A bridge, as shown in Fig. 1-16(b), can be used to connect two networks at the data link layer. This approach is useful, for example, when the networks have different data link layers but the same network layer. A connection between an Ethernet and a tokenbus would normally be a bridge. The frames from the Ethernet arrive at the bridge in Ethernet form and are copied to the tokenbus in tokenbus form, or vice versa. Bridges are smar (full of software); they can be programmed to copy frames selectively and make necessary changes while doing so.