DHCP Pool Calculator

Calculate a safe DHCP pool and generate RouterOS, Cisco IOS and ISC DHCP configuration.

Calculator ISP Toolkit Runs in your browser

Result

Network
192.168.50.0/24
Pool start
192.168.50.21
Pool end
192.168.50.254
Leases available
234
MikroTik RouterOS
/ip pool add name=pool-3232248320 ranges=192.168.50.21-192.168.50.254
/ip dhcp-server network add address=192.168.50.0/24 gateway=192.168.50.1 dns-server=1.1.1.1,8.8.8.8
Cisco IOS
ip dhcp excluded-address 192.168.50.1 192.168.50.20
ip dhcp pool NETVORX
 network 192.168.50.0 255.255.255.0
 default-router 192.168.50.1
 dns-server 1.1.1.1 8.8.8.8
ISC DHCP template
subnet 192.168.50.0 netmask 255.255.255.0 {
  range 192.168.50.21 192.168.50.254;
  option routers 192.168.50.1;
  option domain-name-servers 1.1.1.1, 8.8.8.8;
  default-lease-time 8h;
}
The gateway is not automatically inside the dynamic range. Ensure any other static devices are included in the reserved count or excluded separately.

About DHCP Pool Calculator

Turn a subnet into a deployable DHCP range while reserving infrastructure addresses at the start of the usable space. The same validated inputs produce RouterOS, Cisco IOS and ISC DHCP templates.

Pool boundaries

The dynamic pool begins after the requested reserved block and ends at the last usable address. The network, broadcast and gateway are checked before configuration is generated.

Deployment checklist

Confirm that statically addressed switches, access points, printers and servers are outside the dynamic range. Check relay addresses, authoritative-server placement, lease duration, DNS policy and failover behaviour. The generated commands are intentionally a starting template: vendor software versions and existing configuration can require different names or syntax. Review the candidate, back up the current configuration and test one client before migrating an entire VLAN.

Common use cases

  • Create a new VLAN scope.
  • Compare vendor configuration syntax.
  • Check usable lease capacity.

Edge cases and gotchas

  • Before activation, compare the proposed range with live leases, static assignments, reservations and relay configuration. A duplicate address can cause intermittent outages that are difficult to diagnose, so test on an isolated client and monitor server logs.

Frequently asked questions

Is the gateway included in the dynamic pool?
No automatic exception is needed when it is inside the reserved starting block. Otherwise exclude it explicitly before deployment. Also reserve every infrastructure or statically assigned address that could conflict with a client lease, and confirm existing reservations on the active server.
How should lease duration be chosen?
Use shorter leases for transient or scarce pools and longer leases for stable clients. Balance address recovery against renewal traffic, outages and operational policy.