Cabletron Systems SSIM-H2-02 manual Spanning Tree Configuration, Broken Ethernet Cloud

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This loop can be resolved by making sure that only one translational link is in the forwarding state or by using the same LAN segment number for all translational links.

Using two different LAN segment numbers has some interesting advantages. If the Ethernet cloud becomes physically separated into two parts (see below), both parts can still communicate via the Token Ring cloud. If the Ethernet cloud is not split and the root of the spanning tree is on the Token Ring side, there might be a loss of connectivity between Ethernet stations depending on the CRF numbers configured. To avoid such hazardous situations, follow the recommendations for the spanning tree parameter (described below).

Figure 8. Broken Ethernet Cloud

Spanning Tree Configuration

Running the IEEE Spanning Tree Protocol (STP) will create a single spanning tree covering the entire network. Depending on the topology and configured path costs, there will be one or more forwarding links between the two clouds.

If there are multiple translational links in multiple switches, the path costs on these links should be selected so that only one forwards. This will prevent ARE duplication and the looping problem.

Normally this can be achieved by assigning very large path costs on both sides of the translational links so that at most one can be forwarding. The SmartStack SSIM-H2-02 provides support for STP cost manipulation which does not require cost configuration on both sides of the link.

SSIM-H2-02 Fast Ethernet - Translational Switch SmartStack Interface Module Installation and User Guide Configuration