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comcast routing issue question

  • From: Jim Popovitch
  • Date: Thu Nov 30 00:23:25 2006
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Question:  What could cause the first trace below to succeed, but the
second trace to fail?

$ mtr 69.61.40.35
HOST: blue                        Loss%   Snt   Last   Avg  Best Wrst
  1. 192.168.3.1                   0.0%     1    4.3   4.3   4.3   4.3
  2. 73.62.48.1                    0.0%     1   10.6  10.6  10.6  10.6
  3. 68.86.108.25                  0.0%     1   11.4  11.4  11.4  11.4
  4. 68.86.106.54                  0.0%     1    9.8   9.8   9.8   9.8
  5. 68.86.106.9                   0.0%     1   20.5  20.5  20.5  20.5
  6. 68.86.90.121                  0.0%     1   11.3  11.3  11.3  11.3
  7. 68.86.84.70                   0.0%     1   27.7  27.7  27.7  27.7
  8. 64.213.76.77                  0.0%     1   24.5  24.5  24.5  24.5
  9. 208.50.254.150                0.0%     1   39.4  39.4  39.4  39.4
 10. 208.49.83.237                 0.0%     1   46.6  46.6  46.6  46.6
 11. 208.49.83.234                 0.0%     1   40.7  40.7  40.7  40.7
 12. 69.61.40.35                   0.0%     1   43.9  43.9  43.9  43.9

$ mtr 69.61.40.34
HOST: blue                        Loss%   Snt   Last   Avg  Best  Wrst
  1. 192.168.3.1                   0.0%     1    1.1   1.1   1.1   1.1
  2. 73.62.48.1                    0.0%     1    9.9   9.9   9.9   9.9
  3. 68.86.108.25                  0.0%     1    9.3   9.3   9.3   9.3
  4. 68.86.106.54                  0.0%     1    9.6   9.6   9.6   9.6
  5. 68.86.106.9                   0.0%     1    9.0   9.0   9.0   9.0
  6. 68.86.90.121                  0.0%     1   18.2  18.2  18.2  18.2
  7. 68.86.84.70                   0.0%     1   23.9  23.9  23.9  23.9
  8. ???                          100.0     1    0.0   0.0   0.0   0.0


Taking the 69.61.40.33/28 subnet a bit further, .36 drops at 68.86.84.70
but .37 - .39 make it.  .40 drops at 68.86.84.70, but .41 makes it.

Crazy.

-Jim P.