I just installed an OpenWRT router. Previously I was using an Netgear Orbi as the Router and have since made it an AP. Previous to the install of the OpenWRT I was able to access my Motorola Modem by going to http://192.168.100.1/Login.html and now I can not. However, I am able to ping that IP address from my workstation.
What does the routing table look like? Is the .100 network on the wan interface?
Is there any possibility there is another device at .100.1? If the pings are being answered by the modem it should also answer http. Were you pinging from your PC or from the router itself?
Usually no special configuration is required to reach a cable modem at 192.168.100.1-- since the wan interface is running in IP mode and it is the default route for all networks not known to the router. A request for 100.1 will be sent to the modem like a request for any other IP on the Internet.
Well You have these screenshot to help you get back to configuring VPN, But right now we need to remove these rules to get to Modem.
Edit your Firewall to remove the Vpn from the Lan (Top of Pic 1)
Edit your Firewall to remove Vpn entirely (3rd down of Pic1)
Pic two should be cleared automatically by doing the edits on the Firewall page, but check anyway
Reboot as last resort.