Plan an address space without overlaps

Add networks one at a time or in a batch and the planner shows how they fit together, warns when two ranges overlap, carves blocks into VLSM subnets, and works out the supernet that covers a group of routes. It handles IPv6 as well as IPv4, and the plan can be exported for documentation.

Common questions

How do I check whether two CIDR ranges overlap?

Two ranges overlap when one contains the other’s network address: 10.0.0.0/16 contains 10.0.5.0/24, so they collide. Add both here and the planner flags it. Overlaps break VPN tunnels and VPC peering, so check before connecting networks.

What is a supernet or route summary?

One shorter prefix that covers several contiguous networks, such as 10.1.0.0/22 covering 10.1.0.0/24 to 10.1.3.0/24. Summaries keep routing tables small. They only work cleanly when the networks are contiguous and aligned to the summary’s block size.

How should I size IPv6 subnets?

Use a /64 for every LAN or VLAN, because SLAAC and many IPv6 features expect it. Sites usually get a /48 (65,536 /64s) or a /56 (256 /64s), so in IPv6 you plan the number of subnets rather than hosts per subnet.

How do I plan VLSM subnets?

List the subnets with the hosts each needs, sort them largest first, and allocate each from the next free address that fits its block size. Allocating the large ones first stops small subnets breaking up the space.

Which private ranges should I use?

10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 (RFC 1918). Avoid 192.168.0.0/24 and 192.168.1.0/24 for anything that will be reached over a VPN, because home routers use them and the ranges will clash.

Related tools: Cloud VPC Planner · CIDR Calculator · NetBuilder Pro · All tools A–Z