IPRangeExplorer

/9 vs /11 — Subnet Comparison

A /9 subnet is 4× larger than a /11. Every additional bit in the prefix halves the address space — the 2-bit difference between these two means /9 has 22 = 4 times as many addresses.

/9

8.3 million IPs — half a /8

Full reference →
Total IPs 8,388,608
Usable Hosts 8,388,606
Subnet Mask 255.128.0.0
Wildcard Mask 0.127.255.255

Typical Uses

  • →Large regional ISP allocation
  • →Half of a Class A block
  • →Aggregated routing prefix
/11
Full reference →
Total IPs 2,097,152
Usable Hosts 2,097,150
Subnet Mask 255.224.0.0
Wildcard Mask 0.31.255.255

Key Differences

4×
more IPs in /9 than /11
4
/11 subnets fit inside one /9
2
bits of difference in prefix length

How 4 /11 Subnets Divide a /9

Example using 10.0.0.0/9 as the parent block.

# CIDR Network First Usable Last Usable Broadcast Hosts
1 10.0.0.0/11 10.0.0.0 10.0.0.1 10.31.255.254 10.31.255.255 2,097,150
2 10.32.0.0/11 10.32.0.0 10.32.0.1 10.63.255.254 10.63.255.255 2,097,150
3 10.64.0.0/11 10.64.0.0 10.64.0.1 10.95.255.254 10.95.255.255 2,097,150
4 10.96.0.0/11 10.96.0.0 10.96.0.1 10.127.255.254 10.127.255.255 2,097,150

FAQ

What is the difference between /9 and /11?

A /9 has 8,388,606 usable hosts and a /11 has 2,097,150. The subnet masks differ: /9 uses 255.128.0.0 while /11 uses 255.224.0.0. Every additional bit in the prefix halves the number of addresses — so the 2-bit gap means /9 is exactly 4× larger.

How many /11 subnets fit in a /9?

Exactly 4 /11 subnets fit perfectly inside one /9 with no wasted space. To split a /9 into /11s, 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.