On Wed, Nov 25, 2009 at 10:09 PM, Shrinivasan T <[email protected]> wrote:
> I use Virtual Box to host some guest OS.
...
> How it gets the MAC address for the virtual network card?
For the most part, MAC address are randomly assigned by the
hypervisor. The exact details of now MAC addresses are auto
generated is implementation specific.
Some hypervisors use "locally administered address" by starting the
MAC address with 02:xx:xx:xx:xx:xx, and generate the rest randomly.
Others have registered an OEM identifier officially, eg. vmware uses
00:0C:29, Hyper-V uses 00:15:5d for the OUI. The NIC part of the
MAC address is generated randomly.
Please look through wikipedia to understand the terminology:
http://en.wikipedia.org/wiki/MAC_address
> MAC address is unique. How it determines that the MAC address is not there
> in the network already?
There is no fail safe method of creating unique MAC addresses. All
mechanisms only server to reduce the likely hood of duplicate MAC
addresses.
That said, the administrator can manually assign any MAC address
he/she wishes on to virtual NICs.
Auto generated MAC address on virtual NICs is a little tricky because
when you clone VMs, new MAC addresses are automatically generated.
If your guest OS names/identifies network interfaces using MAC addresses,
then all your existing interfaces will not be recognized and the guest OS
will treat it as a new interface. Common problem is that after VM cloning,
eth0 will become eth1.
- Raja
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