Please do NOT put two routers in series. It can be made to work, but is not trival. I suggest you try *ONE* of the following derrangements:
- Convert BEFW11S4 into an access point.
- Leave your BEFSR81 with the current settings.
- Plug a CAT5 cable between the BEFSR81 and one of the *LAN* ports on the BEFW11S4.
- Turn off the DHCP server on the BEFW11S4 and use the one on the BEFSR81.
- Use only one router and replace the BEFSR81 with a switch.
- Remove the BEFSR81 from the system.
- Connect the cable modem to the WAN port of the BEFW11S4.
- If you need more than 4 local LAN ports, get an 8 port switch.
- Double NAT (not recommended but seems to be what you're doing).
- Leave the BEFSR81 with the current settings at 192.168.1.1.
- DHCP server should be on and delivering IP's at 192.168.1.100-150.
- BEFW11S4 set for a WAN IP of 192.168.1.2 and a netmask of 255.255.255.0.
- LAN side of BEFW11S4 is set to 192.168.2.1.
- BEFW11S4 DHCP server is on 192.168.2.100-150.
With a netmask of 255.255.255.0 on the WAN side of the BEFW11S4, clients on the wireless router will be able to see other clients plugged into the BEFSR81 router. However, clients on the BEFSR81 router will not be able to see any clients on the wireless side. If you set the netmask to 255.255.255.252, clients from both LAN's will not be able to see each other. I dunno if this is how you want things to work.