------------------------
 |     TCP/IP Flags     |
 |         by:          |
 |      Neon-Lenz®      |
 ------------------------


 I 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.

 Spreaded by Neon-Lenz® and The Millennium Hackers Association.
 Copyrighted and All Rights Reserved®
 E-Mail:neonlenz@hackermail.net 
 -2000- http://www.mha1.8m.com