3Com 4007, Руководство по внедрению, Страница: 192 / 684

192 C
HAPTER
9: B
RIDGE
-W
IDE AND
B
RIDGE
P
ORT
P
ARAMETERS
If STP State is
“Aging Only”
This option is available on Layer 2 Switching Modules only. With this
option selected, the module does not operate as an STP bridge but does
use two of the STP parameters in certain circumstances related to aging
addresses.
During normal operation, address aging works as described in “Normal
Aging Process” earlier in this section. But the module adjusts the aging
interval when it detects down or disabled ports — it uses the value in the
bridge spanningTree stpForwardDelay
option as the aging interval.
In contrast to how Multilayer Switching Modules work, this aging process
affects all dynamic addresses in the address table, not just the addresses
that are associated with the ports that went down. Multilayer Switching
Modules only flush addresses that are associated with specific ports.
A Layer 2 Switching Module reverts back to using the value in
bridge
agingTime
after a period of time equal to
bridge spanningTree
stpForwar bridge spanningTree stpMaxAge
seconds has
transpired.
Important
Considerations
The factory default values for the aging period (
bridge agingTime
) and
for the STP forward delay (
bridge spanningTree stpForwardDelay
)
align with the recommendations in the IEEE 802.1D specification. Here
are some things to consider when adjusting these values:
■
If you decrease the
bridge agingTime
, you may see increased levels
of network traffic because address entries will age out faster and,
upon receiving frames with unknown source addresses, the bridge
must flood frames to all ports (except the one on which is was
received) in accordance with IEEE 802.1D.
■
If you increase the
bridge agingTime
, flooding may decrease but
movement in edge devices may not be detected as quickly.
■
If you decrease or increase the
bridge spanningTree
stpForwardDelay
(shown as
bridgeFwdDelay
on the
bridge
display
), it will only have an affect if:
■
The STP state is set to
agingOnly
, or
■
The STP state is set to
enabled
and the module is the root bridge.