I have a new VMWare ESXi install with two CentOS VMs. VMWare tools installed, no packet loss when pinging. The downstream throughput from the guests to the rest of the true network or the outside world is extremely limited. At some points, it'll drop as low as 10K/s. However, I can transfer between the two guest VMs at high speeds. Also, I plugged a laptop into the same port with the same net config and it doesn't have issues.

As I said, this is downstream throughput only. I can upload files to external hosts at very high speeds.



The answer was provided by a user on the VMWare discussion boards - http://communities.vmware.com/message/1686884 .

The issue was that ESXi was trying to use full-duplex, and the host network switch wasn't configured to work with it.


So long as you've picked ESXi HCL-compliant parts I doubt it's an ESXi-specific problem - if you get a chance boot up the server with a live linux CD/ISO and test the physical hardware/cabling/switch etc. It could be a misconfiguration of your vswitch or physical switch - can you provide more details please, as much as possible. Are you seeing anything in the logs or on the switch? nothing flapping on the switch ports?

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