Info
cidr chart
Subnet mask in classless notation (IPv4 address space). This is a sheet that you can print off if you wish or put in your bookmarks for future use.
| number of addresses | bits | pref | mask |
|---|---|---|---|
| 1 | 0 | /32 | 255.255.255.255 |
| 2 | 1 | /31 | 255.255.255.254 |
| 4 | 2 | /30 | 255.255.255.252 |
| 8 | 3 | /29 | 255.255.255.248 |
| 16 | 4 | /28 | 255.255.255.240 |
| 32 | 5 | /27 | 255.255.255.224 |
| 64 | 6 | /26 | 255.255.255.192 |
| 128 | 7 | /25 | 255.255.255.128 |
| 256 | 8 | /24 | 255.255.255.0 |
| 512 | 9 | /23 | 255.255.254.0 |
| 1024 | 10 | /22 | 255.255.252.0 |
| 2048 | 11 | /21 | 255.255.248.0 |
| 4096 | 12 | /20 | 255.255.240.0 |
| 8192 | 13 | /19 | 255.255.224.0 |
| 16384 | 14 | /18 | 255.255.192.0 |
| 32768 | 15 | /17 | 255.255.128.0 |
| 65536 | 16 | /16 | 255.255.0.0 |
| 131072 | 17 | /15 | 255.254.0.0 |
| 262144 | 18 | /14 | 255.252.0.0 |
| 524288 | 19 | /13 | 255.248.0.0 |
| 1048576 | 20 | /12 | 255.240.0.0 |
| 2097152 | 21 | /11 | 255.224.0.0 |
| 4194304 | 22 | /10 | 255.192.0.0 |
| 8388608 | 23 | /9 | 255.128.0.0 |
| 16777216 | 24 | /8 | 255.0.0.0 |
| 33554432 | 25 | /7 | 254.0.0.0 |
| 67108864 | 26 | /6 | 252.0.0.0 |
| 134217728 | 27 | /5 | 248.0.0.0 |
| 268435456 | 28 | /4 | 240.0.0.0 |
| 536870912 | 29 | /3 | 224.0.0.0 |
| 1073741824 | 30 | /2 | 192.0.0.0 |
why
Why do we go to these complex ways to define networks?
In the earlier days of networking we had three classes of network address
| class | number of addresses |
|---|---|
| class c | 256 |
| class b | 65535 |
| class a | 16777216 |
The troube here is that RIR and LIRs have large network wastage when their clients do not require a whole class b assignment. Using the cidr notation a /25 might be more appropriate for their needs.