1. About DHCP

View OUCS service level descriptions

The Dynamic Host Configuration Protocol provides an excellent solution to two significant problems with IP addressing.

  • As the number of hosts connected to the internet continues to grow exponentially there is developing a shortage of available IP addresses.
  • As portable computers roam between different networks their IP addresses need to change accordingly, preferably without the need for user intervention.

The central idea of DHCP is that when a computer is attached to a particular network, it may inquire particular details of its environment, and be supplied with an IP address from a special pool. Another mode of operation allows the computer to receive the same address each time, lowering the administrative burden of managing PCs.

If you are a college or departmental network administrator and you wish to join the scheme, then you may need to surrender a pool of IP addresses from your network to be used for DHCP. All addresses in the pool must be registered in the DNS. If you are assigning DNS entries to a large dynamic pool then the networks team may be able to assist in bulk-registration.

The hardware (MAC) addresses of registered clients must be supplied. Client registration is normally on a per-subnet basis. Units with multiple subnets may choose whether or not their registrations are active across all subnets or on just one. It is now possible for OUCS to configure peer trust relationships between units, so host registrations for one unit are valid on another.

On shared subnets, DHCP may be problematic. It is not possible for two different units to use the OUCS DHCP service on a shared subnet simultaneously. One unit may do so, but must use MAC address registration to ensure that clients belonging to other units cannot obtain leases from the OUCS DHCP servers.

You may also register hosts with fixed IP addresses to use DHCP (the fixed addresses must NOT be within your dynamic pool!). Indeed some subnets will only do this and dispense altogether with the need for a dynamic pool.

MAC addresses should be registered via the WWW interface. Contact networks@oucs.ox.ac.uk if you have any questions about this service.

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