The IP datagram

Carries enough information to let the network forward packet to destination in a connectionless way.

Unreliable or best effort service - network does not attempt recovery from failed delivery.

Source address

Destination address

Options

(variable)

Pad

(variable)

TTL

Protocol

Checksum

Data

Ver.

HLen

TOS

Length

Ident

Flags

Offset

0

4

8

19

31

16

IP Packet format (IPv4)

Header is arranged in 32-bit words

Ver. Current version is IPv4

HLen. Length of header in 32-bit words

TOS Type of service

(low delay, high-throughput, or high reliability)

Length 16-bit length of datagram (including header)

in Bytes. Maximum size is 65,535 Bytes

Because the physical network may not support datagrams

this long IP supports fragmentation and reassembly

TTL time to live or hop counter (64 hop default)

Protocol Demultiplexing key, e.g. TCP = 6 , UDP = 17

Checksum 16-bit checksum of the IP header

Options Rarely used

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