4

8

16

32 bits

Ver

IHL

Type of Service/
DSCP & ECN

total length

Identification

 Flags |      Fragment offset

Time to Live

Protocol

Header checksum

Source address

Destination address

Options + Padding

Data

Vers

Version - mark the used version of the IP-protocol, "4" for V4

IHL

Internet Header Length - length of the IP-Header in units of 32 bits (min. 5)

Type of Service























Differentiated Service

old interpretation
Establishing of a service kindliness - for example priority, dilatory installment, reliability

Prec	0	Routine
	1	Priority
	2	Immediate
	3	Flash
	4	Flash override
	5	CRITIC/ECP
	6	Internetwork control
	7	Network control
D	Low delay
T	High throughput
R	High reliability
M	Minimize monetary cost

new interpretation
The DSCP Feld, defined in the RFC2474, replaces the Type Of Sevice Feld (RFC3168) for IPv4

ECN-bits	xx
ECN-Capable Transport (ECT)
Congestion Experienced (CE)
Class Selector PHB (Per Hop Behavior)	xxx000
Assured Forwarding PHB (AF PHB) / Expedited Forwarding PHB (EF PHB)	all other

total length

total length (header + data) of the IP datagram

Identification

for reassembling of fragments

Flags

Fragment offset

position of the current fragment in the datagram in units of 64 bits

Time to Live

Lifespan during handling by router (discarding of the datagram with 0)

Protocol

Transportation protocol (TCP,UDP,ICMP,...)

Header checksum

Checksum of the harder, recalculation through each router (without data)

Source address

senders IP-address

Destination address

receivers IP-address

Options + Padding

optional parameters (0..40 bytes)

C	Copy
Class	0	Control
	1	"Reserved"
	2	Debugging ans measurement
	3	"Reserved"
Option	0	End of Option list
	1	NOP
	2	Security
	3	Loose Source Route
	4	Time stamp	[RFC781],[RFC791]
	5	Extended Security	[RFC1108]
	6	Commercial Security
	7	Record Route	[RFC791]
	8	Strem Identifier	[RFC791],[RFC1122]
	9	Strct Source Route	[RFC791]
	10	Experimental Measurement
	11	MTU Probe	[RFC1063]
	12	MTU Reply	[RFC1063]
	13	Experimental Flow Control
	14	Experimental Access Control
	15
	16	IMI Traffic Descriptor
	17	Extended Internet Proto
	18	Traceroute	[RFC1393]
	19	Adress Extension	[RFC1475]
	20	Router Alert	[RFC2113]
	21	Selective Directed Broadcast Mode	[RFC1770]
	22	NSAP Addresses
	23	Dynamic Packet State
	24	Upstream Multicast Packet
	...

plus filling byte on 32-bit-borders

4

8

16

24

32 bits

Ver

Priority

Flow label

Payload length

Next header

Hop limit

Source address
(128 bits)

Destination address
(128 bits)