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What is a /29 subnet? 8 IPs for a firewall pair and a few servers

By TechCompare · Updated · How we check

At 255.255.255.248, a /29 holds 8 total IPv4 addresses and 6 usable on a conventional subnet. Azure leaves 3 for resources, and AWS doesn't allow this size at all.

Small enough to plan by hand, a /29 gives 8 addresses at 255.255.255.248, with 6 usable on a conventional IPv4 subnet. It's a tight block, sized for a firewall pair, a gateway address, and a handful of servers on one segment. The mask leaves little room for growth, so the plan needs to be settled before the segment goes live.

CIDR
/29
Total addresses
8
6 usable for hosts
Subnet mask
255.255.255.248

CIDR reference table

Every IPv4 prefix from /8 to /32 with its subnet mask, wildcard mask and address counts. Pick a prefix to open its page or the calculator.

PrefixSubnet maskWildcard maskTotal addressesUsable hosts
/8255.0.0.00.255.255.25516,777,21616,777,214
/9255.128.0.00.127.255.2558,388,6088,388,606
/10255.192.0.00.63.255.2554,194,3044,194,302
/11255.224.0.00.31.255.2552,097,1522,097,150
/12255.240.0.00.15.255.2551,048,5761,048,574
/13255.248.0.00.7.255.255524,288524,286
/14255.252.0.00.3.255.255262,144262,142
/15255.254.0.00.1.255.255131,072131,070
/16255.255.0.00.0.255.25565,53665,534
/17255.255.128.00.0.127.25532,76832,766
/18255.255.192.00.0.63.25516,38416,382
/19255.255.224.00.0.31.2558,1928,190
/20255.255.240.00.0.15.2554,0964,094
/21255.255.248.00.0.7.2552,0482,046
/22255.255.252.00.0.3.2551,0241,022
/23255.255.254.00.0.1.255512510
/24255.255.255.00.0.0.255256254
/25255.255.255.1280.0.0.127128126
/26255.255.255.1920.0.0.636462
/27255.255.255.2240.0.0.313230
/28255.255.255.2400.0.0.151614
/29This page255.255.255.2480.0.0.786
/30255.255.255.2520.0.0.342
/31255.255.255.2540.0.0.122
/32255.255.255.2550.0.0.011

Usable hosts are the total minus the network address and the broadcast address. A /31 is the exception: it has neither, so both addresses work as hosts on a point to point link (RFC 3021). A /32 is a single address. The wildcard mask is the subnet mask with every bit flipped, and Cisco IOS access lists and OSPF network commands use it.

This exact /29 mask, pre-loaded. Enter your network address or step the mask up and down.
Edit in the full tool

How this is calculated

The 3 host bits work out to 2^3 = 8 addresses. A /24 holds 32 of these blocks, and the first three in the last octet are .0-.7, .8-.15, .16-.23. The wildcard mask is 0.0.0.7, which is what an access list or OSPF network statement uses to match this block.

Azure and AWS treat this size differently. Azure accepts a /29 and keeps five addresses in every subnet, leaving 3 for resources. AWS allows nothing smaller than a /28, so a /29 isn't an option there.

Verdict

Choose a /29 for a segment with only a few fixed devices, such as a firewall pair, its gateway, and a couple of management hosts. The mask 255.255.255.248 leaves 3 host bits, which gives 8 addresses in all and 6 usable on a conventional subnet.

The neighbors frame the choice. A /28 has 16 addresses and 14 usable. It's also the smallest block AWS accepts. A /30 has 4 addresses and 2 usable, which covers only the two ends of a link.

If the segment runs in Azure, plan around the 3 addresses left for resources. That's a tight budget, so count the appliances and their future interfaces before you pick this size.

More Subnet scenarios

/24 subnet (255.255.255.0)
A /24 subnet, written as 255.255.255.0 in dotted-decimal notation, provides 256 total addresses with 254 usable for hosts (one reserved for the network address and one for broadcast).
View details
/16 subnet (255.255.0.0)
A /16 subnet, written as 255.255.0.0, provides 65,536 total addresses with 65,534 usable for hosts.
View details
/28 subnet (255.255.255.240)
A /28 subnet, written as 255.255.255.240, provides 16 total addresses with 14 usable on a conventional IPv4 subnet.
View details

Related guides

/28 subnet
AWS's smallest subnet, one size up from this block.
View guide
/30 subnet
The point to point size, for a link with exactly two ends.
View guide
/24 subnet
The block that holds a whole set of small segments like this one.
View guide
Bandwidth calculator
Estimate transfer times for the link behind a small segment.
View guide

Frequently asked questions

How many usable IPs are in a /29?
6 on a conventional IPv4 subnet, out of 8. The network address is 192.168.1.8, and the broadcast address is 192.168.1.15. In Azure, 3 addresses are left for resources, because Azure reserves five in every subnet.
Can I create a /29 subnet in AWS?
No. AWS allows subnet sizes from /16 to /28, so a /29 is outside its range. The smallest subnet AWS lets you create is a /28.
Can I create a /29 subnet in Azure?
Yes. A /29 is the smallest IPv4 subnet Azure supports. Azure reserves five addresses in every subnet, which leaves 3 for your resources.
What is the wildcard mask for a /29?
0.0.0.7. It's the reverse of the subnet mask. The bits that identify the network are 0, and the host bits are 1, so the wildcard tells a router which bits to ignore.

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