tracepath6

tracepath6 is a network diagnostic tool used to discover the MTU (Maximum Transmission Unit) path for an IPv6 network. It works by sending UDP packets with progressively increasing hop limits. When a router along the path receives a packet with a hop limit of zero, it sends back an ICMPv6 "Time Exceeded" message. Tracepath6 uses the source address of this ICMPv6 message to identify the router and the packet's payload size to determine the MTU. Unlike ping, which typically sends a single packet, tracepath6 probes multiple packet sizes until it finds the largest one that can traverse the path without fragmentation.

The tool is useful for troubleshooting network connectivity issues, particularly those related to MTU mismatches. An incorrect MTU can lead to dropped packets and slow network performance, even if basic connectivity appears to be present. By identifying the MTU path, network administrators can configure their devices and applications appropriately to avoid these problems. Tracepath6 is available on most Linux-based systems and is a valuable addition to any network troubleshooting toolkit. It provides a non-intrusive way to gather critical information about the underlying network path.