# Sub-Network Partitioning method

Source: Internet
Author: User

As we all know, in order to determine subnets, separate the host and router each interface, resulting in a number of separate network islands, interface to the end of these independent network connections. Each of these independent networks is called a subnet (subnet).

You must know something about IP addresses, right? We know that the TCP/IP protocol that is widely used on the internet is the use of IP addresses to differentiate between different hosts. If you've ever had TCP/IP protocol settings, then you're bound to encounter the term subnet mask (Subnet mask), so do you know what a subnet mask is? What does it do?

We know that the IP address is a 4-byte (total 32bit) number, divided into 4 segments, 8 bits per paragraph, and segments separated by periods. For ease of expression and recognition, the IP address is represented in decimal form, such as 210.52.207.2, which can represent a maximum of 255 decimal digits per paragraph. The IP address consists of two parts, namely the network number (network ID) and the host number (host ID). The network number identifies a subnet on the internet, and the host number identifies a host on the subnet. When an Internet address is decomposed into two domains, it has an important advantage: when IP packets reach another network from one network on the Internet, the selection path can be based on the network rather than the host. This advantage is particularly noticeable in large networks because the routing table stores only network information rather than host information, which can greatly simplify the routing table

Sub-Network Partitioning Basics :

1. Reduce network traffic

2. Improve network performance

3. Simplified management

4. Easy to expand geographical scope

How to create a subnet:

How do I divide subnets? The first thing to memorize is 2 power: 2 of the 0 to 9 of the value of the square is: 1,2,4,8,16,32,64,128,256 and 512 respectively. Also have to understand is: The subnet division is to take away the host bit, this take away part as a subnet bit. So this means more subnets, fewer hosts.

The subnet mask is used to identify which part of the IP address is a network address. Which part is the host address, there are 1 and 0 components, long 32 bits, all 1 of bits represent the network number. Not all networks require subnets, so there are 1 concepts: The default subnet mask (defaulted subnet mask). The default subnet mask for class A IP addresses is 255.0.0.0; Class B is 255.255.0.0; The class C is 255.255.255.0.

Classless Inter-Domain Routing (CIDR):

CIDR is called inter-domain routing without class, ISPs often use this method to assign addresses to customers, and ISPs provide 1 blocks (block size) to customers, similar to this: 192.168.10.32/28, this row of numbers tells you how much your subnet mask is,/28 represents how many digits are 1, max/32. But what you have to know is that, whether it's a class A or B or other class address, the maximum available is only/30, that is, keep 2 digits to the main seat.

CIDR values:

Division A Class B class C address subnet:

Several shortcuts for dividing subnets:

1. How many subnets will be generated by the subnet mask you choose?: 2 of x -2 (x for subnet bits, 2 for 1) PS: Here x is the subnet bit after the default mask is removed, For example, the network address 192.168.1.1, Mask 255.255.255.192, because it is a class C address, the mask is 255.255.255.0. Then 255.255.255.192 (x.x.x.11000000) uses two one as the subnet bit.

2. How many hosts can each subnet have?: 2 y-square -2 (Y represents the host bit, that is, the 2 to 0 portion)

3. Effective subnet is: Valid subnet number =256-10 subnet mask (result called block size or base numbers)

5. The effective host for each subnet is?: Ignoring the addresses of all 0 and all 1 in the subnet is the valid host address.

According to the above shortcut to divide the specific example of the subnet:

1. Subnet number =2*2-2=2

2. Number of hosts = 2 of the 6 square -2=62

3. Effective subnet?: Block size=256-192=64; So the first subnet is 192.168.10.64, and the second is 192.168.10.128.

5. The effective host range is: the host address of the first subnet is 192.168.10.65 to 192.168.10.126; the second is 192.168.10.129 to 192.168.10.190

I know that the example I'm lifting has only one subnet bit, which is usually illegal (as stipulated by the RFC document). But there's nothing in the world, is there? This subnet mask can help you when you need two subnets per subnet for 126 hosts, but it is implemented under special circumstances. In the Cisco router's global configuration mode, enter the IP subnet-zero command to tell your router to break the rules and use a 1-bit subnet mask (This command is usually default on all routers running Cisco IOS 12.x)

1. Subnet Number = 2

2. Number of hosts = 2 of the 7 square -2=126

3. Effective subnet?: Block size=256-128=128; So the first subnet is 192.168.10.0, and the second is 192.168.10.128.

5. The effective host range is: the host address of the first subnet is 192.168.10.1 to 192.168.10.126; the second is 192.168.10.129 to 192.168.10.254

Attention! This is not a C-class address subnet mask, but this subnet division is a bit difficult, but! This mask is very useful because it creates 510 subnets each subnet has 126 hosts, a good combination.

1. Subnet Number = 2 of the 9-time Square -2=510

2. Number of hosts = 2 of the 7 square -2=126

3. Effective subnet: Block size=256-255=1,2,3, ... This is the third eight-bit value, but you can't forget that there is one more subnet in the fourth eight-bit group. So the fourth eight-bit group is divided into two subnets. For example, the third eight-bit group represents Subnet 3, and the two subnets of the fourth eight-bit group are 172.16.3.0 and 172.16.3.128

172.16.0.255 and

172.16.255.127

5. The effective host range is: the host address of the first subnet is 172.16.0.129 to 172.16.0.254; The last 1 are 172.16.255.0 to 172.16.255.126.

(add: Some people may ask why the first subnet is not 172.16.0.0---172.16.0.128? Don't forget! The subnet and host bits cannot be 0 or all 1, 172.16.0.0 represents the entire 172.16.x.x network, similarly, the last subnet can not be 172.16.255.128---172.16.255.255. )

1. Subnet number =2*2-2=2

2. Number of hosts = 2 of the 14 square -2=16382

3. Effective subnet?: Block size=256-192=64; So the first subnet is 172.16 64.0, and the last 1 is 172.16.128.0.

5. The effective host range is: the host address of the first subnet is 172.16.64.1 to 172.16.127.254; the second is 172.16.128.1 to 172.16.191.254

1. Subnet = 2 of 11 -2=2046 (because the class B address default mask is 255.255.0.0, so the network bit is 8+3=11)

2. Number of hosts = 2 of the 5 square -2=30

3. Effective subnet?: Block size=256-224=32; So the first subnet is 172.16.0.32, and the last 1 is 172.16.255.192.

172.16.255.223

5. The effective host range is: the host address of the first subnet is 172.16.0.33 to 172.16.0.62; the last 1 are 172.16.255.193 to 172.16.255.223.

A-class address subnetting is no different from Class B and Class C, except that the mask is changed from 16-bit and 8-bit to 24-bit.

Let's just give you a simple example:

1. Subnet Number = 2 of the 8-time Square -2=254

2. Number of hosts = 2 of the 16 square -2=65534

3. Effective subnet: Block size=256-255=1,2,3, ...; So the first subnet is 10.1.0.0, and the last 1 is 10.254.0.0.

10.254.255.255

5. The effective host range is: the host address of the first subnet is 10.1.0.1 to 10.1.255.254; The last 1 are 10.254.0.1 to 10.254.255.254.

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