D-Link DES-3226 manual Bridge Protocol Data Units, Variable Description Default Value

DES-3226 NWay Standalone Fast Ethernet Switch User’s Guide

below)	address
Priority	A relative priority for each switch –	32768
	lower numbers give a higher
	priority and a greater chance of a
	given switch being elected as the
	root bridge
Hello Time	The length of time between	2 seconds
	broadcasts of the hello message by
	the switch
Maximum Age Timer	Measures the age of a received	20 seconds
	BPDU for a port and ensures that
	the BPDU is discarded when its
	age exceeds the value of the
	maximum age timer.
Forward Delay Timer	The amount time spent by a port	15 seconds
	in the learning and listening states
	waiting for a BPDU that may
	return the port to the blocking
	state.

Table 5-1. STP Parameters – Switch Level

The following are the user-configurable STP parameters for the port or port group level:

Variable	Description	Default
		Value
Port Priority	A relative priority for each port –	32768
	lower numbers give a higher
	priority and a greater chance of a
	given port being elected as the root
	port
Port Cost	A value used by STP to evaluate	100 –	100Mbps
	paths – STP calculates path costs	Fast	Ethernet
	and selects the path with the	ports
	minimum cost as the active path.

Table 5-2. STP Parameters – Port Group Level

Bridge Protocol Data Units

For STP to arrive at a stable network topology, the following information is used:

•The unique switch identifier

•The path cost to the root associated with each switch port

•The port identifier

STP communicates between switches on the network using Bridge Protocol Data Units (BPDUs). Each BPDU contains the following information:

•The unique identifier of the switch that the transmitting switch currently believes is the root switch

•The path cost to the root from the transmitting port

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