Which of the following is used by Traceroute to determine the path a packet takes?

Traceroute utilizes the Time to Live (TTL) value in its packets to determine the path that a packet takes across a network. When a packet is sent with a specific TTL, each router along the path decrements this TTL by 1. If the TTL reaches 0, the router will drop the packet and send back an ICMP Time Exceeded message to the sender. By incrementing the TTL value with each successive packet sent, Traceroute can determine the address of each router (or hop) that the packet passes through until it reaches its destination. This method provides an effective way to map the route that packets take through the network, pinpointing where delays or issues might occur.

The other options play roles in network communications but do not directly contribute to how Traceroute determines the packet's path. IP addresses identify endpoints, while protocol identifiers define how the communication should be processed, and packet size can influence transmission efficiency but does not assist in tracing the route.