Tuma,
take a look at this state diagram from
<http://www.faqs.org/rfcs/rfc793.html>
personally, I don't think you can describe this diagram in words and
get it right, especially if you're trying to get it by playing
"20 questions"...
hope this helps,
-Pete.
(actually, you should take a look at the rfc webpage, and read the
information around this diagram....)
September 1981
Transmission Control Protocol
Functional Specification
+---------+ ---------\ active OPEN
| CLOSED | \ -----------
+---------+<---------\ \ create TCB
| ^ \ \ snd SYN
passive OPEN | | CLOSE \ \
------------ | | ---------- \ \
create TCB | | delete TCB \ \
V | \ \
+---------+ CLOSE | \
| LISTEN | ---------- | |
+---------+ delete TCB | |
rcv SYN | | SEND | |
----------- | | ------- | V
+---------+ snd SYN,ACK / \ snd SYN +---------+
| |<----------------- ------------------>| |
| SYN | rcv SYN | SYN |
| RCVD |<-----------------------------------------------| SENT |
| | snd ACK | |
| |------------------ -------------------| |
+---------+ rcv ACK of SYN \ / rcv SYN,ACK +---------+
| -------------- | | -----------
| x | | snd ACK
| V V
| CLOSE +---------+
| ------- | ESTAB |
| snd FIN +---------+
| CLOSE | | rcv FIN
V ------- | | -------
+---------+ snd FIN / \ snd ACK +---------+
| FIN |<----------------- ------------------>| CLOSE |
| WAIT-1 |------------------ | WAIT |
+---------+ rcv FIN \ +---------+
| rcv ACK of FIN ------- | CLOSE |
| -------------- snd ACK | ------- |
V x V snd FIN V
+---------+ +---------+ +---------+
|FINWAIT-2| | CLOSING | | LAST-ACK|
+---------+ +---------+ +---------+
| rcv ACK of FIN | rcv ACK of FIN |
| rcv FIN -------------- | Timeout=2MSL -------------- |
| ------- x V ------------ x V
\ snd ACK +---------+delete TCB +---------+
------------------------>|TIME WAIT|------------------>| CLOSED |
+---------+ +---------+
TCP Connection State Diagram
Figure 6.
Wang wrote On 07/18/07 07:40 PM,:
> Hi,
>
> I have some questions regarding some TCP concepts.
>
> According to Richard Stevens, when the active-close end of a TCP
> connection sends FIN and receives the corresponding ACK from the other
> end, the connection is "half closed". In this state, the active-close
> end cannot send but can receive date from its peer.
>
> Question 1: it sounds the "half closed" state is the same as the
> WAIT_FIN_2 state?
>
> Question 2: when the passive-close end receives the FIN, how does it
> know whether the other end wants to stay in the half closed state (in
> this case, it should send data) or to do a full close (in this case,
> it should send FIN)?
> Seems half-close is achieved by using the shutdown() function, so in
> other words, both close() and shutdown() cause FIN to be sent, but
> what's the difference between them so that close() causes the peer to
> send FIN also, while shutdown() caused the peer to delay the FIN?
>
> According to Richard, "A TCP connection is said to be half-open if one
> end has closed or aborted the connection without the knowledge of the
> other end."
>
> Question 3: what's meaning of "without the knowledge of the other
> end"? Does it mean "don't know the status of the other end", or "the
> other end doesn't know that I've closed/aborted the connection"?
>
> Question 4: seems the term "half open" is also used in the context of
> the SYN flood DoS attack, to describe the state of "SYN sent and
> SYN-ACK received, but the last ACK not sent". Clearly the "half open"
> here is not same as the one we talked above. Is it a valid usage of
> this term?
>
> Thanks.
> _______________________________________________
> networking-discuss mailing list
> [email protected]
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