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 */
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).
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).
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.
(1)Normal sequence chart (including active open/close, passive open/close)
(2)simultaneous open
(3)simultaneous close
zhangskd @ csdn blog