IPv4 Packet Structure

bit offset	0–3				4–7				8–13						14-15		16–18			19–31
0	Version				Header Length				Differentiated Services Code Point						Explicit Congestion Notification		Total Length
32	Identification																Flags			Fragment Offset
64	Time to Live								Protocol								Header Checksum
96	Source IP Address
128	Destination IP Address
160	Options ( if Header Length > 5 )
160 or 192+	Data

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 Basic IPv6 Header – Hop-by-Hop Options 0 Destination Options (with Routing Options) 60 Routing Header 43 Fragment Header 44 Authentication Header 51 Encapsulation Security Payload Header 50 Destination Options 60 Mobility Header 135 No next header 59 TCP 6 UDP 17 ICMPv6 58								Hop Limit
8	64	Source Address
12	96
16	128
20	160
24	192	Destination Address
28	224
32	256
36	288

Extension Header = Routing Header (#43)

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
40	320	Next Header = Destination Options (#60)								HdrExLen								Rout. Type								Seg. Left
44	352	Reserved
48	384	Home B

Extension Header = Destination Options (#60)

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
52	416	Next Header = Fragment Header (#44)								HdrExLen								Opt. Type								Opt. Len
56	448	0								0								Opt. Type								Opt. Len
60	480	Home A

Extension Header = Fragment Header (#44)

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
64	512	Next Header = TCP (#6)								Reserved								Fragment Offset											Res			M
68	544	Identification