/29 vs /31 — Subnet Comparison
A /29 subnet is 4× larger than a /31. Every additional bit in the prefix halves the address space — the 2-bit difference between these two means /29 has 22 = 4 times as many addresses.
6 usable hosts — tiny cluster
Typical Uses
- →Small server cluster (web + app + db)
- →Infrastructure management segment
- →Very small office or branch
2 host addresses — RFC 3021 P2P
Typical Uses
- →Point-to-point link (more efficient than /30)
- →Router interface addressing with RFC 3021 support
- →BGP peering links
Key Differences
How 4 /31 Subnets Divide a /29
Example using 10.0.0.0/29 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 |
FAQ
What is the difference between /29 and /31?
A /29 has 6 usable hosts
and a /31 has 2.
The subnet masks differ: /29 uses 255.255.255.248
while /31 uses 255.255.255.254.
Every additional bit in the prefix halves the number of addresses — so the 2-bit gap means
/29 is exactly 4× larger.
How many /31 subnets fit in a /29?
Exactly 4 /31 subnets fit perfectly inside one /29 with no wasted space. To split a /29 into /31s, just increment the last 2 bits of the network address for each new subnet.
Which should I choose?
/29 is typically used for: Tiny server cluster or infra segment. /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.