/0 vs /2 — Subnet Comparison
A /0 subnet is 4× larger than a /2. Every additional bit in the prefix halves the address space — the 2-bit difference between these two means /0 has 22 = 4 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 4 /2 Subnets Divide a /0
Example using 10.0.0.0/0 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 0.0.0.0/2 | 0.0.0.0 | 0.0.0.1 | 63.255.255.254 | 63.255.255.255 | 1,073,741,822 |
| 2 | 64.0.0.0/2 | 64.0.0.0 | 64.0.0.1 | 127.255.255.254 | 127.255.255.255 | 1,073,741,822 |
| 3 | 128.0.0.0/2 | 128.0.0.0 | 128.0.0.1 | 191.255.255.254 | 191.255.255.255 | 1,073,741,822 |
| 4 | 192.0.0.0/2 | 192.0.0.0 | 192.0.0.1 | 255.255.255.254 | 255.255.255.255 | 1,073,741,822 |
FAQ
What is the difference between /0 and /2?
A /0 has 4,294,967,294 usable hosts
and a /2 has 1,073,741,822.
The subnet masks differ: /0 uses 0.0.0.0
while /2 uses 192.0.0.0.
Every additional bit in the prefix halves the number of addresses — so the 2-bit gap means
/0 is exactly 4× larger.
How many /2 subnets fit in a /0?
Exactly 4 /2 subnets fit perfectly inside one /0 with no wasted space. To split a /0 into /2s, just increment the last 2 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.