Pathchar

(Tool written by Van Jacobson of LBL's Network Research Group. Selected binaries are available at ftp://ftp.ee.lbl.gov/pathchar.) pathchar usage notes (man page still under construction.) Pathchar servers are currently running at several vBNS sites, gathering pathchar statistics for future use in plotting trends.

The Internet has no central control or administration. In terms of ability to grow and scale this is a great strength. But in terms of ability to diagnose and fix problems it has been a serious weakness -- packets usually cross many administrative boundaries on their way from a source to a destination and often the only point of agreement between those separate administrations is that all problems are someone else's fault.

Ten years ago the Internet was plagued with routing problems and I developed a tool called traceroute (ftp://ftp.ee.lbl.gov/traceroute.tar.gz) that allowed any user, anywhere on the Internet, to trace the path packets take and isolate routing loops and black holes. Today the Internet appears to be experiencing severe congestion problems. I've developed a new tool, pathchar (ftp://ftp.ee.lbl.gov/pathchar/), that allows any user to find the bandwidth, delay, average queue and loss rate of every hop between any source & destination on the Internet. A surprisingly large amount of mathematics is required to do live analysis of a busy (and often broken) network path. --Van Jacobson, abstract for April 97 MSRI talk