The subnet mask is also called the network mask, address mask, and sub-network mask. It is used to indicate which bits of an IP address identify the subnet where the host is located and which bits identify the host's bit mask. code. The subnet mask cannot exist alone, it must be used in conjunction with an IP address. The subnet mask has only one effect, which is to divide an IP address into two parts: the network address and the host address. Subnetmask (subnetmask) is the basic knowledge that every person who uses the Internet must master. Only by mastering it can you really understand the settings of TCP/IP protocol. Below we will explain in a simple way what is the subnet mask.
advantage
subnetting (subnetting) of:
1. 2.
reduce network traffic and improve network performance
3. simplify management
4. easy to expand the geographic scope of
how to create a subnet: how
subnetting first of all to memorize a power of 2:? 0 th to 9 th power of 2 The values are: 1, 2, 4, 8, 16, 32, 64, 128, 256, and 512. It should also be understood that the subnetting is by taking the host bit and taking the removed part as a subnet bit. So this means that the more subnets you divide, the fewer hosts there will be.
subnet mask (SubnetMasks):
subnet mask is used to distinguish which part of the IP address is the network address, which is the host address, 1 and 0, length 32 Bits, all 1 bits represent the network number. Not all networks require subnets, so a concept is introduced: default subnetmask (defaultsubnetmask). The default subnet mask for class A IP addresses is 255.0.0.0 ; Class B is 255.255.0.0; Class C is 255.255.255.0.
ClasslessInter-DomainRouting (CIDR):
CIDR Inter-Domain Routing known, ISP common method of assigning addresses to such customers, ISP to provide customers one block (blocksize), like this :192.168.10.32/28, this row of numbers tells you what your subnet mask is, /28 represents how many bits are 1, the maximum /32. But there is a little system home to be special reminder. You must also know that whether it is A or B or other class address, the maximum available is only /30, that is, 2 bits are reserved for the host.
CIDR value:
1. Class address mask 255.0.0.0:/8(A default mask)
2. mask 255.255.0.0:/16 ( class B addresses default mask)
3. class address mask 255.255.255.0:/24(C default mask)
divided A class B class C subnet address:
several shortcut
subnetting:
1. select your subnet mask number of subnets will have:? x 2 to the power of -2 (x represents the subnet bits, That is, the part where the binary is 1) PS: The x here refers to the subnet bit after removing the default mask, for example, the network address 192.168.1.1, the 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 1s as the subnet bits.
2. How many hosts can each subnet:? Y th power of 2 -2 (y on behalf of host bits, that is part of a binary 0)
3. valid subnet It is: valid subnet number = 256-10 binary subnet mask (called a blocksize results or basenumber) broadcast address
4. each subnet is:?? = broadcast address next subnet number - 1
5. valid hosts per subnet are:? ignore subnet address are all 0 and 1 are all that remains is a valid host addresses
last valid one. next host address subnet number = 2 (i.e., the broadcast address -1)
the particular examples described above shortcut subnetting:
example 1 class C addresses: the network address 192.168.10.0; subnet mask 255.255.255.192 (/26)
1. subnets = 2 * 2-2 = 2
2. hosts for power = 6 2 = 62 -2
3. valid subnets: blocksize = 256-192 = 64; so the first subnet 192.168.10.64, is a second broadcast address 192.168.10.128
4.?: The next subnet-1. So the broadcast addresses of the 2 subnets are 192.168.10 respectively. 192.168.10.191
5. .127 and host range are effectively: a first host address 192.168.10.65 subnet is to 192.168.10.126; second is 192.168.10.129 to 192.168.10.190
address example
category C 2: network address 192.168.10.0; subnet mask of 255.255.255.128 (/26)
I know I cite this example is only one subnet bits, which is generally not legitimate (as specified in the RFC documentation). But! There is no absolute thing in the world, isn't it? This subnet mask can help you when you need 126 hosts per subnet on two subnets, but this is done in special cases. Enter the ipsubnet-zero command in the Cisco router's global configuration mode to tell your router to break the rules and use a 1-bit subnet mask (this command is usually present by default on all routers running CISCOiOS12.x)
< BR> 1. subnets = 2
2. hosts 7 = -2 =
3. effective power subnet 2 126
: blocksize = 256-128 = 128;? so the first subnet 192.168.10.0, for the second broadcast address 192.168.10.128
4.: -1 so the next subnet broadcast address is 192.168.10.127 two subnets and 192.168, respectively. 10.255
5. valid host range is: a host address of the first subnet is 192.168.10.1 to 192.168.10.126; second is 192.168.10.129 to 192.168.10.254
class B examples 1 address: network address: 172.16.0.0; subnet mask 255.255.255.128 (/25)
Note that this is not a class C subnet mask address, but this is a certain difficulty subnetting! However, this mask is very useful because it creates 510 subnets with 126 hosts per subnet, one A good combination.
