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If two ports to the root have the same path cost, the STP device selects the one with the highest priority (lowest value), an arbitrary value that you assign. To block traffic on a particular segment, assign it low port priority (high value)
If more ports have the same priority value assigned, the lowest port number will be selected.
➽Note! All bridge relay functions in the switch use the same bridge identifier. As a consequence, you must not divide one switch into two or more VLANs by connecting them together and using the spanning tree protocol. The tree will collapse since the same bridge will be seen in several places in the network.
IEEE 802.1D Spanning Tree Protocol (STP)
When the IEEE 802.1D Spanning Tree Protocol is active, a port within that domain will require several seconds to make the transition from the blocking state to the forwarding state, when the port is initially activated (for example, joins an existing ring or activates a dedicated link.) Some client or server applications may attempt to establish session activity during this time, resulting in error messages indicating a connection failure. These applications should be configured to wait at least 30 seconds after the LAN link is active, before attempting to establish session activity. This delay can be reduced by modifying the 802.1D Spanning Tree Protocol default parameters.
If STP is enabled on a dedicated port, and a station is attached to it, it takes at least 30 seconds for the port to start forwarding frames, when default STP parameters are used. The client and server stations may have given up before then and the first many packets are lost.
In general, STP should not be enabled on ports, which are intended for dedicated stations. Shared media do not have the same problem, because the port will stay attached to the Hub, even though all stations have closed.
Another reason for not enabling STP on dedicated ports is that the whole spanning tree domain will go into Topology Change state each time a station opens or closes. This will cause the whole spanning tree domain to use short aging timers, which means that all address tables will be trashed. The result is a lot of unknown station broadcasts, before the tables converge again.
To disable STP on a port, select the STP Mode Forwarding for this port. Refer to the “STP Mode” parameter on page 105.
SmartStack | Switch Configuration |
