Difference between revisions of "What is a Netmask?"
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A '''Netmask''' is a 32-bit "mask" used to divide an IP address into subnets and specify the network's available hosts. In a netmask, two bits are always automatically assigned. For example, in 255.255.225.0, "0" is the assigned network address. In 255.255.255.255, "255" is the assigned broadcast address. The 0 and 255 are always assigned and cannot be used. | A '''Netmask''' is a 32-bit "mask" used to divide an IP address into subnets and specify the network's available hosts. In a netmask, two bits are always automatically assigned. For example, in 255.255.225.0, "0" is the assigned network address. In 255.255.255.255, "255" is the assigned broadcast address. The 0 and 255 are always assigned and cannot be used. | ||
− | Netmask defines how "large" a network is or if you're configuring a rule that requires an IP address and a Netmask, the Netmask will signify to what range of the Network the rule will apply to: | + | Netmask defines how "large" a network is or if you're configuring a rule that requires an IP address and a Netmask, the Netmask will signify to what portion or range of the Network the rule will apply to: |
− | + | {| class="wikitable" | |
− | + | |+ | |
− | + | ! style="width: 200px; background: black; color: white;" | IP | |
− | + | ! style="width: 200px; background: black; color: white;" | Netmask | |
− | + | ! style="width: 200px; background: black; color: white;" | Description | |
− | + | |- | |
− | + | ! style="text-align: left; vertical-align: top;" | 192.168.55.161 | |
− | + | | style="text-align: left; vertical-align: top;" | 255.255.255.255 | |
− | + | | style="text-align: left; vertical-align: top;" | Only applies to 192.168.55.161''' | |
− | + | |- | |
− | + | ! style="text-align: left; vertical-align: top;" | 192.168.55.0 | |
− | + | | style="text-align: left; vertical-align: top;" | 255.255.255.0 | |
− | + | | style="text-align: left; vertical-align: top;" | Applies to IPs in the 192.168.55.0 - 192.168.55.255 range | |
− | + | |- | |
− | + | ! style="text-align: left; vertical-align: top;" | 192.168.55.240 | |
− | + | | style="text-align: left; vertical-align: top;" | 255.255.255.240 | |
− | + | | style="text-align: left; vertical-align: top;" | 192.168.55.240 - 192.168.55.255 | |
− | + | |- | |
− | + | ! style="text-align: left; vertical-align: top;" | 192.168.55.161 | |
− | + | | style="text-align: left; vertical-align: top;" | 255.255.255.0 | |
− | + | | style="text-align: left; vertical-align: top;" | 192.168.55.0 - 192.168.55.255 | |
− | + | |- | |
− | + | ! style="text-align: left; vertical-align: top;" | 192.168.0.0 | |
− | + | | style="text-align: left; vertical-align: top;" | 255.255.0.0 | |
− | + | | style="text-align: left; vertical-align: top;" | 192.168.0.0 - 192.168.255.255 | |
− | + | |- | |
− | + | |} | |
− | |||
− | |||
− | |||
− | |||
− | |||
Sometimes you will see that a Netmask is defined by one number, e.g., '''24'''. This number is the length of the Netmask in bits: | Sometimes you will see that a Netmask is defined by one number, e.g., '''24'''. This number is the length of the Netmask in bits: | ||
− | + | {| class="wikitable" | |
− | + | |+ | |
− | + | ! style="width: 200px; background: black; color: white;" | Netmask | |
− | + | ! style="width: 100px; background: black; color: white;" | 255. | |
− | + | ! style="width: 100px; background: black; color: white;" | 255. | |
− | + | ! style="width: 100px; background: black; color: white;" | 255. | |
− | + | ! style="width: 100px; background: black; color: white;" | 255 | |
− | + | |- | |
− | + | ! style="text-align: left; vertical-align: top;" | Netmask length | |
− | + | | style="text-align: center; vertical-align: top;" | 8 | |
