Open Plan (/plan).
You see nested prefixes and their child subnets, with utilization. Click a subnet to open /subnets/{id}.
The plan page spells the rule: reservation pins an IP to a device (MAC, DUID, or client-id). Exclude keeps an address out of DHCP (gateway, VIP, something already used). Dynamic leases are what dhcpd already handed out — look them up in the header search.
Create a prefix
Admin only. Add a CIDR and optional description (example: 10.10.0.0/16 as the container). Prefixes nest; they are the plan, not the DHCP scope.
Create a subnet
Under a prefix, create a subnet whose CIDR is the broadcast domain (example: 10.20.20.0/24). Then on the subnet screen set:
- Gateway
- VLAN, site, VRF (optional)
- Lease time (seconds, default 86400)
- Renew / rebind (optional)
- Authoritative
- DDNS on/off, adapter, forward zone, reverse zone
- NTP servers (option 42)
The DHCP plane reads these rows. There is no second “ISC config” to keep in sync.
Pools, reservations, excludes, and options are on the same subnet page. Lab walk-through: First subnet. See Subnet.