Timothy
Parker Consulting Incorporated
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DHCP,
WINS and DNS Windows
NT offers server support for DHCP (Dynamic Host Configuration Protocol) and WINS
(Windows Internet Naming Service). Both
DHCP and WINS are relative newcomers to the IP address assignment and naming
service arena, which previously has been dominated by DNS (Domain Name System).
DNS has been used for years on UNIX systems, and is employed throughout
the Internet and most connected networks. Both WINS and DHCP make networking
just a little less bothersome for most Windows 95 and Windows 3.X users,
simplifying the network configuration process an administrator must perform on
those clients. Does
the lack of support for DHCP and WINS in the larger market limit their
usefulness, and do DHCP and WINS offer anything DNS doesn’t?
That’s a question many administrators are facing as they choose which
of the services to implement on their networks.
In this article, we take a look at the three services, how they perform,
how they can interact, and the type of support you will find for all three.
Despite what most people think, DNS does not directly compete with DHCP
(although it does the same task as WINS), and often the three services can be
combined together to offer the maximum flexibility for a network. DHCP There
are a couple of misconceptions about DHCP that should be cleared up.
First, DHCP isn’t a totally new protocol.
Its roots lie in the TCP/IP BOOTP (Boot Protocol) system used to supply
boot-up instructions and configuration information mostly to diskless
workstations. Second, Microsoft
didn’t design DHCP. It was
designed (albeit with considerable Microsoft support) by the Internet
Engineering Taskforce (IETF) due to the widely recognized need among TCP/IP
users to provide a method of dynamic IP address allocation.
This non-Microsoft origin helps explain why DHCP isn’t the Windows-only
orphan that WINS is. Currently
there are DHCP support products for many platforms, including UNIX.
Like
WINS, DHCP is also installed on a Windows NT server and provides two primary
services for easing the load on administrators: it allows many TCP/IP parameters
for the entire network to be defined at the server and transmitted to clients
automatically, and it provides for automatic configuration of TCP/IP services on
client machines. This usually eliminates the need for a Windows client user to
configure TCP/IP. If a client
machine is moved from one location on the network to another, DHCP takes care of
the automatic reconfiguration for the that machine.
This is especially handy for laptop devices, as well as machines that
move between a number of local area networks regularly.
Laptops are the most obvious beneficiary of the roving plug-in function.
A laptop simply needs a network connection and then DHCP can handle the
configuration. Otherwise, the
laptop configuration may need to be manually adjusted with every move. DHCP
is based on standard client-server models.
Machines are organized into groups called scopes, which is a logical
division of machines rather than a physical separation.
One or more Windows NT machines are designated as DHCP servers, each of
which has all the configuration parameters for any client that may attach itself
to the network. A pool of generic IP addresses is maintained by the server
for dynamic allocation to new clients. A
client is any type of machine (usually just Windows 95 and Windows NT) which
connects to a network. On startup
the client communications with the server and receives any TCP/IP configuration
details it needs.. While
the advantages of DHCP don’t really become useful for small network of a dozen
or so clients, as the network size grows DHCP becomes more and more handy.
When DHCP is running on a network, plugging in a new machine is almost
trivial, at least from the networking aspect.
To add a Windows 95 or Windows 3.X machine, the network configuration
consists of telling the client which network protocol is in use and the IP
address of the DHCP server. DHCP takes care of the rest of the configuration, including
assigning an IP address. (While it
may not sound like a lot of timesaving, the client would normally have to have
its IP address, subnet mask, gateway IP address, domain name, and DNS server
address entered and checked for validity.)
Also
important is the ability to alter the configuration on every machine on the
network with one change on the DHCP server.
For example, suppose a gateway or DNS server IP address changes on your
network. Normally, you would have
to visit each client and alter its IP address reference manually.
With DHCP, a single change on the DHCP server is propagated to all
clients quickly and takes effective almost immediately.
That’s a huge time saver, especially for networks with server IP
addresses that change regularly. Some
administrators don’t want to allow totally dynamic IP address allocation, and
DHCP allows quite a but of flexibility in that respect.
An administrator can restrict the range of IP addresses, or specify
particular addresses (reserved addresses) for some machines that shouldn’t
have a dynamic IP address. As a side benefit of DHCP, if a network has more machines
than IP addresses available for connection to the Internet, for example, DHCP
can be set to expire IP addresses after a set period of time and hence allow
more clients to connect to the Internet (a procedure called leasing).
DHCP doesn’t have to conflict with DNS, as many administrators think.
