A packet is sent to a router that does not have the destination address in its route table. What mechanism allows it to be forwarded toward the proper destination?

A packet is sent to a router that does not have the destination address in its route table. What mechanism allows it to be forwarded toward the proper destination?

• A. Root Internet servers
• B. Gateway of last resort
• C. Reverse DNS
• D. Border Gateway Protocol

Answer: (B)

When a router doesn’t have a specific path to the destination in its routing table, it uses a default route, known as the gateway of last resort. This predefined path forwards the packet to a next-hop router (often the ISP’s edge router) that can determine how to reach networks beyond the local router’s knowledge. In effect, the gateway of last resort acts as a catch-all route for destinations that aren’t explicitly listed. Root Internet servers are part of the DNS infrastructure, not routing decisions. Reverse DNS is about mapping an IP back to a domain name, not how packets are forwarded. Border Gateway Protocol is a routing protocol that exchanges path information between autonomous systems; it helps learn routes, but the immediate mechanism for handling an unknown destination is the default route via the gateway of last resort.

When a router doesn’t have a specific path to the destination in its routing table, it uses a default route, known as the gateway of last resort. This predefined path forwards the packet to a next-hop router (often the ISP’s edge router) that can determine how to reach networks beyond the local router’s knowledge. In effect, the gateway of last resort acts as a catch-all route for destinations that aren’t explicitly listed.

Root Internet servers are part of the DNS infrastructure, not routing decisions. Reverse DNS is about mapping an IP back to a domain name, not how packets are forwarded. Border Gateway Protocol is a routing protocol that exchanges path information between autonomous systems; it helps learn routes, but the immediate mechanism for handling an unknown destination is the default route via the gateway of last resort.