how to add more than 254 ip address

[rizduan7]

hello everyone!

i have one Forti Gate 60E

i have configured the Forti Gate to use this range Dhcp 192.168.1.50-192.168.1.240 

my sub net mask 255.255.255.0 

but it seems like i need more IP address, can someone help me to increase available IP address?

[ebilcari]

You have to change your subnet on the interface to a bigger one for ex. 192.168.0.0/23 (255.255.254.0). It will allow you to have 510 hosts.

Another example 192.168.2.0/23, it will allow 192.168.2.1 - 192.168.3.254

[rizduan7]

hello thank you for replying to me

so i need to change the IP/network mask?

[akanibek]

@rizduan7 ,

yes, you should change it on interface IP address. Then, it should affect to your DHCP pool on interface (Section - DHCP).

[rizduan7]

the picture i show above correct?

[ebilcari]

Yes it should look something like this:

Be careful to use the range that is not used in other interfaces (not overlapping) and not used in other network devices in your network.

[rizduan7]

i see, so my current address right now 192.168.1.1/255.255.255.0 

and my dhcp range 192.168.1.50-192.168.1.240 255.255.255.0

so i should change the address 192.168.1.1/255.255.254.0 is it correct? 

and what should i change at my dhcp range? 

My current setting

[ebilcari]

If you plan to change the subnet mask to 255.255.254.0, for the new network the GW is recommended to be at the beginning or at the end like 192.168.0.1

and the useful range for DHCP will be 192.168.0.2-192.168.1.254

As I mentioned earlier you have to check that this part of the subnet (192.168.0.0/24) doesn't overlap with other networks configured in your environment. 
In case it overlaps you have to create a new network for this interface using the  private IP ranges that are available [10.0.0.0/8, 172.16.0.0/12 or other subnet from 192.168.0.0/16]

[pavankr5]

Hello @rizduan7 ,

I would suggest to change the Subnet Mask modify the subnet mask from 255.255.255.0 (/24) to 255.255.254.0 (/23). This will accommodate a larger range of IP addresses. It will allow you to have 510 hosts.

With the new subnet mask, you need to update the DHCP range accordingly. In your case, the original DHCP range was 192.168.1.50-192.168.1.240, which was based on the previous subnet mask (255.255.255.0). To reflect the new subnet mask (255.255.254.0), you should adjust the DHCP range to start from 192.168.0.50 (one subnet down) and end at 192.168.1.254 (the last address in the current subnet). This will ensure that the DHCP range falls within the updated subnet.
Updated DHCP range: 192.168.0.50-192.168.1.254 with a subnet mask of 255.255.254.0

Update the DHCP range configuration in your FortiGate firewall to reflect the new range. Additionally, you will need to reconfigure the subnet mask on all devices in your network to match the updated subnet mask (255.255.254.0 /23). This includes the FortiGate firewall, DHCP clients, and any other network devices.
let me know if you have any queries

Thanks 

Pavan

[rizduan7]

i see but currently i have windows that i make as server and this windows use 192.168.1.5 subnet mask 255.255.255.0 and my gateaway 192.168.1.1 , what will happens to this two? or nothing happens to this two ? if i change my subnet mask to 255.255.254.0 and dhcp range 192.168.0.50-192.168.1.254?

i also have fortigate vpn setup at my fortigate firewall . what will happens to my vpn setup?