Tcp/ip Flags Options

**kingaff** · 23-Feb-2007, 08:02 AM

wrote this small white paper to introduce you to the flags
in TCP headers. I hope you'll gain knowledge from this, and
if not.. bad luck ;-) So let's begin :

The TCP-header contains about 6 fields with one bit for flags.
There are currently 6 flags in a TCP-header and those are :

URG = This flag lets the receiving TCP-module know that the
the field of the Urgent Pointer points to urgent data.
(The TCP-Module needs to process urgent data than any
other data)

ACK = This flag notes that the field ACK-number has a valid
ACK-number. This helps TCP trusting the DATA.

PSH = This flag calls a PUSH. If this flag is on, then the
TCP-module has to send the data from the segment directly
to the target application. Normally, the TCP-Module would
keep the incoming data in a buffer and sends them untill
the target application's buffer is full. The PSH-flag lets
the TCP-Module know that the data of this segment does not
have to arrive in the buffer. Telnet-Applications for example
uses this flag. Because of that, TCP sends the inputted keys
of the user directly to the Telnet-server. This lets the user
see the typed-letters immediately, without lag.

RST = This flag asks the receiving TCP-module to let the connection
recover (reset). TCP sends a msg with this RST-flag if there
are any problems detected with the connection. Most of the
applications stops when they receive this flag, but it's
possible with the help of the RST-flag advanced algorithms
to write which programs can recover from crashes in hardware
or software.

SYN = This flag instructs the receiving TCP-Module to synchronize
sequence numbers. TCP uses this flag to let the receiving
TCP-Module know that the sender wants send new data.

FIN = This flag lets the receiving TCP-Module know that the sender
is finished with sending of data. This flag stops the data-
stream in one-way. The receiving TCP-Module has to send a
msg with the FIN-flag to close the whole connection.

Well that's a short introduction to TCP-Flags, for more information
i would recommend you to read RFC's, and other TCP/IP related books,
text-files and documents.

23-Feb-2007, 08:02 AM	#1 (permalink)
kingaff Fixed Error! Posts: 330 Join Date: Feb 2007 Rep Power: 2 IM:	Tcp/ip Flags Options wrote this small white paper to introduce you to the flags in TCP headers. I hope you'll gain knowledge from this, and if not.. bad luck ;-) So let's begin : The TCP-header contains about 6 fields with one bit for flags. There are currently 6 flags in a TCP-header and those are : URG = This flag lets the receiving TCP-module know that the the field of the Urgent Pointer points to urgent data. (The TCP-Module needs to process urgent data than any other data) ACK = This flag notes that the field ACK-number has a valid ACK-number. This helps TCP trusting the DATA. PSH = This flag calls a PUSH. If this flag is on, then the TCP-module has to send the data from the segment directly to the target application. Normally, the TCP-Module would keep the incoming data in a buffer and sends them untill the target application's buffer is full. The PSH-flag lets the TCP-Module know that the data of this segment does not have to arrive in the buffer. Telnet-Applications for example uses this flag. Because of that, TCP sends the inputted keys of the user directly to the Telnet-server. This lets the user see the typed-letters immediately, without lag. RST = This flag asks the receiving TCP-module to let the connection recover (reset). TCP sends a msg with this RST-flag if there are any problems detected with the connection. Most of the applications stops when they receive this flag, but it's possible with the help of the RST-flag advanced algorithms to write which programs can recover from crashes in hardware or software. SYN = This flag instructs the receiving TCP-Module to synchronize sequence numbers. TCP uses this flag to let the receiving TCP-Module know that the sender wants send new data. FIN = This flag lets the receiving TCP-Module know that the sender is finished with sending of data. This flag stops the data- stream in one-way. The receiving TCP-Module has to send a msg with the FIN-flag to close the whole connection. Well that's a short introduction to TCP-Flags, for more information i would recommend you to read RFC's, and other TCP/IP related books, text-files and documents.

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