Exploring TCP state machine by graphs

States

 

TCP includes 11 states, they are:

LISTEN

SYN_SENT

SYN_RECV

ESTABLISHED

FIN_WAIT1

CLOSE_WAIT

FIN_WAIT2

LAST_ACK

TIME_WAIT

CLOSED

CLOSING

 

@include/net/tcp_states.h：

/* Definitions for the TCP protocol sk_state field. */#ifndef _LINUX_TCP_STATES_H#define _LINUX_TCP_STATES_Henum {    TCP_ESTABLISHED = 1,    TCP_SYN_SENT,    TCP_SYN_RECV,    TCP_FIN_WAIT1,    TCP_FIN_WAIT2,    TCP_TIME_WAIT,    TCP_CLOSE,    TCP_CLOSE_WAIT,    TCP_LAST_ACK,    TCP_LISTEN,    TCP_CLOSING,    /* Now a valid state */    TCP_MAX_STATES    /* leave at the end! */};#define TCP_STATE_MASK 0xF#define TCP_ACTION_FIN (1 << 7)enum {    TCPF_ESTABLISHED = (1 << 1),    TCPF_SYN_SENT = (1 << 2),    TCPF_SYN_RECV = (1 << 3),    TCPF_FIN_WAIT1 = (1 << 4),    TCPF_FIN_WAIT2 = (1 << 5),    TCPF_TIME_WAIT = (1 << 6),    TCPF_CLOSE = (1 << 7),    TCPF_CLOSE_WAIT = (1 << 8),    TCPF_LAST_ACK = (1 << 9),    TCPF_LISTEN = (1 << 10),    TCPF_CLOSING = (1 << 11)};#endif /* _LINUX_TCP_STATES_H */

 

View of Server

 

Passive open and passive close often performed by Server, the normal routine is illustrated as follow.

I denote the passive open/close transitions with a blue line (normal transitions are in bold).

 

View of Client

 

Ative open and Active close often performed by Client, the normal routine is illustrated as follow.

I denote the active open/close transitions with a green line (normal transitions are in bold).

 

As a whole

 

We know while most TCP state transitions are normal, it also has some unnormal transitions, including:

simultaneous open

simultaneous close

RST and etc.

I use dashed line to denote this kind of transitions.

 

 

 

 

 

Sequence chart

 

（1）Normal sequence chart (including active open/close, passive open/close)

 

 

（2）simultaneous open

 

 

 （3）simultaneous close

 

     

 

Author

 

zhangskd @ csdn blog