Red Hat NETSCAPE MANAGEMENT SYSTEM 4.5 Manual de usuario descargar pdf (Pagina 218)

Networking

218

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When the algorithm generates the last 24 bits of the MAC address, the first 16 bits are

set to the same values as the last 16 bits of the console operating system’s primary IP

address.

The final eight bits of the MAC address are set to a hash value based on the name of

the virtual machine’s configuration file.

ESX Server keeps track of all MAC addresses that have been assigned to network

adapters of running and suspended virtual machines on a given physical machine.

ESX Server ensures that the virtual network adapters of all of these virtual machines

have unique MAC addresses.

The MAC address of a powered-off virtual machine is not remembered. Thus it is

possible that when a virtual machine is powered on again it can get a different MAC

address.

For example, if a machine had IP address 192.34.14.81 (or in hex, 0xc0220e51) and the

configuration file hashed to the value 95, the MAC address would have the following

value:

00:05:69:0e:51:95

Since there are only eight bits that can vary for each MAC address on an ESX Server

machine, this puts a limit of 256 unique MAC addresses per ESX Server machine. This

in turn limits the total number of virtual network adapters in all powered-on and

suspended virtual machines to 256. This limitation can be eliminated by using the

method described in the section Setting MAC Addresses Manually (below).

Note: The use of parts of the console operating system’s IP address as part of the

MAC address is an attempt to generate MAC addresses that are unique across

different ESX Server machines. However, there is no guarantee that different ESX

machines with physical network adapters that share a subnet always generate

mutually exclusive MAC addresses.

Setting MAC Addresses Manually

In order to work around both the limit of 256 virtual network adapters per physical

machine and possible MAC address conflicts between virtual machines, the MAC

addresses can be assigned manually by system administrators. VMware uses a

different OUI for manually generated addresses: 00:50:56. The addresses can be set by

adding the following line to a virtual machine’s configuration file:

ethernet0.address = 00:50:56:XX:YY:ZZ

where XX is a valid hex number between 00 and 3F and YY and ZZ are valid hex

numbers between 00 and FF. The value for XX must not be greater than 3F in order to

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Red Hat NETSCAPE MANAGEMENT SYSTEM 4.5 Manual de usuario Pagina 218