DHCP server

by Johannes Helmig [Published on 1 Nov. 1999 / Last Updated on 1 Nov. 1999]

TCP/IP has become for more and more installations the preferred network
protocol, also pushed by the explosive growth of the Internet, which is
based on TCP/IP.

When using a network with only Windows95 and WindowsNT4 based systems,
you will have to assigned the IP-addresses manually (Windows98 includes an
IP-Auto-Configuration system
), but more and more server-systems offer the
automatic assignment of IP-addresses via:
DHCP (Dynamic Host Configuration Protocol)


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The installation of the DHCP-server on Windows NT4 server (the DHCP-server
is NOT included in Windows NT4 workstation )
is very simple:

In the Network-configuration,
tab: Services, click on "Add"
and then select:
"Microsoft DHCP Server"

The following notice will be displayed:

The system running the DHCP-server (distributing IP-addresses to other systems)
itself MUST use a static IP-address (manually assigned) , it can NOT request
to receive an IP-address from any DHCP-server (itself or another DHCP server).

Like after all changes to the network configuration, you have to reboot:


Configuration of the DHCP-server

Although the DHCP-server is listed
as a Networking service, it is NOT
configured from the Network applet
(the Properties button is grayed out)
The "DHCP - Manager" has been
added to the menu for the
"Administrative Tools"
You need to define now a range of IP-addresses
to be distributed.
This range is called: "Scope".

To be able to define Scope, click first on the
entry "Local Machine" to expand the entry,
the "+" -sign needs to change to the "-"-sign.
Only then you are able to select from the
menu: "Scope" the option "Create"


You assign the range of IP-addresses to be assigned by DHCP-server
( in the example: all IP-addresses between 102.54.107.1 and 192.54.107.49):

usually, an IP-address is NOT assigned permanently, but only for a limited
time, called the "Lease Duration".

On selected the "OK"-button, you will be asked on whether to activate
the scope, select "Yes":


The yellow light-bulb indicates, that
the scope is now active and that the
DHCP-server is ready to assign the
IP-addresses.
To display the IP-range ("Scope") for
viewing/editing, select from the menu
"Scope" the option "Properties"

Setting up a connected Windows systems to use the DHCP-server is very simple:

In the Network-configuration,
select the properties for the
TCP/IP-protocol and just make
sure, that it defines to
"obtain an IP address automatically"


To verify the assigned IP-address on a Windows95/98 system, run the
"WINIPCFG" program (usually from the RUN-menu)(On Windows NT, use IPCONFIG):

In this example, DHCP assigned the IP-address 192.54.107.1.
But there is no "Default gateway" defined !


TCP/IP requires more than just the IP-address, for communication outside
the local network-cable (the local "subnet"), it needs to know the IP-address
of the Gateway (also called Router).
DHCP can be configured to provide also this information to the clients:

make sure, that your Scope is selected
(highlighted in blue), then select from the
menu: "DHCP Options", then "Scope"


From the list of
"Unused Options", select
"Router", then use the
"Add"-button.
Once the "Router" is
an "Active Option",
click on the button
"Value" to define the
IP-address for the Router.
On the expanded Windows,
click on "Edit Array",
allowing then to enter
the IP-address of the
Router, then select the
"Add"-button to get the
new values displayed in
the list of IP-addresses.

Press "OK" to exit this
window.
The IP-address of the
Router is displayed.

Press "OK" to close the
DHCP-Options window.


The DHCP-Mananger is now displayed
for the scope also the option for the
Router.

When now checking on Windows95/98 with WINIPCFG:

the IP-address for the "Default Gateway" is defined.

If your configuration requires the use of WINS, it can be also configured
as an option of the DHCP-server.


DHCP can also be used to assigned IP-addresses for incoming RAS-
connections
:


To view the list of IP-address already
assigned, select from the menu: "Scope"
the option "Active Leases"
In this example, 192.54.107.1 is assign
to a LAN user, while 192.54.107.2
is assigned to the Modem to handle
incoming RAS TCP/IP-connections.

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