What information does a switch look up in the MAC address table before forwarding a frame?

When a switch receives a frame, it examines the destination MAC address to determine where to forward the frame. The MAC address table, also known as the content-addressable memory (CAM) table, contains a list of MAC addresses associated with specific ports on the switch. By looking up the destination MAC address in this table, the switch can identify the corresponding port to which the frame should be sent. This process is critical for efficient frame switching within a local area network, ensuring that frames reach their intended devices without unnecessary flooding to all ports.

The other options provide useful information in specific contexts, but they do not play a crucial role in the decision-making process for forwarding a frame. For instance, while the source MAC address can be recorded in the MAC address table to help learn where devices are located on the network, it is not used to determine forwarding paths for outgoing frames. Frame length and VLAN information are also important for network operation and maintenance, but they do not directly influence the decision to forward a frame to its destination. Thus, focusing on the destination MAC address is essential for effective frame forwarding in a switched network environment.