During the last month I have been very busy building a new infrastructure at a client site. I’m responsible for the overall technical solution and the basis, a VMware vSphere infrastructure build on five Dell PowerEdge R805′s, Dell EqualLogic PS5000 and 6000 storage and Cisco switches for LAN, DMZ and IP storage networking.

Just before the customer initiated their functional test period we discovered that the overall Windows network  performance was slow. We did several test like copying an 8 GB file from local vmdk to local vmdk and VM to VM and found that the storage performance was no issue but the network performance was very slow.

In the last few years that I have been working with virtualization I have always been a fan of a static network configuration. Meaning, when I configure ESX networking I like my network interfaces and physical switch ports to be configured at 1000MB full duplex if the switch/network interface combination allows it. The idea is that if you purchase gigabit network interfaces and switches you know the maximum speeds. So you configure it to run at it’s maximum capacity, eliminating overhead and using as much bandwidth as possible purely for data transfer.

So when we experienced slow network performance I had a colleague check the Cisco LAN switches for errors, drops, packet loss or any other flaw which might indicate a speed or duplex mismatch. None were found so I assumed that the network configuration was not the issue. But as we know by now, ‘Assumption is the mother of all fuck-ups!‘.

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When I am troubleshooting I like to have a list of items I can check for either in my head or on paper. Amongst the knowledge base articles of VMware, I found an article about troubleshooting VMs that are having network connection issues.

The article is provides items you can check for when a VM is having connection issues. And with each item they are giving a link to other helpful articles.

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