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Bridge Spanning Tree 5-17
Bridging
Hello Time
This parameter indicates, in seconds, the length of time the Root Bridge (or bridge
attempting to become the Root) waits before resending Configuration BPDUs.
The range for this field is 1 to 10 seconds, with a default value of 2 seconds. The
Root Bridge sets the Hello Time.
Max Age
This parameter displays the bridge’s BPDU ageing timer. This controls the
maximum time a BPDU can be retained by the bridge before it is discarded.
During normal operation, each bridge in the network receives a new
Configuration BPDU before the timer expires. If the timer expires before a
Configuration BPDU is received, it indicates that the former Root is no longer
active. The remaining bridges begin Spanning Tree operation to select a new Root.
The current Root Bridge on the network sets the Max Age time. The range for this
field is 6 to 40 seconds, with a default value of 20 seconds.
Forwarding Delay
This parameter displays the time period which elapses between states while the
bridge is moving to the Forwarding state. For example, while moving from a
Blocking to a Forwarding state, the port first moves from Blocking to Listening to
BPDU activity on the network, remains there for the Forward Delay period, then
moves to the Learning State (and remains in it for the Forward Delay period), and
finally moves into a Forwarding state. This timer is set by the Root Bridge. During
a topology change, the Forward Delay is also used as the Filtering Database
Aging Time (refer to Filtering Database, page 5-21), which ensures that the
Filtering Database maintains current topology information.
Hold Time
This parameter displays, in seconds, the minimum time that can elapse between
the transmission of Configuration BPDUs through a bridge port. The Hold Time
ensures that Configuration BPDUs are not transmitted too frequently through any
bridge port. Receiving a BPDU starts the Hold Timer. After the Hold Timer
expires, the port transmits its Configuration BPDU to send configuration
information to the Root. The Hold Time is a fixed value, as specified by the IEEE
802.1d specification.
The following fields are applicable to each bridge port on the selected module:
Priority
If two or more ports on the same bridge are connected to the same LAN segment,
they will receive the same Root ID/Root Cost/Bridge ID information in
Configuration BPDUs received at each port. In this case, the BPDU’s Port ID
information – the transmitting port’s identifier and its manageable Priority
component – is used to determine which is the Designated Port for that segment.
A lower assigned value gives the port a higher Priority when BPDUs are
compared. The allowable range is 0-FF hexadecimal (0-255 decimal); the default is
80 hexadecimal.