bad subnet mask

samrd33 · ‎03-19-2017

I'm trying to configure a router but keep getting a bad subnet mask error

IP address for this interface: 192.168.1.0

Subnet mask for this interface [255.255.255.0] : 255.255.255.0

% Bad subnet mask.

% Enter an subnet mask of the form 'X.X.X.X', where each

letter corresponds to a decimal number between 0 and 255.

Any suggestions?

Mark Malone · ‎03-20-2017

Hi

you cant have a .0 on an interface that's the network address it needs to be between .1 - .254

Joseph W. Doherty · ‎03-20-2017

To clarify what Mark is saying, the .0 is always the network address for a /24.

Julio E. Moisa · ‎03-20-2017

Hi

As Joseph and Mark mentioned:

- You can use the subnet mask under the interface only. Example: 255.255.255.0 or 255.255.254.0.
- The 192.168.1.0/24 is basically the network segment. Now you could use the ip ending in "0" example: if the mask is changed to /23 but it means the network segment is 192.168.0.0/23 so you will have 510 valid IPs to be used.

Here you need to verify if the problem is the subnet mask or the IP included under the interface, in this case as the subnet mask is /24 you need to include a valid IP different with ending "0" or "255". Under the interface you can configure valid IP addresses only.

Network: 192.168.1.0/24
Valid IP addresses: 192.168.1.1 to 192.168.1.254
Broadcast IP address: 192.168.1.255 <--- Cannot be used either.

If you have a subnet /23 this is the information:

Network: 192.168.1.0/23
Valid IP addresses: 192.168.0.1 to 192.168.1.254 <--- the 192.168.1.0 is included on the valid IP addresses range so it can be used under a interface.
Broadcast IP address: 192.168.1.255 <--- Cannot be used either.

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