tcp和ip的格式

.-------+-------+---------------+---------------------------------.
|Version | IHL |Type of Service | Total Length |
|-------+-------+---------------+--------------------------------|
| Identification |Flags| Fragment Offset |
|---------------+---------------+---------------------------------|
| Time to Live | Protocol | Header Checksum |
|---------------+---------------+---------------------------------|
| Source Address |
|-------------------------------------------------------------------|
| Destination Address |
`-------------------------------------------------------------------'

version:协议的版本号,目前主要是ipv4
type of service:可以是最小时延,最大吞吐量,最高可靠性,最小费用
total length:数据包长度

.-------------------------------+----------------------------------.
| Source Port | Destination Port |
|-------------------------------+----------------------------------|
| Sequence Number |
|-------------------------------------------------------------------|
| Acknowledgment Number |
|-------------------+-+-+-+-+-+-+-----------------------------|
| Data | |U|A|P|R|S|F| |
| Offset| Reserved |R|C|S|S|Y| I | Window |
| | |G|K|H|T|N|N| |
|-------+----------------+-+-+-+-+-+-+-----------------------|
| Checksum | Urgent Pointer |
`-------------------------------------------------------------------'

URG:紧急指针有效位
ACK:确认位
PSH:紧急上传位
RST:连接重置位
SYN:同部位,用于初始化
FIN:终止连接位