Abstract: An arrangement for interconnecting groups of users into collision domains in a Local Area Network such as an Ethernet comprises a plurality of repeater groups, with each repeater group being connected to a group of user stations. The arrangement also comprises an electronically reconfigurable switch matrix. The switch matrix comprises a plurality of segment lines (or other transmission media) each of which is used to form one collision domain or Ethernet segment. Switch elements under the control of a microcontroller selectively connect particular repeater groups (and the associated user groups) to particular segment lines to form Ethernet segments, each Ethernet segment being a single collision domain. Internetworking devices such as bridges and routers may also be connected to the switch matrix to interconnect particular collision domains.