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Topic: Format, Classification and Distribution Of IP Address |
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AllAboutIP
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| Format, Classification and Distribution Of IP Address |
Conceptually, a 32-bit IP address takes the format of
ClassId | NetworkId | HostId
ClassId -- for classification of IP address;
NetworkId -- for identifying which network the IP address belongs to
HostId -- for identifying the host
Defining IP address in such a way is to extract each portion quickly.
Spencer
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AllAboutIP
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| Classification Based On ClassId |
IP address can be classified among 5 classes, based on ClassId
...................0........8........16.......24.....31
..................+--------+--------+--------+--------+
..Class A.........|0.NetId.|...........HostId.........|
..................+--------+--------+--------+--------+
..Class B.........|10......NetId....|.....HostId......|
..................+--------+--------+--------+--------+
..Class C.........|110.........NetId.........|.HostId.|
..................+--------+--------+--------+--------+
..Class D.........|1110.......multicast address.......|
..................+--------+--------+--------+--------+
..Class E.........|11110....reserved for future use...|
..................+--------+--------+--------+--------+
In humans friendly format:
....................Lowest Address....Highest Address
------------------+-----------------+-----------------+
..Class A.........|.....0.1.0.0.....|.126.0.0.0.......|
..................+-----------------+-----------------+
..Class B.........|...128.1.0.0.....|.191.255.0.0.....|
..................+-----------------+-----------------+
..Class C.........|...192.0.1.0.....|.223.255.255.0...|
..................+-----------------+-----------------+
..Class D.........|...224.0.0.0.....|.239.255.255.255.|
..................+-----------------+-----------------+
..Class E.........|...240.0.0.0.....|.247.255.255.255.|
..................+-----------------+-----------------+
where, 127.0.0.0 is reserved for loopback and inter-process communication on the local machine; all 0s refers to network itself; and all 1s is reserved for broadcasting.
Spencer |
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AllAboutIP
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Portland, OR |
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| IP Address Distribution Among Classes |
As shown above, Class A devotes 7 bits to network ID which counts for 2^7=128 networks and 24 bits to host ID which counts for 2^24=16,777,216 hosts within each network.
So, only handful of networks belong to Class A. Who are they? Here is a partial list of them with the gigantic Class A network:
----Class A IP Address ------ Organization
--------------------------+-------------------------
3.0.0.0 – 3.255.255.255 --- GE
4.0.0.0 – 4.255.255.255 --- Level 3
6.0.0.0 – 7.255.255.255 --- DOD
8.0.0.0 – 8.255.255.255 --- Level 3
9.0.0.0 – 9.255.255.255 --- IBM
11.0.0.0 – 11.255.255.255 --- DOD
12.0.0.0 – 12.255.255.255 --- AT&T
13.0.0.0 – 13.255.255.255 --- Xerox
15.0.0.0 – 15.255.255.255 --- HP
16.0.0.0 – 16.255.255.255 --- DEC
17.0.0.0 – 17.255.255.255 --- Apple
18.0.0.0 – 18.255.255.255 --- MIT
19.0.0.0 – 19.255.255.255 --- Ford
20.0.0.0 – 20.255.255.255 --- CS
21.0.0.0 – 22.255.255.255 --- DOD
24.0.0.0 – 24.255.255.255 --- Various U.S. Cable Networks
25.0.0.0 – 25.255.255.255 --- Royal Signals and Radar Establishment
26.0.0.0 – 26.255.255.255 --- DOD
28.0.0.0 – 30.255.255.255 --- DOD
32.0.0.0 – 32.255.255.255 --- AT&T
33.0.0.0 – 33.255.255.255 --- DOD
34.0.0.0 – 34.255.255.255 --- Halliburton
35.0.0.0 – 35.255.255.255 --- Merit Network
38.0.0.0 – 38.255.255.255 --- Performance Systems International
40.0.0.0 – 40.255.255.255 --- Eli Lilly and Company
41.0.0.0 – 41.255.255.255 --- AfriNIC
43.0.0.0 – 43.255.255.255 --- Japan Inet
44.0.0.0 – 44.255.255.255 --- Amateur Radio Digital Communications
45.0.0.0 – 45.255.255.255 --- Interop Show Network
47.0.0.0 – 47.255.255.255 --- Bell
48.0.0.0 – 48.255.255.255 --- Prudential
51.0.0.0 – 51.255.255.255 --- Department of Social Security of UK
52.0.0.0 – 52.255.255.255 --- DuPont
53.0.0.0 – 53.255.255.255 --- Mercedes-Benz
54.0.0.0 – 54.255.255.255 --- Merck
55.0.0.0 – 55.255.255.255 --- DOD
56.0.0.0 – 56.255.255.255 --- USPS
57.0.0.0 – 57.255.255.255 --- SITA
58.0.0.0 – 61.255.255.255 --- APNIC
62.0.0.0 – 62.255.255.255 --- RIPE
63.0.0.0 – 63.127.255.255 --- UUNet
73.0.0.0 – 73.191.255.255 --- Comcast
80.0.0.0 – 80.255.255.255 --- RIPE
Class B address devotes 16 bits to host ID which accounts for 2^16=65,536 hosts within each network.
Class C address devotes 8 bits to host ID which means that a Class C network can have up to 2^8 = 256 hosts hooked to its network.
Spencer
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posted on: 12/14/2005 02:59:39 AM
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