A Layer 2 Ethernet Switch Constructs A MAC Address Table. What Information Is Contained In This Table?
A TCP And/Or UDP Port Numbers Associated With Each Frame
B A Mapping Of IP Addresses To The Ports From Which They Were Learned
C IP Route Entries Learned Via Routing Protocols (E.G. OSPF)
D A Mapping Of MAC Addresses To The Ports From Which They Were
The correct answer and explanation is :
The correct answer is D: A mapping of MAC addresses to the ports from which they were learned.
Explanation:
In Layer 2 Ethernet switches, the primary role is to forward Ethernet frames based on MAC (Media Access Control) addresses. A MAC address table (also known as a forwarding table or content-addressable memory (CAM) table) is maintained by the switch to facilitate efficient frame forwarding.
How the MAC Address Table Works:
When a switch receives a frame, it checks the source MAC address and the port from which the frame was received. It then records this information in the MAC address table. The key information stored in the MAC address table is:
- MAC Address: The unique identifier for network devices (like computers, printers, etc.) on the network. Each device has a unique MAC address assigned to its network interface card (NIC).
- Port Number: The port on the switch where the frame was received.
For example, if a frame is received on port 1 with a source MAC address of 00:1A:2B:3C:4D:5E, the switch will create an entry in its MAC address table that looks something like this:
- MAC Address:
00:1A:2B:3C:4D:5E - Port:
1
Now, when a frame is later sent with a destination MAC address of 00:1A:2B:3C:4D:5E, the switch will know to forward it out through port 1.
Why Other Options Are Incorrect:
- A: TCP and/or UDP Port Numbers: These are Layer 4 information (Transport Layer) and are not stored in a MAC address table. Layer 2 (Ethernet) switches do not deal with TCP or UDP port numbers.
- B: A Mapping of IP Addresses to the Ports From Which They Were Learned: This is the job of Layer 3 devices like routers, not Layer 2 switches. IP-to-port mappings are generally maintained in routing tables.
- C: IP Route Entries Learned via Routing Protocols (e.g., OSPF): Routing tables with IP routes are maintained by routers, not Layer 2 switches.
Thus, option D is the correct answer because the MAC address table in Layer 2 switches maps MAC addresses to switch ports to determine where to forward frames.