Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Network speed between a VM and another machine which is not residing on the same host, is 11MB/s at most.




  • ESXi5 version is
  • VM has the latest Vmware Tools installed
  • VM is using E1000 network driver
  • Physical box has Win Srv 2008 R2 as the OS
  • CrystalDiskMark says the drive on physical box can read/write 100MB/s
  • vCenter is another vm on esx
  • both vm and physical box are showing 1Gbps link speed
  • Configuration > Networking shows vmnic0 as 1000 Full
  • NTttcp is a client/server tool from Microsoft for measuring pure network throughput

Here's what I've done so far:


  • VM is running Filezilla FTP Server (default settings, one user account made)
  • Physical box is running Filezilla FTP Client (default settings)
  • Physical box is uploading a big file to FTP server
  • Transfer speed (as observed by Windows Task Manager on both machines): ~11MB/s (bad)
  • Physical box is downloading that file from FTP server
  • Transfer speed (as observed by Windows Task Manager on both machines): still ~11MB/s (bad)

Could it be disk performance issue?


  • Physical box is running ntttcpr.exe -a 6 -m 6,0,VM_IP_ADDRESS
  • VM is running ntttcps.exe -a 6 -m 6,0,PHY_BOX_IP_ADDRESS
  • Transfer speed (as observed by Windows Task Manager on both machines): ~11MB/s (bad)

Could it be switch performance issue?


  • physical box is running vSphere Client
  • I open Summary > Storage > datastore > Browse Datastore... from physical box and upload a file to datastore
  • Transfer speed (as observed by Windows Task Manager on physical box): ~26-36MB/s (good)

Could it be a vm specific issue?


  • Installed ntttcp to another vm on the same esx server
  • Measured network performance between vms on the same esx server with NTttcp
  • Transfer speed (as observed by Windows Task Manager on physical box): ~90-120MB/s (excellent :)

I have another esx server on the same site, connecting to the same datastore and same switch. Those two ESX servers have both 2 NICs. One NIC goes to switch while the other goes directly to the other ESX server.

  • vMotioned one of the testing vms off to the other ESX host
  • Measured network performance between vms on different esx servers with NTttcp
  • Transfer speed (as observed by Windows Task Manager on physical box): ~11MB/s (bad)

While I'm aware of these:

they did not help (or I must have been missed something)

share|improve this question
You are certain that everything has a 1gb/s link speed, and hasn't fallen back to 100mb/s – Zoredache Mar 29 '12 at 22:10
Well, Veeam Backup residing on this physical box can pump data from the same esx host (from its port 902), using the same wire, through the same switch with speeds of up to 90MB/s and Links speed is 1Gbps everywhere (in task manager of vm, on esx networking configuration, in task manager of physical box), so it has to be something related to ESX internal config. – Henno Mar 29 '12 at 22:41
What kind of switch? – SpacemanSpiff Mar 30 '12 at 1:45
Is your switch smart enough to provide port statistics? Check for errors and flow control. – Max Alginin Mar 30 '12 at 3:08
I have same problem. It is not problem with ethernet because I was transfer between host at the same IBM Enclosure and I only got around 11MB/s – user147542 Nov 29 '12 at 8:35

11Mb/s is too close to 100Mbps to be only a coincidence. It's clear that you have a problem with one of the network ports, either on the switch or on one of your servers's NIC, not being set to 1Gbps/full duplex. There's no doubt about that. The question is which one.

Make sure all your NICs are set to 1Gbps/full duplex, and that every single port of all network devices between all of your servers and storage devices (switches and routers) are also set to 1Gbps/full duplex.

share|improve this answer
up vote 3 down vote accepted

When I put a crossover cable between physical box and a laptop and witnessed excellent speed and then put a switch between and the speed was still great and then changed the IP addresses from 192.168.0.x to real IP addressses that I had for the physical box and the VM, it occurred to me that while the ESX and physical box are just over the switch for each other, their different IP subnets dictate that all traffic shared between them has to go through the ISP router which is also connected to the same switch.

So, due to different subnets, the traffic went through my ISP's box which shaped it down to 100Mbps!

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.