Cheatography
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In this cheat sheet, TCP and UDP headers will be reviewed.
Transport Layer
Number of Layer |
4th Layer of OSI Model |
Role |
Transport Data |
Protocols |
UDP - TCP |
PDU (Protocol Data Unit) |
Segment |
Address |
Port Number |
UDP Features
Type of Connection |
Connectionless (Does Not Need Connection Setup) |
Application |
Time-Sensitive Connections |
Number of Fields in Header |
Four Field Header |
TCP Features
Type of Connection |
Connection-Oriented (Needs Connection Setup) |
Application |
Reliable Connections |
Number of Fields in Header |
Eleven Field Header |
Commands
Active UDP Connections |
|
Active TCP Connections |
|
UDP Header Fields
Source Port 16-bit |
Port on The Receiver's Side |
Destination Port 16-bit |
Port on The Sender's Side |
Length 16-bit |
The Number of Bytes in The UDP Header And Any Data Follows |
Checksum 16-bit |
Calculated Value for Ensuring Data Integrity |
TCP Ports
Source Port 16-bit |
The Port on The Sender Side |
Destination Port 16-bit |
The Port on The Receiver Side |
Stream |
A Communication Between Two Endpoints |
TCP Segment Length |
The Value of The TCP Payload (The Data That Follows The TCP Header) |
|
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Sequencing and Acknowledging in TCP
Sequence Number 32-bit |
The Byte Number of The First Byte of Data |
Next Sequence Number |
Current Sequence Number Plus The TCP Segment Length |
Acknowledgment Number 32-bit |
The Sequence Number of The Next Byte The Receiver Expects to Receive |
Offset |
Indicates The Length of The TCP Header |
Flags in TCP
Reserved |
3-bit |
For Future Use |
Nonce |
1-bit |
Experimental Use |
CWR |
1-bit |
Respond to Indications of Network Congestion with Congestion Avoidance |
ECE |
1-bit |
Notify The Endpoints of Any Network Congestion to Avoid Dropping Packets |
URG |
1-bit |
Indicates a Packet That Should Have Priority |
ACK |
1-bit |
Acknowledging The Data Was Received |
PSH |
1-bit |
Informing Data Should Be Sent Immediately |
RST |
1-bit |
Aborting The TCP Connection |
SYN |
1-bit |
Synchronizing The Sequence Numbers |
FIN |
1-bit |
closing The Connection |
Dissecting Window Size
Window Size 16-bit |
Controls The Flow of Data |
Scaling Factor |
A Value For Expanding Window Size |
Window Size Scaling Factor |
2 ^ (Scaling Factor) if Scaling Factor >= 0 |
Calculated Window Size |
Window Size * Window Size Scaling Factor |
Additional Header Values in TCP
Checksum |
A Calculated Value For Error Detection |
Urgent Pointer |
Points to The Sequence Number of Urgent Data |
Options |
Extra Options Like Timestamps And No-operation |
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