When the end of the 256 MAC addresses are handed out, the search for an available address starts back at the first address in the pool.
If a virtual machine is deleted, the MAC address becomes available for reuse. Once a dynamic MAC address has been assigned it is not changed.Īs the MAC addresses are assigned, eventually the 256 MAC addresses in the pool are handed out to virtual machines. This means that you could have 256 virtual machines with a single network adapter, 128 virtual machines with two network adapters, 126 virtual machines with two network adapters and 4 internal networks defined, and any other combination that equals 256 devices. By default, there can only be a total of 256 devices using MAC addresses from the dynamic pool. In addition, when internal virtual networks are created the virtual adapter created on the Hyper-V host uses a MAC address from the pool. If the virtual machine had multiple active network adapters, then each adapter receives a MAC address from the pool. The first time a virtual machine is powered on and it is configured for using a dynamic MAC address, it is assigned the next available value in the MAC address pool range. To set the range of 256 addresses, the last octet of the MinimumMacAddress is set to 00 and the last octet of the MaximumMacAddress is set to FF. This gives 00-15-5d-01-85 as the first five octets. So if the IP address of the first enumerated NIC was 192.168.1.133, the last two octets are converted to hexadecimal 1.133 becomes 01-85 and used as the next two octets in the MAC address.
The remaining three octets are generated by using the last two octets of the IP address of the first enumerated NIC in the Hyper-V host, converted to hexadecimal. To provide MAC addresses, Microsoft had to register to obtain its own identifier (00-15-5d), so all Hyper-V MAC address ranges start with these three octets. It is stored as a range of 256 values defined by two key values: MinimumMacAddress and MaximumMacAddress.Ī MAC address has two parts to it, the OEM identifier and the unique value. When Hyper-V is installed, a MAC address pool is created and stored in the registry at HKLM\Software\Microsoft\Windows NT\CurrentVersion\Virtualization A dynamic address is one that Hyper-V assigns from its MAC address pool. A static MAC address is one that the Hyper-V administrator assigns to the virtual machine. Hyper-V allows a virtual machine to be created with a static or dynamic MAC address.
#FIND VMWARE MAC ADDRESS HOW TO#
This article describes how MAC address pools work in Hyper-V, how it is possible to accidentally deploy hosts with duplicate MAC address pools, how to modify the default pool, how to detect if you are experiencing a duplicate MAC address situation with virtual machines, and how using SCVMM 2008 to manage your Hyper-V hosts can prevent duplicate MAC addresses. Hyper-V has an algorithm to deal with duplicate MAC addresses on a single host, but not across multiple hosts.
#FIND VMWARE MAC ADDRESS WINDOWS#
Windows Server 2008 Hyper-V provides virtual machines with a pool of Media Access Control (MAC) addresses when Hyper-V is installed.
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