3Com 4007, Implementation Manual, Page: 190 / 684

190 C
HAPTER
9: B
RIDGE
-W
IDE AND
B
RIDGE
P
ORT
P
ARAMETERS
Normal Aging Process Each module records in its address table the source address of every
received frame (that is not otherwise filtered or discarded) along with the
appropriate port number.
At the time the table entry is created, an aging bit for that entry is set
to 1. When the entry is refreshed (i.e., the port receives a frame with the
same address), the bit is changed to 0. At specific intervals, the module
scans the address table for addresses that have bit values of 1 and
removes or
ages out those entries. Once the scan and removal process
has finished, bits at 0 change to 1 so that if their entries are not refreshed
by the time of the next scan, they will be aged out at that time.
Thus, it can take from less than one to two intervals to age out an
address table entry under normal circumstances. From the module’s
Administration Console, you can modify the aging interval using the
bridge agingTime
command.
If the STP State
is Enabled
When you set the
bridge spanningTree stpState
option to enabled
and the module is operating in a stable STP network configuration, the
module ages all dynamically learned addresses as described in “Normal
Aging Process” (the preceding section). Two situations can affect this
process:
■
Module receives notice of an STP topology change
■
Module detects a port down event
STP Topology Change
During the time that the root bridge sends CBPDUs with the topology
change flag set, the module uses a different (usually shorter) interval to
age addresses in accordance with STP rules:
If the module is operating as the root bridge, it uses the forward delay
value that exists in its configuration. From the Administration Console,
you can modify the value using the
bridge spanningTree
stpForwardDelay
command. This value is shown in the
bridgeFwdDelay
field of the
bridge display
.
If the module is not operating as the root bridge, it uses the value that is
assigned to it by the root bridge via the CBPDU. This value is shown in the
forwardDelay
field of the
bridge display
. To adjust this value, you
must find and connect to the root bridge.