Did you tried reading the following for identifying your IP ?
In case you have public IP on your 1st router.
As i understand Rut955 is connected on LAN of another router ? Right or no ?
So in case the above statement is true . There must be one IP assigned from 1st router IP pool to Rut955 from your 1st router that IP will be WAN IP of Rut955 . So , you need to do port forwarding to Rut955 from your 1st router . And as Rut955 is using http port 80 by default , may be your 1st router is also using the same 80 port as http. So, at the same time you cannot use the port 80 on both devices .
It must be changed on any of one router. I hope it helps.
If i am unable to understand your scenario please provide me with a topology , how everything is connected , what are IP addresses on LAN and WAN , What ports are being used on both sides.
Thank you .