“A UDP packet walks into a bar. The bartender doesn’t acknowledge him.”
"TCP packet tries to get past the firewall on the way to the bar. Firewall says “hey, you’re out of order”."
"FTP-​​data packet tries to get past the checkpoint firewall when someone changed the bar policy. “Hey, first packet is not SYN”"
"A broadcast walk into the bar, everyone stops what they are doing to look"
"An IPv6 NS packet walks into a bar and yells, “Is anyone in here named John Smith?”. When no one answers, he sits down and orders a beer."