− | + | | style="text-align: center; vertical-align: top;" | 16 | |
− | + | | style="text-align: center; vertical-align: top;" | 24 | |
− | + | | style="text-align: center; vertical-align: top;" | 32 | |
− | + | |- | |
− | + | |} | |
− | |||
So, for example, a Netmask that is 24-bits long is '''255.255.255.0''': | So, for example, a Netmask that is 24-bits long is '''255.255.255.0''': | ||
− | + | {| class="wikitable" | |
− | + | |+ | |
− | + | ! style="width: 200px; background: black; color: white;" | Netmask | |
− | + | ! style="width: 100px; background: black; color: white;" | 255. | |
− | + | ! style="width: 100px; background: black; color: white;" | 255. | |
− | + | ! style="width: 100px; background: black; color: white;" | 255. | |
− | + | ! style="width: 100px; background: black; color: white;" | 0 | |
− | + | |- | |
− | + | ! style="text-align: left; vertical-align: top;" | Netmask length | |
− | + | | style="text-align: center; vertical-align: top;" | 8 | |
− | + | | style="text-align: center; vertical-align: top;" | 16 | |
− | + | | style="text-align: center; vertical-align: top;" | 24 | |
− | + | | style="text-align: center; vertical-align: top;" | - | |
− | + | |- | |
− | + | |} | |
− | |||
A Netmask that is 16-bits long is '''255.255.0.0''': | A Netmask that is 16-bits long is '''255.255.0.0''': | ||
− | + | {| class="wikitable" | |
− | + | |+ | |
− | + | ! style="width: 200px; background: black; color: white;" | Netmask | |
− | + | ! style="width: 100px; background: black; color: white;" | 255. | |
− | + | ! style="width: 100px; background: black; color: white;" | 255. | |
− | + | ! style="width: 100px; background: black; color: white;" | 0 | |
− | + | ! style="width: 100px; background: black; color: white;" | 0 | |
− | + | |- | |
− | + | ! style="text-align: left; vertical-align: top;" | Netmask length | |
− | + | | style="text-align: center; vertical-align: top;" | 8 | |
− | + | | style="text-align: center; vertical-align: top;" | 16 | |
− | + | | style="text-align: center; vertical-align: top;" | - | |
− | + | | style="text-align: center; vertical-align: top;" | - | |
− | + | |- | |
− | + | |} | |
− | |||
And so on. | And so on. | ||
− | |||
− |
Revision as of 10:44, 16 January 2018
Main Page > FAQ > Networking > What is a Netmask?A Netmask is a 32-bit "mask" used to divide an IP address into subnets and specify the network's available hosts. In a netmask, two bits are always automatically assigned. For example, in 255.255.225.0, "0" is the assigned network address. In 255.255.255.255, "255" is the assigned broadcast address. The 0 and 255 are always assigned and cannot be used.
Netmask defines how "large" a network is or if you're configuring a rule that requires an IP address and a Netmask, the Netmask will signify to what portion or range of the Network the rule will apply to:
IP | Netmask | Description |
---|---|---|
192.168.55.161 | 255.255.255.255 | Only applies to 192.168.55.161 |
192.168.55.0 | 255.255.255.0 | Applies to IPs in the 192.168.55.0 - 192.168.55.255 range |
192.168.55.240 | 255.255.255.240 | 192.168.55.240 - 192.168.55.255 |
192.168.55.161 | 255.255.255.0 | 192.168.55.0 - 192.168.55.255 |
192.168.0.0 | 255.255.0.0 | 192.168.0.0 - 192.168.255.255 |
Sometimes you will see that a Netmask is defined by one number, e.g., 24. This number is the length of the Netmask in bits:
Netmask | 255. | 255. | 255. | 255 |
---|---|---|---|---|
Netmask length | 8 | 16 | 24 | 32 |
So, for example, a Netmask that is 24-bits long is 255.255.255.0:
Netmask | 255. | 255. | 255. | 0 |
---|---|---|---|---|
Netmask length | 8 | 16 | 24 | - |
A Netmask that is 16-bits long is 255.255.0.0:
Netmask | 255. | 255. | 0 | 0 |
---|---|---|---|---|
Netmask length | 8 | 16 | - | - |
And so on.