Spanning Tree Protocol Entity (STPE)

Aging Timer

The Aging Timer is a configurable parameter found in the Bridge Parameters

 

Record. It allows learned station addresses to be aged in the station address cache

 

and deleted once their age has reached the value of the Aging Timer parameter. This

 

allows automatic updates for certain dynamic conditions, such as when a station is

 

physically moved from one part of the network to another. Provided the Aging Timer

 

is low enough to age out the station that is being moved, the entry is deleted and,

 

once the station becomes active at its new location, the bridge relearns its new

 

location and forwards packets to it properly.

 

The Aging Timer is also used when there is a topological change to the network.

 

Generally, if a bridge, based on the automatic spanning tree algorithm, notices that a

 

link must be moved to or from a block state (moved to or from the spanning tree),

 

then the bridge informs the root bridge by means of a special message sent out the

 

root port. This message includes a flag that indicates a topological change has

 

occurred. The root bridge, in turn, informs all the bridges in the network that a

 

change has occurred by setting a flag in the hello message. Once a bridge is informed

 

of a change in the topology by the hello flag, it switches the timer value used in aging

 

to a value equal to the Forward Delay time. This allows the bridge to more quickly

 

relearn new station locations, if a topology change occurs due to node or link

 

failures. Note that the topological change messages are sent at the same rate as the

 

Hello Time interval. This limits the speed and gives the lower time boundary so that

 

bridges can adjust to the change.

 

 

Bridging

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Release 5.2M

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EXP Computer S200 manual Aging Timer, Location and forwards packets to it properly, Bridges can adjust to the change