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Bridge Spanning Tree 4-37
Bridging
Root Bridge
Displays the MAC address of the bridge that is currently functioning as the Root
Bridge.
Root Cost
Indicates the cost of the data path from this bridge to the Root Bridge. Each port
on each bridge adds a ÒcostÓ to a particular path that a frame must travel. For
example, if each port in a particular path has a Path Cost of 1, the Root Cost
would be a count of the number of bridges along the path. (You can edit the Path
Cost of bridge ports as described later.) The Root BridgeÕs Root Cost is 0.
Root Port
This Þeld displays the identiÞer (the physical index number) of the device bridge
port that has the lowest cost path to the Root Bridge on the network. If the device
is currently the Root Bridge, this Þeld will read 0.
Protocol
Displays the Spanning Tree Algorithm Protocol type the device is currently using.
The choices are:
¥ 802.1
¥ DEC (DEC Lanbridge 100)
¥ None
The following four Þelds display values used for various Spanning Tree timers
that are set at the Root Bridge and this bridge. In Spanning Tree operations, the
value used for the tree is the one set at the Root Bridge (with the exception of
Hold Time, which is a Þxed value); but you can change the value for each bridge
on your network in the event that it becomes Root.
TIP
Part of a bridgeÕs IdentiÞer is based on its MAC address. In most network installations,
performance differences between bridges may be negligible. You may, however, Þnd your
data bottle-necked in installations where both a low-performance bridge and a
high-performance bridge are attached to the same LAN segment and the two (or more)
bridges have the same Priority component set (e.g., at the default 8000 Hex). In such a
scenario you may want to alter the Priority component of the higher performance bridge to
ensure that it becomes root for the segment (or overall root). Remember, if Priority
components are equal, the bridge on the segment with the lowest MAC address would
have a better chance of being selected as the root bridgeÑas it would have a lower Bridge
IdentiÞer. If your bridges come from multiple vendors, they will have different MAC
address values (e.g., Cabletron devices have a lower MAC address than 3Com devices); if
they come from the same vendor, the bridge with the earlier manufacture date will have the
lower MAC address value.