Lecture

Networking Lesson Plan Week 8 Addendum


Windows Server 2000/2003

DHCP


Dynamic Host Configuration Protocol


DHCP Overview


DHCP is used to automatically configure network clients with various networking settings.

DHCP is used by default on Windows machines. The students can view the network settings assigned by DHCP using the ipconfig utility.



Leasing an IP Address


Students mainly need to understand the four-packet process that is necessary for the leasing of an IP address from a DHCP server.

The packets are referred to in the text as: DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, and DHCPACK.




Renewing an IP Address


There are two different types of leases: permanent and timed.

Administrators should use timed leases in most cases as it facilitates IP addressing configuration changes. Timed leases will therefore ease administration tasks.

Students may need to be reminded that a client computer does not attempt to renew its lease after it has expired. A client machine attempts to renew its lease after 50% of the lease time has expired. This helps prevent network problems

The renewal process only requires two packets to complete. Therefore, it requires less traffic to renew a lease than it does to request a lease.





Installing and Authorizing the DHCP Service


A DHCP service must both be installed and authorized before becoming fully functional.

Unauthorized DHCP servers could potentially wreak havoc in a networking setting. Therefore, any DHCP service installed must be authorized by a user with sufficient administration privileges.


Do these Activities in the Textbook

Activity 4-1: Installing DHCP


This is a simple activity that involves the installation of the DHCP service. The activity should pose no problem for the average student.


Authorizing the DHCP Service


Most students will not realize that a DHCP service needs to be authorized before it becomes fully functional. It is probably a safe assumption that most students will have never installed their own DHCP service. This service tends to be provided “behind the scenes” so that the average user has no control or experience with this concept.

Authorization is not difficult provided you have the proper administration rights.


Activity 4-2: Starting an Authorized DHCP Server


This is an activity in starting a service and using the Event Log.

The toughest part of this activity will be for students to find the appropriate record within a potentially lengthy log file. Therefore, make sure students follow instructions carefully.


Activity 4-3: Installing the Active Directory Service


The list of instructions for this activity is somewhat long. However, Microsoft provides an easy to use interface for the installation of the Active Directory Service. Therefore, as long as you make sure they understand the options in the configuration wizard, this will be another easy activity.


Activity 4-4: Starting an Unauthorized DHCP Server


This is an activity in finding records in the System Log.


Activity 4-5: Authorizing a DHCP Server


From the previous activity, students learned of what is recorded within the System Log whenever an unauthorized DHCP server is started. In this activity, students will fix the problem by activating the service.

The instructions for this activity are easy. The only difficulty students could potentially have is if they attempt this activity without the proper administration privileges.


Configuring DHCP Scopes


DHCP configuration can be accomplished via the provided snap-in or through a command line utility called NETSH.

The snap-in is an easy way to configure DHCP. However, have students practice using the NETSH command as it might save configuration time in certain situations.

Scope may sound like a complicated topic for some students. However, it is just a fancy word for the range of IP addresses that a DHCP server is allowed to hand out.

There are two different ways to define scope. One way is to allow all available addresses minus the statically assigned addresses. The other method is to use a range of addresses not already assigned for use in static situations.



Activity 4-6: Creating a Scope


In this activity, students will be setting up a scope on their new DHCP server so that it can assign IP addresses to client machines. The instruction list is a little long but easy to follow.


Activity 4-7: Activating and Testing a Scope


This activity is meant to be performed in a group. One person will run the DHCP server while the other runs the client machine.

Have partners switch roles and re-perform the activity.


Superscopes


A superscope is used to combine multiple scopes. The concept is simple. However, the reasons for superscoping may not be clear to students.

A company may start with a single class C network and grow to eventually require two class C networks. In order to keep the DHCP server from offering leases from both scopes, a superscope is configured so that only a single lease can be offered.

This is a tricky concept. Make sure students fully understand how a superscope is useful in some networking situations.


