Only bridges in the spanning tree forward the frame, adding their bridge number and attached ring number as it is forwarded. The spanning-tree explorer reduces the number of frames sent during the discovery process. The value can range from 2 to 30 bytes. The source initially sets the largest frame size, but bridges can lower it if they cannot accommodate the requested size. This number does not have to be unique unless it is parallel with another bridge connecting two rings.
Bridges add to the frame their bridge number and the ring number onto which the frame is forwarded.
Routes are alternating sequences of ring and bridge numbers that start and end with ring numbers. A single RIF can contain more than one -routing descriptor field. Newer IBM bridge software programs combined with new LAN adapters support 13 hops.