Methods and apparatus for testing a network that reassembles fragments into datagrams. A packet receiver may extract a plurality of instrumentation blocks from a packet received from the network. The packet receiver may determine if the received packet constitutes a correctly reassembled datagram based on information contained within the plurality of instrumentation blocks. The packet receiver may accumulate and report test statistics indicative of a number of correctly reassembled datagrams received and a number of incorrectly reassembled datagrams received.