Transmission Control Protocol Flashcards
Row 1 contents
Source port, destination port
source and destination ports
Purpose: determine what port the communication came from (source) and where it’s going to (destination)
Size: 2B
Row 2 contents
sequence number
By the source machines, TCP stack and is used to make certain that packets are arranged in the proper sequence when they arrive
Extra: important for defeating man in the middle attacks
Row 3 contents
Acknowledge number
Echo of the sequence number sent back by the receiving system. If the package is not received by the sender in a fixed amount of time another request is made
Row four contents
Data offset, reserved, TCP, flags, window size
TCP flags
FIN:the normal soft closing of a connection
SYN: the opening of a connection
RST: hard to close of a connection; usually use to communicate a packet, arrived at the wrong port
PSH:push the data past the buffer to the application
ACK:acknowledgment of a packet; all packets after a three-way handshake, should have this set
URG:indicates the following data is urgent
Window size
Row: three
Purpose: communicate the size of the window. The TCP stack has to buffer packets; can identify the OS that sent the packet.
Size: 2B
Row five contents
Checksum, urgent pointer
Checksum
Row: five
Purpose: uses a simple algorithm to check for errors; I.E. An integrity checker.
size: 2B
URG pointer
Row: five
Purpose: points to the last bite of the sequence number of urgent data; URG must be set to activate this field
Row six contents
Options
Like IP options varies in length
Padding
Necessary to bring TCP header to a multiple of 32 bits
describe the three steps of a TCP three-way handshake
Step one: client sends a packet with the SYN flag
Step two: server response with a packet with the SYN – ACK flag
Step three: client sends a packet with the ACK flag set that acknowledges the response of the sender
Data transfer can begin after this
