User manual

Configuration through the web interface
78
lease
A lease is the length of time that the DHCP server specifies, during which a client host
can use an assigned IP address. When the DHCP server grants a lease to a client, the
lease is active. Before the lease expires, the client typically needs to renew its address
lease assignment with the DHCP server. A lease becomes inactive when it expires or it
is deleted at the server, or if the client actively releases the lease. The duration of a lease
determines when it will expire and how often the client needs to renew it with the DHCP
server in order to retain the lease.
A DHCP server will never grant a lease to its own address. There is no need for its own
address to be in the exclusion range; the DHCP server simply protects its address from
being offered.
grace period
When a DHCP client actively releases a lease, or when the lease expires without being
renewed by the client, the DHCP server does not immediately delete the lease record
and return the associated IP address to the available address pool. A grace period is the
interval of time for which the lease record is retained before the DHCP server
automatically deletes the record from its lease list, thereby making the IP address
available for lease assignment to another client. The grace period is not a configurable
value. See also the discussion of the grace period and what it means when the DHCP
server is running in "View and manage current DHCP leases" on page 191.
reservation
You may use a reservation to create a permanent address lease assignment by the DHCP
server. Reservations assure that a specified hardware device on the subnet can always
use the same IP address. Address lease reservations associate a specific IP address with
a specific client's Ethernet MAC address.
options
Options are other client configuration parameters that the DHCP server can assign when
serving leases to DHCP clients. Most options are defined in RFC 2132. The DHCP
server in Digi device supports a limited set of options:
– Option 3: Routers on Subnet
– Option 6: DNS Servers