IP Address Planner

How IP Planning Works

IP address planning is a critical step in network design that ensures efficient use of address space while accommodating future growth. The planner starts with a base CIDR block (e.g., 10.0.0.0/16) and segments it into smaller subnets based on your requirements. Each segment specifies a name, the number of devices it needs to support, and an optional growth percentage to buffer for future expansion. The planner sorts segments by required size (largest first) and allocates contiguous address blocks from the base range.

For each segment, the planner calculates the required subnet size by adding the growth buffer to the device count, then adding two addresses for the network and broadcast addresses. It determines the smallest prefix length that can accommodate the required hosts, constrained by the base prefix. The result is a table showing each planned subnet with its name, CIDR notation, network address, prefix length, total hosts, and usable hosts. This structured approach prevents overlapping allocations and ensures consistent addressing across your network infrastructure.

Best practices for IP planning include using RFC 1918 private address ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) for internal networks, starting with a generous base allocation, applying consistent growth percentages across similar segments, and documenting VLAN IDs alongside subnet assignments. The planner supports these conventions and provides a clear, exportable view of your addressing scheme suitable for inclusion in network documentation and change management records.

Hierarchical Allocation for Route Summarization

A well-structured IP plan follows a hierarchical allocation model. The base CIDR block is divided into regional or functional blocks, each of which is further subdivided into site or segment subnets. This hierarchy directly supports route summarisation: if all subnets in a data centre fall under 10.1.0.0/20, the upstream router can advertise a single prefix instead of dozens of /24s. The planner enforces contiguity within the base block, ensuring that the resulting allocations are summarisable at each level of the hierarchy.

Data centre IPAM introduces additional considerations such as loopback addresses for network devices, point-to-point links between routers (/31 or /30 subnets), and infrastructure service ranges for DNS, NTP, and load balancers. A comprehensive plan reserves dedicated blocks for each of these purposes rather than scattering them across the main allocation. By separating infrastructure addressing from workload addressing, you simplify troubleshooting and reduce the risk of accidental overlap between critical services and dynamic workloads.