Spanning Tree Operations
STP operation for each bridge can be broken down into three
main steps:
The main information to be concerned with is the Root ID
(bridge that the transmitting bridge thinks is the root), Bridge ID, and cost
(which is the cost to the root bridge). The STP topology is considered converged
after a root bridge has been selected and each bridge has selected its root
port, designated bridge, and which ports will participate in the STP topology.
STP uses these configuration messages (BPDUs) as it transitions port states to
achieve convergence.
Spanning tree elects one bridge on the LAN to be the master
bridge. This bridge is called the root bridge.
The root bridge is special because all the path calculation through the network
is based on the root. The bridge is elected based on the Bridge ID (BID), which
is comprised of a 2-byte Priority field plus a 6-byte MAC address. In spanning
tree, lower BID values are preferred. In a default configuration, the Priority
field is set at 32768. Because the default Priority field is the same for all
the bridges, the root selection is based on the lowest MAC address. One method
of selecting a specific bridge to be the root is to manually alter the Priority
field to a lower value. Regardless of what the MAC address is, the Priority
field decides what bridge is going to be the root, assuming that all bridges do
not have the same priority value. For the remainder of this chapter, the figures
depict a switch, which at its fundamental level is a glorified bridge. (See Figure 1-15.)
Sections
Comments (0 posted)
Syndication
