???????????&?????????
????1.?????????????client ??? 192.168.30.58
????server??:   192.168.30.203
????2.???????????
????server ??????tcpdump ??????

?????????????????????????е??????????????????????????????????????????????????????????????????????? ????? ftp-data??20????? ?? ???49404??????????????????????????????????????
?????????????е?????

?????????????????е?client???????????????????е??????????????????????????￡????????￡?
????PORT ???? ???????????????? PORT a??b??c??d??e??f?????? a??b??c??d ?????????????? IP ?????e??f ????????? 2 ?? 10 ??????????????? e×256 ?? f ??????????? ????????μ?e??f???192??252. ??????????????????????49404
????3.???????????
????server ??????tcpdump ??????

??????????????????? tcpdump ????????????? -X ???????????????????????????????????????????????????е????????
?????????????е?????

?????塢???
????1.??????????????????????21??20 ?????????????????????????????????????????????????????????
????2.?????????????????21??????????????????????????????????????????????????????????????
????3.??iptables ?У?????????ftp ?????????????飬????ip_conntrack_ftp
????4.??????????????????ftp????????????????????????????????