TMG NAT question

Hi Guys,

I have a TMG server with ip 192.168.1.8 for NAT purpose;

and i have a router with ip 192.168.1.1;

My domain environment is all in 192.168.1.x subnet;

we point the gateway of all computer in the domain to the router 192.168.1.1;

It seems sometimes even if the router is down, we can connect to internet;

but sometimes even if the router is online, we cant connect to internet;

Do we need to setup the gateway on the router to point to the TMG server?

Is that when clients are in the same subnet with the TMG server, they can automatically find the TMG to access internet?

Weicong888