IP Addresses are limited

The IP address range allocated to UC Davis is a finite resource that needs to be managed carefully so all users can have access to the campus network. To protect this limited resource, Communications Resources has established guidelines to control the size of allocated IP address ranges.

Three factors contribute to the need to apply restraint in allocating and using address space:

  • Address ranges double in size with each increment. This leads to a large amount of unused address space, sometimes in excess of 50%.
  • Each address range that is allocated consumes addresses that are not actually usable for departmental hosts.
  • The network itself requires a certain amount of address space for routers, switches, backbone links, etcetera.

A table of address range size increments is shown below:

Nomenclature Number of Host Addresses
/23 507
/24 251
/25 123
/26 59
/27 27
/28 11


How the Network Operations Center (NOC) can help you manage IP address allocation

Departments should exercise due diligence in analyzing their needs and shall exercise reasonable restraint in requesting address space. In order to assist with this, the NOC will provide support, upon request, by performing scans of routing tables to determine the number of unique devices in use on a department's address range.

Expanded address space will be granted if a department's address space is more than 80% utilized. In most cases, a department will be asked to provide a letter to the NOC identifying the need for additional address space. Documentation is required because the need might be based upon hosts that are only occasionally used and thus may not show up in a scan, or on planned increases in numbers of departmental computers.

Expanding address space typically requires changing the addressing for the department's entire range. Departments must be prepared to perform this transition within a reasonable period of time agreed upon between the NOC and the department at the time more address space is assigned.

To request more IP address space, please send an email to the NOC at noc@ucdavis.edu.