Our Connectivity Detector is pretty weak. Here is a description of how it works from a different thread here...
It sends out RTP data to a known multicast address, and listens for data on that address as well. If it receives data, then network receive is true. If the person you are receiving data from receives your data (in other words if the data is flowing in both directions) then network send is true. If both network send and network receive are true, then you are multicast enabled between those 2 points. We also have (or should have, depending on if the machine reboots and whether or not we remember to restart it) a machine here that is also running Connectivity Detector. It is a well-known host. If you receive data from the well-known host and your are multicast enabled, then we mark you as having Internet2 connectivity.
