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In a pure Token Ring network, an All Routes Explorer (ARE) frame generated from Station A traverses all rings only one time based on a Routing Information Field (RIF) expanded by each
This issue can be resolved by making sure that only one translational link can be in the forwarding state.
Preventing Frame Looping
The network presented in Figure 6 was free of the ARE looping issue because the entire the Ethernet cloud had the same LAN Segment number – each switch had the same number for its Ethernet ports.
In Figure 7, the switches have different LAN segment numbers for Ethernet ports (3 and 4). In this configuration, an infinite loop is created in addition to the frame duplication issue.
Station A sends an ARE frame to Ring1, for example IP ARP with destination MAC being Broadcast. This frame is converted to a transparent broadcast and sent on Ethernet link 1. The frame is then received by the switch on link 2 and sent as an ARE frame to Ring 2 – note that the RIF does not contain LAN Segment 4. The ARE frame is then forwarded by Bridge 1 and switch link 1 back to the Ethernet, and so on.
Figure 7. Frame Looping
Configuration |