A bridge operation sin both physical and data link layer of OSI model. At physical layer it works like repeater as it regenerates the signal and performs inter connection of different physical media types such as coaxial cable, twisted pair work etc. Bridges technology supports two data link layer protocols called LIC ( Logical Link Control) MAC ( Media Access Control). Bridges when work in data link layer it can check the physical (MAC) address fro source and destination contain in a frame and hence deciding whether to forward or discard the frame. For example it source and destination are on the same network segment the bridge filters the frame. If destination is on a different network segment the bridge forwards the frame. Bridges are made to divide a big network into smaller sub network known as segments.
Bridges are different to repeaters as they have filtering capacity which is not available with repeaters. Bridges sends the data frames only to the concerned segment thus preventing excess traffic. For e, g, if a network is divided in four segments. Segments i1 send a frame destined for another host on segment 3 the bridge forwards the frame only to segment 3 and not the segment 2 and 4 thus blocking unwanted traffic.