Uniqcli

Subnet & VLSM calculator: plan IPv4 address space

Normalize a prefix and allocate aligned LAN, /31 point-to-point and /32 host requests inside it.

Networking

IPv4 CIDR and VLSM allocator

Normalize a prefix and allocate aligned LAN, /31 point-to-point and /32 host requests inside it.

Example inputs · Replace these with your measurements to build your plan.

Modes: lan reserves network/broadcast; p2p means exactly two endpoints; host means exactly one.

Method, example and sources
  1. Normalize the parent IPv4 address to its prefix boundary.
  2. Choose a power-of-two LAN block including network and broadcast addresses.
  3. Allocate largest blocks first on aligned boundaries.
  4. Use /31 only for two-endpoint point-to-point links and /32 for a single host.

Worked example. The /24 example allocates /26, /27, /31 and /32 blocks: 99 addresses allocated and 157 unallocated. A /31 supplies two endpoints without a broadcast address.

Your planning result

Aligned IPv4 allocation

Largest blocks are allocated first. /31 is point-to-point; /32 is one host, not a normal LAN.

Parent network
192.0.2.0/24
Parent addresses
256
Parent usable endpoints
254
Allocated addresses
99
Unallocated addresses
157
IPv4 CIDR and VLSM allocator: detailed result
RequestPrefixFirst endpointLast endpointBroadcastAddresses
office192.0.2.0/26192.0.2.1192.0.2.62192.0.2.6364
lab192.0.2.64/27192.0.2.65192.0.2.94192.0.2.9532
uplink192.0.2.96/31192.0.2.96192.0.2.97No broadcast2
loopback192.0.2.98/32192.0.2.98192.0.2.98No broadcast1
  • DHCP reservations, gateways and overlapping existing allocations are not inferred. The parent input may contain a host address; it is normalized to its network boundary.

From the catalog

Routers & Gateways

Explore related listings, then confirm the exact model requirements against your plan. These listings are not an automatic compatibility or capacity verdict.

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How to use this result

Different subnet requests need different block sizes. Allocating the largest first prevents a small allocation from fragmenting the boundary required by a larger network. A LAN request includes space for its network and broadcast addresses; it does not silently include your gateway, DHCP reservations or future endpoints. Add those requirements to the requested endpoint count.

What to verify next

A /31 has special point-to-point semantics under RFC 3021, and a /32 identifies one address. Neither is a general substitute for a broadcast LAN. The worksheet starts with a clean parent prefix and does not discover existing allocations, routes or DHCP exclusions. Reconcile the result with your address plan before configuring switches, routers or services.

Worked example

The /24 example allocates /26, /27, /31 and /32 blocks: 99 addresses allocated and 157 unallocated. A /31 supplies two endpoints without a broadcast address.

Subnet & VLSM calculator: plan IPv4 address space — Uniqcli