Activity 4-8: Configuring a Superscope


This activity involves creating two scopes. First, students should create a normal scope. Then, students will create a superscope encompassing the two previously created scopes.

Everything the student needs to complete this activity can be found in the DHCP snap-in.


Activity 4-9: Deleting a Superscope


This activity is easy. Just remind students to delete only the superscope and not the scopes within it.


Multicast Scopes


Multicast scopes deliver multicast addresses over to applications that request them.

Although this is sometimes used, students must understand that such situations are very rare. Most applications that use multicasts are hard coded with the required addresses and do not need a DHCP server to issue an address.


Activity 4-10: Creating a Multicast Scope


This activity is similar to a previous activity where a student was required to create a regular scope. The only difference in this activity is the fact that students must specify that they are creating a multicast scope.



Even though it is important that students know how to do this, it should be noted that it is rare for client machines to request multicast addresses from DHCP servers.


Creating DHCP Reservations


A reservation is used to assign a specific IP address to a client machine. The reservation is made based on the MAC address of the client machine.

Explain that a reservation is sometimes more convenient to assign a fixed IP address than is using a static configuration on the client side.

Reservations are also useful for machines connected to firewalls as the firewall rules can be configured based upon an IP address. Since an IP address is reserved for a certain machine, the firewall rules are ensured to apply to the correct machine.

Explain the potential problems of reservations. One potential inconvenience is that the reservation must be reconfigured if the network adapter of the client machine is changed.


Activity 4-12: Creating and Testing a Reservation


Students should be instructed to pair up for this activity.

One student will be responsible for configuring the client while the other will be configuring the server.

As with any other activity that involves required communication between two machines, allow enough time for troubleshooting problems.

The point of this activity will be for students to reserve an IP address for a specific client machine.


Configuring DHCP Options


Although handing out IP addresses is perhaps the most important job of the DHCP server, other configurations are handed out by the server as well.

Students should know that they can configure the DHCP server to hand out information such as default gateway, DNS server, WINS server, and others.


Activity 4-13: Setting Server Options


This activity involves configuring the DHCP server with the DNS option. This is an easy activity to perform. However, make sure students know why they may need to do this.



Activity 4-14: Setting Scope Options


In this activity, students set up the DHCP server to provide default gateway information. This activity will not take long.


Activity 4-15: Testing Server & Scope Options


This activity is best done in groups.

In this activity, one person will activate the DHCP scope while the other tests to see if a client machine retrieves the configuration settings entered in previous activities.

Allow troubleshooting time since this activity involves computer to computer communication.


Vendor and User Classes


It is likely that students have not heard of these topics. Therefore, it may be necessary to spend a little more time discussing them and how they are useful.

Vendor classes are operating system based.

User classes are either connection based or administrator based.

The classes are used to specify specific options to client machines.


Configuring a DHCP Relay


DHCP packets are all broadcasting packets. Therefore, students should realize that these packets cannot travel across routers.

In most practical situations, routers will exist on a network. In addition, a single DHCP server will be desired even in the presence of this router.

Students should become familiar with the concept of a DHCP relay. This relay picks up client lease requests and forwards them to the appropriate DHCP server. The relay also transmits the reply from the DHCP server back to the client machine.

Make sure it is very clear that one should not configure a DHCP server to also act as a relay. To do so will result in the machine exhibiting erratic behavior.

If students wonder how the relay solves the router problem, explain that the relay listens for client requests and forwards them to the server as a unicast communication. Unicast communications can travel across routers as they are not broadcasts.




Activity 4-16: Configuring a DHCP Relay


This activity is a little longer than most. However, recommend that students carry out this activity as configuring DHCP relays can be very useful in practical situations.

Make sure students uninstall the DHCP service from this machine before configuring it as a relay. This will help remind students that a machine should never be both a DHCP server and relay.




DNS


Name Types


There are two standard network access methods that students should be able to distinguish. These are WinSock and NetBIOS.

WinSock names are referred to as host names.

