Exam H12-211 topic 1 question 235 discussion

There are two routers (RTA and RTB) between the source device and destination device. The Tracert command is used to detect the path between the two devices. During detection of the first hop (RTA), the source device sends a UDP packet with a TTL of 1 to an interface with a large interface number on the destination device. The TTL turns to 0 when the packet arrives at RTB, upon which RTA sends an ICMP ______ message to the source device.