The /8 prefix means the first 8 bits of the address identify the network and the remaining 24 identify the host. Written out, the mask is 255.0.0.0, in binary 11111111.00000000.00000000.00000000, and its Cisco wildcard or inverse form is 0.255.255.255. It covers 16,777,216 addresses, of which 16,777,214 can be given to hosts.
| CIDR prefix | /8 |
|---|---|
| Subnet mask | 255.0.0.0 |
| Mask in binary | 11111111.00000000.00000000.00000000 |
| Wildcard (inverse) mask | 0.255.255.255 |
| Host bits | 24 |
| Total addresses | 16,777,216 |
| Usable hosts | 16,777,214 |
| Block size (magic number) | whole octet 1 |
A 10.0.0.0/8 splits into exactly 1 subnet of this size.
| Network | First host | Last host | Broadcast |
|---|---|---|---|
| 10.0.0.0/8 | 10.0.0.1 | 10.255.255.254 | 10.255.255.255 |
A /8 falls exactly on an octet boundary, so there is no magic number to work out: octet 1 of the mask is 255 and every subnet starts where the previous one ended, counting octet 1 up by one.
A /8 is a whole legacy class A: 16.7 million addresses. Only one of them matters day to day, 10.0.0.0/8, the largest RFC 1918 private block. Nobody runs a flat /8. It is the top of the tree, the space an enterprise carves into regional /16s and then into per-VLAN /24s.
A /8 holds 16,777,216 addresses in total. After reserving the network and broadcast addresses, 16,777,214 are usable by hosts.
The /8 subnet mask is 255.0.0.0 in dotted-decimal notation.
The wildcard mask, also called the inverse mask, is 0.255.255.255. It is the bitwise inverse of 255.0.0.0 and is what Cisco access lists and OSPF network statements expect.
The /8 mask written out bit by bit is 11111111.00000000.00000000.00000000: 8 ones followed by 24 zeros.