On Ethernet, Bridges link subnetworks that use the same protocol. They use the Ethernet address to decide which data packets the Bridges can and cannot accept. The necessary information is taken from tables. Depending on the Bridge that is used, it may be necessary for the network administrator to enter these tables, or the Bridge may create the tables itself dynamically. If necessary, Bridges can convert the physical type of the network (e.g. from Ethernet to ISDN).