Cabletron Systems SSIM-H2-02 manual Technical Background

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Technical Background

For each CRF with a translational link, spanning tree should be enabled. For SRT CRF, the default STP algorithm is IEEE 802.1D. Only this spanning tree algorithm can be used for translational links.

A translational link has its own LAN segment number and recognizes source routing. However, the translational link is an element of a transparent network and frames are passed through only in the forwarding state. This restriction applies to all frames, including ARE and specifically-routed frames.

Only one link of a CRF at a time may become forwarding. To achieve this, the spanning tree costs of the internal BRF-to-CRF link will be modified according to the CRF connection attribute. The BRF-to-CRF link is a virtual internal link and exists only for spanning tree purposes. The spanning tree cost of each primary connection remains unmodified.

Note that in the Secondary 1 and Secondary 2 connections, different values are added to the cost of the internal BRF-to-CRF link to ensure that, when the Primary fails, the Secondary 1 will become forwarding the Secondary 2.

Cost modification of BRF-to-CRF link:

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For the Secondary 1 connection, the cost of the internal BRF-to-CRF link is increased by 20,000.

For the Secondary 2 connection, the cost of the internal BRF-to-CRF link is increased by 40,000.

In Figure 11, the SmartStack TR Switch 2 and Ethernet switch 2 know that the root path cost seen from the secondary link is 20,000 higher than the root path cost of the primary link seen by the TR.

With TR switch 1 and Ethernet switch 1. The secondary link will be blocked on the internal CRF-to-BRF link.

To configure spanning-tree costs for a backup connection to Ethernet manually, set each connection attribute to Primary and then change spanning-tree costs on each side of the backup link.

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