tcpdump only captures incoming packets in a tcp connection

[wen lui <esolvepolito () gmail com>]

Hi, all

      I wrote a program based on tcp and put it on a PlanetLab node A. The
program initiates a tcp connection with another host B(tcp listening port
30000).

      I used tcpdump on planetlab node to capture packets without any filter

       tcpdump - i eth0

      I notice all the packets I captured are only incoming packets, the
outgoing packets like TCP SYN packet and  TCP ACK packet are missing.

      On Host B I also use tcpdump and I can see the TCP SYN and ACK from  A

       I tried wget and udp sending on the Planetlab node and I can capture
outgoing packets. So this means tcpdump on Planetlab node can be infuenced
by specific program?

        what are potential reasons for this? thanks!

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