18.7.3 检测半打开连接
如果一方已经关闭或者异常终止连接而另一方却还不知道,我们将这样的TCP连接成为半打开的。
任何一端的主机异常都可能导致发生这种情况,只要不打算在半打开连接上传输数据,
扔处于连接状态的一方就不会检测另一方已经出现异常
node1:/root/test#tcpdump -i eth1 '((tcp) and ( ( host 192.168.137.3)))'
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
00:29:44.579714 IP node1.58001 > node2.discard: Flags [S], seq 4069725600, win 14600, options [mss 1460,sackOK,TS val 12799610 ecr 0,nop,wscale 6], length 0
00:29:44.581724 IP node2.discard > node1.58001: Flags [S.], seq 682751229, ack 4069725601, win 14480, options [mss 1460,sackOK,TS val 116893883 ecr 12799610,nop,wscale 7], length 0
00:29:44.581779 IP node1.58001 > node2.discard: Flags [.], ack 1, win 229, options [nop,nop,TS val 12799612 ecr 116893883], length 0
00:29:47.145033 IP 192.168.137.1.55582 > node2.ssh: Flags [P.], seq 3491907355:3491907391, ack 2317960111, win 16425, length 36
00:29:47.145069 IP node2.ssh > 192.168.137.1.55582: Flags [.], ack 36, win 145, length 0
00:30:03.816344 IP 192.168.137.1.55972 > node2.ssh: Flags [P.], seq 102175961:102175997, ack 3143807591, win 16425, length 36
00:30:03.816364 IP node2.ssh > 192.168.137.1.55972: Flags [.], ack 36, win 175, length 0
00:30:05.885840 IP 192.168.137.1.55881 > node2.ssh: Flags [P.], seq 761658358:761658394, ack 3173805010, win 16119, length 36
00:30:05.885852 IP node2.ssh > 192.168.137.1.55881: Flags [.], ack 36, win 155, length 0
00:30:19.726826 IP 192.168.137.1.55582 > node2.ssh: Flags [P.], seq 36:88, ack 1, win 16425, length 52
00:30:19.727077 IP node2.ssh > 192.168.137.1.55582: Flags [.], ack 88, win 145, length 0
00:30:19.729197 IP node2.ssh > 192.168.137.1.55582: Flags [P.], seq 1:133, ack 88, win 145, length 132
00:30:19.748949 IP node2.ssh > 192.168.137.1.55582: Flags [P.], seq 133:249, ack 88, win 145, length 116
00:30:19.749166 IP 192.168.137.1.55582 > node2.ssh: Flags [.], ack 249, win 16363, length 0
00:30:19.990986 IP 192.168.137.1.55582 > node2.ssh: Flags [P.], seq 88:140, ack 249, win 16363, length 52
00:30:19.992849 IP node2.ssh > 192.168.137.1.55582: Flags [P.], seq 249:301, ack 140, win 145, length 52
00:30:20.142911 IP 192.168.137.1.55582 > node2.ssh: Flags [P.], seq 140:192, ack 301, win 16350, length 52
00:30:20.145969 IP node2.ssh > 192.168.137.1.55582: Flags [P.], seq 301:353, ack 192, win 145, length 52
00:30:20.307517 IP 192.168.137.1.55582 > node2.ssh: Flags [P.], seq 192:244, ack 353, win 16337, length 52
00:30:20.310981 IP node2.ssh > 192.168.137.1.55582: Flags [P.], seq 353:405, ack 244, win 145, length 52
00:30:20.374872 IP 192.168.137.1.55582 > node2.ssh: Flags [P.], seq 244:296, ack 405, win 16324, length 52
00:30:20.376401 IP node2.ssh > 192.168.137.1.55582: Flags [P.], seq 405:457, ack 296, win 145, length 52
00:30:20.504175 IP 192.168.137.1.55582 > node2.ssh: Flags [P.], seq 296:348, ack 457, win 16311, length 52
00:30:20.507394 IP node2.ssh > 192.168.137.1.55582: Flags [P.], seq 457:509, ack 348, win 145, length 52
00:30:20.706140 IP 192.168.137.1.55582 > node2.ssh: Flags [.], ack 509, win 16298, length 0
00:30:20.708090 IP 192.168.137.1.55582 > node2.ssh: Flags [P.], seq 348:400, ack 509, win 16298, length 52
00:30:20.709273 IP node2.ssh > 192.168.137.1.55582: Flags [P.], seq 509:561, ack 400, win 145, length 52
00:30:20.906934 IP 192.168.137.1.55582 > node2.ssh: Flags [.], ack 561, win 16285, length 0
00:30:20.913041 IP 192.168.137.1.55582 > node2.ssh: Flags [P.], seq 400:452, ack 561, win 16285, length 52
00:30:20.918790 IP node2.ssh > 192.168.137.1.55582: Flags [P.], seq 561:613, ack 452, win 145, length 52
00:30:20.953858 IP node2.ssh > 192.168.137.1.55582: Flags [P.], seq 613:681, ack 452, win 145, length 68
00:30:20.954371 IP 192.168.137.1.55582 > node2.ssh: Flags [.], ack 681, win 16255, length 0
00:30:22.988827 IP node2.ssh > 192.168.137.1.55881: Flags [F.], seq 1, ack 36, win 155, length 0
00:30:22.988837 IP 192.168.137.1.55881 > node2.ssh: Flags [.], ack 2, win 16119, length 0
00:30:22.991399 IP 192.168.137.1.55881 > node2.ssh: Flags [F.], seq 36, ack 2, win 16119, length 0
00:30:22.991530 IP node2.ssh > 192.168.137.1.55881: Flags [.], ack 37, win 155, length 0
00:30:23.005079 IP node2.ssh > 192.168.137.1.55972: Flags [F.], seq 1, ack 36, win 175, length 0
00:30:23.005085 IP 192.168.137.1.55972 > node2.ssh: Flags [.], ack 2, win 16425, length 0
00:30:23.005086 IP node2.ssh > 192.168.137.1.55582: Flags [F.], seq 681, ack 452, win 145, length 0
00:30:23.005087 IP 192.168.137.1.55582 > node2.ssh: Flags [.], ack 682, win 16255, length 0
00:30:23.005089 IP 192.168.137.1.55582 > node2.ssh: Flags [F.], seq 452, ack 682, win 16255, length 0
00:30:23.007392 IP node2.ssh > 192.168.137.1.55582: Flags [.], ack 453, win 145, length 0
00:30:23.013601 IP 192.168.137.1.55972 > node2.ssh: Flags [F.], seq 36, ack 2, win 16425, length 0
00:30:23.013609 IP node2.ssh > 192.168.137.1.55972: Flags [.], ack 37, win 175, length 0
00:31:02.570247 IP node1.58001 > node2.discard: Flags [P.], seq 1:5, ack 1, win 229, options [nop,nop,TS val 12877601 ecr 116893883], length 4
00:31:02.582680 IP node2.discard > node1.58001: Flags [R], seq 682751230, win 0, length 0