OPS235 Lab 8 - Fedora17

Install and Configure a DHCP Server

Objectives

• To install, configure, and test ISC's DHCP Server

Reference

• man pages for dhcpd, dhcpd.conf, dhcpd.leases, dhcp-options, dhclient, dhclient-conf
• Fedora DHCP Configuration Guide
• Internet Software Consortium DHCP page

Required materials

• Fedora 12 Live CD or a classmate on the same pod
• One SATA hard disk in a removable drive tray with Fedora host and 3 Fedora Virtual Machines installed
• Completion of Lab 6

Lab Preparation

Update your systems
It is advisable to perform a yum update on your Fedora host and all 3 VM's.

Backup your VMs before proceeding
If you did not do it at the end of Lab 7, stop all of your VMs and backup your VM disk images.

ISC DHCP packages Overview
The version of DHCP server (rpm package name called "dhcp-4.1.1-9.fc12.x86_64" ) that comes with Fedora is maintained and distributed by the Internet Software Consortium (http://www.isc.org). The source package that you can download from ISC includes not only the DHCP server, but also a DHCP client and a DHCP relay agent. However, Fedora separates it into two RPM packages: the DHCP client package called "dhclient-4.1.1-9.fc12.x86_64" and the DHCP server package called "dhcp-4.1.1-9.fc12.x86_64". The DHCP client package is installed by default by the workstation installation.

Completing the Lab

Investigation 1: How do you install the DHCP Server.

Note!
Complete the following steps on your fedora3 VM.

• To check that you have dhclient installed, enter the command:
  • rpm -q dhclient
• If the package is not installed, you will get the message "package dhclient is not installed", otherwise, you will get the version information of the rpm package. Install the dhclient package if it was not installed.
• Check to see if the dhcp server package is installed.
• Follow the normal procedure to install the DHCP server rpm package called dhcp using yum.
• Enter the command to list all the files installed from the DHCP server package.
• What file appears to be a sample configuration file?
• Copy the sample dhcpd.conf file to the /etc/dhcp directory making sure it is named /etc/dhcp/dhcpd.conf
• Answer the Investigation 1 question in your log book.

Investigation 2: What configuration options and directives need to be set in dhcpd.conf?

Note!
Complete the following steps on your fedora3 VM.

• Study the man pages of dhcpd, dhcpd.conf, dhcp-options, and dhcpd.leases and make notes in your log book. In particular, look up the meaning and possible value(s), if any, for the following configuration options:
  • broadcast-address
  • default-lease-time
  • max-lease-time (How is this different from default-lease-time?)
  • domain-name
  • domain-name-servers
  • fixed-address
  • group
  • hardware
  • host
  • host-name
  • range
  • routers
  • subnet
  • subnet-mask
• Study the sample dhcpd.conf file to see examples of how these options are used.
• Answer the Investigation 2 question in your log book.

Investigation 3: How do I configure dhcpd settings to be applied to all subnets?

Note!
Complete the following steps on your fedora3 VM.

• Edit /etc/dhcp/dhcpd.conf and examine the top section of the file.
• Make the following changes to the global settings:
  • domain-name should be set to "ops235.org"
  • domain-name-servers should be set to 192.168.235.1
  • default-lease-time should be set to 20 minutes
  • max-lease-time should be set to 1 hour
• Answer the Investigation 3 question in your log book.

Note!
As global settings these will affect all subnets unless they are separately declared for individual subnets.

Investigation 4: How do I configure dhcpd to provide IP configuration to my virtual network?

Note!
Complete the following steps on your fedora3 VM.

• Edit /etc/dhcp/dhcpd.conf and add a new subnet delcaration for your virtual network
• The network address is 192.168.235.0/255.255.255.0 and the range of host addresses should be from 51 to 60
• Also add a default gateway for the virtual network of 192.168.235.1
• Save the file.
• Open another terminal window (ssh into fedora3 from fedora host as user root) and issue the following command:
  • tail -f /var/log/messages
• This will show you the last 10 lines of /var/log/messages continue to display new lines as they are added to the log.
• In your original terminal prompt attempt to start the dhcpd service.
• You should see new lines being added to the messages file.
• If the service fails to start any error messages will be logged in the messages file. Read the errors and attempt to fix your configuration file.
• If the service starts successfully you should see success messages in the log.
• If your service starts successfully edit the configuration file and introduce an error by removing a semicolon or closing curly bracket.
• Restart your service and observe the error messages generated.

