VMWare Workstation - Changing subnet settings for host-only network from Class C to Class B

[kyrlon]

On VMWare Workstation, I get an error when attempting to modify the subnet mask to class B or 255.255.0.0 a newly established Host-Only network. Here is a post with more flushed out explanation on the topic.

EDIT:
Adding the entire post to provide consistency

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I have followed the instructions from the VMware page that explains how to Add a Host-Only Virtual Network to my configurations, but I also want to change the subnet mask for my new interface. I have tried to follow the instructions provided from another doc, but I get an error when attempting to modify the subnet mask to class B or 255.255.0.0. For instance, the network settings I want to use are within the range 10.8.241.0/16. This works with no problem in VirtualBox:

however, I receive the error notice win Vmware when I attempt to apply the same kind of settings:

Does anyone know why this is the case? I am not aware of any network files that I could manually modify on a Windows 10 host machine as described in Linux systems from here or here

[CarltonR]

As a matter of interest, what happens if you use 255.0.0.0 as the subnet mask attributed to the 10.8.241.0 IP address ?

Note: it's a pity that you were unable to include the full post provided on the other link to the question posted here, it would have provided consistency, but hay-ho.

[kyrlon]

Updated original post to mirror the link that was provided. As for changing subnet mask to 255.0.0.0 with 10.8.241.0 IP address, I receive the same error as mentioned above unfortunately.

[CarltonR]

I have just setup a test environment for VMware Workstation on a Windows based system, with the same configuration as you have entered (10.8.241.0, 255.255.0.0) and received the same error message as you got.

However, when changing the third octet of the subnet mask to 255.255.255.0 there were no issues, and it was accepted with no error message.  Modifying the third octet to any other 'theoretically' valid values forced the error message to return.

Run out of time, so when I have a moment, I will put my networking thinking cap on to try and figure out why this might be occurring.

[CarltonR · Accepted solution]

After giving this some thought, and validating the assessment on VMware Workstation the following has been determined.

It appears that the Assignment of Classless Inter-Domain Routing (CIDR) blocks is being used to determine the IP/Subnet Mask for the Virtual Network.  So in short the subnet Network ID must fall within the last assigned active bit of the IP (network address/host address/subnet mask).  Plus, VMware requires that at least last [4th] octet of the Host ID contains a zero.

So to use your example 10.8.241.0:

	Binary Subnet Mask	Subnet Mask	Outcome
	11111111.11111111.11111111.00000000	255.255.255.0	Validates
	11111111.11111111.11111110.00000000	255.255.254.0	Fails
	11111111.11111111.11111100.00000000	255. 255.252.0	Fails
	11111111.11111111.11111000.00000000	255.255.248.0	Fails
	11111111.11111111.11110000.00000000	255.255.240.0	Fails
	-	-
	11111111.11111111.00000000.00000000	255.255.0.0	Fails
	11111111.00000000.00000000.00000000	255.0.0.0	Fails

IP Binary ID:	00001010.00001000.11110001.00000000	24 bits
IP	10.           8.         241.           0

You could adjust the virtual network IP and subnet to get close to what your requirements are, and then use the VMs to further divide them up into the desired subnets.  You could use 10.8.0.0/16 which would give you the 65,534 available addresses, which might be a tad bit excessive within an VM environment, unless you're trying to emulate an existing service for testing purposes.

Another example based on 192.168.40.0

	Binary Subnet Mask	Subnet Mask	Outcome
	11111111.11111111.11111111.00000000	255.255.255.0	Validates
	11111111.11111111.11111110.00000000	255.255.254.0	Validates
	11111111.11111111.11111100.00000000	255. 255.252.0	Validates
	11111111.11111111.11111000.00000000	255.255.248.0	Validates
	11111111.11111111.11110000.00000000	255.255.240.0	Fails

IP Binary ID:	11000000.10101000.00101000.00000000	21bits
IP	192.         168.        40.           0

I hope that this all makes sense.

[kyrlon]

Thank you so much with your response (especially regarding CIDR) ! I believe your suggestion of 10.8.0.0/16 is an appropriate alternative. I'm glad this headache I experienced was not only unique to me.