My belief is that an unmanaged plug-and-play layer 2 network switch only deals with MAC addresses.
When computer A on a local network wants to communicate with computer B for example through the unmanaged switch, does the switch simply just forward the Ethernet frames to computer B? If so, how does it know the destination MAC address initially?
Initially when computer A only knows about the computer B's IP address? Does the switch internally keep track of IP addresses matching the MAC addresses? Thanks in advance.
Best Answer
An unmanaged switch doesn't use/care for/understand IP addresses at all.
A managed L2 switch uses IP addresses for management only. Some L2 switches also support limited L3/IP functionality like ACLs. L3 switches use IP addresses for L3 forwarding = routing as well.
Yes. A basic switch forwards frames by destination MAC address only. Whether higher layers use IPv4, IPv6 or anything else doesn't concern the switch.
A switch ("multiport MAC bridge") learns locations of MAC nodes from the source addresses they use in the frames they send.
If no frame has been sent from a node, its MAC is initially unknown and the switch needs to mimick a repeater hub by flooding the unknown frame to all its ports but the source port.
For IPv4, broadcast-based ARP is used to resolve an IP address to its corresponding MAC address (for MAC-based networks): A broadcasts an ARP request with B's IP address, B replies with its interface MAC address. IPv6 uses multicast-based NDP.
No. A switch only cares for MAC addresses. Matching IP addresses to those MAC addresses is up to the hosts (or more generally up to the L3 nodes, including routers).