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Date:      Fri, 29 Aug 2008 13:03:16 +0800
From:      EdwardKing <zhangsc@neusoft.com>
To:        FreeBSD <freebsd-questions@freebsd.org>
Subject:   Why tcpdump don't work?
Message-ID:  <032001c90994$8cb3e760$3f83a8c0@neusofteaf5839>

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I have a server and a client,they use TCP to communication.For example,when client send a message to server,the server return the same message to client,then client show it.When client or server shutdown,it will send FIN.So I want to use tcpdump to watch it. The server and client in the same machine,the IP is 172.0.10.2 and the port is 9999

#ifconfig
le0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500
 options=8<VLAN_MTU>
 ether 00:0b:31:76:35:31
 inet6 fe80::20c:29ff:fe76:356a%le0 prefixlen 64 scopeid 0x1 
 inet 172.0.10.2 netmask 0xffffff00 broadcast 172.0.10.255
 media: Ethernet autoselect
 status: active
plip0: flags=108810<POINTOPOINT,SIMPLEX,MULTICAST,NEEDSGIANT> metric 0 mtu 1500
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
 inet6 ::1 prefixlen 128 
 inet6 fe80::1%lo0 prefixlen 64 scopeid 0x3 
 inet 127.0.0.1 netmask 0xff000000 

#tcpdump tcp port 9999 and host 172.0.10.2
tcpdump:verbose output suppressed,use -v or -vv for full protocol decode 
listening on le0,link-type EN10MB (Ethernet),capture size 96 bytes

#tcpdump -v tcp port 9999 and host 172.0.10.2
tcpdump:listening on le0,link-type EN10MB (Ethernet),capture size 96 bytes

when client and server communication or client shutdown,tcpdump don't show any message!
Why? I am very puzzle with it!  How to show server and client tcp communication information by using tcpdump? 

Thanks!


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