Tips #
- Cisco suggest routers use the highest IP addresses, and devices the lowest.
- When using variable length subnet masking (VLSM): identify the starting point; find the required subnets and order from largest to smallest; calculate the number of bits required for each subnet and how many host addresses are created; calculate subnets remembering to start at zero.
Private Address Ranges #
| Class | CIDR Block | Range |
|---|---|---|
| A | 10.0.0.0/8 | 10.0.0.0 - 10.255.255.255 |
| B | 172.16.0.0/12 | 172.16.0.0 - 172.31.255.255 |
| C | 192.168.0.0/16 | 192.168.0.0 - 192.168.255.255 |
Subnetting Cheatsheet #
| Wildcard | 127 | 63 | 31 | 15 | 7 | 3 | 1 | 0 |
|---|---|---|---|---|---|---|---|---|
| Subnet Count | 2 | 4 | 8 | 16 | 32 | 64 | 128 | 256 |
| Group Size | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
| Mask | 128 | 192 | 224 | 240 | 248 | 252 | 254 | 255 |
| CIDR 4 | /25 | /26 | /27 | /28 | /29 | /30 | /31 | /32 |
| CIDR 3 | /17 | /18 | /19 | /20 | /21 | /22 | /23 | /24 |
| CIDR 2 | /9 | /10 | /11 | /12 | /13 | /14 | /15 | /16 |
| CIDR 1 | /1 | /2 | /3 | /4 | /5 | /6 | /7 | /8 |