This test is used to determine if a webserver will reduce its packet size when asked to by an ICMP Packet Too Big (PTB) message. This test is important because if there is a tunnel in the path back to a client that reduces the maximum transmission unit (MTU) of the path, and the server filters PTB messages, then the server will probably not reduce its packet size so that the client can receive the data. You can read about the algorithm used in the test and some recent results in large-scale testing in this paper. The algorithm was devised by Medina, Allman, and Floyd in 2004. Before running a test you must first register your email. Click here to do so.
Usage: In the simplest case, enter your email address and a URL of a webserver to check. Check the IPv4 or IPv6 box to control which IP protocol to use. To control the specific IP address to test, enter it in the appropriate box at the bottom of this form.