网络通信

tcp/ip协议各层简介

应用层：格式化字符串传输控制层：处理包 3次握手 4次分手源端口号->目标端口号网络层：网络号主机号下一跳（成本低且传输可靠）源IP地址->目标IP地址数据链路层：mac地址下一跳的mac地址源MAC地址->目标MAC地址

exec 22<> /dev/tcp/www.baidu.com/80     #linux中一切皆文件 22为管道 <>进出
echo -e "GET / HTTP/1.1\n" >& 22   #发送命令到22管道
cat <& 22  # 打印22管道收到的响应

exec 创建一个socket通信（内核内部完成） echo 用户空间程序员人实现应用层协议

lsof命令lsof（list open files）是一个列出当前系统打开文件的工具

linux命令-lsof

tcp模型

应用层 -> 传输控制层 -> 网络层 -> 传输链路层 -> 物理层

1. 传输控制层

netstat -natp

socket套接字 ip+prot : ip+port
udp 无连接且不可靠
tcp 面向连接的可靠的传输

连接 ---> 三次握手双方开辟资源为对方服务（内核）

3次握手

确认机制ack

socket 数据传输

套接字唯一表示

ip+prot : ip+port

port 限制 65535个

4次分手

抓包

curl www.baidu.com  #一个完整的网络生命周期

ping www.baidu.com


tcpdump -nn -i eth0 port 80 | grep  180.101.49.11

建立连接


20:17:47.431427 IP 172.16.13.190.54444 > 180.101.49.11.80: Flags [S], seq 3907241968, win 29200, options [mss 1460,sackOK,TS val 15378414 ecr 0,nop,wscale 6], length 0
20:17:47.442390 IP 180.101.49.11.80 > 172.16.13.190.54444: Flags [S.], seq 2051857229, ack 3907241969, win 8192, options [mss 1452,sackOK,nop,nop,nop,nop,nop,nop,nop,nop,nop,nop,nop,wscale 5], length 0
20:17:47.442398 IP 172.16.13.190.54444 > 180.101.49.11.80: Flags [.], ack 1, win 457, length 0

发送数据



20:17:47.442438 IP 172.16.13.190.54444 > 180.101.49.11.80: Flags [P.], seq 1:78, ack 1, win 457, length 77: HTTP: GET / HTTP/1.1
20:17:47.453663 IP 180.101.49.11.80 > 172.16.13.190.54444: Flags [.], ack 78, win 908, length 0
20:17:47.455084 IP 180.101.49.11.80 > 172.16.13.190.54444: Flags [P.], seq 1:1441, ack 78, win 908, length 1440: HTTP: HTTP/1.1 200 OK
20:17:47.455088 IP 172.16.13.190.54444 > 180.101.49.11.80: Flags [.], ack 1441, win 502, length 0
20:17:47.455091 IP 180.101.49.11.80 > 172.16.13.190.54444: Flags [P.], seq 1441:2782, ack 78, win 908, length 1341: HTTP
20:17:47.455094 IP 172.16.13.190.54444 > 180.101.49.11.80: Flags [.], ack 2782, win 547, length 0

断开连接


20:17:47.455172 IP 172.16.13.190.54444 > 180.101.49.11.80: Flags [F.], seq 78, ack 2782, win 547, length 0
20:17:47.464421 IP 180.101.49.11.80 > 172.16.13.190.54444: Flags [P.], seq 1441:2782, ack 78, win 908, length 1341: HTTP
20:17:47.464426 IP 172.16.13.190.54444 > 180.101.49.11.80: Flags [.], ack 2782, win 547, options [nop,nop,sack 1 {1441:2782}], length 0
20:17:47.466294 IP 180.101.49.11.80 > 172.16.13.190.54444: Flags [.], ack 79, win 908, length 0
20:17:47.466438 IP 180.101.49.11.80 > 172.16.13.190.54444: Flags [F.], seq 2782, ack 79, win 908, length 0
20:17:47.466444 IP 172.16.13.190.54444 > 180.101.49.11.80: Flags [.], ack 2783, win 547, length 0
20:17:50.484533 IP 180.101.49.11.80 > 172.16.13.190.54444: Flags [R], seq 2051860012, win 0, length 0