3、SYN-SENT
node2:/root#netstat -atnp | grep -i 8080
tcp 0 1 192.168.171.103:16707 192.0.2.1:8080 SYN_SENT 25943/packetdrill
客户端发送 SYN 报文等待 ACK 的过程进入 SYN-SENT状态。同时会开启一个定时器，如果超时还没有收到ACK会重发 SYN。
node2:/root#netstat -na |grep 1.1.1.1
tcp 0 1 192.168.137.3:18824 1.1.1.1:8080 SYN_SENT
node2:/root#
node2:/root/test#time python t19.py
Traceback (most recent call last):
File "t19.py", line 6, in <module>
s.connect(("1.1.1.1",8080))
File "/usr/local/python27/lib/python2.7/socket.py", line 224, in meth
return getattr(self._sock,name)(*args)
socket.error: [Errno 110] Connection timed out
real 1m3.033s
user 0m0.021s
sys 0m0.007s
node2:/root#tcpdump -S -i eth1 '((tcp) and (port 8080) )'
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
20:31:22.137177 IP node2.18839 > one.one.one.one.webcache: Flags [S], seq 42287086, win 14600, options [mss 1460,sackOK,TS val 315723831 ecr 0,nop,wscale 7], length 0
20:31:23.137125 IP node2.18839 > one.one.one.one.webcache: Flags [S], seq 42287086, win 14600, options [mss 1460,sackOK,TS val 315724831 ecr 0,nop,wscale 7], length 0
20:31:25.138218 IP node2.18839 > one.one.one.one.webcache: Flags [S], seq 42287086, win 14600, options [mss 1460,sackOK,TS val 315726833 ecr 0,nop,wscale 7], length 0
20:31:29.138849 IP node2.18839 > one.one.one.one.webcache: Flags [S], seq 42287086, win 14600, options [mss 1460,sackOK,TS val 315730833 ecr 0,nop,wscale 7], length 0
20:31:37.139324 IP node2.18839 > one.one.one.one.webcache: Flags [S], seq 42287086, win 14600, options [mss 1460,sackOK,TS val 315738834 ecr 0,nop,wscale 7], length 0
20:31:53.140281 IP node2.18839 > one.one.one.one.webcache: Flags [S], seq 42287086, win 14600, options [mss 1460,sackOK,TS val 315754835 ecr 0,nop,wscale 7], length 0