1. subnets = 7 th -2 = 126
3. 2. -2 9 th effective number of 2 = 510
host = 2 Subnet?: blocksize=256-255=1, 2,3,... This is the value of the third octet, but you can't forget that there is also a subnet in the fourth octet. group. So the fourth octet component is two subnets. The third example shows two subnets of octet 3, and that the fourth octet of 172.16.3.0 and 172.16.3.128
4. broadcast address: the next sub -1. so the first and last subnet broadcast address of a subnet are
172.16.0.255 and
172.16.255.127
5. valid host are: first subnet host address is 172.16.0.129 to 172.16.0.254; the last one is 172.16.255.0 to 172.16.255.126
(home system add: Some people may ask why is not the first subnet 172.16 .0.0---172.16.0.128? Don't forget! The subnet bit and host bit cannot be all 0s or all 1, 172.16.0.0 represents the entire 172.16.xx network. Similarly, the last subnet cannot be . 172.16.255.128 --- 172.16.255.255 a)
class address example B 2: network address: 172.16.0.0; subnet mask 255.255.192.0 (/18)
1. number of subnets = 2 * 2-2 = 2
2. number of hosts 14 th = -2 =
3. valid subnet 2 16382
:? blocksize = 256-192 = 64; so the first Subnet is 172.16.64.0, the last one is the broadcast address 172.16.128.0
4.: -1 next subnet broadcast address so that two subnets are 172.16.127.255 and 172.16.191.255
5. valid host are: a first host address 172.16.64.1 subnet is to 172.16.127.254; second type is an example
B address 172.16.128.1 to 172.16.191.254
3: network address: 172.16.0.0; subnet mask 255.255.255.224 (/27)
1. subnets power = 11 -2 = 20,462 (the default mask because class B address is 255.255. 0.0, so the network bit is 8 + 3 = 11)
2. hosts fifth power = -2 = 30
3. valid subnet 2:? blocksize = 256-224 = 32; so the first subnet 172.16.0.32, the last one is the broadcast address 172.16.255.192
4.: next subnet -1 so the first and last subnet one subnetwork. broadcast addresses are 172.16.0.63 and
172.16.255.223
5. valid host range is: a first subnet host address is 172.16.0.33 to 172.16.0.62; final 1 Is 172.16.255.193 to 172.1 6.255.223
A class address subnetting with Class B and Class C and there is no difference, but the mask changed from 16-bit and 8-bit 24-bit only.
simply give an example:
network addresses: 10.0.0.0; subnet mask 255.255.0.0 (/16)
1. subnets = 2 power of -2 8 2 number = 254
host power = 16 -2 =
3. valid subnet 2 65534
:? blocksize = 256-255 = 1,2 , 3, ......; 10.1.0.0 so the first subnet, the last one is the broadcast address 10.254.0.0
4.: the first child so subnets -1 Finally, a network and subnet broadcast address and are 10.1.255.255
10.254.255.255
5. valid host range is: a first subnet host address 10.1.0.1 is to 10.1.255.254; the last one is 10.254.0.1 to 10.254.255.254