In a source-routing bridged LAN, a frame that must pass through one or more bridges to reach its destination carries its travel directions in a routing information field (RIF) in the frame header.
Figure 17.1 shows how this works in a Token Ring LAN. Each Token Ring and each source-routing bridge in the figure has been assigned a numeric identifier. By established convention, these are written using hexadecimal characters. To describe the dotted line route from station X to server Y shown in the figure, the instructions in the RIF would say:
Enter ring X'201.
Cross bridge X'8, and enter ring X'203.
Cross bridge X'6, and enter ring X'214.
Cross bridge X'3, and enter ring X'180. The destination MAC address is on this ...