GATE CS 2004 Q16 — Data Link Layer: Framing, Error Detection, MAC, Ethernet Bridging

To determine which statement is NOT true, let us analyze each option based on the functionalities of a transparent bridge (Layer 2 device) and a router (Layer 3 device):

• Option A: Both bridge and router selectively forward data packets.
  True. A bridge selectively forwards frames based on MAC addresses to reduce collision domains, while a router selectively forwards packets based on IP addresses to determine the best path.
• Option B: A bridge uses IP addresses while a router uses MAC addresses.
  False. A bridge operates at the Data Link Layer (Layer 2) and uses physical MAC addresses for forwarding. A router operates at the Network Layer (Layer 3) and uses logical IP addresses for routing. This statement is the exact reverse of how they operate.
• Option C: A bridge builds up its routing table by inspecting incoming packets.
  True. A transparent bridge uses a process called backward learning. It inspects the source MAC address of incoming frames to dynamically build and update its forwarding table.
• Option D: A router can connect between a LAN and a WAN.
  True. Routers are designed to connect different networks, such as connecting a local area network (LAN) to a wide area network (WAN) like the Internet.

Since Option B is false, it is the correct answer.