Intel ZT 8101 10/100 user manual STP Parameters for the Switch Level

Switch Management and Operating Concepts

•On the switch level, STP calculates the Bridge Identifier for each switch and then sets the Root Bridge and the Designated Bridges.

•On the port level, STP sets the Root Port and the Designated Ports.

The factory default settings should cover the majority of installations. Setting up STP using values other than the defaults can be complex. Therefore, we recommend that you keep the default factory settings, and STP will automatically assign root bridges/ports and block loop connections.

Influencing STP to choose a particular switch as the root bridge using the Priority setting, or influencing STP to choose a particular port to block using the Port Priority and Port Cost settings is, however, relatively simple.

For example, if all switches have STP enabled with default settings, the switch with the lowest MAC address in the network becomes the root switch. By increasing the priority (lowering the priority number) of the best switch, STP can be forced to select the best switch as the root switch.

STP Parameters for the Switch Level

The following are the user-configurable STP parameters for the switch level.

Parameter	Description	Default Value
	Specifies the combination of the user-set priority and
	the switch's MAC address. The bridge identifier
Bridge Identifier	consists of two parts: a 16-bit priority and a 48-bit	32768 + MAC address
	Ethernet MAC address. The only portion that a user
	can configure is the priority.
	Specifies the relative priority for each switch. Lower
Priority	numbers specify a higher priority and a greater chance	32768
	of a given switch being elected as the root bridge.
	Specifies the length of time between broadcasts of the
	hello message by the switch. It can be set from 1 — 10
Hello Time	seconds. This interval is not used until the switch	2 seconds
	becomes (if ever) the root bridge.
	The Hello Time parameter cannot be longer than the
	Max Age parameter.
	Measures the age of a received BPDU for a port, and
Max Age	ensures that the BPDU is discarded when its age	20 seconds
	exceeds the value of the Max Age parameter.
	It can be set from 6—40 seconds.
	Specifies the time a port can remaining in the listening
Forward Delay	state while moving from the blocking state to the	15 seconds
	forwarding state.
	It can be set from 4—30 seconds.

Use the following formulas when setting these parameters:

•Max Age <= 2 x (Forward Delay -1 second)

•Max Age >= 2 x (Hello Time + 1 second)

32 Intel® NetStructure™ ZT 8101 10/100 Ethernet Switch User’s Manual