I have a Fritzbox from the internet provider and behind it my IPFire. In the IPFire the access to pages via IP addresses is blocked (URL filter: Block pages which are accessed via the IP address).
Now I noticed that I can access the Fritz.Box web interface http://192.168.178.1/ from my network behind the IPFire (10.10.1.0). I would like to know why this is possible because the network is located in the internet (behind RED) from the clients point of view or has this to do with the private IP address or address range (192.168.x.x)?
I don’t get your english - maybe because mine is too bad. Your situation is like this:
Internet <-> FritzBox <-> IPFire <-> Clients
You wonder, if it’s normal that your clients can access the FritzBox Webinterface? That it totally normal because your IPFires Gateway on RED is the IP of your FritzBox, and even if not the requests of the clients will be still send to your FritzBox, because the IP is not within the IP range of IPFires local area network and IPFire does NAT to RED.