hello Athar,

With the 7.2 code, ISP fallback can be performed using a new feature called "static route tracking" using the SLA commands... this seems a little confusing, but it just works on icmp polling and once if the first ISP is down, the routing table installs the backup route ... without this, since the ethernet interface never goes down, even if the first ISP WAN link goes down, the ASA keeps sending packets to the router..

you can find some info on this command on the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/multisec/asa_sw/v_7_2/cmd_ref/s8_711.htm#wp1190857

you need to give your default gateways , as below:

hostname(config)# route outside 0.0.0.0 0.0.0.0 192.168.0.1 track 1

hostname(config)# route dmz 0.0.0.0 0.0.0.0 192.168.100.1 254

and associate this with the SLA commands... Give it a shot and let us know if this works..

Hope this helps.. all the best.. rate replies if found useful..

Raj