Computer communications that are to be recorded are visible to a network interface on a recording computer. The network interface receives the packets to be recorded. The network layer of the recording computer implements a subset of the normal IP module in the network layer. The IP module in the network layer assumes that most IP datagrams are correctly addressed, internally consistent and of the expected protocol type. The recording computer allocates the received datagrams to a recording session based upon at least a first value of a field that is at a fixed position within the datagram. The datagrams for a session are ordered into an ordered recording stream based upon a timestamp within the datagram. The datagrams are also checked for criteria that indicate an error condition. The allocated and ordered datagrams are recorded or associated with other datagrams that have been allocated to the same session.