This test is used to determine the Path MTU towards a particular IP address, to identify where in an IP path tunnels begin, and if any routers do not send PTB messages when they should. Usually, you'd enter your own IPv4/IPv6 address to test to see if there is a tunnel topologically close to you that could explain poor connectivity. The IP address you enter must be responsive to our probe packets so that we can infer whether all packets are being lost, or just large ones. Please ensure you configure your operating system and firewalls to permit UDP probes to port 33435, and to send ICMP destination unreachable messages. You can read more about the algorithm used in the test and some results from testing with jumbo-packet capable hosts in this paper. Before running a test you must first register your email. Click here to do so.
Usage: Enter your email address and the IP address of a host to check.