There are three ways that a DHCP server either assigns
or sends an IP address to a client:
—The DHCP server assigns a
permanent IP address to a client from its
On the firewall, a
the allocation is permanent.
—The DHCP server assigns a reusable
IP address from
of addresses to
a client for a maximum period of time, known as a lease.
This method of address allocation is useful when the customer has
a limited number of IP addresses; they can be assigned to clients
who need only temporary access to the network.
—The network administrator chooses
the IP address to assign to the client and the DHCP server sends
it to the client. A static DHCP allocation is permanent; it is done
by configuring a DHCP server and choosing a
to correspond to the
client firewall. The DHCP assignment remains in place even if the client
disconnects (logs off, reboots, has a power outage, etc.).
allocation of an IP address is useful, for example, if you have
a printer on a LAN and you do not want its IP address to keep changing, because
it is associated with a printer name through DNS. Another example
is if a client firewall is used for something crucial and must keep the
same IP address, even if the firewall is turned off, unplugged,
rebooted, or a power outage occurs.
Keep the following points
in mind when configuring a
It is an address from the
You can configure multiple reserved addresses.
If you configure no
the clients of the server will receive new DHCP assignments from
the pool when their leases expire or if they reboot, etc. (unless
you specified that a
If you allocate every address in the
, there are no dynamic
addresses free to assign to the next DHCP client requesting an address.
You may configure a
. In this case,
the DHCP server will not assign the
any firewall. You might reserve a few addresses from the pool and
statically assign them to a fax and printer, for example, without