invalid IP for this subnet mask entered

[aniisss47657]

Hi all,

I have the following 5 networks with the following ip address ranges and subnet masks.

NetA : 204.15.5.2 - 204.15.5.15              255.255.255.240                   

NetB : 204.15.5.18 - 204.15.5.47            255.255.255.224

NetC : 204.15.5.50 - 204.15.5.51            255.255.255.252

NetD : 204.15.5.54 - 204.15.5.67            255.255.255.240  

NetE : 204.15.5.70 - 204.15.5.99             255.255.255.224

As I attempt to configure PCs I receive the error "invalid IP for this subnet mask entered" 

However, this only occurs for the following IP addresses. 

204.15.5.15      NetA

204.15.5.31      NetB

204.15.5.32      NetB

204.15.5.95      NetE

204.15.5.96      NetE

204.15.5.97      NetE

What would be the cause of this? 

[LanDownUnda]

Hi Aniisss,

It looks like for NetA you have picked the broadcast IP address which is an unusable IP address in the /28 subnet.

If you choose a /28 for 204.15.5.0 than the following applies:

-Range: 204.15.15.1 through to 204.15.15.14

-Broadcast Address: 204.15.15.15

For NetB you have picked an IP address that doesn't belong in that /27 subnet. If you used an IP address between the range of 204.15.5.33 through to 204.15.5.62 than this will work as they are usable hosts.

If you get stuck with Subnet calculations than Subnet Calculators are a quick and easy way to fix up these errors when they come up.

I hope this helps!

[aniisss47657]

If my range is 204.15.15.1 through to 204.15.15.14, and 204.15.15.15 is the broadcast and 204.15.15.0 is the subnet ID, what would the default gateway be? Do I have only 13 usable IP addresses?

[Cristian Matei]

Hi,

   Per your used subnet mask:

            - 204.15.5.15 is a broadcast address, the last in the subnet

            - 204.15.5.31 is a broadcast address, the last in the subnet

            - 204.15.5.31 is a network address, the first in the subnet

            - 204.15.5.95 is a broadcast address, the last in the subnet

            - 204.15.5.96 is a network address, the first in the subnet

These IP's can't be assigned to a host, as those IP's represent the network itself, or everyone in the subnet (broadcast address), this it cannot uniquely identify a host. You're going wrong with the subnets. For example:

NetB : 204.15.5.18 - 204.15.5.47            255.255.255.224

The IP's you're trying to use from the above range, span across two different subnets. Per the /27 mask used, the correct subnets are:

204.15.5.0-204.15.5.31 /27 (204.15.5.0 is the network address, 204.15.5.31 is the broadcast address)

204.15.5.31 -204.15.5.63/27 (204.15.5.31 is the network address, 204.15.5.63 is the broadcast address)

204.15.5.64-204.15.5.95/27

Regards,

Cristian Matei.

[aniisss47657]

Hi Cristian,

How would I achieve this without wasting any address space.

I need 14 hosts in NetA, 28 hosts in NetB, 2 hosts in NetC, 7 hosts in NetD and 28 hosts in NetE.

Thanks

[Cristian Matei]

Hi,

    If your scope is to perfectly match those requirements and not the into consideration future host addition in any subnet:

NetA : 204.15.5.0 - 204.15.5.15              255.255.255.240                   

NetB : 204.15.5.32 - 204.15.5.63            255.255.255.224

NetC : 204.15.5.96 - 204.15.5.99            255.255.255.252

NetD : 204.15.5.16 - 204.15.5.31            255.255.255.240  

NetE : 204.15.5.64 - 204.15.5.95             255.255.255.224

Regards,

Cristian Matei.