浅谈HTTP（简）TCP概念深入

Posted 2021-06-24 Adorable_Rocy

前言：当一个HTTP请求发送出去时，例如（www.baidu.com），是如何解析他的地址的呢？

1.DNS

1.当域名被传入过来的时候，会依据DNS服务器进行解析，得到域名的IP地址，向目标地址发送请求

[root@FATCATS network-scripts]# cat ifcfg-eth0 
DEVICE="eth0"
BOOTPROTO="dhcp"
ONBOOT="yes"
TYPE="Ethernet"
PERSISTENT_DHCLIENT="yes"

拓展：dhcp是动态分配IP地址，会根据当前网段进行IP地址的分发，从而完成无需手动分配也能获取分配的IP地址

2.以太网卡

我们可以根据自己的需定，创建网卡，我们在这里拓展已存在的网卡

[root@FATCATS network-scripts]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether fa:16:3e:87:18:ba brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.91/24 brd 192.168.0.255 scope global noprefixroute dynamic eth0
       valid_lft 55356sec preferred_lft 55356sec
    inet6 fe80::f816:3eff:fe87:18ba/64 scope link 
       valid_lft forever preferred_lft forever

A：这个网卡是做什么的呢？
B：网卡中有mac地址以及IP地址，可以通过IP地址ping通

3.抓包

抓取80端口的数据包：tcpdump -nn -i eth0 port 80 or arp

[root@FATCATS ~]# tcpdump -nn -i eth0 port 80 or arp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes

11:20:35.893420 IP 192.168.0.91.33446 > 180.101.49.12.80: Flags [S], seq 3059338248, win 29200, options [mss 1460,sackOK,TS val 775175501 ecr 0,nop,wscale 7], length 0
11:20:35.904263 IP 180.101.49.12.80 > 192.168.0.91.33446: Flags [S.], seq 3944752105, ack 3059338249, win 8192, options [mss 1452,sackOK,nop,nop,nop,nop,nop,nop,nop,nop,nop,nop,nop,wscale 5], length 0
11:20:35.904284 IP 192.168.0.91.33446 > 180.101.49.12.80: Flags [.], ack 1, win 229, length 0

11:20:35.904356 IP 192.168.0.91.33446 > 180.101.49.12.80: Flags [P.], seq 1:78, ack 1, win 229, length 77: HTTP: GET / HTTP/1.1
11:20:35.915403 IP 180.101.49.12.80 > 192.168.0.91.33446: Flags [.], ack 78, win 908, length 0
11:20:35.916379 IP 180.101.49.12.80 > 192.168.0.91.33446: Flags [.], seq 1:1453, ack 78, win 908, length 1452: HTTP: HTTP/1.1 200 OK
11:20:35.916388 IP 192.168.0.91.33446 > 180.101.49.12.80: Flags [.], ack 1453, win 251, length 0
11:20:35.916397 IP 180.101.49.12.80 > 192.168.0.91.33446: Flags [P.], seq 1453:2782, ack 78, win 908, length 1329: HTTP
11:20:35.916403 IP 192.168.0.91.33446 > 180.101.49.12.80: Flags [.], ack 2782, win 274, length 0
11:20:35.916517 IP 192.168.0.91.33446 > 180.101.49.12.80: Flags [F.], seq 78, ack 2782, win 274, length 0
11:20:35.925923 IP 180.101.49.12.80 > 192.168.0.91.33446: Flags [P.], seq 1453:2782, ack 78, win 908, length 1329: HTTP
11:20:35.925937 IP 192.168.0.91.33446 > 180.101.49.12.80: Flags [.], ack 2782, win 274, options [nop,nop,sack 1 {1453:2782}], length 0
11:20:35.927487 IP 180.101.49.12.80 > 192.168.0.91.33446: Flags [.], ack 79, win 908, length 0
11:20:35.927609 IP 180.101.49.12.80 > 192.168.0.91.33446: Flags [F.], seq 2782, ack 79, win 908, length 0
11:20:35.927619 IP 192.168.0.91.33446 > 180.101.49.12.80: Flags [.], ack 2783, win 274, length 0

如上图所示：三次握手的过程

# FLAG1
11:20:35.893420 IP 192.168.0.91.33446 > 180.101.49.12.80: Flags [S], seq 3059338248, win 29200, options [mss 1460,sackOK,TS val 775175501 ecr 0,nop,wscale 7], length 0
# FLAG2
11:20:35.904263 IP 180.101.49.12.80 > 192.168.0.91.33446: Flags [S.], seq 3944752105, ack 3059338249, win 8192, options [mss 1452,sackOK,nop,nop,nop,nop,nop,nop,nop,nop,nop,nop,nop,wscale 5], length 0

11:20:35.904284 IP 192.168.0.91.33446 > 180.101.49.12.80: Flags [.], ack 1, win 229, length 0

FLAG1:

• Client —> Server
• Flags [S] , seq 3059338248, win 29200
• S --> SYN

FLAG2:

• Sever —> Client
• Flags [S.] , seq 3944752105, ack 3059338249, win 8192
• SYN + ack(. 代表的就是ack)
• ack = 3059338249 序列号是+1的

三次握手完整过程如上所示