Technical Background - Enterasys SSIM-H2-02 Installation And User Manual

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:
•
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
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Configuration