Dhcp Servers - D-Link DFL-1660 User Manual

5.2. DHCP Servers

5.2. DHCP Servers
DHCP servers assign and manage the IP addresses taken from a specified address pool. In
NetDefendOS, DHCP 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.
Multiple DHCP Servers
The administrator has the ability to set up one or more logical DHCP servers in NetDefendOS.
Filtering of DHCP client requests to different DHCP servers is based on a combination of:
• 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.
• Relayer IP - The relayer IP address in the IP packet is also used to determine the server. The
default value of all-nets means that this 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.
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.
Using Relayer IP Address Filtering
As explained above a DHCP server is selected based on a match of both interface and relayer IP
filter. Each DNS server must have a relayer IP filter value specified and the possible values are as
follows:
• The default value is all-nets (0.0.0.0/0). 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 will match DHCP requests that come from a local client only. DHCP requests
that have been relayed by a DHCP relayer will be ignored.
• A specific IP address. This is the IP address of the DHCP relayer through which the DHCP
request has come. Requests from local clients or other DHCP relayers will be ignored.
Configurable DHCP Options
A number of options which relate to the response sent to clients can be configured for each DHCP
server instance:
• Netmask - netmask sent to the DHCP Client.
• Gateway Address - what IP should be sent to the client for use as the default gateway. If 0.0.0.0
is specified the IP given to the client will be sent as the gateway.
• Domain Name - The domain which the client will belong to.
• Lease Time - the time, in seconds that a DHCP lease should be provided to a host after which
the client must renew the lease.
• DNS Servers - DNS servers the client can use for DNS lookup.
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Chapter 5. DHCP Services