IPv6 Subnets: Design Principles and Addressing at Scale

1. Understanding IPv6 Subnetting

IPv6 subnetting differs significantly from IPv4. IPv6 addresses are 128-bit, written in hexadecimal format (e.g., 2001:db8:abcd:0012::1), allowing an almost unlimited address space.

Unlike IPv4, IPv6 subnetting focuses less on conserving addresses and more on:

• Simplicity

• Hierarchical design

• Scalability

2. IPv6 Address Structure

An IPv6 address typically consists of:

• Global Routing Prefix – assigned by an ISP or RIR

• Subnet ID – used by the organization

• Interface ID – identifies the host

In most real-world deployments:

• /64 is the standard subnet size

• Each subnet contains 2⁶⁴ addresses

This allows features like Stateless Address Autoconfiguration (SLAAC) to function properly.

3. Common IPv6 Subnet Prefixes

Unlike IPv4, IPv6 does not use broadcast addresses. Instead, it relies on multicast and anycast for network communication.

4. Benefits of IPv6 Subnetting

IPv6 subnetting provides major advantages:

• Practically unlimited address space

• No need for NAT in most designs

• Improved routing aggregation

• Built-in support for security (IPsec)

• Better support for modern networks (IoT, cloud, mobile)

5. IPv6 vs IPv4 Subnetting – Key Differences