最近在写tcp/ip的下位机，所以学了不少关于网络和协议的东西。总体上来说，很复杂。不过还是有据可循的。
这是通过wireshark抓包得到的
这是一个简单的ping命令，得到的数据。
Frame 207: 74 bytes on wire (592 bits), 74 bytes captured (592 bits) 线路上传输了74字节，实际接收74个字节
Arrival Time: Jan 1, 2000 08:09:10.326362000 中国标准时间 时间
Epoch Time: 946685350.326362000 seconds 包间隔时间
Time delta from previous captured frame: 0.087277000 seconds
Time delta from previous displayed frame: 0.087277000 seconds
Time since reference or first frame: 12.473428000 seconds
Frame Number: 207
Frame Length: 74 bytes (592 bits) 帧长度
Capture Length: 74 bytes (592 bits) 捕获长度
Frame is marked: False
Frame is ignored: False
Protocols in frame: eth:ip:icmp:data 协议层级
Coloring Rule Name: ICMP 包含协议
Coloring Rule String: icmp || icmpv6
Ethernet II, Src: D-Link_60:3b:42 (f0:7d:68:60:3b:42), Dst: Tp-LinkT_4f:6f:f2 (94:0c:6d:4f:6f:f2)
源mac地址 目标mac地址
Destination: Tp-LinkT_4f:6f:f2 (94:0c:6d:4f:6f:f2)
Address: Tp-LinkT_4f:6f:f2 (94:0c:6d:4f:6f:f2)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
. ... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Type: IP (0x0800) ip类型
Internet Protocol, Src: 192.168.1.111 (192.168.1.111), Dst: 192.168.1.1 (192.168.1.1)
源ip地址 目标ip地址
Version: 4 版本号
Header length: 20 bytes 头字节长度
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00) 差分服务字段
0000 00.. = Differentiated Services Codepoint: Default (0x00)
.... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 60 IP包长度
Identification: 0x31e7 (12775) 标志字段 不一样，具体为什么不知道
Flags: 0x00 标记字段
Fragment offset: 0 分段偏移
Time to live: 64 生存期
Protocol: ICMP (1) 包内封装协议
Header checksum: 0xc519 [correct] 头校验
Source: 192.168.1.111 (192.168.1.111) 源ip
Destination: 192.168.1.1 (192.168.1.1) 目标ip
Internet Control Message Protocol
Type: 8 (Echo (ping) request) 类型：请求
Code: 0 代码：0
Checksum: 0x495c [correct] 校验
Identifier: 0x0300 标识码
Sequence number: 256 (0x0100) 序列码，应该是ping一次加一次
Sequence number (LE): 1 (0x0001)
Data (32 bytes) 数据
Data: 6162636465666768696a6b6c6d6e6f707172737475767761...
Length: 32
源mac地址 目标mac地址 ip类型 版本与字节数
94 0c 6d 4f 6f f2 f0 7d 68 60 3b 42 08 00 45 00
Ip包长 标志段 标记 偏移 生存期 icmp包 头检验 源ip
00 3c 31 e7 00 00 40 01 c5 19 c0 a8 01 6f
目标ip 类型 校验 标识码 序列码 数据
c0 a8 01 01 08 00 49 5c 03 00 01 00 61 62 63 64 65 66
67 68 69 6a 6b 6c 6d 6e 6f 70 71 72 73 74 75 76
77 61 62 63 64 65 66 67 68 69