if my understanding is correct, the following is what happens when a host A wants to communicate with a machine X outside its network.
1) The host ,checks it routing table to find out if there is any direct routes to the machine.
2) It finds out that the machine is outside its network and has to sent the packets to the default gateway(router) R.
3) The host sents an ARP broadcast to get the mac of the router R.
4) After getting the MAC, the host creates a packet with src IP and MAC as that of the host A, dest IP of the remote machine X and dest MAC of the router R.
5)The router R receives the packet, either drops its or sents its to its next hope, which can be another router or the remote machine X itself.

Can anyone explain, how the steps would be, if i set the default gateway of the host A as host A itself...?