IP Address Structure Introduction

techip · Joined: 14 Aug 2006 Posts: 16

An IP Address consists of a 32 bit logical address. The address is divided into two fields:

1) Network Address:
Assigned by InterNIC (Internet Network Information Center).
In fact most ISPs (internet service providers) purchase a number of addresses and assign them individually.

2) Host Address:
An address that identifies the single nodes throughout the network. It can be assigned by the network manager, by using protocols for it such as DHCP, or the workstation itself.

[The IP networking protocol is a logically routed protocol, meaning that address 192.13.84.9 will be on the same physical wire as address 192.13.84.10 (of course this is not always true. It depends on the subnet mask of the network, but all of that can fill a text of its own)

IP Address Structure:

---.---.---.---

^ ^
| |
network | host

Every " --- " = 8 bits.
The first bits ===> network address
The last bits ===> host address.

with 8 bits you can present from 0-255 . (binary=(2 to the power of -1)

Example:
11000010.01011010.00011111.01001010 (binary)
194.90.31.74 (decimal)

IP address CLASSES :
We can classify IP addreses to 5 groups. You can distinguish them by comparing the "High Order" bits (the first four bits on the
left of the address):
type | model | target | MSB |addr.range |bit number| max.stations|
| | groups | | |net./hosts| |
------|--------|--------|-----|--------------|----------|-------------|
A |N.h.h.h | ALL | 0 | 1.0.0.0 | 24/7 | 16,777,214 |
| | ACCEPT | | to | | |
| | HUGE | | 127.0.0.0 | | |
| | CORPS | | | | |
-----------------------------------------------------------------------
|N.N.h.h | TO ALL | 10 | 128.1.00 | 16/14 | 65,543 |
B | | LARGE | | to | | |
| | CORPS | | 191.254.00 | | |
-----------------------------------------------------------------------
|N.N.N.h |TO ALOT | 110 | 192.0.1.0 | 8/22 | 254 |
C | |OF | | to | | |
| |SMALL | | 223.225.254 | | |
| |CORPS | | | | |
-----------------------------------------------------------------------
D | NONE |MULTI-CA|1110 | 224.0.0.0 | NOT FOR | UNKNOWN |
| |ST ADDR.| | to | USUAL | |
| |RFC-1112| |239.255.255.255| USE | |
-----------------------------------------------------------------------
E | NOT FOR|EXPERIME|1,1,1,1| 240.0.0.0 |NOT FOR| NOT FOR USE|
| USE |NTAL | | to |USE | |
| |ADDR. | |254.255.255.255| | |
-----------------------------------------------------------------------

N=NETWORK , h=HOST .

Notice the address range 127.X.X.X.
These addresses are assigned to internal use to the network device, and are
used as an application tool only. For example: 127.0.0.1, the most common one, is called the loopback address - everything sent here goes directly back to you, without even traveling out on the wire.

Also, some IPs are reserved for VPNs - Virtual Private Networks. These are local area networks over wide area networks that use the Internet Protocol to communicate, and each computer inside the network is assigned with an IP address. So, suppose a certain computer wants to send a data packet to another host on the network with the IP 'x', but there's also another host on the Internet that has the same IP - what happens now? So this is why you cannot use these and other forms of reserved IPs on the Internet.

EXTRA:

Distinguishing different groups:

You have to compare the first byte on the left in the address as follows:

Type | First byte | MSB
| in decimal |
----------------------------
A | 1-127 | 0
----------------------------
B | 128-191 | 10
----------------------------
C | 192-223 | 110
----------------------------
D | 224-239 | 1110
----------------------------
E | 240-254 | 1111
----------------------------