Wednesday, June 18, 2008

How To Decide Static Mac address for Virtual machine

This is useful for software that is licensed by the MAC address of the server it is running on or if you migrate a physical server to virtual and want to keep the same MAC address. A VM’s MAC address will change if the location of the VM changes, ie. different path on the same host. During a hot migration (Vmotion) the location of the VM does not change, this is also true of a VM that changes hosts due to HA/DRS migration. During a cold migration the location of the VM does change so the MAC address of the VM will change.
MAC addresses are hex values and consist of six groups of hex numbers. The first 3 octets of the MAC address is a unique code assigned to each NIC vendor, this is also called the Organizationally Unique Identifier (OUI), VMware’s OUI is “00:50:56”. The last 3 octets are assigned to all of the NIC’s for that vendor. Each MAC address must be unique to avoid conflicts with other network devices. You do not have to use the VMware assigned range (00:50:56) for your NIC’s. If you are coming from a physical server you can use the previous NIC’s range instead, (ie. HP/Compaq NIC’s use 00:08:02) as the first 3 octets. Just make sure the physical NIC and virtual NIC with the same MAC address are not active on the same physical network at the same time. There are several methods for setting a static MAC address on a VM which are listed below. If you use the first method you must stay inside VMware’s allowed MAC addresses (00:50:56:00:00:00 – 00:50:56:3F:FF:FF) or the VM will not start. You need to maintain the pool of this MAC address to avoid conflict

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