/17 vs /19 — Subnet Comparison
A /17 subnet is 4× larger than a /19. Every additional bit in the prefix halves the address space — the 2-bit difference between these two means /17 has 22 = 4 times as many addresses.
32K IPs — half a /16
Typical Uses
- →Half of a /16 VPC split public/private
- →Large campus segment
Key Differences
How 4 /19 Subnets Divide a /17
Example using 10.0.0.0/17 as the parent block.
| # | CIDR | Network | First Usable | Last Usable | Broadcast | Hosts |
|---|---|---|---|---|---|---|
| 1 | 10.0.0.0/19 | 10.0.0.0 | 10.0.0.1 | 10.0.31.254 | 10.0.31.255 | 8,190 |
| 2 | 10.0.32.0/19 | 10.0.32.0 | 10.0.32.1 | 10.0.63.254 | 10.0.63.255 | 8,190 |
| 3 | 10.0.64.0/19 | 10.0.64.0 | 10.0.64.1 | 10.0.95.254 | 10.0.95.255 | 8,190 |
| 4 | 10.0.96.0/19 | 10.0.96.0 | 10.0.96.1 | 10.0.127.254 | 10.0.127.255 | 8,190 |
FAQ
What is the difference between /17 and /19?
A /17 has 32,766 usable hosts
and a /19 has 8,190.
The subnet masks differ: /17 uses 255.255.128.0
while /19 uses 255.255.224.0.
Every additional bit in the prefix halves the number of addresses — so the 2-bit gap means
/17 is exactly 4× larger.
How many /19 subnets fit in a /17?
Exactly 4 /19 subnets fit perfectly inside one /17 with no wasted space. To split a /17 into /19s, 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.