/4 Subnet Mask ReferenceIPv4
Networking's most famous /4 needs no introduction: <code>224.0.0.0/4</code> is multicast, the former Class D territory where one packet reaches many willing listeners at once. The mask is <code>240.0.0.0</code> and the block spans 224.0.0.0 through 239.255.255.255.
/4 facts at a glance
- Subnet mask
- 240.0.0.0
- Wildcard mask
- 15.255.255.255
- Binary mask
- 11110000.00000000.00000000.00000000
- Total addresses
- 268,435,456
- Usable hosts
- 268,435,454 (excludes network & broadcast)
- Block size
- 268,435,456 addresses (228)
- Typical role
- Aggregation and supernetting
Example /4 networks
A /4 spans a large share of the address space, so one aligned example says it all.
| Network | Usable range | Usable hosts |
|---|---|---|
| 192.0.0.0/4 | 192.0.0.1 – 207.255.255.254 | 268,435,454 |
How to calculate a /4 mask
A /4 mask sets the first 4 bits of a 32-bit number to 1 and leaves the remaining 28 bits as 0. In binary that reads 11110000.00000000.00000000.00000000, which converts to dotted decimal 240.0.0.0. Each block covers a contiguous run of 228 = 268,435,456 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving 15.255.255.255.
Where /4 is used
- One-to-many delivery such as video distribution and market-data feeds.
- Routing protocol chatter: OSPF hello packets target 224.0.0.5 and 224.0.0.6.
- Lab work with multicast groups, IGMP, and PIM.
Well-known residents include 224.0.0.1, the all-hosts group on a link, and the OSPF pair 224.0.0.5 and 224.0.0.6. A multicast address never appears as the source of a packet.
The familiar usable-hosts arithmetic does not really apply here: multicast groups have members, not hosts, so the minus-two figure is a formality.
Frequently asked questions
What is 224.0.0.0/4 used for?
IP multicast. A sender transmits once to a group address and the network delivers copies to subscribed receivers, saving bandwidth compared with unicasting to each member.
How many addresses are in a /4?
268,435,456, one sixteenth of IPv4. The nominal usable figure is 268,435,454, though multicast semantics make the distinction academic.
What subnet mask corresponds to /4?
<code>240.0.0.0</code> (wildcard <code>15.255.255.255</code>): the first four bits are set, matching exactly the addresses that begin with binary 1110.
Open this block in a calculator
Open the /4 block in the subnet calculator