Ensuring someone is listening before telling a joke

  • Alice (speaking to Bob): Bob, I have a good joke to tell, can I call you at 12:00 ?
  • Bob (turns head towards Alice): OK, fine for me, but can we make it at 13:00 ?
  • Alice (nodding): Works for me.
  • At 13:00, Alice starts telling a joke.

Did you recognize the three way TCP handshake ?


  • Alice: Client
  • Bob: Server


  • I have a good joke to tell: TCP segment with SYN flag
  • 12:00: initial sequence number
  • OK: TCP segment with SYN and ACK flag
  • 13:00: acknowledgment number (initial sequence number + 1)
  • Works for me: TCP segment with ACK flag, acknowledgment of the server acknowledgment

More details on this in https://www.linuxjournal.com/article/6447 and remember tcpdump uses a dot(‘.’) to indicate segments with the ACK flag.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s