一方突然断电重启，之前建立的连接信息丢失，另一方并不知道
这个场景在前面 keepalive 那里介绍过。客户端和服务器一开始三次握手建立连接，中间没有数据传输进入空闲状态。这时候服务器突然断电重启，之前主机上所有的 TCP 连接都丢失了，但是客户端完全不知晓这个情况。等客户端有数据有数据要发送给服务端时，服务端这边并没有这条连接的信息，发送 RST 给客户端，告知客户端自己无法处理，你趁早死了这条心吧。
node2:/tmp/newcx#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
11:04:30.501471 IP node2.42303 > node1.webcache: Flags [S], seq 2155267241, win 14600, options [mss 1460,sackOK,TS val 281712196 ecr 0,nop,wscale 7], length 0
11:04:30.501605 IP node1.webcache > node2.42303: Flags [S.], seq 3405760072, ack 2155267242, win 14480, options [mss 1460,sackOK,TS val 4294802733 ecr 281712196,nop,wscale 6], length 0
11:04:30.501620 IP node2.42303 > node1.webcache: Flags [.], ack 3405760073, win 115, options [nop,nop,TS val 281712196 ecr 4294802733], length 0
11:04:30.501736 IP node2.42303 > node1.webcache: Flags [P.], seq 2155267242:2155267246, ack 3405760073, win 115, options [nop,nop,TS val 281712196 ecr 4294802733], length 4
11:04:30.501844 IP node1.webcache > node2.42303: Flags [.], ack 2155267246, win 227, options [nop,nop,TS val 4294802733 ecr 281712196], length 0
11:04:30.502124 IP node1.webcache > node2.42303: Flags [P.], seq 3405760073:3405760086, ack 2155267246, win 227, options [nop,nop,TS val 4294802733 ecr 281712196], length 13
11:04:30.502134 IP node2.42303 > node1.webcache: Flags [.], ack 3405760086, win 115, options [nop,nop,TS val 281712196 ecr 4294802733], length 0
11:05:30.562330 IP node2.42303 > node1.webcache: Flags [P.], seq 2155267246:2155267250, ack 3405760086, win 115, options [nop,nop,TS val 281772257 ecr 4294802733], length 4
11:05:30.563528 IP node2.42303 > node1.webcache: Flags [R.], seq 2155267250, ack 3405760086, win 115, options [nop,nop,TS val 281772258 ecr 4294802733], length 0