Campus DHCP Service
In order to use the campus network, all devices connected to it must be configured with a number of different parameters. The Dynamic Host Configuration Protocol (DHCP) automatically configures network devices with the parameters they need to utilize the network. DHCP is an alternative to manual configuration of these parameters. The campus DHCP service is available on the campus wired network. In order to make use of the service, a network device must be registered with the service and it must be configured to use DHCP to obtain its network settings. A web application is available for self service registration of devices by students, faculty and staff.
Registering a Device with the Campus DHCP Service
To register a device, you first need to determine the hardware address of the device's wired network interface. The hardware address is commonly called the Ethernet address or the Media Access Control (MAC) address. See this article on how to find your MAC address. Make sure you find the hardware address for the wired network connection to the campus network; your device may have multiple network connections (including wireless) that each have different hardware addresses.
With the hardware address is hand, log in to the NetReg application. Select your registration context, usually your name. Click on Add New Device and enter the hardware address. (If you land on a different page, click on Register devices for DHCP Service from the sidebar.) Registration via the web application allows the registered device to obtain dynamic DHCP service on any network with available addresses.
Methods of Address Assignment and DHCP
When a DHCP server assigns an IP address to a device, the assignment - called a DHCP lease - is of finite duration. DHCP allows devices to renew leases to continue to use an IP address beyond the time the device's current lease is valid. After a DHCP lease for an IP address expires without renewal, the DHCP server may issue a lease for the IP address to a different device. There are two important implications of this behavior. First, the use of finite duration DHCP leases permits the DHCP server to automatically reuse IP addresses, encouraging more efficient use of IP address space. Second, a device may get a different IP address each time it requests a lease.
The change of the IP address assigned to a device over a period of time can present some problems in certain cases. The device may run a protocol, such as NFS, that doesn't handle changes in IP addresses well. The device may run a service, such as remote desktop, where the user of the device wishes to have a constant identifier for connecting to the service. The campus DHCP service has features - fixed assignment of IP addresses and dynamic DNS, discussed below - to address these problems.
IP addresses are assigned to network devices for use on the campus network in one of two different ways.
- Fixed assignment of an IP address (commonly called fixed DHCP) to a device is performed by the campus Hostmaster. The hardware address of the device should be registered with the campus DHCP service prior to contacting Hostmaster to request a fixed assignment. By default, the generic hostname for the IP address associated with the fixed assignment is placed in the departmental or other specific subdomain associated with the subnet. Custom hostnames, aliases and other DNS records associated with the IP address of a fixed assignment may be requested along with the fixed assignment request.
- Dynamic assignment of an IP address (commonly called dynamic DHCP) to a device is performed by the DHCP servers as part of assigning a DHCP lease to the device. A single device may receive a different IP address each time it connects to the network. IP addresses are automatically recycled after use. Before dynamic assignment is used on a subnet, the contact for subnet must ask the campus Hostmaster to create a pool of addresses for dynamic assignment. The hostnames for IP addresses in dynamic pools are placed in the LIPS.Berkeley.EDU subdomain; see the FAQ for details.
For information on the mechanics of arranging service, please see the FAQ.
The different types of service exist to meet the different needs of devices attached to the campus wired network. For most devices, dynamic assignment is the recommend choice. Dynamic assignment does not require campus Hostmaster interaction; it is the default type of service for all registrations made via the self service registration web page. IP addresses are automatically recycled as devices connect to the network and leave it. Dynamic DNS provides a way for users of services on the device (such as remote desktop) to connect to the device using a single hostname regardless of the IP address the device is using. Fixed assignment is useful in situations where a device makes use of a protocol that does not handle changes in the device's IP address gracefully (e.g. NFS). Devices that provide a commonly used service (e.g. printers) are also candidates for fixed assignment. Static assignment is required when a device does not support DHCP. Servers or other critical infrastructure are also candidates for static assignment.
Dynamic DNS with DHCP
Dynamic DNS allows the campus DHCP servers to associate a hostname in the DNS with an IP address at the time the IP address is assigned to a device as part of a DHCP lease. When the DHCP lease expires, the hostname is removed from the DNS. By associating a hostname with a device, dynamic DNS ensures that whenever the device has an IP address assigned by the campus DHCP servers the device is reachable via its hostname.
Dynamic DNS is only available when dynamic address assignment is used. With fixed assignment, DNS records are associated with the IP address of the fixed assignment.
All dynamic DNS hostnames are in the subdomain dyn.Berkeley.EDU.
Support for the Campus DHCP Service
DHCP registration questions can be sent to firstname.lastname@example.org. Contact CSS-IT for device configuration support. See http://sharedservices.berkeley.edu/it/