester 1, 2009/10 18
  19. 19. 50" occurrences of loops 30 October 2009 CS5229 Semester 1, 2009/10 19
  20. 20. loops can last for hours 30 October 2009 CS5229 Semester 1, 2009/10 20
  21. 21. clustered geographically and temporally 30 October 2009 CS5229 Semester 1, 2009/10 21
  22. 22. confined within one AS 30 October 2009 CS5229 Semester 1, 2009/10 22
  23. 23. Routing Error 30 October 2009 CS5229 Semester 1, 2009/10 23
  24. 24. 1 mfd-01.rt.connix.net 8 ms 4 ms 3 ms 2 sl-dc-5-s2/0-512k.sprintlink.net 39 ms 39 ms 39 ms 3 sl-dc-6- f0/0.sprintlink.net 39 ms 38 ms 50 ms 4 psi-mae-east-1.psi.net 48 ms 66 ms * 5 * * core.net218.psi.net 90 ms 6 192.91.187.2 1139 ms 1188 ms * 7 * * * 8 biu-tau.ac.il 1389 ms * * 9 tau.man.ac.il 1019 ms * * 10 * * * 11 * cisco301s1.huji.ac.il 1976 ms * 12 * * * 13 * * * 14 * * cisco101e5.huji.ac.il 1974 ms 15 * * * 16 * cisco103e2.gr.huji.ac.il 1010 ms 1069 ms 17 cisco101e01.cc.huji.ac.il 2132 ms * * 18 cisco102e13.huji.ac.il 888 ms 976 ms 2005 ms 19 cisco103e2.gr.huji.ac.il 1657 ms * * 30 October 2009 CS5229 Semester 1, 2009/10 24
  25. 25. A route to London ends up in Israel? 30 October 2009 CS5229 Semester 1, 2009/10 25
  26. 26. Route Fluttering 30 October 2009 CS5229 Semester 1, 2009/10 26
  27. 27. 1 fpls.postech.ac.kr 2 ms 2 ms 2 ms 2 fddicc.postech.ac.kr 3 ms 2 ms 2 ms 3 ktrc-postech.hana.nm.kr 57 ms 123 ms 30 ms 4 gateway.hana.nm.kr 31 ms 31 ms 31 ms 5 hana.hana.nm.kr 33 ms 140 ms 32 ms 6 bloodyrouter.hawaii.net 825 ms 722 ms 805 ms 7 usa-serial.gw.au 960 ms 922 ms 893 ms 8 national-aix-us.gw.au 1039 ms * * 9 * rb1.rtr.unimelb.edu.au 903 ms rb2.rtr.unimelb.edu.au 1279 ms 10 itee.rtr.unimelb.edu.au 1067 ms 1097 ms 872 ms 11 * * mulkirri.cs.mu.oz.au 1468 ms 12 mullala.cs.mu.oz.au 1042 ms 1140 ms 1262 ms 30 October 2009 CS5229 Semester 1, 2009/10 27
  28. 28. Taken from Paxson’s PhD Thesis: Alternate routes are taken for packets from WUSTL to U Mannheim 30 October 2009 CS5229 Semester 1, 2009/10 28
  29. 29. Are Routes Stable? 30 October 2009 CS5229 Semester 1, 2009/10 29
  30. 30. are network paths predictable? 30 October 2009 CS5229 Semester 1, 2009/10 30
  31. 31. end-to-end measurement: " the same path? 30 October 2009 CS5229 Semester 1, 2009/10 31
  32. 32. prevalence" “given a route r observed at present, how likely to observe r again in future?” 30 October 2009 CS5229 Semester 1, 2009/10 32
  33. 33. persistence" “given a route r observed at time t, how long before this route is likely to have changed?” 30 October 2009 CS5229 Semester 1, 2009/10 33
  34. 34. 1, 1, 1, 1, 2, 1, 1, 1, 1 30 October 2009 CS5229 Semester 1, 2009/10 34
  35. 35. prevalence of r = k/n" we make n traceroute and k of them shows route r " 30 October 2009 CS5229 Semester 1, 2009/10 35
  36. 36. 36
  37. 37. in one instance, two sites exhibit 9 diff routes 30 October 2009 CS5229 Semester 1, 2009/10 37
  38. 38. At UCL, the prevalence of dominant routes is below 0.5 30 October 2009 CS5229 Semester 1, 2009/10 38
  39. 39. In general, paths are dominated by a single route, but there is significant site-to-site variations. 30 October 2009 CS5229 Semester 1, 2009/10 39
  40. 40. persistence" “given a route r observed at time t, how long before this route is likely to have changed?” 30 October 2009 CS5229 Semester 1, 2009/10 40
