Route discovery

· First the src stn. Transmits the single route broadcast frame on its LAN without the route designator field.
· this frame should appear exactly once and hence selected bridges form spanning tree
· Once the selected bridge at the first hop receives this frame
§ inserts an incoming LAN number
§ bridge number
§ outgoing LAN number in the routing information field
· Then forwards on outgoing LAN
· At the other hop when a selected bridge receives this frame inserts bridge number and outgoing LAN number and forwards on outgoing LAN
· Non selected bridge simply ignore this frame
· Once the receiver gets this frame it broadcasts all routes broadcast frame with no route designator fields
· This frame generates all possible routes back to the src stn
· After collecting all routes the source station selects the best route and saves it

· To prevent all routes broad cast frames from circulating in the network, the bridge first checks whether the outgoing LAN number is already recorded, if so it does not forward the frame