IPRangeExplorer

/27 vs /31 — Subnet Comparison

A /27 subnet is 16× larger than a /31. Every additional bit in the prefix halves the address space — the 4-bit difference between these two means /27 has 24 = 16 times as many addresses.

/27

30 usable hosts — small workgroup

Full reference →
Total IPs 32
Usable Hosts 30
Subnet Mask 255.255.255.224
Wildcard Mask 0.0.0.31

Typical Uses

  • →Small workgroup LAN
  • →Network device management subnet
  • →Cloud NAT gateway subnet
/31

2 host addresses — RFC 3021 P2P

Full reference →
Total IPs 2
Usable Hosts 2
Subnet Mask 255.255.255.254
Wildcard Mask 0.0.0.1

Typical Uses

  • →Point-to-point link (more efficient than /30)
  • →Router interface addressing with RFC 3021 support
  • →BGP peering links

Key Differences

16×
more IPs in /27 than /31
16
/31 subnets fit inside one /27
4
bits of difference in prefix length

How 16 /31 Subnets Divide a /27

Example using 10.0.0.0/27 as the parent block.

# CIDR Network First Usable Last Usable Broadcast Hosts
1 10.0.0.0/31 10.0.0.0 10.0.0.0 10.0.0.1 10.0.0.1 2
2 10.0.0.2/31 10.0.0.2 10.0.0.2 10.0.0.3 10.0.0.3 2
3 10.0.0.4/31 10.0.0.4 10.0.0.4 10.0.0.5 10.0.0.5 2
4 10.0.0.6/31 10.0.0.6 10.0.0.6 10.0.0.7 10.0.0.7 2
5 10.0.0.8/31 10.0.0.8 10.0.0.8 10.0.0.9 10.0.0.9 2
6 10.0.0.10/31 10.0.0.10 10.0.0.10 10.0.0.11 10.0.0.11 2
7 10.0.0.12/31 10.0.0.12 10.0.0.12 10.0.0.13 10.0.0.13 2
8 10.0.0.14/31 10.0.0.14 10.0.0.14 10.0.0.15 10.0.0.15 2
9 10.0.0.16/31 10.0.0.16 10.0.0.16 10.0.0.17 10.0.0.17 2
10 10.0.0.18/31 10.0.0.18 10.0.0.18 10.0.0.19 10.0.0.19 2
11 10.0.0.20/31 10.0.0.20 10.0.0.20 10.0.0.21 10.0.0.21 2
12 10.0.0.22/31 10.0.0.22 10.0.0.22 10.0.0.23 10.0.0.23 2
13 10.0.0.24/31 10.0.0.24 10.0.0.24 10.0.0.25 10.0.0.25 2
14 10.0.0.26/31 10.0.0.26 10.0.0.26 10.0.0.27 10.0.0.27 2
15 10.0.0.28/31 10.0.0.28 10.0.0.28 10.0.0.29 10.0.0.29 2
16 10.0.0.30/31 10.0.0.30 10.0.0.30 10.0.0.31 10.0.0.31 2

FAQ

What is the difference between /27 and /31?

A /27 has 30 usable hosts and a /31 has 2. The subnet masks differ: /27 uses 255.255.255.224 while /31 uses 255.255.255.254. Every additional bit in the prefix halves the number of addresses — so the 4-bit gap means /27 is exactly 16× larger.

How many /31 subnets fit in a /27?

Exactly 16 /31 subnets fit perfectly inside one /27 with no wasted space. To split a /27 into /31s, just increment the last 4 bits of the network address for each new subnet.

Which should I choose?

/27 is typically used for: Small workgroup / management subnet. /31 is better for: Modern P2P links (RFC 3021). Choose the smallest prefix that comfortably fits your host count — over-allocating wastes address space, but under-allocating means painful renumbering later.

Related Comparisons

/24 vs /27 /26 vs /27 /27 vs /28 /30 vs /31