DHCP Technical Corner for LAN Administrators and TSCs

Reporting DHCP problems
Send an email to noc@ucdavis.edu or call 752-7656 for help.

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What is DHCP?
DHCP stands for "Dynamic Host Configuration Protocol". DHCP's purpose is to enable individual computers on an IP network to extract their configurations from a server (the 'DHCP server') or servers, in particular, servers that have no exact information about the individual computers until they request the information. The overall purpose of this is to reduce the work necessary to administer a large IP network. The most significant piece of information distributed in this manner is the IP address.

Network/Subnet - Range of IP addresses that are assigned to a department/VLAN. (i.e. dhcp_1 = 192.168.44.1 - 192.168.44.251)
Dynamic Range - A dynamic range is a group of addresses that a DHCP server assigns. These addresses have a lease time. When the lease expires, they are available for the DHCP server to reassign.
Static Address - A static address is an IP address that is fixed to a particular device.
Hardware Ethernet/MAC Address - (Media Access Control) A MAC address is a unique 48-bit number(usually represented as a 12-digit hexadecimal number) that is encoded in the circuitry of a device to identify it on a local area network.
Lease Time - Lease time is the length of time that a computer can use a dynamic IP address.

Campus DHCP Service
Information Technology has installed a DHCP server to assist the campus in using this technology.

In order to provide accountability on the UC Davis Network, we ask all our users to register their MAC (adapter) addresses with the campus. Therefore, the DHCP server will ONLY issue an IP address to MAC addresses that have been registered.

The software package that UC Davis has chosen for deployment of campus DHCP service is called NetID.

There are two methods to register a computer hardware Ethernet address. You can add the address into the "NetID" department pool, which will only allow access to your network. Or you can have your end users register their address (which stores the address in the "Mothra" pool) and this will allow them to use public NAMs across campus.

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Why use Campus DHCP service?
Your end users with laptops may want to move back and forth between several locations on campus (such as their office and a classroom). DHCP will allow you to set up the network configuration on their laptop once, and it will then work in both locations. You may also want to use DHCP on all your computers to ease the burden of administering all the IP addresses. DHCP will also decrease the possibility of computer network configuration errors.
Benefits of Using Campus DHCP

Simple configuration of machine on client's side
Only need to configure machine once and can plug in anywhere on campus that is DHCP enabled
Network Administrators have more control over authorized use of their subnet
Central support on a 7/24 basis
Provides better security through central authorization and accountability
Easy to learn NetID.

How to configure DHCP on NetID.
You need to send an email to noc@ucdavis.edu to request that your network be configured on the campus DHCP server. The NOC will respond to your request with instructions. After your network is configured you can use the NetID tool to administer DHCP on your network.
Information you need to setup DHCP

VLAN
Range of IP addresses to use for DHCP
List of Hardware Ethernet (MAC) Addresses that you wish to register in the departmental pool

NOTE: Please plan to turn off your local DHCP server as you transition to the campus DHCP service.

Detailed configuration instructions:

How to configure DHCP clients
Instructions can be used for both ResNet and laptop configurations. These are the basic steps you must take to use the campus DHCP service.
Link to configuring your computer for DHCP

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Can I use my own DHCP server instead of the campus server?
Yes, you can run your own DHCP server on your network. However, if your end users wish to move between your departmental DHCP server and public NAMs served by the campus DHCP server, you will need to make sure they follow the instructions to register their Hardware Ethernet (MAC) Address. Otherwise, their computer will work on your departmental network, but not on the larger campus network.

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How to test DHCP service on a computer

Step 1: Do release all/renew all (to reset your IP Address)

Windows XP

Open command window (type "cmd" in Run)
Type "ipconfig /release *"
Type "ipconfig /renew *"
Close command window

Windows 95/98

Select "Run" from Start Menu
Enter "winipcfg" and press enter/return
Select the ethernet adapter from the pull down menu
Select "release all"
Select "renew all"
Close winipcfg

Windows NT

Open command window (type "cmd" in Run)
Type "ipconfig /release"
Type "ipconfig /renew"
Close command window

MacOS 8.5

Open "TCP/IP" control panel
Change to "Manual address"
Change back to "DHCP"

MacOS X

Open the "Network" control panel
Select the appropriate interface from the Show pull down menu
Click on the TCP/IP button
Select "Using DHCP" from the Configure IPv4 pull down menu
Click the "Renew DHCP Lease" button

Step 2: Look for DHCP server address - (169.237.250.250 or 128.120.252.9)

Windows XP

Open command window (type "cmd" in Run)
Type "ipconfig /all"
Close command window

Windows 95/98

Select "Run" from Start Menu
Enter "winipcfg" and press enter/return
Select the ethernet adapter from the pull down menu
Select "more info"
Close winipcfg

Windows NT

Open command window (type "cmd" in Run)
Type "ipconfig /all"
Close command window

MacOS 8.5 - Mac OS X

From the Apple menu, choose System Preferences
Click the "Network" icon
Choose your computers Ethernet adapter from the Show pop-up menu, below the Location menu

How to maintain the DHCP service
Make sure you Register Your Ethernet (NIC) Card with the campus Computing Accounts department. Also, delete MAC addresses of systems no longer in use or when a machine changes owners.

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How to register MAC addresses for a department
UC Davis employees have a six (6) MAC address maximum device registration for DHCP, which is problematic for LAN Administrators who wish to register entire departments. The Network Operations Center can register additional MAC addresses for a LAN administrator so that the MAC addresses do not count against the limit of six. To coordinate the registration of more than six MAC addresses, please email the NOC at hostclerk@ucdavis.edu.

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DHCP Technical Corner for LAN Administrators and TSCs

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