Industrial Communications Handbook August 2016

when upgrading an existing network, and one of the most satisfying when working on a Greenfield project. From a Greenfield perspective, one needs a list of de- vices (or expected devices) on the network, how these devices will be segregated (VLAN assignments), and any restrictions on what ranges can be utilised (some- time ranges may be assigned on a site-by-site basis, for instance). Once all this information has been gathered it becomes a simple matter of subnetting IP ranges to break them down into smaller groups, which should then cater for the number of devices in each VLAN. With the free tools available online it becomes a straightfor- ward task. IPs are then assigned to the actual devices and all the assignments are documented. It is necessary to add a bunch of devices to an existing network, things

can become more complicated, depending on how well the original design catered for expansion. In a best case scenario no extra VLANs (and thus IP ranges) are need- ed and all existing ranges have open IP addresses for each new device to be added. In many cases however, the existing ranges are too small for the expansion re- quired. This is where things can become painful. Some- times it will suffice to make small changes to existing subnet masks to include other devices, as long as this does not overlap with existing ranges. In other cases, redesign of the IP structuring for the network, and reas- signment of all existing IP addresses to cater for the new design, will be required. Furthermore this will involve large amounts of reconfiguration of existing devices on the network to accommodate the new structure. Finally,