A, subnetting based
1. Several of the benefits of subnetting:
(1) to reduce network traffic
(2) improve the network performance
(3) simplify management
(4) can be more flexible form a large coverage network
2. You'd better follow the steps below for subnetting:
1) confirmation required network ID number
(2) to confirm what we need in each subnet host ID number
(3) based on the above need, create the following contents:
- set a mask for the entire network
- for each physical network segment to set a different subnet ID
- to determine the host addresses per subnet and legal address range

Second, carries on the subnetting
When to select an available network mask, and need to infer from this number of subnet mask to the legitimate host, network address and the broadcast address, need to do is answer the following question 5:
- this was chosen how many subnet mask will produce?
- each subnet and there will be many a legitimate host number?
- what is legal subnet number?
- what is the broadcast address per subnet?
- what is legal in each subnet host number?
1. A class C address subnet division (110 x x x x x, 192 ~ 223) example:
192.168.10.0/25
A: how many subnets --? Because/25=1 0 0 0 0 0 0 0, so the number of subnet is 21=2,
- how many legitimate host number? Because/25=1 0 0 0 0 0 0 0, so the legitimate host number number is 27-2=126 (to remove the subnet addresses and broadcast address),
- legal subnet number? Calculate 1 0 0 0 0 0 0 0=128, 256-128=128 (block size),
- what is the broadcast address?
The host - what is legal?
Subnet address 0, 128
The first host 1 129
Finally a host number 126 254
The broadcast address, 127, 255

2. A class B address subnet partition (10 x x x x x x, 128 ~ 191) example:
Along/18
A: how many subnets --?/18=1 1 0 0 0 0 0 0 0 0 0 0 0 0, 0.0 so the subnet number is 22=4,
- how many legitimate host number? Because/18=1 1 0 0 0 0 0 0 0 0 0 0 0 0, 0.0 so the legitimate host number number is 214-2=16382,
- legal subnet number? Calculate 1 1 0 0 0 0 0 0=192, 256-192=64 (block size), we should be clear this is the third group of eight bits catch block size,
- what is the broadcast address?
The host - what is legal?
Subnet address 0.0 64.0 128.0 192.0
The first host no. 0.1 64.1 128.1 192.1
Finally a host number 63.254 127.254 191.254 255.254
The broadcast address 63.255 127.255 191.255 255.255

3. The class A address subnet division (0 x x x x x x x, 1 ~ 126) example:
10.0.0.0/9
A: how many subnets --?/9=1 0 0 0 0 0 0 0 0 0 0 0 0 0.0 0.0 0 0 0 0 0 0 0, so the number of subnet is 21=2,
- how many legitimate host number? Because/9=1 0 0 0 0 0 0 0 0 0 0 0 0 0.0 0.0 0 0 0 0 0 0 0, so the legitimate host number number is 223-2=... ,
- legal subnet number? Calculate 1 00 0 0 0 0 0=128, 256-128=128 (block size), we should be clear this is the second group of eight bits calculated block size,
- what is the broadcast address?
The host - what is legal?
Subnet addresses 0.0.0 128.0.0
The first host 0.0.1 128.0.1
The final host 127.255.254 128.255.254
The broadcast address 127.255.255 128.255.255

Three, the method of calculating subnet summary
Step 1, calculate the block size (such as:/9 should be calculated in the second group of eight bits block size;/18 in addition to calculating the second group of eight bits on the block size, should also be calculated on a third group of eight bits block size; 27/2, 3 a group of eight bits than calculate the block size on the outside, should also calculate the fourth group of eight bits in the block size);
Step 2, write a subnet number follow change only that a group of eight bits on the block size, so increases slowly;
Step 3, follow when writing the legitimate host a subnet number range change only that a group of eight bits on the block size and host a number;
Step 4, write in a subnet broadcast address to follow the number one greater than the last one legitimate hosts,


Enclosed: how to calculate the two IP address is on the same network segment (computer)?
PC1 (192.168.1.1/255.255.255.0) & lt; -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- - & gt; PC2 (192.168.2.1/255.255.0.0), assuming that the PC1 and PC2 communications:
Step 1, according to the 192.168.1.1/255.255.255.0 PC1 can be calculated by the corresponding segment for 192.168.1.0
Step 2, PC2 IP and PC1 mask of its configuration and operation:
192.168.2.1:1 1 0 0 0 0 0 0. 1 0 0 1 0 0 0. 0 0 0 0 0 0 0. 1 0 0 0 0 0 0 0 1
255.255.255.0:1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0
1 1 0 0 0 0 0 0. 1 0 0 1 0 0 0. 0 0 0 0 0 0 1 0. 0 0 0 0 0 0 0 0 - to - 192.168.2.0
Step 3, calculated by above knowable PC1 and PC2 think it is not in the same network segment,