Packet discards at VMXNET3 adapter on ESXi host
Strange Packet discards
In the last time I encountered to a strange problem.
The following components have been involved:
Win2008 R2 servers with VMXNET3 Adapters.
Used VMware configuration
- vCenter Server 5.1.0a
- ESXi 5.1 Patch 1
Looking at “netstat -e” shows the following strange output.
The discard counters for for send and receive side were growing and had also the same amount.
The output got my special attention, because the RX and TX counters shows always the same value.
Example “netsat -e” output collected with the tool CRWinNetDiag:
======================= netstat -e ===========================
Interface Statistics
received send
Bytes 1445355112 3181346202
Unicastpakets 1704730 2459144
Non-Unicastpakets 260454 1471
Discarded 657 657
Error 0 0
Unknown Protocol 0
_____________________________________________________________
So the follwing investigation at the ESXi host shows a misconfigured Parameter.
ethernet0.emuRxMode = “0”
The parameter should be enabled in environments with a high multicast rate.
After the parameter was set to:
ethernet0.emuRxMode = “1”
The “netstat -e” output looks like:
======================= netstat -e ===========================
Interface Statistics
received send
Bytes 1345356213 3191356110
Unicastpakets 1804730 2559144
Non-Unicastpakets 250453 1672
Discarded 0 0
Error 0 0
Unknown Protocol 0
_____________________________________________________________
So this problem that in burst situations packets has been discarded could be fixed.
Have you seen this behaviour, too? Please tell me!
CRnetPACKETS 
I saw this at a Win 7 virtual machine on VMvisor 5.5.0 update 1, too.
The parameter ethernetx.emuRxMode=1 enables the SplitRx mode, which allows a host to use multiple physical CPUs to process network packets received in a single network queue
But in my environment there is no way to fix this issue, because my machine has only 1 physical processor.
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