IP Subnetting Issue

[ronzoni01]

It' s been 5 years since I' ve studied/brushed up on my subnetting skills so i' m a bit rusty. I have run into an issue in one of my offices. The main interface is currenlty running on 192.168.5.1/255.255.255.0 for about the last 4 years. We have since doubled our staff in the office and between the servers, phones and employees, we' ve quickly run out of IPs. I' m trying to expand the network now so I can at least double the IP Space available. Using classless ip routing, can I expand the network to allow for 510 maximum addresses by adjusting the interface to 192.168.4.1/255.255.254.0? Would I run into any issues? We' re currently using a FortiGate200A Firewall if that matters. If this would work, I could simply adjust the default route to 4.1 and update the DHCP server to include the new addresses. I thank anyone ahead of time for responding.

[ronzoni01]

not sure how that triple post just happened!

[rwpatterson]

You really wouldn' t need to change the default gateway. So it' s in the middle...it will still work. What you are proposing looks valid from my end.

[ronzoni01]

ORIGINAL: rwpatterson You really wouldn' t need to change the default gateway. So it' s in the middle...it will still work. What you are proposing looks valid from my end.

rwpatterson, a quick question. You state that I could leave the default gateway in the middle. would that means i leave the interface settings the same but just change the Netmask portion of it? change it from 192.168.5.1/255.255.255.0 to 192.168.5.1/255.255.254.0 ?

[abc987]

Your new network is 192.168.4.0/23. It' s not necessary that your gateway is at the first IP (192.168.4.1) or the last (192.168.5.254). So you can left your Interface-IP on 192.168.5.1, only change the subnetmask to /23 (255.255.254.0)

[rwpatterson]

Both correct.

[byrann21]

I found that discussion useful.

[ronzoni01]

Thank you rwpatterson

[emnoc]

Changing the mask on the FGT is just one step, but all of the existing host would need their masks adjust to /23. This is simple to do in a DHCP env, but if you have the 1st 254 adddress hardcoded, you might seen some long hours.

[ronzoni01]

Yes, I need to update the DHCP server settings and then update our site-to-site VPN connections as well as any local servers.