Ipv4 Dhcp Server - D-Link NetDefendOS User Manual

5.3. IPv4 DHCP Server

A NetDefendOS DHCP Server object assigns and manages IP addresses taken from a specified
address pool. These servers are not limited to serving a single range of IP addresses but can use
any IP address range that can be specified by a NetDefendOS IP address object.
The DHCPServer object is used for IPv4 addresses and the DHCPv6Server object is used for IPv6
objects. The two are configured in very similar ways although the underlying implementations
are very different. The IPv6 server also provides several options which do not exist for IPv4. DHCP
relay and IP pools cannot currently be used with IPv6 DHCP.
Multiple DHCP Servers
The administrator has the ability to set up one or more logical IPv4 or IPv6 DHCP servers in
NetDefendOS. Filtering of DHCP client requests to different DHCP servers is based on a
combination of the following DHCP Server properties:
• Interface
Each NetDefendOS interface can have, at most, one single logical DHCP server associated
with it. In other words, NetDefendOS can provision DHCP clients using different address
ranges depending on what interface they are located on.
• Relay Filter
The value of the Relay Filter property is also used to determine which DHCP Server object to
use. The default value of all-nets means that all addresses are accepted and only the interface
is considered in making a DHCP server selection. The other options for this parameter are
described further below.
Searching the Server List
Multiple DHCP servers form a list as they are defined, the last defined being at the top of the list.
When NetDefendOS searches for a DHCP server to service a request, it goes through the list from
top to bottom and chooses the first server with a matching combination of interface and relayer
IP filter value. If there is no match in the list then the request is ignored.
The DHCP server ordering in the list can, of course, be changed through one of the user
interfaces.
Setting the Relay Filter Property
As explained above, the DHCP Server object used for a client is selected based on a match of both
the Interface and Relay Filter properties of the object. A DHCP Server object must have a Relay
Filter value specified and the possible values are the following:
• 0.0.0.0/0
The default value is 0.0.0.0/0 (all-nets). This means all DHCP requests will match this filter
value regardless if the DHCP requests comes from a client on the local network or has arrived
via a DHCP relayer.
• A value of 0.0.0.0
The value 0.0.0.0 will match DHCP requests that come from a local client only. DHCP requests
that have been relayed by a DHCP relayer will be ignored.
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Chapter 5: DHCP Services