The subnet mask is a term in information technology that refers to the 32-bit binary numbers are used to distinguish Network Id and Host Id, showing the location of a host is there on the local network or outside networks.
RFC 950 defines the use of a subnet mask is also called as an address mask as a 32-bit value used to distinguish the network ID of the host ID in an IP address. The bits of the subnet mask is defined, is as follows:
1. All the bits that are intended to be used by the network ID is set to a value of 1.
2. All the bits that are intended to be used by the host identifier is set to value 0
Each host on a network that uses TCP / IP requires a subnet mask despite being on a network with one segment only. Whether it's the default subnet mask (used when using class-based network ID) or a customized subnet mask (which is used when making a subnet or supernet) must be configured in each node TCP / IP.
methods that can be used to represents the Subnet mask:
1. Dotted Decimal Notation
2. Length notation Prefik Network
Dotted decimal
A subnet mask is usually expressed in dotted decimal notation (dotted decimal notation), as well as IP addresses. After all bits are set as the network ID and host ID, the 32-bit value will be converted to dotted decimal notation. It should be noted, that although represented as a dotted decimal notation, the subnet mask is not an IP address.
The default subnet mask based on IP address classes and used in a TCP / IP that is not divided into multiple subnets. The table below mentions some of the default subnet mask by using dotted decimal notation. The format is:
RFC 950 defines the use of a subnet mask is also called as an address mask as a 32-bit value used to distinguish the network ID of the host ID in an IP address. The bits of the subnet mask is defined, is as follows:
1. All the bits that are intended to be used by the network ID is set to a value of 1.
2. All the bits that are intended to be used by the host identifier is set to value 0
Each host on a network that uses TCP / IP requires a subnet mask despite being on a network with one segment only. Whether it's the default subnet mask (used when using class-based network ID) or a customized subnet mask (which is used when making a subnet or supernet) must be configured in each node TCP / IP.
methods that can be used to represents the Subnet mask:
1. Dotted Decimal Notation
2. Length notation Prefik Network
Dotted decimal
A subnet mask is usually expressed in dotted decimal notation (dotted decimal notation), as well as IP addresses. After all bits are set as the network ID and host ID, the 32-bit value will be converted to dotted decimal notation. It should be noted, that although represented as a dotted decimal notation, the subnet mask is not an IP address.
The default subnet mask based on IP address classes and used in a TCP / IP that is not divided into multiple subnets. The table below mentions some of the default subnet mask by using dotted decimal notation. The format is:
<alamat IP www.xxx.yyy.zzz>, <subnet mask www.xxx.yyy.zzz>
| Address Class | Subnet mask (binary) | Subnet mask (decimal) |
|---|---|---|
| Kelas A | 11111111.00000000.00000000.00000000 | 255.0.0.0 |
| Kelas B | 11111111.11111111.00000000.00000000 | 255.255.0.0 |
| Kelas C | 11111111.11111111.11111111.00000000 | 255.255.255.0 |
Keep in mind that the default subnet mask value of the above can be customized by the network administrator, during the process of distribution networks (subnetting or supernetting). For example, the address 138.96.58.0 is a class B network ID of which has been divided into several subnets by using a number of 8-bit. The eight bits are used as the host ID will be used to display the network identifier that has been divided into subnets. Subnet used is a total of 24 bits (255.255.255.0) that can be used to define custom network ID. Network identifier that has been such a subnet and the subnet mask used will be further down by using the following notation:
138.96.58.0, 255.255.255.0
Representation prefix length (prefix length) of a subnet mask
Because the network ID bits should always be chosen in a contiguous form of high-order bits, then there is a means used to represent a subnet mask by using the bits that define the network ID as a prefix to the network using network prefix notation as listed in the table below. Notation network prefix notation is also known as Classless Inter-Domain Routing (CIDR) which is defined in RFC 1519. The format is as follows:
/<jumlah bit yang digunakan sebagai network identifier>
| Address Class | Subnet mask (binary) | Subnet mask (decimal) | Prefix Length |
|---|---|---|---|
| Kelas A | 11111111.00000000.00000000.00000000 | 255.0.0.0 | /8 |
| Kelas B | 11111111.11111111.00000000.00000000 | 255.255.0.0 | /16 |
| Kelas C | 11111111.11111111.11111111.00000000 | 255.255.255.0 | /24 |
For example, a class B network ID of 138.96.0.0 with subnet mask 255.255.0.0 can be represented in prefix length notation as 138.96.0.0/16.
Because all hosts that are within the same network using the same network ID, then all hosts that are within the same network must use the same network ID as defined by the subnet mask the same. For example, the notation is not the same as the notation 138.23.0.0/16 138.23.0.0/24, and both networks are not in the same address space. Network ID 138.23.0.0/16 has a range of valid IP addresses from 138.23.0.1 to 138.23.255.254, while network ID 138.23.0.0/24 only have a range of valid IP addresses from 138.23.0.1 to 138.23.0.254.
Because all hosts that are within the same network using the same network ID, then all hosts that are within the same network must use the same network ID as defined by the subnet mask the same. For example, the notation is not the same as the notation 138.23.0.0/16 138.23.0.0/24, and both networks are not in the same address space. Network ID 138.23.0.0/16 has a range of valid IP addresses from 138.23.0.1 to 138.23.255.254, while network ID 138.23.0.0/24 only have a range of valid IP addresses from 138.23.0.1 to 138.23.0.254.
Determine the address of the Network Identifier
To determine the network ID of an IP address using a subnet mask, can be done using a mathematical operation, namely by using the comparison logic operations AND (AND comparison). In an AND comparison, the value of the two things that will be compared is true only when two of the item is true, and to false if one of them false. By applying this principle into bits, a value of 1 would be obtained if the two bits compared to 1, and the value 0 if there is one among the comparable value is 0.
This will perform a comparison with the logical AND operation using 32-bit IP address and with 32-bit subnet mask, which is known as bitwise logical AND operation of comparison. The results of bitwise operations the IP address with a subnet mask that is what is called a network ID.
Example:
To determine the network ID of an IP address using a subnet mask, can be done using a mathematical operation, namely by using the comparison logic operations AND (AND comparison). In an AND comparison, the value of the two things that will be compared is true only when two of the item is true, and to false if one of them false. By applying this principle into bits, a value of 1 would be obtained if the two bits compared to 1, and the value 0 if there is one among the comparable value is 0.
This will perform a comparison with the logical AND operation using 32-bit IP address and with 32-bit subnet mask, which is known as bitwise logical AND operation of comparison. The results of bitwise operations the IP address with a subnet mask that is what is called a network ID.
Example:
Alamat IP 10000011 01101011 10100100 00011010 (131.107.164.026) Subnet Mask 11111111 11111111 11110000 00000000 (255.255.240.000) ------------------------------------------------------------------ Network ID 10000011 01101011 10100000 00000000 (131.107.160.000)
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