A Single Network

If A wants to talk to B, well, they're on the same LAN (Local Area Network), so A addresses the packet directly to B:

So "A" can send a packet to "B" like this:

Source IP	192.168.1.1	(A)
Destination IP	192.168.1.2	(B)
Data	Hello B! This is the Data

Unfortunately, it's not as simple as that. The IP address identifies the machines at a software (logical) level, but the physical (MAC) layer isn't the same as the logical (IP) layer.

• The IP layer needs to be able to route from Alaska to Zebediela. It works at a relatively high level.
• The MAC layer only needs to talk to machines on the local network (LAN). It works at a low level.

Source IP	192.168.1.1	(A)
Source MAC	01:C0:F2:69:31:21	(A)
Destination IP	192.168.1.2	(B)
Destination MAC	03:A0:B3:27:A2:2E	(B)
Data	Hello B! This is the Data

So how does A find out what B's MAC address is?