pfsense behind a router
I have a router with firewall configured with WAN and LAN. Can I setup pfsense in LAN with this scenario ?- 2 NICs of pfsense firewall configured in same LAN, one will be connecting to Router's LAN interface and other one to the LAN switch?
To accomplish what?
When you put a router on a network with other hosts you can run into asymmetric routing issues.
I have an interface set up that is just for "WAN" interfaces of other routers.
My router doesn't have extensive URL based web filtering options, basic thought behind this setup was to put all outbound traffic through pfsense
Why not just use pfSense?
Else you would want to make a bridge of the two interfaces and set up a transparent proxy.
Though you might just want to set up pfSense as a single-interface host on your network and use it as a pfBlocker/DNSBL DNS server.
Moving to the cache/proxy forum since that is closer to what you are asking for but I'd look hard at DNS-based blocking instead.
Can I ask for a little more info, are you setting up a pfsense box for filtering (something like squid)? I have a pfsense box setup behind a standard router and it works well, like you my router (I have used BT and Sky routers) have little to no filtering.