Originally Posted by
BigLar
OK - but ...
If I, say, map the drive on my RAID to my desktop, I talk to it using, what? ... TCP/IP? The RAID has a static IP, but how does the switch know where to send the data? Does it "ask" and see who responds, and then set up a virtual connection or what? If it's something like that, then, sure, I don't need a router. What if it's a DHCP-assigned IP?
Yes, your desktop is communicating via TCP/IP with the RAID server.
The switch doesn't know anything. It's just a pipe that connects your computer and RAID. Well, a smart switch would be able to do some processing of the data, but a standard dumb switch doesn't really, beyond inspecting each packet to see which MAC it's going to and directing the packet to the appropriate port on the switch. In contrast, a hub (which you don't really see anymore) would broadcast all packets to everything connected to it.
At the very low level, I think that your PC will send a broadcast over the local network to ask who has the IP address of the RAID server. The RAID server will reply with its MAC address, and then your PC connects directly using that.
A DHCP-assigned IP doesn't make a difference. Your router is presumably your DHCP server. When a network device requests an IP, the router assigns it one. The device hangs on to that IP until I think halfway until its lease expires, at which point it requests another one. If the router isn't available on the network at that point, eventually the IP lease will expire and the device will lose its IP.