IP protocol under Internet Layer protocol

Internet Layer Protocol Features

Running on the OSI network layer
Non-connection oriented protocol
Processing data packets independently
Layered addressing
Best effort transfer
No Data recovery function

The Internet layer mainly contains IP, ICMP, ARP, rarp several protocols.

This is a major IP protocol.

IP PDU Header

First line: 4bit identifies the protocol version of IP Good, now the generic ipv4;4bit identifies the length of the PDU header, 8bit partition service: Used to get a better service, known as the service type in the old standard, but has not actually been used. Renamed to Differentiated Services only in the use of differentiated services ( DiffServ), this field does not work. The total length of the 16bit message is not used in the general case.

The second line: 16bit identification: 16 bits, it is a counter, usually, each send a message, the value will be added 1, also for the packet Shard, in the same packet of several shards, the value is the same; 3bit flag: 3 bits, at present only two bits meaningful; slice offset: 12 bits, Refers to the relative position of a longer grouping in the original group after the Shard. Slice offset in 8 bytes
Indication: (flag): 3 digits, only the latter two is meaningful
Df:don ' t Fragment, the middle one, only allows shards when df=0
Mf:more Fragment, the highest, mf=1 indicates that there are shards behind. Mf=0 represents the Last Shard

The value of the slice offset can be well represented

You can see that the slice offset value is the position value of the first byte of each shard/8

The third line: 8bit time to live: The maximum number of routers that can be passed in the network, as a TTL, and 8bit protocol: identifies what protocol is used for the upper layer. TCP, UDP, ICMP, and so on.
The value of TTL can be modified by modifying the kernel to achieve a camouflage effect,
The Code of the Protocol is visible in the/etc/protocols file, which identifies the code of all common protocols

Line four: source IP address 32bit

Line five: Destination IP address 32bit

Range of IP addresses:

a:1-126
b:128-191
c:192-223
d:224-239 Multicast Address
e:240-255

IP protocol under Internet Layer protocol