How to allow address groups to communicate

Hi There,

Let me try another approach since any further use of network jargon may complicate things.

What I understood so far is that you want the two subnets to communicate where one has/32 subnets assigned to a domain controller.

Imagine your Fortigate as a house and you can relate the subnets as different rooms. Now for anyone to move from one room to another, one need to pass through the doors. These doors are the route(inside the routing table) that allows one to move from one room to another. If anyone wants to go from room 1 to room 2, one need to go through the specific doors.

Likewise, if anyone want to go from room 1 to room 3, one cannot use the room 2 door but have to use the door specific to 1 and 3. So routes are cleared in terms of doors. Specific routes(door) allow specific subnets(rooms) to communicate with each other. This means that, for your problem, we have to check whether the door is there or not or it's just a room with no door at all(weird I know) Hence we have to verify the routing as one of the checks. 

Secondly, firewalls also have firewall policies that allow any connection from one subnet to another. Consider this firewall policy as a security guard standing in front of the door. So, even if you have the door if the security guard does not have your name on his permit list, you won't be able to pass just yet. Hence we have to check the firewall policy as well in your case.

For example, if one of the subnets is 192.168.1.1/24 (don't stress too much /xx at this stage) and wants to reach 10.10.10.1/32, then we can try to ping(as good as say "hello") from 192 to 10 and will run some test at the FortiGate. Please follow the below steps:

Step 1:
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Go to the PC, and press the window+R at the same time. A small window will open, type cmd and click ok. A black window will open. For example, if the domain controller IP address is 10.10.10.1 then in this black window, type ping 10.10.10.1 -t and keep this running.

Step 2:
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Now login to your FortiGate CLI type the sniffer command and hit enter. You will see some outputs After 3-4 min, press ctrl+c in the FortiGate CLI window(where you run the sniffer command) and this should stop the commands outputs. After that run the command "get router info routing-table all" and hit enter. You will get some outputs. Now, navigate to the top right corner of the black window in the FortiGate CLI page and click the down arrow and this should download a file to your download folder. FYI, refer to the attached photos to assist you with each section of "ping", "sniffer", "route table" and "log file".

Please share this file here so that we can check this further. We aim to verify things one by one so as not to overwhelm the situation.

Thanks