Students will be interested to learn how Internet servers are accessed through fully qualified domain names such as www.google.com. The FQDN consists of both a host name and a DNS domain name. Here, the host name is www and the domain name is google.com.

In order for the world to access your computer through a FQDN, you must register it with a registrar. The registrar will merge your domain name with the worldwide DNS lookup system. This registration is very important if you wish others throughout the world to be able to use this simple name in place of an IP address to access resources.

Although NetBIOS is slowly disappearing, it is still prevalent enough to warrant that students become familiar with it.

NetBIOS was used for all networking functions in pre-Windows 2000 machines.

NetBIOS can be complicated or simple depending upon the level at which you explain the concepts to students. At the very least, students should know what NetBIOS is and when it should be used.




Teaching Tip

It might be interesting for students to research how they can get their domain name registered with a worldwide DNS lookup system. Have them research the costs associated with the registrations and who provides the services.



Activity 6-1: Viewing Computer Names


In this activity, students will be viewing various names associated with a computer.

The ipconfig utility can be used to view your host name and DNS suffix.

Use nbtstat to view NetBIOS information.


Activity 6-2: Removing Active Directory and the DNS Service


In this activity, students will be removing both the Active Directory and DNS services.

After the services are uninstalled, the computer names viewed in Activity 6-1 will be reviewed to note any changes.

This activity will take longer than most activities. Also, you may wish to skip this activity if you desire to use the Active Directory and DNS services at a later date.


Host Name Resolution


WinSock applications work very hard in order to try to resolve host names to IP addresses. There are a number of methods the applications attempt. Students should be familiar with each one and in what order they are performed.

The resolution steps are:

  1. check to see if the host name is the same as the requesting machine’s host name

  2. check for the entry in the DNS cache

  3. query a DNS server

  4. attempt NetBIOS resolution

In the last attempt, the machine attempts NetBIOS resolution. NetBIOS names are more restrictive than host names. Therefore, if a host name is too long to be a NetBIOS name, then the host name is truncated to a valid NetBIOS name.


Configuring a HOSTS File for Name Resolution


Try not to complicate things. A HOSTS file is just a simple text file that is used to assist in name resolution.

The file is very easy to modify and use. Viewing a sample HOSTS file should be sufficient for students to learn how to use it.

Make sure students understand that the HOSTS file is not allowed to have an extension in its filename. Extensions are sometimes automatically appended when using some text editing software.


Activity 6-3: Configuring a HOSTS File


This is an easy activity. Students will enter an IP address and its corresponding host name within a HOSTS file.

Upon modification of the file, students should check to make sure their alterations take effect.


Managing the DNS Cache


The DNS cache is a combination of the HOSTS file and previous DNS server query results.

Each DNS query entry has a certain amount of time to live. This ensures that outdated information does not stay within the cache and also keeps the cache from growing too large.

Instruct students on how to clear the cache using the ipconfig utility. This concept will also be demonstrated in the following activity.


Activity 6-4: Viewing and Purging the DNS Cache


This is an easy activity. Students are only required to view and clear the DNS cache.


Using DNS for Name Resolution


The idea of this short section is that you can manually specify the address for a DNS server for name resolution.


Forward Lookup


This is the most common task performed by a DNS server. The forward lookup involves resolving a host name into an IP address.

Students should realize that a forward lookup within an organization and a forward lookup across the Internet is a very different process that varies considerable in complexity.

In a forward lookup within an organization, the local DNS server merely responds with the IP address of the host. This entire process requires only two packets.

In a lookup over the Internet, the client machine first contacts the local DNS server for the required information. If the local server does not have this information, then a recursive lookup is performed in order to obtain the information required.

There are only thirteen root servers over the Internet. Their job is to provide the addresses of DNS servers responsible for top-level domain names.


Reverse Lookup


If students understand the concept of a forward lookup, then the concept of a reverse lookup will be easily understood.

A reverse lookup is the exact opposite of a forward lookup. A reverse lookup attempts to resolve an IP address to a host name.

