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_H enum {
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),
TCP_CLOSE_WAIT = (1 << 8),
TCP_LAST_ACK = (1 << 9),
TCP_LISTEN = (1 << 10),
TCP_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