BLOG LIST
Blog List
Network CIDR Notation
Many firewalls and network devices use CIDR (Classless Inter-Domain Routing) notation rather than the common subnet mask 255.x.x.x when configuring addresses and networks. Refer to the CIDR Subnet Table to find the CIDR equivalent of a decimal subnet mask.
| Subnet Mask | CIDR Prefix | Total IP Addresses | Usable IP Addresses | Number of /24 networks |
|---|---|---|---|---|
| 255.255.255.255 | /32 | 1 | 1 | 1/256th |
| 255.255.255.254 | /31 | 2 | 2* | 1/128th |
| 255.255.255.252 | /30 | 4 | 2 | 1/64th |
| 255.255.255.248 | /29 | 8 | 6 | 1/32nd |
| 255.255.255.240 | /28 | 16 | 14 | 1/16th |
| 255.255.255.224 | /27 | 32 | 30 | 1/8th |
| 255.255.255.192 | /26 | 64 | 62 | 1/4th |
| 255.255.255.128 | /25 | 128 | 126 | 1 half |
| 255.255.255.0 | /24 | 256 | 254 | 1 |
| 255.255.254.0 | /23 | 512 | 510 | 2 |
| 255.255.252.0 | /22 | 1024 | 1022 | 4 |
| 255.255.248.0 | /21 | 2048 | 2046 | 8 |
| 255.255.240.0 | /20 | 4096 | 4094 | 16 |
| 255.255.224.0 | /19 | 8192 | 8190 | 32 |
| 255.255.192.0 | /18 | 16,384 | 16,382 | 64 |
| 255.255.128.0 | /17 | 32,768 | 32,766 | 128 |
| 255.255.0.0 | /16 | 65,536 | 65,534 | 256 |
| 255.254.0.0 | /15 | 131,072 | 131,070 | 512 |
| 255.252.0.0 | /14 | 262,144 | 262,142 | 1024 |
| 255.248.0.0 | /13 | 524,288 | 524,286 | 2048 |
| 255.240.0.0 | /12 | 1,048,576 | 1,048,574 | 4096 |
| 255.224.0 0 | /11 | 2,097,152 | 2,097,150 | 8192 |
| 255.192.0.0 | /10 | 4,194,304 | 4,194,302 | 16,384 |
| 255.128.0.0 | /9 | 8,388,608 | 8,388,606 | 32,768 |
| 255.0.0.0 | /8 | 16,777,216 | 16,777,214 | 65,536 |
| 254.0.0.0 | /7 | 33,554,432 | 33,554,430 | 131,072 |
| 252.0.0.0 | /6 | 67,108,864 | 67,108,862 | 262,144 |
| 248.0.0.0 | /5 | 134,217,728 | 134,217,726 | 1,048,576 |
| 240.0.0.0 | /4 | 268,435,456 | 268,435,454 | 2,097,152 |
| 224.0.0.0 | /3 | 536,870,912 | 536,870,910 | 4,194,304 |
| 192.0.0.0 | /2 | 1,073,741,824 | 1,073,741,822 | 8,388,608 |
| 128.0.0.0 | /1 | 2,147,483,648 | 2,147,483,646 | 16,777,216 |
| 0.0.0.0 | /0 | 4,294,967,296 | 4,294,967,294 | 33,554,432 |
Where do CIDR numbers come from?
The CIDR number comes from the number of ones in the subnet mask when converted to binary.
The common subnet mask 255.255.255.0 is 11111111.11111111.11111111.00000000 in binary. This adds up to 24 ones, or /24 (pronounced ‘slash twenty four’).
A subnet mask of 255.255.255.192 is 11111111.11111111.11111111.11000000 in binary, or 26 ones, hence /26.
"Niente è più costante del cambiamento."
[Robert Mac Farlane]200
[Robert Mac Farlane]200
eulogika
Via Pitagora, 11/A
35030 - Rubano - Padova
Italia
35030 - Rubano - Padova
Italia
2023 Eulogika srl | Powered by Eulogika | VAT 04247880281| SDI 7HE8RN5