/5 Subnet Mask ReferenceIPv4
A /5, masked <code>248.0.0.0</code>, is an eight-lane slice of IPv4: 134,217,728 addresses, or eight consecutive /8-sized networks under one summary. Outside aggregation exercises, deployments are vanishingly rare.
/5 facts at a glance
- Subnet mask
- 248.0.0.0
- Wildcard mask
- 7.255.255.255
- Binary mask
- 11111000.00000000.00000000.00000000
- Total addresses
- 134,217,728
- Usable hosts
- 134,217,726 (excludes network & broadcast)
- Block size
- 134,217,728 addresses (227)
- Typical role
- Aggregation and supernetting
Example /5 networks
A /5 spans a large share of the address space, so one aligned example says it all.
| Network | Usable range | Usable hosts |
|---|---|---|
| 192.0.0.0/5 | 192.0.0.1 – 199.255.255.254 | 134,217,726 |
How to calculate a /5 mask
A /5 mask sets the first 5 bits of a 32-bit number to 1 and leaves the remaining 27 bits as 0. In binary that reads 11111000.00000000.00000000.00000000, which converts to dotted decimal 248.0.0.0. Each block covers a contiguous run of 227 = 134,217,728 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving 7.255.255.255.
Where /5 is used
- Supernetting practice on five-bit boundaries.
- Mapping broad regions of the space, such as the fully reserved top slice 248.0.0.0/5 (248-255).
- Certification coursework on variable-length masking.
Worked example: <code>72.0.0.0/5</code> stretches from 72.0.0.0 to 79.255.255.255. Every /5 aligns on a first-octet multiple of eight.
Frequently asked questions
What is the mask for a /5?
<code>248.0.0.0</code>, wildcard <code>7.255.255.255</code>. Five one-bits fix the top of the first octet in steps of eight.
How many addresses are in a /5?
134,217,728 total and 134,217,726 usable by convention: twice a /6 and half a /4.
How many /8s are inside a /5?
Eight. For instance, 72.0.0.0/5 contains the /8 networks beginning 72, 73, 74, 75, 76, 77, 78, and 79.
Open this block in a calculator
Open the /5 block in the subnet calculator