Subnet Cheat Sheet
Complete reference guide for CIDR notation, subnet masks, IP ranges, and private networks. Your essential quick reference for network engineering.
CIDR Notation Quick Reference
| CIDR | Subnet Mask | Wildcard Mask | Total IPs | Usable IPs |
|---|---|---|---|---|
/32 |
255.255.255.255 |
0.0.0.0 |
1 | 1 |
/31 |
255.255.255.254 |
0.0.0.1 |
2 | 2* |
/30 |
255.255.255.252 |
0.0.0.3 |
4 | 2 |
/29 |
255.255.255.248 |
0.0.0.7 |
8 | 6 |
/28 |
255.255.255.240 |
0.0.0.15 |
16 | 14 |
/27 |
255.255.255.224 |
0.0.0.31 |
32 | 30 |
/26 |
255.255.255.192 |
0.0.0.63 |
64 | 62 |
/25 |
255.255.255.128 |
0.0.0.127 |
128 | 126 |
/24 |
255.255.255.0 |
0.0.0.255 |
256 | 254 |
/23 |
255.255.254.0 |
0.0.1.255 |
512 | 510 |
/22 |
255.255.252.0 |
0.0.3.255 |
1,024 | 1,022 |
/21 |
255.255.248.0 |
0.0.7.255 |
2,048 | 2,046 |
/20 |
255.255.240.0 |
0.0.15.255 |
4,096 | 4,094 |
/19 |
255.255.224.0 |
0.0.31.255 |
8,192 | 8,190 |
/18 |
255.255.192.0 |
0.0.63.255 |
16,384 | 16,382 |
/17 |
255.255.128.0 |
0.0.127.255 |
32,768 | 32,766 |
/16 |
255.255.0.0 |
0.0.255.255 |
65,536 | 65,534 |
/15 |
255.254.0.0 |
0.1.255.255 |
131,072 | 131,070 |
/14 |
255.252.0.0 |
0.3.255.255 |
262,144 | 262,142 |
/13 |
255.248.0.0 |
0.7.255.255 |
524,288 | 524,286 |
/12 |
255.240.0.0 |
0.15.255.255 |
1,048,576 | 1,048,574 |
/11 |
255.224.0.0 |
0.31.255.255 |
2,097,152 | 2,097,150 |
/10 |
255.192.0.0 |
0.63.255.255 |
4,194,304 | 4,194,302 |
/9 |
255.128.0.0 |
0.127.255.255 |
8,388,608 | 8,388,606 |
/8 |
255.0.0.0 |
0.255.255.255 |
16,777,216 | 16,777,214 |
Note: /31 networks (RFC 3021) can use both IPs for point-to-point links without
network/broadcast addresses.
Private IP Address Ranges (RFC 1918)
| Class | CIDR Block | IP Range | Total IPs | Typical Use |
|---|---|---|---|---|
| Class A | 10.0.0.0/8 |
10.0.0.0 - 10.255.255.255 |
16,777,216 | Large enterprises |
| Class B | 172.16.0.0/12 |
172.16.0.0 - 172.31.255.255 |
1,048,576 | Medium organizations |
| Class C | 192.168.0.0/16 |
192.168.0.0 - 192.168.255.255 |
65,536 | Home/small office |
Special Use IP Addresses
| CIDR Block | Purpose | RFC |
|---|---|---|
0.0.0.0/8 |
Current network (only valid as source) | RFC 1122 |
127.0.0.0/8 |
Loopback addresses | RFC 1122 |
169.254.0.0/16 |
Link-local (APIPA) | RFC 3927 |
192.0.0.0/24 |
IETF Protocol Assignments | RFC 6890 |
192.0.2.0/24 |
Documentation (TEST-NET-1) | RFC 5737 |
198.18.0.0/15 |
Benchmark testing | RFC 2544 |
198.51.100.0/24 |
Documentation (TEST-NET-2) | RFC 5737 |
203.0.113.0/24 |
Documentation (TEST-NET-3) | RFC 5737 |
224.0.0.0/4 |
Multicast | RFC 5771 |
240.0.0.0/4 |
Reserved for future use | RFC 1112 |
255.255.255.255/32 |
Limited broadcast | RFC 919 |
IPv6 Quick Reference
| Prefix | Purpose | Scope |
|---|---|---|
::/128 |
Unspecified address | - |
::1/128 |
Loopback | Host |
fe80::/10 |
Link-local unicast | Link |
fc00::/7 |
Unique local address (ULA) | Site |
2000::/3 |
Global unicast | Global |
ff00::/8 |
Multicast | Various |
Common Subnet Sizes
| Hosts Needed | CIDR | Subnet Mask | Usable IPs |
|---|---|---|---|
| 2 | /30 |
255.255.255.252 |
2 |
| 6 | /29 |
255.255.255.248 |
6 |
| 14 | /28 |
255.255.255.240 |
14 |
| 30 | /27 |
255.255.255.224 |
30 |
| 62 | /26 |
255.255.255.192 |
62 |
| 126 | /25 |
255.255.255.128 |
126 |
| 254 | /24 |
255.255.255.0 |
254 |
| 510 | /23 |
255.255.254.0 |
510 |
| 1,022 | /22 |
255.255.252.0 |
1,022 |
Quick Formulas
Number of Subnets: 2borrowed bits
Hosts per Subnet: 2host bits - 2
CIDR to Hosts: 2(32 - CIDR) - 2
Hosts to CIDR: 32 - log₂(hosts + 2)