What is a default gateway and how is it used in IPv4 networks?

• A. The router address on the local subnet used to reach destinations outside the local network; non-local traffic is sent to it.
• B. The IP address of the destination host on the same subnet; used for direct delivery.
• C. A DNS resolver used to translate domain names into IPs for internal hosts.
• D. A firewall that blocks all inbound traffic by default to protect the network.

Answer: (A)

A default gateway is the router’s address on your local network that hosts use to send traffic to destinations outside their own subnet. When a device wants to reach an IP that isn’t on its local subnet, it forwards the packet to this gateway. The gateway then takes responsibility for delivering the packet toward the destination, often through multiple routers, until it arrives at the target. In home networks, the gateway is usually the router’s LAN IP (for example, 192.168.1.1). It often also performs NAT to let many devices share a single public IP when accessing the internet.

Why the other ideas don’t fit: sending directly to a destination on the same subnet doesn’t involve the gateway because those packets can be delivered directly on the local link; a DNS resolver is about translating domain names to IPs, not about routing traffic; and while a gateway/router might include firewall features, the term default gateway specifically refers to the path used to reach non-local networks, not a firewall function.