  41. 41. Summary: occur over large time scale 30 October 2009 CS5229 Semester 1, 2009/10 41
  42. 42. seconds and minutes: flutter and tightly coupled routers 30 October 2009 CS5229 Semester 1, 2009/10 42
  43. 43. 10s of minutes: " 9% 30 October 2009 CS5229 Semester 1, 2009/10 43
  44. 44. hours:" intra network changes" (4%) 30 October 2009 CS5229 Semester 1, 2009/10 44
  45. 45. 6+ hours:" intra network changes" (19%) 30 October 2009 CS5229 Semester 1, 2009/10 45
  46. 46. 68% shows persistence over days 30 October 2009 CS5229 Semester 1, 2009/10 46
  47. 47. Are Routes Symmetric? 30 October 2009 CS5229 Semester 1, 2009/10 47
  48. 48. 49%" of routes are asymmetric" (>1 diff city) 30 October 2009 CS5229 Semester 1, 2009/10 48
  49. 49. 30%" of routes are asymmetric" (>1 diff AS) 30 October 2009 CS5229 Semester 1, 2009/10 49
  50. 50. Are Routes Optimal? 30 October 2009 CS5229 Semester 1, 2009/10 50
  51. 51. “The End-to-End Effects of Internet Path Selection”" S. Savage et al. 30 October 2009 CS5229 Semester 1, 2009/10 51
  52. 52. host default path 52
  53. 53. path metrics (delay, loss rate, bandwidth) 120 35 10 50 20 30 95 53
  54. 54. Uses Paxson’s Dataset + 3 New Sets " (UW1, UW3, UW4) 30 October 2009 CS5229 Semester 1, 2009/10 54
  55. 55. Can we find alt path with shorter RTT? 30 October 2009 CS5229 Semester 1, 2009/10 55
  56. 56. A 120 35 10 C 50 B 20 30 95 56
  57. 57. 57
  58. 58. Can we find alt path with lower loss rate? 30 October 2009 CS5229 Semester 1, 2009/10 58
  59. 59. Assuming that losses are uncorrelated A 0.3 0.03 0.1 C 0.1 B 0.05 0.07 0.15 59
  60. 60. 60
  61. 61. Can we find alt path with higher bandwidth? 30 October 2009 CS5229 Semester 1, 2009/10 61
  62. 62. A 100kbps 256kbps C 340kbps 10kbps B 1Mbps 128kbps 50kbps 62
  63. 63. optimistic model A 120,0.3 35,0.03 10,0.1 C 50,0.1 D B 20,0.05 30,0.07 95,0.15 loss rate ACDB = 0.3 63
  64. 64. pessimistic model A 120,0.3 35,0.03 10,0.1 C 50,0.1 B 20,0.05 30,0.07 95,0.15 loss rate ACDB = 0.5 64
  65. 65. 65
  66. 66. 66
  67. 67. Are these better alt paths due to a small set of hosts? 30 October 2009 CS5229 Semester 1, 2009/10 67
  68. 68. For each node, remove from graph, repeat experiments. Find 10 nodes which affected the results the most. A 256kbps 10kbps B 1Mbps 50kbps 68
  69. 69. 69
  70. 70. For each node, find how many times it appears as an intermediate host in some superior alternate path. A 3 C-A-B, D-A-E-B, F-A-G-C B 2 A-B-C, D-B-A-E : : : 70
  71. 71. 71
  72. 72. Are these better alt path due to a small set of ASes? 30 October 2009 CS5229 Semester 1, 2009/10 72
  73. 73. Alt Direct 73
  74. 74. 74
  75. 75. Are shorter alt path due to less congestion? 30 October 2009 CS5229 Semester 1, 2009/10 75
  76. 76. Estimate prop delay as the 10%-tile delay on a path 30 October 2009 CS5229 Semester 1, 2009/10 76
  77. 77. 77
  78. 78. Prop Delay 2 3 1 RTT 4 5 6 30 October 2009 CS5229 Semester 1, 2009/10 78
  79. 79. 79
  80. 80. Conclusion:" Can often find better path by routing through another host 30 October 2009 CS5229 Semester 1, 2009/10 80
  81. 81. Impact:" Inspired overlay networks" (Skype, PPLive, etc.) 30 October 2009 CS5229 Semester 1, 2009/10 81

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