TCPCopy vs Tcpreplay

TCPCopy and tcpreplay are different in the following aspects.

First, TCPCopy can be used by high-level applications, while tcpreplay can not. Since tcpreplay is unable to synchronize Seq/Ack numbers or maintain any TCP state, it is unable to establish a valid TCP session with a server. Thus, it is ineffective for high-level applications. However, TCPCopy can capture the online flow, send the captured data to a target server in real-time and establish valid TCP sessions with the target server, so it can be used by high-level applications.

Second, compared with tcpreplay, TCPCopy has less influence on the online server. Tcpreplay often works with packets captured and saved by sniffers/ packet capturing tools, such as tcpdump. When the online system is busy, tcpdump may influence the online file IO and the packet loss rate may be high. Moreover, as the captured packets should be saved, tcpdump seldom captures packets continuously for a few days. On the contrary, TCPCopy does not need many file IO operations, and can copy online packets to a target server in real-time for several days.

Third, TCPCopy keeps more online features than tcpreplay. When replaying with tcpreplay, the source IP address in the packet may be modified and different from online environments. Also it is hard for tcpreplay to keep the packets’ online delay feature precisely because of the timing issues, which makes the replaying effect different from online environments. By contrast, TCPCopy captures and sends packets in real-time, so the packets sent to the target server may keep many characteristics of online packets, such as delay and client packet attributes.

Lastly, it is more complex to use tcpreplay than TCPCopy. Compared with tcpreplay, we think TCPCopy is easier to learn and easier to use.