03.26.01
Dynamic Host Configuration Protocol, or as it is better known, DHCP,
is a complex network addressing system that isn't all that difficult
to use. If you are still manually configuring your IP addresses, this
article is well worth reading. If you have any questions, comments or
suggestions, we would love to hear from you. Read on and enjoy.
Jay Fougere
How To Simplify Dynamic Addressing With DHCP Editor
To begin with, what will DHCP do for you? It will assign IP addresses
along with the appropriate subnet masks so that you will not have to
manually configure all of the machines on your network with IP
addresses. DHCP can pass options to the DHCP client, such as default
gateway addresses, DNS server addresses and the DNS domain name.
Dynamic addressing can also reduce your workload by configuring
clients automatically and, if configured properly, they will be
error free. In Windows 2000, DHCP can even be set up to dynamically
update DNS.
No longer do you, as network administrator, have to maintain large
lists of computers and their IP addresses. No longer will you be
troubleshooting connectivity problems that result from mistakes in
manual configurations. You will be able to configure your DHCP
server(s) and DHCP related options once. After that, all that you
will have to do is to configure each local machine to obtain an IP
address from a DHCP server. The host machine does not even have to
know the address of the DHCP server. It will find the server
automatically, as long as it is on the same subnet or you have bootp
forwarding routers separating your subnets.
When you boot a DHCP client, it will broadcast a request for an IP
address. A DHCP server will then assign an address from its address
pool with a specified length of time that the client can use that
particular address (along with any server/scope options that have
been configured). This is known as a lease. The client will attempt
to renew the lease when it is approximately 50% expired. In event
that it cannot renew the lease at this time, it will try again at a
later time. If at that point it still cannot contact the DHCP server
that had granted the lease, it will broadcast for any available DHCP
server to obtain a new lease. Any leases that have expired will
result in those addresses being returned to the address pool on the
DHCP server.
Want to increase to your customer list and boost your profitability?
Look for 'Reseller' link".
This all sounds great, you say, but what are the limitations? What
may be viewed as a problem is the fact that DHCP requests are
restricted to a single subnet. DHCP requests do not cross routers
into other subnets. The reason that it seems a problem is that DHCP
was intentionally designed to stay within the subnet so as not to
create bottlenecks on your network. For example, you have a network
with many clients (by many I mean several thousand). If all of these
clients were to send DHCP requests out on the network at the same
time, the amount of traffic on the network could exceed the
capabilities of the network. By restricting requests to a single
subnet, network traffic can be dramatically reduced.
Suppose that you have several subnets in your network but each subnet
does not warrant its own DHCP server. In that event, you would set up
a DHCP relay agent on each subnet. DHCP relay agents listen for DHCP
requests and then forward (accross routers, etc...) these requests to
the appropriate DHCP server(s). A typical DHCP server can handle
thousands of IP addresses, especially if that server is dedicated to
serving out DHCP leases.
Another problem would be a rogue DHCP server on the network. This is
the case in which a DHCP server that should not be handing out IP
addresses is doing just that. This can result in all kinds of
connectivity and configuration problems that can be very difficult to
trace. Windows 2000 has done much to remedy this type of problem by
requiring that all DHCP servers be authorized in Active Directory
before they can hand out IP addresses. If the DHCP server in question
is not a Windows 2000 server, you will still have to manually
shutdown the DHCP service on that particular machine.
|
|
 |
|
Today we are going to discuss setting up DHCP on a Windows 2000
server. The first thing that you will have to do is verify that the
DHCP service is installed on your machine. Simply go to
Start / Programs / Administrative Tools and see if DHCP is there. If it
is not there, you can verify that it is not installed by going to
"services" and checking there.
In the event that DHCP is not installed on your machine, simply go
to Control Panel and double click "Add / Remove Programs". Next,
select "Add / Remove Windows Components" and then select "Networking
Services" and finally select "Details". Check the box next to DHCP
and press OK and then complete the Windows Components Wizard. That
is it, DHCP is now installed on your machine.
Now, you will need to configure DHCP on your server. Go to DHCP on
the Administrative Tools menu. In the Console Tree view (the left
side of the DHCP management console), you should see your server. If
it is not there, go to Action and select Add Server. Next, simply add
your server (it will be the default choice).
Once your server is visible in the Console Tree, you will need to add
a scope or scopes. A scope is the pool of addresses that you will be
able to assign to clients either by reservation (more on reservations
in a sec') or by lease. A scope is created by right-clicking the
server name in the Console Tree and selecting New Scope.
Whether you are a parent watching your kid's internet use, or you are
a teacher monitoring your class or you are a manager looking over
his business interests...
This brings up, you guessed it, the New Scope Wizard, which functions
much in the same way as any other Microsoft Wizard. The first thing
that you will have to do is to assign a name to the scope. If you are
going to be using many scopes, make each name represents something
about that particular subnet. For instance, some example names may be
"first floor", "satellite office", "factory floor", "DHCP server1"
etc... You can then add a description if you like. This is for your
own reference, much like the names that you choose.
The next step is choosing the range of addresses and the subnet mask
that you will be using. Subnetting is beyond the scope (no pun
intended) of this article, however, you can read more about it here.
You will then be asked to choose a range of addresses to exclude
from distribution. This range of addresses would be those that
corellate to statically configured hosts, such as servers, gateways
or even network printers.
Lastly, you will be asked to configure options for the scope.
Documentation for these options can be found in the typical places
(help index, technet, etc..) and is beyond the scope of this article;
there may be more on that in a later issue. This will be where you
can configure default gateway addresses, DNS server addresses, etc...
to pass to the DHCP client. In regards to options; options can be
configured at the server or scope level. If you have several acopes
that will all use the same options, configure them at the server
level. If each scope will need individual options, configure them at
the scope level. If you have a combination (ie. options that should
be configured at the server level and options that should be
configured at the scope level) this can also be done, however, keep
in mind that scope options will override server options. For example,
if you configure the server to hand out a gateway address of X.X.X.X
and the scope to hand out a gateway address of Y.Y.Y.Y, the client
that obtains a lease through that scope will have a gateway of
Y.Y.Y.Y . One last note on options, not all operating systems will
support all options. 100% compatibility will only be achieved in pure
Windows 2000 networks. This will not prevent a client from recieving
lease, it will simply determine which options that client will
implement.
Once you have completed the Wizard, you will notice that your scope
has a red down arrow on it. This is because the scope has not been
activated. To activate the scope, simply right click the scope in
the Console Tree and select "Activate". That is it, try booting up a
client and check to see if it recieves an appropriate address. For
some really cool command line tools to check out your configuration,
click here.
|
|
