Hi,
if we suppose the 2 hosts are in the same subnet:
-host A is going to do a bitwise AND of its netmask and own IP address and compare the result of same operation done between its netmask and destination address.
-if the result is the same which it is if they are on same subnet then it is gonna search for a L2 mapping corresponding to host B IP address
To do so it first looks into its arp cache and if there is no entry for this IP then it is going to emit a broadcast ARP request
-the ARP request which is a L2 broadcast is flooded by the switch attached to host A to all ports which means to link between switches and the second switch does the same so finally it is hear by host B
-Host B sends an unicast arp reply and the switch connected to host B learns the src MAC of host B and puts an entry in its CAM table then as it has still no entry for dst MAC of host A it will flood the unknown unicast frame which finally arrives on Host A and at the same time it puts an entry in its CAM table for the src MAC of host B
Now the same happens on the other switch when it receives the reply and finally there are entries in the CAM tables of both switches for the MAC addresses of host A and B
Host B depending of implementations when seeing the arp request either fills its arp cache with the src MAC of host A and its IP or when replying to host A at L3 will also initiate an arp request.
Regards.
Alain
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