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Incorrect Configuration of MTU on vSwitch Causes Packets to Drop (1008676)

Details

  • If Jumbo Frames are enabled on an ESX host and VMNIC Maximum Transmission Unit (MTU) is set at MAX (9000), dropped packets are observed in vmkernel log files.
  • The vmkernel/vmkwarning log contains entries similar to:

    Apr 7 19:06:36 [host name] vmkernel: 2:01:49:21.635 cpu2:9826)WARNING: LinNet: LinNetTimeoutCheckOutputListHealth:4246: vmnic3: dropped 31164; Xmited 8405
    Apr 7 19:06:37 [host name] vmkernel: 2:01:49:22.635 cpu2:9883)WARNING: LinNet: LinNetTimeoutCheckOutputListHealth:4246: vmnic3: dropped 31080; Xmited 8212
    Apr 7 19:06:38 [host name] vmkernel: 2:01:49:23.634 cpu2:9827)WARNING: LinNet: LinNetTimeoutCheckOutputListHealth:4246: vmnic3: dropped 32329; Xmited 8422
    Apr 7 19:06:39 [host name] vmkernel: 2:01:49:24.635 cpu2:9827)WARNING: LinNet: LinNetTimeoutCheckOutputListHealth:4246: vmnic3: dropped 25647; Xmited 8358
    Apr 7 19:06:40 [host name] vmkernel: 2:01:49:25.635 cpu2:9860)WARNING: LinNet: LinNetTimeoutCheckOutputListHealth:4246: vmnic3: dropped 34205; Xmited 8341
  • This issue causes performance degradation of the vSwitch.

Solution

Physical NIC Maximum MTU limitation based on the type of the NIC may vary. If the configured MTU value on a vSwitch is greater than the maximum MTU value supported by the up-link physical NIC card then dropped packets may occur.

To resolve this issue, configure the VMNIC MTU based on the manufacture supported MAXMTU. The sent packets must be within the MTU boundary. This is applicable for ESX 3.5 and later.
 
For more information onconfiguring Jumbo Frames, see iSCSI and Jumbo Frames configuration on ESX/ESXi (1007654).

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