Reverse lookups are commonly used for network log files so as to make them easier to read or understand.


DNS Record Types


Students should know that DNS records are created on a DNS server in order to resolve queries.

Ensure that students are familiar with the most common types of DNS records. These records are provided in Table 6-3.


Using NSLOOKUP


The purpose of the NSLOOKUP utility is to query DNS records.

NSLOOKUP is a command-line utility.

This utility is extremely useful in troubleshooting DNS problems. Students should know that this is the utility of choice for assessing any kind of problem with their DNS server.

NSLOOKUP can be run in two different modes: command-line mode and interactive mode. Students should know that this utility is most powerful when run in interactive mode.


Activity 6-5: Performing DNS Lookups with NSLOOKUP


This activity will demonstrate the effectiveness of the nslookup utility for determining DNS functionality.

Students should be encouraged to complete this activity as this command-line utility is easy to forget about. The NSLOOKUP utility has the potential for greatly reducing the troubleshooting time associated with repairing a network with DNS problems.


NetBIOS Name Resolution


The important concept of this section is that there are a number of techniques employed by client machines when attempting to resolve NetBIOS names. These techniques are always attempted in a specified order.

Client machines attempt the following resolution methods until one succeeds:

  1. check the NetBIOS cache

  2. contact a WINS service

  3. attempt a network broadcast

  4. check the LMHOSTS file

  5. attempt host name resolution

The above steps may be altered in Windows Server 2003 by configuring the node type. Students need to know that one can change the node type of the system only through editing the appropriate key in the Windows registry.


Using a LMHOSTS File for Name Resolution


The concept of a LMHOSTS file is very similar to the concept of the HOSTS file. Therefore, you should not have to dwell on this topic for long.

This file is a simple text file that stores IP addresses and NetBIOS names.

More advanced knowledge of this file will be obtained through the next activity.


Activity 6-6: Creating an LMHOSTS File


In this activity, students will create an LMHOSTS file and add an entry in order to test NetBIOS name resolution.

This activity is very important in ensuring that students understand how to create and manipulate properly an LMHOSTS file.


Using WINS for Name Resolution


In order for a WINS server to be useful, all client machines within the network should be configured to utilize WINS. Especially important is to remember to configure the machine running the WINS server itself to use the WINS service.

WINS offers advantages over traditional NetBIOS resolution techniques. These enhancements are:

  1. functions across routers

  2. dynamic update capability

  3. automatic update capability

  4. client configuration through DHCP

  5. integration with DNS

The final important topic introduced in this section is the four major tasks performed by a WINS server. These tasks will be described in more detail in subsequent sections. For now, ensure students know what these tasks are: name registration, name renewal, name query, and name release.


Name Registration


Name registration merely involves the registration of a client computer’s NetBIOS name with a WINS server at boot up.

There are two situations that may occur during name registration. In the first scenario, the name is not already registered and so the registration is successful. In the other scenario, the name is already registered. In this case, the WINS server attempts to contact the machine that already registered the NetBIOS name. If successful, registration fails. If unsuccessful, registration succeeds and the new machine is registered with the NetBIOS name.


Name Renewal


After the TTL of a name registration is half complete, the client computer attempts a name renewal. This is a two packet process.



Name Release


This is a two packet process that is invoked whenever a client machine is shut down. This frees up the NetBIOS name with the WINS server.


Name Query


This is the process in which a NetBIOS name is actually resolved to an IP address.

This process is a two-packet process.

The WINS server is contacted only after the name is not found in the NetBIOS cache.


Troubleshooting Name Resolution


This section tries to provide some simple troubleshooting techniques for network problems. Have the students read this section. However, they will ultimately need experience troubleshooting real systems with real problems before becoming proficient at troubleshooting. Try to provide them with real-world or hands-on troubleshooting exercises.


The following services need expansion of their individual lectures


FTP

Telnet

File Server

Print Server

Web Services

File Application Server

MMS

Streaming Video

Chat rooms

Etcetera,etcetera,etcetera