Before a spanning tree bridge can operate, it must first prune its topology to a nonlooping tree. In so doing, it follows several well-ordered procedures. See Figure 4-15. The first task is to determine an anchor point from which to calculate a cost through the network. This process is used to identify one bridge among all the bridges in the routing domain to be a “root.” This root selection is arbitrary based on the comparison of the ID of the root, an assumed cost to the root (which is a 0 from all bridges initially because they think themselves as the root), the designated root ID, and the port ID on the root. This number concatenated from left to right is examined by each bridge when it receives messages from ...

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