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Configuring a /30 IP block and a /26 IP block

Posted on 2016-08-28
Medium Priority
Last Modified: 2016-08-29
My ISP gave me a /30 address that is to be used to route my /26 block of IP addresses.

/30 block ISP side my side (Fortigate firewall)

/26 block of addresses /26

Internal network

My network is able to browse the internet just fine, with all internet traffic going through the gateway.  How do I setup my network to utilize the /26 block of addresses?

Thank you for any suggestions.
Question by:lawemcsd
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LVL 37

Expert Comment

ID: 41773635
it depends on the devices before the FortiGate firewall as well as the FortiGate device itself.

1. please advise your the model of your FortiGate device.

2. please advise if there is any device to use the /26 IPs before the FortiGate firewall, or everything is behind or protected by the FortiGate firewall?
LVL 31

Expert Comment

ID: 41773652
How do I setup my network to utilize the /26 block of addresses?
Typically you should create Nat pool for your IP address range (/26 block) and then just create NAT translation rules that your private IP address range use that nat pool, so traffic gets natted with that IP address range. Default route is still the same - next hop is The rest is up to ISP - they need to configure route(s) that will  point to your WAN ip address as next hop to reach your /26 block.

Author Comment

ID: 41773982
Hi, Thanks for the responses.

I'm using a Fortigate 800c. And the /26 address would all be behind the firewall.  

Do I need to establish a port to  act as the gateway for  What's ideal?

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LVL 31

Assisted Solution

Predrag earned 1000 total points
ID: 41774244
/26 address would all be behind the firewall
In that case you don't NAT traffic for those, just create routes (if needed) and that's it (sure ther should be some gateways somewhere :) ). However, not sure for configuration details on Fortigate.
LVL 71

Accepted Solution

Qlemo earned 1000 total points
ID: 41774645
It depends on what you want to do, but you
either use a DMZ for those /26 addresses, just routing them thru and allowing "interesting" or all traffic
or create port-forwarding for /26 addresses on FortiGate (with appropriate NAT policies allowing traffic) to (private) LAN IPs.

The DMZ has the advantage that traffic is kept separate for public IPs and LAN, and you are able to define granular access rules (policies) for DMZ <=> LAN traffic. DMZ is more secure.

Author Closing Comment

ID: 41775714
Thanks folks!

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