The TCP/IP Stack

A simple IP Header

[ Version | Length | DSCP | TTL | Protocol ]

• Version: 4 or 6, depending on whether IPv4 or IPv6 is being used
• Length: The length of the packet in bytes
• Differentiated Services Code Point: Contains bandwidth sensitive data (e.g. VoIP)
• Time To Live (TTL): A counter that is decremented every time a packet goes through a router. Maximum value is 255
• Protocol: Usually TCP or UDP

TCP

• Connection-Oriented Protocol
• Data is broken up and given a sequence number

Three Way Handshake

Used to start a TCP connection. This dance must be performed by two machines before they can send TCP data

1. SYN: Machine 1, “Are you there”
2. SYN-ACK: Machine 2, “Yes I’m Here”
3. ACK: Machine 1, “Cool, I’m sending data” (or requesting data, which is itself data…)

UDP

UDP Header

[ Source Port | Destination Port | Length | Checksum ]