Troubleshooting Tip:
Troubleshooting produces the best results when you are methodical in your approach. Try to fix the first error mentioned before fixing subsequent errors. Often the first error may cause multiple error messages as the configuration file is parsed. When you think you have fixed the first error try to start your service and if it fails check the log again. Fix one error at a time.

• When you have successfully started your service answer the Investigation 4 question in your log book. You may want to include all of the syntax you used.

Investigation 5: How do I test my dhcpd service on my virtual network?

Note!
Complete the following steps on your fedora2 and fedora3 VM's.

• On a fedora3 terminal window make sure that the command tail -f /var/log/messages is running.
• On fedora2 change the configuration of the eth1 (or your interface name) to receive dynamic address configuration
• Save your changes and restart NetworkManager
• Observe the messages that get logged. You should see output similar to the following:

Mar 24 13:28:24 fedora3 dhcpd: DHCPDISCOVER from 52:54:00:61:00:e7 via eth2
Mar 24 13:28:25 fedora3 dhcpd: DHCPOFFER on 192.168.235.51 to 52:54:00:61:00:e7 via eth2
Mar 24 13:28:25 fedora3 dhcpd: DHCPREQUEST for 192.168.235.51 (192.168.235.13) from 52:54:00:61:00:e7 via eth2
Mar 24 13:28:25 fedora3 dhcpd: DHCPACK on 192.168.235.51 to 52:54:00:61:00:e7 via eth2

Note!
These messages record the DHCP lease transaction that consists of 4 broadcast packets, DISCOVER, OFFER, REQUEST and ACKNOWLEDGE. Try researching on the internet how this transaction differs from a DHCP lease renewal.

• On fedora2 confirm the IP address assignment using ifconfig
• Answer the Investigation 5 question in your log book.

Investigation 6: Where does the dhcp server store a record of leased addresses?

Note!
Complete the following steps on your fedora2 and fedora3 VM's.

• If your fedora3 DHCP server successfully issued the proper IP address configuration values to fedora2, check the file called /var/lib/dhcpd/dhcpd.leases
• You should see contents similar to:

lease 192.168.235.51 {
  starts 3 2010/03/24 17:28:25;
  ends 3 2010/03/24 17:48:25;
  cltt 3 2010/03/24 17:28:25;
  binding state active;
  next binding state free;
  hardware ethernet 52:54:00:61:00:e7;
}

Note!
dhcpd records address leases in this file. If the service is restarted it reads in the file to know which addresses are currently leased and for how long.

• On the client fedora2 check the contents of the/var/lib/dhclient directory. The files in this directory is where the dhclient stores its record of leases.
• Answer the Investigation 6 question in your log book.

Investigation 7: How can I lease the same address every time?

Note!
Complete the following steps on your fedora2 and fedora3 VM's.

Note!
Even though DHCP gives out IP address dynamically, it also has the ability to reserve an IP address for a certain computer. In this sense it's almost as if the client computer has a static IP even though it uses DHCP to get it. This is useful if you want to be able to put entries in your /etc/hosts file and not have to worry about the entry becoming invalid over time. In Linux we refer to this as supplying a fixed address to a host. Microsoft calls it a reservation.

• Create a host declaration for fedora2. Make sure you record the correct hardware ethernet setting that corresponds to the MAC address of the interface in fedora2.
• Give it the fixed-address 192.168.235.12

Note!
When supplying fixed-address it is important that the address assigned is exclusive of any ranges that have been declared. Otherwise it may be possible for 2 different hosts to receive the same address.

• Start your service and test the address assignment by releasing your current address on fedora2 and then requesting a new address. Use the following commands on fedora2:
  • dhclient -r eth1
  • dhclient eth1
• Confirm that you received the fixed address you were supposed to.
• Answer the Investigation 7 question in your log book.

Completing the lab

Arrange proof of the following on the screen:

• DHCP server log file showing a lease occuring
• DHCP server configuration file showing subnet and host declaration
• DHCP server lease file
• DHCP client lease file

Preparing for the Quizzes

• What protocol and port does dhcp use?
• What file is used to configure dhcpd?
• Can a dhcp server also be a dhcp client?
• What is the difference between max-lease-time and default-lease-time?
• What unit of measurement does default-lease-time require?
• What dhcp option is used for configuring a default gateway?
• What is the parameter range in the DHCP server configuration file used for?
• What is the purpose of a dhcp relay agent?
• Why might a dhcp relay agent be required?