TCP Flags

• TCP uses six 1-bit flags to manage a connection

• SYN (S)

• • Used to initialize sequence numbers
  • Only appears in the first packet sent by each host when a connection is established

• ACK (A)

• • Indicates that the acknowledgement number is valid
  • Almost always set once a connection is established

• PSH (P)

• • Indicates that the TCP data in the packet should be given to the application immediately
  • Mostly obsolete today, as this is normal receiver behavior