Cabletron Systems SPECTRUM, User Manual

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The Filtering Database Window 6-13
Using the 7C0x SmartSwitch Bridge View
MtuExceedDiscard
Mtu stands for “maximum transfer unit”; it is the largest frame size that can be
processed by the 7C0x SmartSwitch. A port discards any received frames that are
larger than the Mtu; this field lists how many such frames were discarded.
The information in the Bridge Statistics window is a snapshot of the data. When
you open the Bridge Statistics window, the application polls the devices for
information. Devices are not polled again until you click mouse button 1 on the
Update
button, or close, then re-open the Statistics window.
The Filtering Database Window
In Transparent bridging, each bridge port uses the device’s Filtering Database to
determine a packet’s route through the bridge. The Filtering Database is created
from permanent entries made via management, and from entries learned as the
bridge collects and stores the source address and port association from each
packet it receives.
When in the Forwarding state, the bridge examines each received packet and
compares the destination address to the contents of the Filtering Database. If the
destination address is located on the network from which the packet was
received, the bridge filters (does not forward) the packet. If the destination
address is located on a different network, the bridge forwards the packet to the
appropriate network. If the destination address isn’t found in the Filtering
Database, the bridge forwards the packet to all networks. To keep Filtering
Database entries current, older entries are purged after a period of time, which is
called the Dynamic Ageing Time.
The Filtering Database has two types of entries: Forwarding and Static. The
Forwarding view of the Filtering Database contain addresses that the bridge
learns from network traffic (also known as dynamic entries) as well as all the
static entries. Learned entries are subject to the bridge’s Dynamic Ageing Timer;
entries that aren’t accessed within the time specified by the ageing timer are
purged. Static entries may be subject to the ageing timer, depending on how the
entries were added. Static entries enter the Filtering Database in two ways: either
automatically, when permanent database entries are copied to the Filtering
Database, or manually when you move a Forwarding entry to the Static Table.
NOTE
When a device is reset, statistics windows and/or statistics displays in the Bridge View
windows may display very large numbers for one polling interval. This is due to the
resetting of counters.