Yurlie/21 Subnet Mask Reference
The subnet mask for prefix length /21 is 255.255.248.0. A medium IPv4 subnet with 2.048 total addresses and 2.046 usable host addresses.
/21255.255.248.00.0.7.255FFFFF8002.04621 / 32Binary Representation
11111111.11111111.11111000.0000000000000000.00000000.00000111.111111111-bits (network): 21 · 0-bits (host): 11 · Total: 32 bits
Common Uses for 255.255.248.0
- Multiple office campuses
- 2,046 usable hosts
Frequently Asked Questions
What is the subnet mask for /21?
The subnet mask for prefix length /21 is 255.255.248.0. In hexadecimal it is 0xFFFFF800. The binary representation is 11111111.11111111.11111000.00000000.
What is the inverse (wildcard) mask of 255.255.248.0?
The wildcard mask (inverse mask) of 255.255.248.0 is 0.0.7.255. Wildcard masks are used in Cisco IOS ACLs and OSPF configurations to specify which bits of an IP address to match.
How many host IPs does 255.255.248.0 give?
With subnet mask 255.255.248.0 (/21), you get 2.048 total IPs, minus 2 reserved (network + broadcast) = 2.046 usable host addresses.
What CIDR prefix corresponds to 255.255.248.0?
The subnet mask 255.255.248.0 corresponds to CIDR prefix /21. This means 21 bits are used for the network portion and 11 bits for host addresses.
Complete Subnet Mask Reference /0–/32
| Prefix | Subnet Mask | Wildcard | Hex | Usable Hosts |
|---|---|---|---|---|
| /0 | 0.0.0.0 | 255.255.255.255 | 00000000 | 4.294.967.294 |
| /1 | 128.0.0.0 | 127.255.255.255 | 80000000 | 2.147.483.646 |
| /2 | 192.0.0.0 | 63.255.255.255 | C0000000 | 1.073.741.822 |
| /3 | 224.0.0.0 | 31.255.255.255 | E0000000 | 536.870.910 |
| /4 | 240.0.0.0 | 15.255.255.255 | F0000000 | 268.435.454 |
| /5 | 248.0.0.0 | 7.255.255.255 | F8000000 | 134.217.726 |
| /6 | 252.0.0.0 | 3.255.255.255 | FC000000 | 67.108.862 |
| /7 | 254.0.0.0 | 1.255.255.255 | FE000000 | 33.554.430 |
| /8 | 255.0.0.0 | 0.255.255.255 | FF000000 | 16.777.214 |
| /9 | 255.128.0.0 | 0.127.255.255 | FF800000 | 8.388.606 |
| /10 | 255.192.0.0 | 0.63.255.255 | FFC00000 | 4.194.302 |
| /11 | 255.224.0.0 | 0.31.255.255 | FFE00000 | 2.097.150 |
| /12 | 255.240.0.0 | 0.15.255.255 | FFF00000 | 1.048.574 |
| /13 | 255.248.0.0 | 0.7.255.255 | FFF80000 | 524.286 |
| /14 | 255.252.0.0 | 0.3.255.255 | FFFC0000 | 262.142 |
| /15 | 255.254.0.0 | 0.1.255.255 | FFFE0000 | 131.070 |
| /16 | 255.255.0.0 | 0.0.255.255 | FFFF0000 | 65.534 |
| /17 | 255.255.128.0 | 0.0.127.255 | FFFF8000 | 32.766 |
| /18 | 255.255.192.0 | 0.0.63.255 | FFFFC000 | 16.382 |
| /19 | 255.255.224.0 | 0.0.31.255 | FFFFE000 | 8.190 |
| /20 | 255.255.240.0 | 0.0.15.255 | FFFFF000 | 4.094 |
| /21 | 255.255.248.0 | 0.0.7.255 | FFFFF800 | 2.046 |
| /22 | 255.255.252.0 | 0.0.3.255 | FFFFFC00 | 1.022 |
| /23 | 255.255.254.0 | 0.0.1.255 | FFFFFE00 | 510 |
| /24 | 255.255.255.0 | 0.0.0.255 | FFFFFF00 | 254 |
| /25 | 255.255.255.128 | 0.0.0.127 | FFFFFF80 | 126 |
| /26 | 255.255.255.192 | 0.0.0.63 | FFFFFFC0 | 62 |
| /27 | 255.255.255.224 | 0.0.0.31 | FFFFFFE0 | 30 |
| /28 | 255.255.255.240 | 0.0.0.15 | FFFFFFF0 | 14 |
| /29 | 255.255.255.248 | 0.0.0.7 | FFFFFFF8 | 6 |
| /30 | 255.255.255.252 | 0.0.0.3 | FFFFFFFC | 2 |
| /31 | 255.255.255.254 | 0.0.0.1 | FFFFFFFE | 2 |
| /32 | 255.255.255.255 | 0.0.0.0 | FFFFFFFF | 1 |