Since DHCP can be configured to provide static IP addresses to machines
(especially DNS servers), there is no problem with supporting both DNS and DHCP
on the same network. For
many administrators, the primary advantage of DHCP is that is concentrates most
of the network configuration information at one source: the DHCP server.
If there’s a problem with the network configuration, it can usually be
traced from the server instead of having to check every machine on the network.
This centralized configuration concept pays extra dividends as the
network size increases over a few dozen machines, and is especially useful on
intranets with a number of subnets. Since
DHCP is almost trivial to install and configure, and it runs from both NT
Workstation and NT Server, it is almost a no-brainer to include it on network
configurations. Client software is
built in to Windows 95, and available through the 32-bit Microsoft TCP/IP stack
for Windows for Workgroups. UNIX
systems support DHCP through commercial products, and Macintosh DHCP stacks are
being introduced. With this kind of
flexibility, DHCP should be running on most networks, especially large ones. WINS WINS
was developed by Microsoft as a means of using the features of DHCP for name
resolution. Although it doesn’t
have to run with DHCP, WINS often is supported at the same time.
WINS has one major advantage over DNS, it’s direct competitor: DNS
doesn’t support dynamic names and IP addresses, instead requiring static
information in its database. WINS
was designed to allow dynamic IP address resolution.
(More specifically, WINS resolves NetBIOS names to dynamic IP addressees.
There is a difference between a machine’s NetBIOS name, which applies
only to Windows machines, and the TCP/IP host name, which may not be anything
like the NetBIOS name in some cases.) WINS
maintains a database similar to DNS. The
database, which is located on a Windows NT server, provides a computer name to
IP address mapping, allowing other computers on the Windows NT network to use
the WINS system to connect to other machine by supplying a machine name instead
of an address. Why would you want to use WINS instead of the Internet-standard
DNS? There are a number of reasons,
the most important of which is support for Windows features that did not have to
be considered when DNS was introduced. WINS
better integrates NetBIOS systems with TCP/IP by providing the ability to use
NetBIOS’ long name support (especially important for Windows NT and Windows 95
users) and eliminating many configuration problems.
WINS is totally proprietary to Microsoft Windows operating systems and
does not work with DNS or with other platforms. WINS
has a few important advantages over DNS. Probably
the most important for most networks is the direct support of NetBIOS names
during IP address resolution, as already mentioned.
Another advantage that becomes important for larger networks is the
ability to use WINS across an IP router, which cannot usually be done with
NetBIOS name resolution broadcast techniques.
WINS works across entire networks with no regard to the intervening
routers, and in the process drops network traffic from client broadcasting. To
use WINS, one Windows NT machine on a network must be set as the primary WINS
server. It has a fixed IP address
that all other Windows client machines (Windows 3.X, Windows 95, and Windows NT)
have embedded in their WINS configuration sheet. When a name resolution is required, the client Windows
machine contacts the WINS server
with the machine name to be found and receives back the IP address. Other Windows NT machines on the network can be assigned as
WINS secondary servers, if needed to support a heavy WINS request load. DNS The
Domain Name System (DNS) has been available for decades and has its roots in
UNIX, hence the somewhat cumbersome configuration processes it needs.
The major advantage to DNS is that because it has been around for so long
it is reliable, efficient, and available on most platforms.
Most DNS servers are UNIX-based, although Windows NT can act as a DNS
server with the proper software. Configuring
DNS requires a bit of forethought as to how a network is going to function.
The machines on the network to be managed by the DNS server are allocated
to a group called a zone (similar to a subnetwork in principle, but the IP
addresses don’t have to be distinct from other subnetworks). Within each zone,
there may be one or more secondary name servers, with the primary and secondary
name servers holding duplicate information. The name servers within a zone
communicate with each other using a zone transfer protocol to ensure their
tables are in sync and clients can connect to either primary or secondary
machines for name resolution. There may be several zones managed by one DNS
server. The
steps involved in setting up a DNS server are to configure the primary DNS
server (followed by any secondary servers, if there are any), then set up the
domain and authority delegation. Each
client that is to use the server must have DNS client software installed.
The format of DNS records is rather complex to non-UNIX administrators,
with several files and record formats involved.
To
greatly simplify, the files hold a list of IP addresses and the names that are
assigned to that IP address. Several
names and aliases can be assigned to a single IP address.
