/0 vs /4 — Subnet Comparison
A /0 subnet is 16× larger than a /4. Every additional bit in the prefix halves the address space — the 4-bit difference between these two means /0 has 24 = 16 times as many addresses.
The entire IPv4 internet
Typical Uses
- →Default route / route of last resort
- →Firewall "allow all" or "deny all" rule
- →BGP full routing table advertisement
Key Differences
How 16 /4 Subnets Divide a /0
Example using 10.0.0.0/0 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 0.0.0.0/4 | 0.0.0.0 | 0.0.0.1 | 15.255.255.254 | 15.255.255.255 | 268,435,454 |
| 2 | 16.0.0.0/4 | 16.0.0.0 | 16.0.0.1 | 31.255.255.254 | 31.255.255.255 | 268,435,454 |
| 3 | 32.0.0.0/4 | 32.0.0.0 | 32.0.0.1 | 47.255.255.254 | 47.255.255.255 | 268,435,454 |
| 4 | 48.0.0.0/4 | 48.0.0.0 | 48.0.0.1 | 63.255.255.254 | 63.255.255.255 | 268,435,454 |
| 5 | 64.0.0.0/4 | 64.0.0.0 | 64.0.0.1 | 79.255.255.254 | 79.255.255.255 | 268,435,454 |
| 6 | 80.0.0.0/4 | 80.0.0.0 | 80.0.0.1 | 95.255.255.254 | 95.255.255.255 | 268,435,454 |
| 7 | 96.0.0.0/4 | 96.0.0.0 | 96.0.0.1 | 111.255.255.254 | 111.255.255.255 | 268,435,454 |
| 8 | 112.0.0.0/4 | 112.0.0.0 | 112.0.0.1 | 127.255.255.254 | 127.255.255.255 | 268,435,454 |
| 9 | 128.0.0.0/4 | 128.0.0.0 | 128.0.0.1 | 143.255.255.254 | 143.255.255.255 | 268,435,454 |
| 10 | 144.0.0.0/4 | 144.0.0.0 | 144.0.0.1 | 159.255.255.254 | 159.255.255.255 | 268,435,454 |
| 11 | 160.0.0.0/4 | 160.0.0.0 | 160.0.0.1 | 175.255.255.254 | 175.255.255.255 | 268,435,454 |
| 12 | 176.0.0.0/4 | 176.0.0.0 | 176.0.0.1 | 191.255.255.254 | 191.255.255.255 | 268,435,454 |
| 13 | 192.0.0.0/4 | 192.0.0.0 | 192.0.0.1 | 207.255.255.254 | 207.255.255.255 | 268,435,454 |
| 14 | 208.0.0.0/4 | 208.0.0.0 | 208.0.0.1 | 223.255.255.254 | 223.255.255.255 | 268,435,454 |
| 15 | 224.0.0.0/4 | 224.0.0.0 | 224.0.0.1 | 239.255.255.254 | 239.255.255.255 | 268,435,454 |
| 16 | 240.0.0.0/4 | 240.0.0.0 | 240.0.0.1 | 255.255.255.254 | 255.255.255.255 | 268,435,454 |
FAQ
What is the difference between /0 and /4?
A /0 has 4,294,967,294 usable hosts
and a /4 has 268,435,454.
The subnet masks differ: /0 uses 0.0.0.0
while /4 uses 240.0.0.0.
Every additional bit in the prefix halves the number of addresses — so the 4-bit gap means
/0 is exactly 16× larger.
How many /4 subnets fit in a /0?
Exactly 16 /4 subnets fit perfectly inside one /0 with no wasted space. To split a /0 into /4s, just increment the last 4 bits of the network address for each new subnet.
Which should I choose?
Choose based on how many hosts you need. Use the hosts → prefix calculator on the homepage to find the right size for your requirements.