S3 IP is 192.168.1.99

If your LAN is different, you have to setup your S3 first.
Plug your computer directly to the S3.
Change your computer IP for 192.168.1.10, for example.
Go to the S3 interface using http://192.168.1.99 et change WAN setup from static address to DHCP client (network > wan > edit > protocol), apply changes, then replug to your router (and restore your computer IP).

(sorry if bad english, I'm french)