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Conflicts MAC addresses between VMs

Created: Feb 12, 2021 18:32:02Latest reply: Feb 13, 2021 15:14:53 375 4 0 0 0
  HiCoins as reward: 1 (problem unresolved)

media access control address (MAC address) is a unique identifier assigned to a network interface controller (NIC)for use as a network address in communications within a network segment. Using ARP process share the  network hosts MAC addresses in the broadcast domain. A switch dynamically builds its MAC address table by examining the source MAC addresses of the frames received on a port. The MAC address table contains the hosts MAC address information that the switch uses to forward traffic between ports.

The virtual machine environments  The VMware Universally Unique Identifier(UUID) generates MAC addresses that are checked for conflicts. MAC Addresses are created by using three parts, the VMware OUI, the SMBIOS UUID or the unique ID of the host and a hash based on the name of the entity that the MAC address is being generated .

 

The problem

sharing a MAC address with another virtual machine generate identical MAC addresses cause conflicts if the virtual machines are on the same network.

 

I found that separating the networks using VLANs might solve the problem but it is not solution in my environment. As well as  creating specific  MAC address pool for each virtual machine will not solve my problem if I will connect my virtual machines with another virtual machine third party  .


I want solution because I didn’t find the best efforts to ensure that multiple connected virtual machines can autogenerate Unique MAC addresses .


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Recommended answer

DDSN
Admin Created Feb 13, 2021 01:51:04

Hi Iyad,
If you want to guarantee that the same MAC address is assigned to a given virtual machine every time, even if the virtual machine is moved, or if you want to guarantee a unique MAC address for each virtual machine within a networked environment, you can assign the address manually instead of allowing VMware Workstation to assign it automatically.
To assign the same, unique MAC address to any virtual machine manually, use a text editor to remove three lines from the configuration file and add one line. The configuration file has a.vmx extension at the end of the filename. On a Linux host, a virtual machine created with an earlier VMware product may have a configuration file with a .cfg extension.
Remove the three lines that begin with the following from the configuration file:
ethernet[n].generatedAddress
ethernet[n].addressType
ethernet[n].generatedAddressOffset
In these options, [n] is the number of the virtual Ethernet adapter — for example ethernet0.
Add the following line to the configuration file:
ethernet[n].address = 00:50:56:XX:YY:ZZ
In this line, XX must be a valid hexadecimal number between 00h and 3Fh, and YY and ZZ must be valid hexadecimal numbers between 00h and FFh. Because VMware Workstation virtual machines do not support arbitrary MAC addresses, you must use the above format.
So long as you choose a value for XX:YY:ZZ that is unique among your hard-coded addresses (where XX is a valid hexadecimal number between 00h and 3Fh, and YY and ZZ are valid hexadecimal numbers between 00h and FFh), conflicts between the automatically assigned MAC addresses and the manually assigned addresses should never occur.

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Iyad
Iyad Created Feb 13, 2021 15:14:16 (0) (0)
Hi DDSN
First thank you for your response.

The automatic mechanism to generate MAC address for the individual Virtual Machine generated that every host will get unique MAC address. I agree with that.
So manually assign MAC address is new risk for the individual Virtual Machine .
I will add comment with extra explanation  
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DDSN
DDSN Admin Created Feb 13, 2021 01:51:04

Hi Iyad,
If you want to guarantee that the same MAC address is assigned to a given virtual machine every time, even if the virtual machine is moved, or if you want to guarantee a unique MAC address for each virtual machine within a networked environment, you can assign the address manually instead of allowing VMware Workstation to assign it automatically.
To assign the same, unique MAC address to any virtual machine manually, use a text editor to remove three lines from the configuration file and add one line. The configuration file has a.vmx extension at the end of the filename. On a Linux host, a virtual machine created with an earlier VMware product may have a configuration file with a .cfg extension.
Remove the three lines that begin with the following from the configuration file:
ethernet[n].generatedAddress
ethernet[n].addressType
ethernet[n].generatedAddressOffset
In these options, [n] is the number of the virtual Ethernet adapter — for example ethernet0.
Add the following line to the configuration file:
ethernet[n].address = 00:50:56:XX:YY:ZZ
In this line, XX must be a valid hexadecimal number between 00h and 3Fh, and YY and ZZ must be valid hexadecimal numbers between 00h and FFh. Because VMware Workstation virtual machines do not support arbitrary MAC addresses, you must use the above format.
So long as you choose a value for XX:YY:ZZ that is unique among your hard-coded addresses (where XX is a valid hexadecimal number between 00h and 3Fh, and YY and ZZ are valid hexadecimal numbers between 00h and FFh), conflicts between the automatically assigned MAC addresses and the manually assigned addresses should never occur.

View more
  • x
  • convention:

Iyad
Iyad Created Feb 13, 2021 15:14:16 (0) (0)
Hi DDSN
First thank you for your response.

The automatic mechanism to generate MAC address for the individual Virtual Machine generated that every host will get unique MAC address. I agree with that.
So manually assign MAC address is new risk for the individual Virtual Machine .
I will add comment with extra explanation  

Extra explanation
My problem is if I have two Virtual Machines VM1 and VM2 each have 50 hosts. If I connect some host in VM1 with some hosts in VM2 in same network all VMs stop working because one host in VM2 have same MAC address with host in VM1 (it happened then I manually assign MAC address to solve this problem).
I read in the internet that if I separate the networks using L3 VLANs the problem will be solve but I am not sure if I will pay a route I will solve the problem.
Also I read that I can create manually MAC addresses pool in VM1 and another different MAC addresses pool in VM2 so I agree that will solve my problem but my VMs some time connected with other VMs (other companies or venders) for supports in same network.
I didn’t find the best efforts to ensure that multiple connected virtual machines can share Unique MAC addresses .
View more
  • x
  • convention:

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