Problem generation is very simple like jamming a network without STP ;-) Ok, so steps of creating my problem is given as follows:

  1. Ping Device A from Device B. Reply is coming.
  2. Generate a network loop by connecting an Ethernet cable to two ports of same Ethernet switch where Device A and B are connected.
  3. After loop, Ping request will not get reply because of loop.
  4. Remove the loop, by removing the looped cable.

After removing the loop it is expected that Device A will start replying in few seconds (4-5 seconds). But it is not responding for 200-250 seconds.

Is it the normal time to respond after recovering from switching loop?

If I am trying to ping other devices in same scenario they will start responding within 4-5 seconds after recovery.

Device A (faulty) has is ARM based Linux Fedora 12 OS with kernel version 2.6.37.

Can anyone through some light, how to fix this problem?

  • 2
    What devices do you use for this topology more exactly: switch models? – laf Nov 27 '13 at 8:19
  • Found this link stackoverflow.com/questions/15372011/… It may help with your problem. – rmaan Nov 27 '13 at 9:09
  • @rmaan it is not working. – linuxexplore Nov 28 '13 at 4:44
  • @laf Any dumb switch. – linuxexplore Nov 28 '13 at 9:32

The problem is with the MAC address table on the switch. Once a loop is created the MAC addresses for device A and device B will be "registered" to multiple switch ports in the MAC address table of the switch. Normal communication from device A to device B will not resume until their MAC addresses age out of the MAC address table on the switch, which is probably in the range of 5 minutes (300 seconds).

Simply removing the loop doesn't cause the MAC address table to age out.

  • I rebooted the Switch but still the problem exists, so I don't think that can create problem. Other devices are also connected in same switch which respond very quickly after recovering the loop. – linuxexplore Nov 28 '13 at 4:47

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