IPv6 Address Planning for Enterprises and ISPs

With IPv4, address planning is about squeezing as much as possible from scarce space. With IPv6 the challenge flips: there is plenty of space, so the goal is a clean structure that is easy to route, secure and understand.

Basic building blocks

• Enterprises usually receive a /48 per site or a larger block such as a /32 from a registry.
• Every LAN segment gets a /64 — required for SLAAC and standard for all subnets.
• Point-to-point links commonly use /127, with a /64 reserved for each.
• Loopbacks use /128 from a dedicated block.

Design the hierarchy

Use the bits between your allocation and the /64 to encode meaning, aligned to nibble (4-bit) boundaries so addresses are readable. For example: region, then site, then function (users, servers, voice, IoT, management).

Good practices

1. Keep a consistent pattern across sites so engineers can read an address.
2. Reserve space for growth at every level.
3. Summarise routes at each level of the hierarchy.
4. Document everything in an IPAM system, not a spreadsheet.
5. Create RPKI ROAs for announced IPv6 prefixes too.

We design IPv6 addressing plans and manage them in our IPAM service. Plan your IPv6 rollout.