The /29 prefix: 8 addresses, 6 usable
A /29 has 3 host bits: 8 addresses, mask 255.255.255.248. Networks begin on multiples of 8 — .0, .8, .16 — thirty-two of them per /24.
If you have ever bought "five static IPs" from a business ISP, you were handed a /29. Six usable addresses, minus one for the provider's gateway, leaves exactly five for your firewall and whatever it NATs or hosts. The math is not a coincidence.
| Prefix length | /29 |
| Subnet mask | 255.255.255.248 |
| Wildcard mask | 0.0.0.7 |
| Total addresses | 8 |
| Usable hosts | 6 |
The classic business static-IP block
A routed /29 is the smallest block most ISPs bother to sell, and it maps neatly onto small-business reality: one address for the router's outside interface, one for the mail server or VPN endpoint, a couple for NAT pools, and a spare or two. Anything larger and they would rather route you a /28.
Inside the data center
You will also meet /29s as transit and peering segments where a pair of routers needs breathing room — redundant handoffs running VRRP, for instance, where two routers, a virtual IP, and the provider's gear comfortably fill the six usable slots. It is the size you pick when a /30 feels claustrophobic but a /28 is pure waste.
CIDR Calculator
Run the math on 10.0.0.0/29 — or any other block
Frequently asked questions
How many IP addresses are in a /29?
8 in total (2^3), of which 6 are usable for hosts.
What is the subnet mask of a /29?
255.255.255.248. Five network bits in the last octet, so blocks start on multiples of 8.
Why did my ISP sell me five usable IPs with a /29?
A /29 has six usable addresses, and the ISP's gateway on your segment consumes one, leaving five for your equipment. That matches the common "five static IPs" business product.
When is a /29 the right size?
When you need a small routed block — static IPs from a provider, a transit segment with redundancy, or a tiny DMZ — and six addresses cover the requirement without waste.