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santosh42
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Guranteed unique mac address for a VM in a ESX ?

Hi,

Please can any one help me understand how the ESX(i) can guarantee unique mac address assignment to the VMs in the Host.

for instance, let's say if i have a VM with mac address x, then how does the ESX gurantee me that there won't be any other VM with the same mac address in the same ESX host.

Also, any idea on how these mac addresses are assigned to the VMs. is there any common MAC address resource pool per ESX ?

Thanks.

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SimonStrutt
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If your ESX is being managed by vCenter, then MAC addresses are assigned from a pool maintained by it.  The vCenter monitors the assignments, and should a duiplicate be detected during VM boot time (following a VM clone for example), then a new MAC address is assigned from the pool.  Each vCenter has a unique ID, and as long as your vCenter's have different unique ID's they won't assign the same MAC's.

It is possible for duplicates to occur, if you've deployed masses of VM's the vCenter pool can run out (not sure what the pool size is) and MAC's can get re-used (but if you've masses of machines the chances of two duplicate MAC's appearing on the same subnet are probably very slim) - see http://kb.vmware.com/kb/2006344.  Also, if you manually assign MAC addresses, then I don't believe the vCenter will check for a duplicate of that at boot time.

I assume standalone ESX's work in much the same way, maintaining their own MAC pool tio divy out ot VM's, using their unique ID to ensure two ESX's don't have the same pools.

"The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell

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harrygunter
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Hi,

Have a look at this link, it will explain how mac's are generated on hosts.

http://pubs.vmware.com/vsphere-esxi-4-1-installable/wwhelp/wwhimpl/js/html/wwhelp.htm#href=server_co...

SimonStrutt
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If your ESX is being managed by vCenter, then MAC addresses are assigned from a pool maintained by it.  The vCenter monitors the assignments, and should a duiplicate be detected during VM boot time (following a VM clone for example), then a new MAC address is assigned from the pool.  Each vCenter has a unique ID, and as long as your vCenter's have different unique ID's they won't assign the same MAC's.

It is possible for duplicates to occur, if you've deployed masses of VM's the vCenter pool can run out (not sure what the pool size is) and MAC's can get re-used (but if you've masses of machines the chances of two duplicate MAC's appearing on the same subnet are probably very slim) - see http://kb.vmware.com/kb/2006344.  Also, if you manually assign MAC addresses, then I don't believe the vCenter will check for a duplicate of that at boot time.

I assume standalone ESX's work in much the same way, maintaining their own MAC pool tio divy out ot VM's, using their unique ID to ensure two ESX's don't have the same pools.

"The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
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santosh42
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Thanks folks for the answers.

that helps me.

Thanks again.

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