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Conditions of issue of IP addresses

The operation of the Internet relies on the cooperation of the various network managers involved and a general willingness by all to maintain good order. If this good order is not maintained, it can give rise to severe disruption of network services requiring much unwelcome work by network managers both local and remote.

University Information Services (UIS) therefore places various conditions on the allocation of IP addresses and DNS entries, in addition to any conditions which are imposed by other rules covering the use of the CUDN, Janet, etc. It is important that these conditions are understood by those to whom allocations are made - please seek clarification from your local network manager or from IP-Register if these conditions are not clear.

  • An IP address is assigned only on a temporary basis; it does not become the property of the person or organisation it is assigned to. When an address ceases to be used for its assigned purpose, UIS (IP-Register) must be informed (usually via local computing or network staff) so that the address can be reassigned for some other purpose. This is necessary because there is a global shortage of IPv4 addresses and because addresses must be aggregated to maintain routing stability.
  • Addresses encode routing information and are therefore specific to the locations they were issued for. While in some instances an address will in fact work in a different location, this can be as a result of temporary routing expedients and should not be relied on. Locations are also recorded centrally as an aid to the diagnosis of network problems and the identification of machines. Therefore please ensure that IP-Register is informed if you wish to move a machine to a new location, whether or not you believe a new address will be necessary.
  • You may not (unless you receive special permission which is not normally granted) advertise the equipment as a mail host, either by headers (such as the "From:" field) in any email, or by MX RR or by any other formal or informal means. Neither may you emit mail except via a recognised mail server ('smarthost') within Cambridge. The central mail switch is available if you have no other arrangement. CUDN routers enforce some restrictions.
  • You should not cause address(es) or name(s) to be registered in any other part of the DNS without previously consulting UIS as such aliases can give a misleading impression about the proper use of the CUDN, Janet and other networks, and can cause confusion leading to the waste of network staff time.
  • You should ensure that your machine is configured with the specified broadcast address, whether by setting explicitly, by selecting "ones" rather than "zeros", or by accepting default behaviour (which in recent equipment is usually right). Seek advice if there appears to be no way to set or display this parameter.
  • Your machine must be configured not to forward IP packets, neither on the same nor any other interface, unless you have explicit approval from UIS.
  • You should not run any routing daemon, such as routed or gated, and you certainly must not allow any such to emit routing data. If you find your system does so in default you must suppress this. The gateway address cited in your allocation notification should be configured explicitly as the default route out of the local subnet.

Specific rules such as those above are made to cover specific problems, but the over-riding object is the maintenance of a working manageable network compliant with local, national and international constraints. It should not be presumed that some particular usage is acceptable simply because no specific prohibition can be found or because no problem is immediately apparent. It is wise to ask before being adventurous.

Useful email addresses and telephone numbers

If you have a local or departmental Computer Officer or equivalent, consult him/her first. Many departments have local procedures and requirements additional to the basic CUDN ones, and premature application to IP-Register can simply waste time. Otherwise,

Last reviewed: April 2016


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