/0 Subnet Mask ReferenceIPv4
The /0 mask, written <code>0.0.0.0</code>, fixes zero network bits, so a single block spans every IPv4 address in existence. You will almost never configure it directly; you meet it constantly as <code>0.0.0.0/0</code>, the default route.
/0 facts at a glance
- Subnet mask
- 0.0.0.0
- Wildcard mask
- 255.255.255.255
- Binary mask
- 00000000.00000000.00000000.00000000
- Total addresses
- 4,294,967,296
- Usable hosts
- 4,294,967,294 (excludes network & broadcast)
- Block size
- 4,294,967,296 addresses (232)
- Typical role
- Default route and internet-wide aggregates
Example /0 networks
A /0 spans a large share of the address space, so one aligned example says it all.
| Network | Usable range | Usable hosts |
|---|---|---|
| 0.0.0.0/0 | 0.0.0.1 – 255.255.255.254 | 4,294,967,294 |
How to calculate a /0 mask
A /0 mask sets the first 0 bits of a 32-bit number to 1 and leaves the remaining 32 bits as 0. In binary that reads 00000000.00000000.00000000.00000000, which converts to dotted decimal 0.0.0.0. Each block covers a contiguous run of 232 = 4,294,967,296 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving 255.255.255.255.
Where /0 is used
- Default routing: <code>0.0.0.0/0</code> is the catch-all table entry that forwards traffic no other route matches.
- ACLs and firewall rules: the wildcard mask <code>255.255.255.255</code> expresses 'match any address'.
- Documentation and diagrams that depict the entire address space as one object.
- The mathematical baseline: every other prefix is simply a subdivision of /0.
Strictly speaking, a /0 has no single network or broadcast address, yet calculators conventionally subtract two, reporting 4,294,967,294 usable hosts. Read that figure as arithmetic convention, not an operational limit.
A default route is the least specific entry possible. Longest-prefix-match guarantees that any narrower route, whether a /24 or a /32, always wins over <code>0.0.0.0/0</code>.
Frequently asked questions
How many IP addresses are in a /0?
Exactly 4,294,967,296, because 2^32 is the size of the whole IPv4 address space. Applying the customary minus-two convention leaves 4,294,967,294 nominally usable addresses.
What does a 0.0.0.0 netmask mean?
No bits identify the network, so all 32 bits are host bits. As a routing destination, <code>0.0.0.0/0</code> matches every possible address, which is why it serves as the default route.
Can I assign a /0 to an interface?
There is no practical reason to. Interfaces carry specific prefixes such as /24, while <code>0.0.0.0/0</code> belongs in routing tables and firewall policies as a pointer toward a next hop.
Is 0.0.0.0/0 the same as 0.0.0.0/8?
No. The /0 covers all 4,294,967,296 addresses; the /8 covers only the 16,777,216 addresses whose first octet is zero, a range set aside for 'this network' and unusable on the Internet.
Open this block in a calculator
Open the /0 block in the subnet calculator