Useful headers

From the corresponding wikipedia articles.

https://en.wikipedia.org/wiki/IPv4

IPv4 header format

Offsets	Octet	0								1								2								3
Octet	Bit	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
0	0	Version				IHL				DSCP						ECN		Total Length
4	32	Identification																Flags			Fragment Offset
8	64	Time To Live								Protocol								Header Checksum
12	96	Source IP Address
16	128	Destination IP Address
20	160	Options (if IHL > 5)
⋮	⋮
60	480

https://en.wikipedia.org/wiki/IPv6_packet

IPv6 Header

Offsets	Octet	0								1								2								3
Octet	Bit	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
0	0	Version				Traffic class								Flow label
4	32	Payload length																Next header								Hop limit
8	64	Source address
12	96
16	128
20	160
24	192	Destination address
28	224
32	256
36	288

https://en.wikipedia.org/wiki/Transmission_Control_Protocol

TCP segment header

Offsets	Octet	0								1								2								3
Octet	Bit	7	6	5	4	3	2	1	0	7	6	5	4	3	2	1	0	7	6	5	4	3	2	1	0	7	6	5	4	3	2	1	0
0	0	Source port																Destination port
4	32	Sequence number
8	64	Acknowledgment number (if ACK set)
12	96	Data offset				Reserved 0 0 0			NS	CWR	ECE	URG	ACK	PSH	RST	SYN	FIN	Window Size
16	128	Checksum																Urgent pointer (if URG set)
20	160	Options (if data offset > 5. Padded at the end with "0" bytes if necessary.)
⋮	⋮
60	480

• URG 32
• ACK 16
• PSH 8
• RST 4
• SYN 2
• FIN 1

https://en.wikipedia.org/wiki/User_Datagram_Protocol

UDP datagram header

Offsets	Octet	0								1								2								3
Octet	Bit	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30	31
0	0	Source port																Destination port
4	32	Length																Checksum

DNS: https://datatracker.ietf.org/doc/html/rfc1035#section-4.1.1