IPv6 subnet sizes explained: /64 vs /56 vs /48

An IPv6 subnet is just a block of IPv6 addresses, identified by a prefix length like /64, /56, or /48. The prefix tells you how many bits are fixed (network part) vs variable (host part). Because IPv6 addresses are 128 bits (versus IPv4’s 32 bits), even a “tiny” IPv6 subnet contains astronomically more addresses than anything in IPv4.

This article explains the three IPv6 subnet sizes you’ll actually encounter, when to use each, and how to request one on your ColossusCloud VPS.

IPv6 subnet basics (coming from IPv4)

In IPv4, you might have a /24 (256 addresses), a /28 (16 addresses), or a single IP. The numbers are small enough to fit in your head. A /24 is a “normal” sized block.

IPv6 is a completely different scale. The numbers are so large they stop being meaningful in human terms. The concepts are the same (a prefix length tells you how big your block is), but every IPv6 subnet is vast by IPv4 standards.

The three IPv6 subnet sizes that matter

/64: one network segment

A /64 is the standard IPv6 subnet size. It’s what goes on a single network segment: a LAN, a VLAN, or the network inside a VPS.

How many addresses in a /64? About 18.4 quintillion (18,446,744,073,709,551,616). More addresses than exist in the entire IPv4 internet. Four times over.

You’ll never use them all, and that’s fine. IPv6 was designed with intentional waste. A /64 is the minimum recommended size for any network because IPv6 features like SLAAC (Stateless Address Autoconfiguration) expect a /64.

When to use /64: One VPS, block of IPv6 addresses for containers, services, or virtual machines on it.

/56: 256 network segments

A /56 contains 256 /64 subnets. Designed for situations where you need multiple separate networks, not just multiple addresses.

When to use /56: Multiple isolated networks inside your VPS: Docker networks, VPN segments, or customer environments that each need their own /64. A /56 lets you carve out separate subnets without requesting more blocks.

/48: 65,536 network segments

A /48 contains 65,536 /64 subnets. Typically assigned to organizations, not individual servers. ISPs and enterprises use /48 blocks to subnet their entire network.

When to use /48: Probably never for a single VPS. This size is for organizations managing large networks with many sites. For VPS hosting, a /64 or /56 covers you.

Visualizing IPv6 subnet hierarchy

/48  ─── contains 65,536 /64 subnets ─── enterprise/organization
 └── /56  ─── contains 256 /64 subnets ─── site/large deployment
      └── /64  ─── single network segment ─── your VPS, your LAN

Each step up by 8 bits multiplies the number of /64 subnets by 256.

Practical IPv6 subnet examples on a VPS

Single server with containers

VPS running Docker, want each container to have its own IPv6 address. A /64 is perfect. Assign addresses from your /64 to each container. All share one network segment but have unique addresses.

Multiple isolated environments

Hosting platform on your VPS, want each customer site to have its own network. Request a /56. Assign a /64 to each customer’s network space. Isolated at the network level, each with their own subnet.

IoT gateway

VPS manages dozens of IoT devices needing publicly reachable IPv6 addresses. A /64 gives every device its own address with room for millions more. No NAT, no port forwarding, direct connectivity.

How to request an IPv6 subnet on ColossusCloud

Every ColossusCloud VPS comes with one IPv6 address by default. To get a routed /64 or /56:

1. Log into the Client Portal
2. Go to your VPS management page
3. Look for the IPv6 networking section
4. Request your preferred subnet size

The subnet gets routed to your VPS’s primary IPv6 address. You configure the individual addresses on your server’s network interfaces.

Do I really need that many addresses?

No, you don’t need quintillions of addresses. Nobody does. IPv6 was designed with abundance on purpose.

With IPv4, addresses were scarce, so people learned to conserve them: NAT, port sharing, private ranges. IPv6 throws that scarcity away. A huge subnet means you never think about address conservation. Assign freely, organize however makes sense, don’t worry about running out.

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Request an IPv6 subnet (/64 or /56) for your VPS through the Client Portal. For setup help, see our IPv6 configuration guides.