YurlieCIDR /21 Subnet Reference
A medium IPv4 subnet with 2.048 total addresses and 2.046 usable host addresses.
Subnet Mask
255.255.248.0Wildcard Mask
0.0.7.255Total IPs
2.048Usable Hosts
2.046Mask (Hex)
FFFFF800Host Bits
11Binary Breakdown
Subnet Mask
11111111.11111111.11111000.00000000Wildcard Mask
00000000.00000000.00000111.11111111Network bits (1s): 21 · Host bits (0s): 11
Common Uses for /21
- Multiple office campuses
- 2,046 usable hosts
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Enter any IP address with /21 prefix to calculate exact network details.
Frequently Asked Questions
What is the subnet mask for /21?
The subnet mask for /21 is 255.255.248.0 (hex: FFFFF800). In binary: 11111111.11111111.11111000.00000000.
How many hosts does a /21 subnet support?
A /21 subnet has 2.048 total addresses. Subtract 2 (network + broadcast) = 2.046 usable host addresses.
What is the wildcard mask for /21?
The wildcard mask (inverse mask) for /21 is 0.0.7.255. Used in Cisco ACLs and OSPF configurations to match the host portion of an address.
What is CIDR /21 used for?
Multiple office campuses. 2,046 usable hosts.
Complete CIDR Reference Table /0–/32
| Prefix | Subnet Mask | Wildcard | Total IPs | Usable Hosts |
|---|---|---|---|---|
| /0 | 0.0.0.0 | 255.255.255.255 | 4.294.967.296 | 4.294.967.294 |
| /1 | 128.0.0.0 | 127.255.255.255 | 2.147.483.648 | 2.147.483.646 |
| /2 | 192.0.0.0 | 63.255.255.255 | 1.073.741.824 | 1.073.741.822 |
| /3 | 224.0.0.0 | 31.255.255.255 | 536.870.912 | 536.870.910 |
| /4 | 240.0.0.0 | 15.255.255.255 | 268.435.456 | 268.435.454 |
| /5 | 248.0.0.0 | 7.255.255.255 | 134.217.728 | 134.217.726 |
| /6 | 252.0.0.0 | 3.255.255.255 | 67.108.864 | 67.108.862 |
| /7 | 254.0.0.0 | 1.255.255.255 | 33.554.432 | 33.554.430 |
| /8 | 255.0.0.0 | 0.255.255.255 | 16.777.216 | 16.777.214 |
| /9 | 255.128.0.0 | 0.127.255.255 | 8.388.608 | 8.388.606 |
| /10 | 255.192.0.0 | 0.63.255.255 | 4.194.304 | 4.194.302 |
| /11 | 255.224.0.0 | 0.31.255.255 | 2.097.152 | 2.097.150 |
| /12 | 255.240.0.0 | 0.15.255.255 | 1.048.576 | 1.048.574 |
| /13 | 255.248.0.0 | 0.7.255.255 | 524.288 | 524.286 |
| /14 | 255.252.0.0 | 0.3.255.255 | 262.144 | 262.142 |
| /15 | 255.254.0.0 | 0.1.255.255 | 131.072 | 131.070 |
| /16 | 255.255.0.0 | 0.0.255.255 | 65.536 | 65.534 |
| /17 | 255.255.128.0 | 0.0.127.255 | 32.768 | 32.766 |
| /18 | 255.255.192.0 | 0.0.63.255 | 16.384 | 16.382 |
| /19 | 255.255.224.0 | 0.0.31.255 | 8.192 | 8.190 |
| /20 | 255.255.240.0 | 0.0.15.255 | 4.096 | 4.094 |
| /21 | 255.255.248.0 | 0.0.7.255 | 2.048 | 2.046 |
| /22 | 255.255.252.0 | 0.0.3.255 | 1.024 | 1.022 |
| /23 | 255.255.254.0 | 0.0.1.255 | 512 | 510 |
| /24 | 255.255.255.0 | 0.0.0.255 | 256 | 254 |
| /25 | 255.255.255.128 | 0.0.0.127 | 128 | 126 |
| /26 | 255.255.255.192 | 0.0.0.63 | 64 | 62 |
| /27 | 255.255.255.224 | 0.0.0.31 | 32 | 30 |
| /28 | 255.255.255.240 | 0.0.0.15 | 16 | 14 |
| /29 | 255.255.255.248 | 0.0.0.7 | 8 | 6 |
| /30 | 255.255.255.252 | 0.0.0.3 | 4 | 2 |
| /31 | 255.255.255.254 | 0.0.0.1 | 2 | 2 |
| /32 | 255.255.255.255 | 0.0.0.0 | 1 | 1 |