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IPv6 /48 subnet: 65,536 /64 networks for a business site

By TechCompare · Updated · How we check

A /48 subnet holds 65,536 /64 networks and 256 /56 blocks, which is room to number many sites and LANs under one allocation.

RIPE-690 says some operators give a /48 to business customers and a /56 to residential ones. The /48 is large: it holds 65,536 /64 networks, or 256 /56 blocks, out of 1,208,925,819,614,629,174,706,176 addresses in all. RFC 6177 says a fixed /48 recommendation isn't nuanced enough for the broad range of end sites.

Prefix
/48
80 host bits
Total addresses
1.21 septillion
2^80
/64 networks
65,536
Each one a LAN
A /48 on the 2001:db8:: example prefix, pre-loaded. Swap in your own prefix or step the length up and down.
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How this is calculated

Think of the /48 in three levels. The /48 covers the whole business, each site takes a /56 from it, and each LAN inside a site gets a /64. The 256 /56 blocks give the business room for that many sites, and every one of them still holds 256 /64s.

Verdict

Use a /48 when a business has several sites, floors or departments to number. Give each site a /56 and each LAN a /64, and keep the spare /56 blocks free for sites you haven't built yet. RIPE-690 says you can't assign less than a /64 to a LAN, so the /64 is the bottom of the plan. Since RFC 6177 no longer recommends /48 as a single default, let the number of sites and LANs set the size. The block runs from 2001:db8:: to 2001:db8:0:ffff:ffff:ffff:ffff:ffff.

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

How many /64s fit in a /48
The worked count and the bit math behind it.
View guide
IPv6 /56 subnet
The home and small-site block a business splits its /48 into.
View guide
IPv6 /64 subnet
One LAN, and why RIPE-690 sets /64 as the smallest LAN size.
View guide
IPv4 vs IPv6 comparison
How IPv6 addressing differs from IPv4.
View guide
/24 subnet
The IPv4 counterpart, for comparison with a familiar block size.
View guide

Frequently asked questions

Is a /48 too big for a small business?
It can be. RFC 6177 says registries now encourage smaller /56 blocks for end sites, so a single office may not need a /48. The block holds 65,536 /64s, and that room only helps when the business has enough sites or LANs to use it.
Why do some operators give businesses a /48?
RIPE-690 describes that split as an operator's choice, not a rule. A business with many sites and LANs has more use for the extra room.
How should a business divide a /48?
Give each site a /56, which holds 256 /64s, and give each LAN inside a site its own /64. The /48 then has 256 /56 blocks to work with. Stop at /64 for each LAN and don't split further.

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