GNS3: ICMP Destination port unreachable - Cisco
learningnetwork.cisco.com › s › questionBasically packets are crafted to a random destination UDP port number. The packets are sent with TTL incrementing from 1 until reaching the desired destination IP address. Once the desired destination IP address is reached, that host will respond with an ICMP Destination Port unreachable message back to the source (Device initiating the traceroute).
ICMP Destination Unreachable messages - OmniSecu
www.omnisecu.com › tcpip › icmp-destinationPlease note that the ICMP Type is 3, which denotes this is an ICMP Destination Unreachable message. Also note that the ICMP Code is 3, which means that specified destination UDP port is not open on the destination computer. In other words, the destination computer is informing the sender using this ICMP message that the UDP port to which the sender was trying to communicate is not reachable.