Differences between current version and previous revision of TcpStates.
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| Newer page: | version 7 | Last edited on Thursday, May 26, 2005 9:23:01 pm | by AristotlePagaltzis | |
| Older page: | version 6 | Last edited on Thursday, May 26, 2005 3:50:19 pm | by DanielLawson | Revert |
@@ -1,33 +1,37 @@
-States of a [TCP] connection.
These can be seen with
-
netstat -at
+States of a [TCP] connection. These can be seen with <tt>
netstat -at</tt>
-;
CLOSED:A theoretical state where a [TCP] connection doesn'
t exist yet.
-;
LISTEN:A state where [TCP] connection is waiting for a connection to be made to it.
-;
SYN_RCVD: A [SYN] has been received, a SYN ACK has been sent, and we are waiting for an [ACK]
-;
SYN_SENT: A [SYN] has been sent to start a connection, the SYN ACK hasn'
t yet been received.
-;
ESTABLISHED: A connection has been established
-;
CLOSE_WAIT:After a [TCP] connection has been closed, the spec says you should make sure that the connection is not reopened for a few minutes to prevent packets that were delayed in the Internet causing the connection to be reopened.
These will disappear by themselves after a while.
This can cause problems on servers that have lots of very short connections (such as a web server) by filling up the OS'
s connection table. See also [EADDRINUSE]
-;
LAST_ACK:A [FIN] has been received, we'
ve sent our own FIN, but we are waiting on the ACK before we can move to the closed state.
-;
FIN_WAIT_1:A FIN has been sent, waiting for a ACK or FIN
-;
FIN_WAIT_2:A FIN has been sent, and an ACK has been received.
More data can be received.
This connection is half open.
-;
CLOSING:A FIN has been sent, and one received, the FIN hasn'
t been ACK'd
yet.
-;
TIME_WAIT:The connection has closed, and is waiting for 2MSL
-----
-The amount of time that a connection waits in various stages is controlled by the OperatingSystem. Some OS'es let you tune these settings. For example, for Linux-based OSes, look in /proc/sys/net/ipv4.
+<tt>
CLOSED</tt>
:
+
A theoretical state where a [TCP] connection doesn’
t exist yet.
+<tt>
LISTEN</tt>
:
+
A state where [TCP] connection is waiting for a connection to be made to it.
+<tt>
SYN_RCVD</tt>
:
+
A [SYN] has been received, a [
SYN] [
ACK]
has been sent, and we are waiting for an [ACK].
+<tt>
SYN_SENT</tt>
:
+
A [SYN] has been sent to start a connection, the [
SYN] [
ACK]
hasn’
t yet been received.
+<tt>
ESTABLISHED</tt>
:
+
A connection has been established
+<tt>
CLOSE_WAIT</tt>
:
+
After a [TCP] connection has been closed, the spec says you should make sure that the connection is not reopened for a few minutes to prevent packets that were delayed in the Internet causing the connection to be reopened. These will disappear by themselves after a while. This can cause problems on servers that have lots of very short connections (such as a web server) by filling up the OS’
s connection table. See also [EADDRINUSE]
+<tt>
LAST_ACK</tt>
:
+
A [FIN] has been received, we’
ve sent our own FIN, but we are waiting on the [
ACK]
before we can move to the closed state.
+<tt>
FIN_WAIT_1</tt>
:
+
A [
FIN]
has been sent, waiting for a [
ACK]
or [
FIN]
+<tt>
FIN_WAIT_2</tt>
:
+
A [
FIN]
has been sent, and an [
ACK]
has been received. More data can be received. This connection is half open.
+<tt>
CLOSING</tt>
:
+
A [
FIN]
has been sent, and one received, the [
FIN]
hasn’
t been [
ACK]ed
yet.
+<tt>
TIME_WAIT</tt>
:
+
The connection has closed, and is waiting for 2MSL
-From /usr/src/linux/Documentation/filesystems/proc.txt:
+!! Tuning your system’s settings
-tcp_syn_retries:
- Number
of times initial SYNs for
a TCP
connection attempt will be retransmitted
. Should not be higher than 255
. This is only the timeout
for outgoing connections
, for incoming connections
the number of retransmits is defined by tcp_retries1
.
+The amount
of time that
a connection waits in various stages is controlled by the OperatingSystem
. Some [OS]es let you tune these settings
. For example,
for [Linux]-based [OS]es
, look at
the control files in <tt>/proc/sys/net/ipv4</tt>. According to <tt>/usr/src/linux/Documentation/filesystems/proc
.txt</tt>:
-tcp_fin_timeout:
- The length
of
time
in
seconds
it
takes to receive a final FIN before the
-
socket is
always
closed.
This
is
strictly
a
violation
of
the
TCP
-
specification, but required to prevent denial-of-service attacks.
-
-
- Defines how
often
an
answer
to
a
TCP connection request is retransmitted
-
before giving up.
-
-
- Defines how often a TCP packet is retransmitted before giving up.
+<tt>tcp_syn_retries</tt>:
+ Number of times initial [SYN]s for a [TCP] connection attempt will be retransmitted. Should not be higher than 255. This is only the timeout for outgoing connections, for incoming connections the number of retransmits is defined by <tt>tcp_retries1</tt>.
+<tt>
tcp_fin_timeout</tt>
:
+ The length of time in seconds it takes to receive a final [
FIN]
before the socket is always closed. This is strictly a violation of the [
TCP]
specification, but required to prevent denial-of-service attacks.
+<tt>
tcp_retries1</tt>
:
+ Defines how often an answer to a [
TCP]
connection request is retransmitted before giving up.
+<tt>
tcp_retries2</tt>
:
+ Defines how often a [
TCP]
packet is retransmitted before giving up.
