Dynamic and Permanent Lease Type

The lease type determines whether the lease policy (lease time and negotiation) is used for the addresses you are configuring. During initial server configuration, DHCP Manager allows you to select either dynamic or permanent leases for the addresses you are adding. The dhcpconfig utility allows only dynamic leases.

When an address has a dynamic lease, the DHCP server can manage the address by allocating it to a client, extending the lease time, detecting when it is no longer in use, and reclaiming it. When an address has a permanent lease, the DHCP server can only allocate it to a client, after which the client owns the address until the client explicitly releases it. When the address is released, the server can assign it to another client. The address is not subject to the lease policy as long as it is configured with a permanent lease type.

When you configure a range of IP addresses, the lease type you select applies to all the addresses in the range. To get the most benefit from DHCP, you should use dynamic leases for most of the addresses. You can later modify individual addresses to make them permanent if necessary, but the total number of permanent leases should be kept to a minimum.

Reserved Addresses and Lease Type

Addresses can be reserved by manually assigning them to particular clients. A reserved address can have a permanent or dynamic lease associated with it. When a reserved address is assigned a permanent lease, the address can only be allocated to the client that is bound to the address, the DHCP server cannot allocate the address to another client, and the address cannot be reclaimed by the DHCP server.

If a reserved address is assigned a dynamic lease, the address can only be allocated to the client that is bound to the address, but the client must track lease time and negotiate for a lease extension as if the address were not reserved. This allows you to track when the client is using the address by looking at the network table.

You cannot create reserved addresses for all the IP addresses during the initial configuration because they are intended to be used sparingly for individual addresses.