Packet Headers

This workshop is about crafting packets so it makes sense to spend enough time understanding what packets are and how they are structured.

Illustrations on this page are reproduced work created and shared by Matt Baxter as seen at https://nmap.org/book/tcpip-ref.html

IP Header

TCP Header

TCP flag	Binary	Decimal	TCP Dump syntax
URG	00100000	32	‘tcp[13] == 32’
ACK	00010000	16	‘tcp[13] == 16’
PSH	00001000	8	‘tcp[13] == 8’
RST	00000100	4	‘tcp[13] == 4’
SYN	00000010	2	‘tcp[13] == 2’
FIN	00000001	1	‘tcp[13] == 1’

SYN-ACK = 00010010 = 18
RST-ACK = 00010100 = 20

TCP flags mnemonic - Unskilled Attackers Pester Real Security Folks

UDP Header

ICMP Header

ARP Header