Campus DHCP Service

What is DHCP?

The Network Group recommends all campus hosts use DHCP to obtain IP address and other network parameters. When a DHCP-configured machine boots, it sends a special request to the network. The DHCP servers receive this request and, if applicable, distribute the IP address, network mask, default route, and other network attributes.

Registering Hosts

All campus hosts must be registered in NetReg. Machines with mode 'static' will be assigned an IP address in NetReg and receive this address through DHCP. Machines with 'dynamic' mode will be assigned an IP address at boot time from the DHCP server.

Why dynamic addressing?

Registering a machine as 'dynamic' in NetReg enables us to more efficiently utilize our available IP space. Some networks permit only dynamic registration (such as the Wireless network). For example, as of October 2002 there are approximately 7,000 registrations on the wireless network, with a peak daily utilization of 2100 hosts. Using dynamic addressing in this instance saves many addresses for other uses.

Dynamic DNS Update

The Network Group has enabled Dynamic DNS Update on most of our dynamic subnets. When machines boot and receive a dynamic address, the hostname registered in NetReg will be updated to reflect the active IP address.

AuthBridge

The wireless network and NetBar AuthBridge network are protected by the Network Group's AuthBridge technology. All machines connected to these networks will receive a 128.2.0.0 address, but unregistered machines will see the AuthBridge registration page. At this time, users can create a permanent registration (proxied to NetReg) or a short-term registration (less than two weeks).

After registration, full network access is immediately granted. Users may need to close and re-open their web browser, however, to avoid further redirection into the AuthBridge registration page.

QuickReg

Many areas of campus have our QuickReg service enabled. When an unregistered machine boots, it will receive an address in the 172.17.0.0 network. Any attempt to open a web page will be directed into NetReg. At that time, only a few clicks are required to register the machine. Information such as the machine's MAC address is automatically loaded from the DHCP server.

Approximately 30 minutes after registration via QuickReg, the newly registered machine can be rebooted and receive a regular 128.2.0.0 address and have full network and Internet connectivity.

DHCP Options

If a system requires additional DHCP options to boot properly, these options can be added using the NetReg system. If the required option is not available, please contact net-dev@andrew.cmu.edu.

Rogue Servers

All DHCP services are provided by the Network Group's three central servers. Any rogue server will be immediately disconnected from the campus network to avoid causing problems for other hosts.

Because the server addresses are configured on our campus routers, they may change any time without notice. However, at present the valid campus servers are: 128.2.4.2, 128.2.4.3, 128.2.32.38. If you suspect a rogue server is in operation, please contact advisor@andrew.cmu.edu.