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Date:      Mon, 27 Nov 2006 15:56:41 -0400
From:      "D G Teed" <donald.teed@gmail.com>
To:        freebsd-ipfw@freebsd.org
Subject:   how to go about diagnosing cause of packet loss
Message-ID:  <dd4da0390611271156g1f0ee1f5yea9c35f65664053d@mail.gmail.com>

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Howdy,

Lately we have been seeing increased packet loss
on our firewall.  Running a ping plotter outside of
the firewall shows the hops are running clean.
>From on or behind the firewall, we have 20 to 50%
packet loss to each hop, reaching several popular test
destinations.

e.g.:
$ mtr -c 100 -r www.cnn.com
HOST:                             Loss%   Snt   Last   Avg  Best  Wrst StDev
  1. vlan-136.acadiau.ca           0.0%   100    0.4   6.1   0.4 179.9  26.5
  2. silverhorde.acadiau.ca        4.0%   100    0.6   0.9   0.3   7.8   1.0
  3. wfvlnsauh05-fe-0-0.aliant.ne 17.0%   100    3.4   6.3   2.6  55.0   8.8
  4. hlfxns01h29-ge-4-0.aliant.ne 27.0%   100    3.6   3.8   2.5  12.4   1.4
  5. rtp629049rts                 15.0%   100    4.2   4.0   2.6   9.1   1.2
  6. core1-halifax_POS5-0.net.bel 22.0%   100    6.2   3.7   2.6   6.2   0.9
  7. core3-montrealak_pos1-1.net.  4.0%   100   24.2  26.8  20.3 126.2  19.2
  8. core1-newyork83_pos_5_0_0.ne 19.0%   100   26.1  26.9  26.0  34.1   1.2
  9. bx4-newyork83_pos_2_0_0.net. 31.0%   100   27.7  28.1  27.1  30.1   0.8
 10. pop1-nye-P8-1.atdn.net        9.0%   100   26.2  45.2  26.2 227.4  48.0
 11. bb2-nye-P0-0.atdn.net        16.0%   100   29.0  31.1  26.3 178.2  19.4
 12. bb2-vie-P12-0.atdn.net       14.0%   100   33.0  46.3  32.3 206.4  37.6
 13. bb2-atm-P3-0.atdn.net        18.0%   100   42.9  44.9  42.5 106.6   9.7
 14. ???                          100.0   100    0.0   0.0   0.0   0.0   0.0

We suspect something in FreeBSD or ipfw has a flaw,
but cannot find it.  Running mtr from the firewall itself
produces slightly different packet loss points than
one hop behind the firewall running mtr.

A reboot initially cleared up the problem, but 10 minutes
later we saw the packet loss again, so I wonder if we
are seeing some sort of saturation.

Does anyone have suggestions no how to troubleshoot/resolve
this problem?

--Donald



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