/3 Subnet Mask ReferenceIPv4
With mask <code>224.0.0.0</code>, a /3 locks three bits and captures the entire top eighth of IPv4: 536,870,912 addresses. That region is deliberately special-purpose, holding multicast plus the reserved experimental range.
/3 facts at a glance
- Subnet mask
- 224.0.0.0
- Wildcard mask
- 31.255.255.255
- Binary mask
- 11100000.00000000.00000000.00000000
- Total addresses
- 536,870,912
- Usable hosts
- 536,870,910 (excludes network & broadcast)
- Block size
- 536,870,912 addresses (229)
- Typical role
- Aggregation and supernetting
Example /3 networks
A /3 spans a large share of the address space, so one aligned example says it all.
| Network | Usable range | Usable hosts |
|---|---|---|
| 192.0.0.0/3 | 192.0.0.1 – 223.255.255.254 | 536,870,910 |
How to calculate a /3 mask
A /3 mask sets the first 3 bits of a 32-bit number to 1 and leaves the remaining 29 bits as 0. In binary that reads 11100000.00000000.00000000.00000000, which converts to dotted decimal 224.0.0.0. Each block covers a contiguous run of 229 = 536,870,912 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving 31.255.255.255.
Where /3 is used
- Explaining where multicast and experimental addressing live.
- Reserved-space accounting when auditing how much of IPv4 is actually assignable.
- Advanced CIDR drills on high-order bit boundaries.
<code>224.0.0.0/3</code> decomposes into multicast <code>224.0.0.0/4</code> (RFC 1112) plus reserved <code>240.0.0.0/4</code>. Neither half is public unicast space, so the block never appears as an allocation.
Frequently asked questions
How many addresses are in a /3?
536,870,912 total; the calculator convention yields 536,870,910 usable, although in reality this slice of space is not host-addressable at all.
Which mask belongs to /3?
<code>224.0.0.0</code>, with wildcard <code>31.255.255.255</code>: three fixed one-bits and twenty-nine host bits.
Can hosts use addresses from 224.0.0.0/3?
No. The range 224.0.0.0 through 255.255.255.255 is multicast (RFC 1112) plus reserved space, so ordinary interfaces never take an address from it.
Open this block in a calculator
Open the /3 block in the subnet calculator