When a client wants to resolve a name, it sends a request to the server
which searches the files for a name match, then returns the IP address to the
client. DNS requires static IP
addresses and cannot support schemes such as DHCP which allows dynamic IP
addresses except through some cumbersome kludges. Do
You Need to Choose? One
of the problems many administrators face when setting up a Windows NT system is
whether to support DHCP, WINS, DNS, or some combination of the three.
The impression most administrators have, based on UseNet traffic and
discussion groups on CompuServe, is that the three are mutually exclusive, or
that at least a choice between WINS and DNS is necessary.
As you have seen so far, this is not really true.
Sometimes you will want to employ all three, depending on the makeup of
your network. A
few simple examples should help clarify the situation.
If your network is all Windows machines (Windows 3.X, Windows for
Workgroups, Windows 95, and Windows NT), then there is really a simple solution:
run both DHCP and WINS. Both services work well over Windows-only networks and
provide all the services you need. Configuring
both DHCP and WINS is trivial, as you will see in a moment. If,
on the other hand, you have a mixed network with Windows, Macintosh, and UNIX
machines (or some other heterogeneous mixture of platforms), you may want to add
DNS to the system too. This is
especially true if the non-Windows machines have static IP addresses, which DNS
handles perfectly. The Windows
machines can then have either static IP address or dynamic, and can be handled
by either DNS or WINS. Finally,
if the network is mostly non-Windows, you are probably going to be running DNS
as the name resolution system, especially if UNIX servers are in the network.
DHCP can still be used for Windows machines and laptops, serving only the
Windows clients and integrating with DNS for name resolution.
WINS could be run for the Windows machines, too, but the configuration
starts to get complicated if the Windows machines are in a considerable
minority. Installing
and Configuring DHCP, WINS, and DNS The
installation routine is similar for all three services: use the Network applet
in the Control Panel and select the Services page tab.
There are two entries in the Services list (click the Add button to see
what’s available): Microsoft DHCP Server and DHCP Relay Agent.
The DHCP Server service is self-explanatory; the DHCP Relay Agent is
responsible for relaying DHCP messages from server to client.
Both services should be installed on the server.
For WINS, the only service is the Windows Internet Name Service.
(If you want to use the NT Performance Monitor or some other networking
performance package to monitor the behavior of WINS, you need to install the
SNMP Service, too.) The DNS server service can be installed with the Microsoft
DNS Server option, which should be done after TCP/IP services are installed and
configured. Windows
NT provides the DHCP Manager application to control DHCP (usually available
under the Administrative Tools option in the Startup menu).
The local server is identified automatically as a DHCP server, and others
can be added (although they must be specified in the fully qualified domain name
format, not NetBIOS names). The
DHCP Manager window lets administrators define scopes (at least one scope must
be defined for DHCP to function properly) with dynamic, reserved (machines that
always are given the same IP address) and excluded IP addresses given.
One a scope is defined it is activated and any clients connecting to the
server are handled properly. If you
are running both DHCP and DNS on the network, assign reserved IP addresses to
all the machines that have a DNS entry, and let the rest be assigned
dynamically. The
WINS Manager provides the interface for administrators to the WINS system.
From the WINS Manager, static name mappings can be established.
Procedures such as backing up the WINS database and configuring
replication to secondary WINS servers can also be performed from there.
A statistics display shows how many resolution requests has been received
by WINS. Finally, the DNS Manager
provides the administrator with a similar service for DNS.
The DNS manager lets administrators define zones and observe statistics
about the DNS server’s requests and service rate. After
the services have been installed, the clients need to be told which services are
active and where to access them. This is usually a matter of activating the
proper service in the Network page of the Windows 95 or Windows 3.X system.
WINS and DNS has a page tab all its own in Windows 95.
To activate DHCP, select the “Obtain an IP Address box” on the
Network IP address page tab. After
that, a reboot of the machine will start the polling of the server. For
non-Windows machines, the configuration of DNS and DHCP depends on the
third-party software, and differs considerably depending on the package.
Under Windows 3.X, there are a number of popular TCP/IP commercial
protocol stacks that support DNS, and DHCP support has started to appear.
Wrapping
Up Hopefully
this article has explained the primary features of DHCP, WINS, and DNS, and how
they work to provide name and IP services to clients. As you have seen, the three services are not exclusive of
each other, and on larger networks work very well together.
The primary advantages of DHCP and WINS are their excellent Windows NT
support and tailoring for the NetBIOS environment.
While DNS is going to be around for many decades to come, it’s nice to
have the option of using WINS on a Windows network for even more flexibility.
Don’t be bashful: give all three services a try! |
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tparker@tpci.com with
questions or comments about this web site.
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