Which protocol enables routing between Layer 3 and Layer 2 networks?

• A. BFD
• B. BGP
• C. IPv4
• D. RIP

Answer: (C)

Routing between a Layer 3 network and Layer 2 networks relies on the IP protocol to carry addressing and forwarding decisions. IPv4 provides the addressing scheme and the forwarding mechanism that lets a router decide how to move packets from one Layer 2 segment to another across networks. In practice, a router connects multiple Layer 2 domains and uses IPv4 to route traffic between them, enabling communication across different subnets and LANs.

Other options don’t fit as the primary enabler here. BFD is about rapidly detecting a failed path, not routing. BGP is a routing protocol used mainly for exchanging reachability between autonomous systems, not for the fundamental act of interconnecting Layer 2 domains via Layer 3. RIP is a basic IPv4-based routing protocol, but the question targets the underlying protocol that makes inter-network routing possible in general, which is IPv4.