RB2011LS-IN sfp not pinging gateway

Dear all, I have got the RB2011LS-IN router with SFP port, my intention is to use the sfp port to connect to the internet service provider, i have tried to configure the sfp port with the given ip address from my service provider, after this i can not ping the given gateway, also the service provider can not ping my firewall. The only thing which seems to work is when i create the sfp port on a bridge with another port e.g eth0 then connect eth0 to a different router then assign the given ip address by isp on that different router, in this case making the RB2011 as a fiber media converter.. I would like some advise on how to be able to configure the sfp as my WAN port and be able to use the RB2011 as my main firewall.